Chapter20 initial push

158 files changed, 20688 insertions, 0 deletions

diff --git a/chapter20/src/main/java/com/seaofnodes/simple/ASMPrinter.java b/chapter20/src/main/java/com/seaofnodes/simple/ASMPrinter.java
new file mode 100644
index 00000000..5cc13210
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/ASMPrinter.java
@@ -0,0 +1,140 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import com.seaofnodes.simple.type.TypeMem;
+import com.seaofnodes.simple.type.TypeRPC;
+
+public abstract class ASMPrinter {
+
+    public static SB print(SB sb, CodeGen code) {
+        if( code._cfg==null )
+            return sb.p("Need _cfg set, run after GCM");
+
+        // instruction address
+        int iadr = 0;
+        for( int i=0; i<code._cfg._len; i++ )
+            if( code._cfg.at(i) instanceof FunNode fun )
+                iadr = print(iadr,sb,code,fun,i);
+        return sb;
+    }
+
+    private static int print(int iadr, SB sb, CodeGen code, FunNode fun, int cfgidx) {
+        // Function header
+        sb.nl().p("---");
+        fun.sig().print(sb);
+        sb.p("---------------------------").nl();
+
+
+        while( !(code._cfg.at(cfgidx) instanceof ReturnNode) )
+            iadr = doBlock(iadr,sb,code,fun,cfgidx++);
+
+        // Function separator
+        sb.p("---");
+        fun.sig().print(sb);
+        sb.p("---------------------------").nl();
+        return iadr;
+    }
+
+    static int doBlock(int iadr, SB sb, CodeGen code, FunNode fun, int cfgidx) {
+        CFGNode bb = code._cfg.at(cfgidx);
+        if( bb != fun && !(bb instanceof IfNode) && !(bb instanceof CallEndNode) && !(bb instanceof CallNode)  && !(bb instanceof CProjNode && bb.in(0) instanceof CallEndNode ))
+            sb.p("L").p(bb._nid).p(":").nl();
+
+        if( !(bb instanceof CallNode) )
+            for( Node n : bb._outputs )
+                iadr = doInst(iadr, sb,code,fun,bb,n);
+
+        return iadr;
+    }
+
+    static int doInst(int iadr, SB sb, CodeGen code, FunNode fun, CFGNode bb, Node n) {
+        final int encWidth = 8;
+        final int opWidth = 5;
+        final int argWidth = 30;
+
+        if( n instanceof  CProjNode ) return iadr;
+
+        // Phis are useful before (and during) reg alloc
+        if( n instanceof PhiNode phi ) {
+            if( phi._type instanceof TypeMem || phi._type instanceof TypeRPC ) return iadr; // Nothing for the hidden ones
+            sb.fix(4," ").p(" ").fix(encWidth,"").p("  ").fix(opWidth,phi._label).p(" ");
+            sb.p(code.reg(n));
+            if( !(n instanceof ParmNode) ) {
+                sb.p(" = phi( ");
+                for( int i=1; i<n.nIns(); i++ )
+                    sb.p("N").p(n.in(i)._nid).p(",");
+                sb.unchar().p(" )");
+            }
+            sb.nl();
+            return iadr;
+        }
+
+        // All blocks ending in a Region will need to either fall into or jump
+        // to this block.  Until the post-reg-alloc block layout cleanup, we
+        // need to assume a jump.  There's no real hardware op here, yet.
+        if( n instanceof RegionNode && !(n instanceof FunNode) ) {
+            sb.hex4(iadr++).p(" ").fix(encWidth,"??").p("  ").fix(opWidth,"JMP").p(" ").fix(argWidth,"L"+n._nid).nl();
+            return iadr;
+        }
+
+        // ProjNodes following a multi (e.g. Call or New results),
+        // get indent slightly and just print their index & node#
+        if( n instanceof ProjNode proj ) {
+            if( proj._type instanceof TypeMem ) return iadr; // Nothing for the hidden ones
+            sb.fix(4," ").p(" ").fix(encWidth,"").p("    ").fix(opWidth,proj._label==null ? "---" : proj._label).p(" ").p(code.reg(n)).nl();
+            return iadr;
+        }
+
+        // ADDR ENCODING  Op--- dst = src op src       // Comment
+        // 1234 abcdefgh  ld4   RAX = [Rbase + off]    // Comment
+        sb.hex4(iadr);
+        sb.p(" ");
+
+        // Encoding
+        int size = 1;           // TODO: Fake encoding size
+        iadr += size;
+        sb.fix(encWidth,"??");
+        sb.p("  ");
+
+        // Op; generally "ld4" or "call"
+        sb.fix(opWidth, n instanceof MachNode mach ? mach.op() : n.label());
+        sb.p(" ");
+
+        // General asm args
+        if( n instanceof MachNode mach ) {
+            int old = sb.len();
+            mach.asm(code,sb);
+            sb.fix(argWidth-(sb.len()-old),""); // Pad out
+
+        } else if( !(n._type instanceof TypeMem) ) {
+            // Room for some inputs
+            sb.fix(5, n._nid+":" );
+            int off = 0;
+            for( int i=0; i<n.nIns(); i++ ) {
+                sb.fix(5, n.in(i) == null ? "___" : String.valueOf(n.in(i)._nid));
+                off += 5;
+                if( off >= argWidth ) break;
+            }
+            if( off < argWidth ) sb.fix(argWidth-off,"");
+        }
+        sb.p(" ");
+
+        // Comment
+        String comment = n.comment();
+        if( comment!=null ) sb.p("// ").p(comment);
+
+        sb.nl();
+
+        // MultiNodes are immediately followed by projection(s)
+        if( !(n instanceof CFGNode) && n instanceof MultiNode ) {
+            for( Node proj : n._outputs ) {
+                assert proj instanceof ProjNode;
+                doInst(iadr,sb,code,fun,bb,proj);
+            }
+        }
+
+        return iadr;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/Ary.java b/chapter20/src/main/java/com/seaofnodes/simple/Ary.java
new file mode 100644
index 00000000..73ada8e0
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/Ary.java
@@ -0,0 +1,217 @@
+package com.seaofnodes.simple;
+
+import java.lang.StringBuilder;
+import java.lang.reflect.Array;
+import java.util.*;
+
+// ArrayList with saner syntax
+public class Ary<E> extends AbstractList<E> implements List<E> {
+    public E[] _es;
+    public int _len;
+
+    public Ary(E[] es) { this(es,es.length); }
+    public Ary(E[] es, int len) { if( es.length==0 ) es=Arrays.copyOf(es,1); _es=es; _len=len; }
+    @SuppressWarnings("unchecked")
+    public Ary(Class<E> clazz) { this((E[]) Array.newInstance(clazz, 1),0); }
+
+    /** @return list is empty */
+    public boolean isEmpty() { return _len==0; }
+    /** @return active list length */
+    public int len() { return _len; }
+    public int size() { return len(); }
+
+    /** @param i element index
+     *  @return element being returned; throws if OOB
+     *  @exception AIOOBE if !(0 <= i < _len)
+     */
+    public E get( int i ) { return at(i); }
+    public E at( int i ) {
+        range_check(i);
+        return _es[i];
+    }
+
+    /** @return last element */
+    public E last( ) { return at(_len-1); }
+
+    /** Add element in amortized constant time
+     *  @param e Element to add at end of list
+     **/
+    public E push( E e ) {
+        if( _len >= _es.length ) _es = Arrays.copyOf(_es,Math.max(1,_es.length<<1));
+        return (_es[_len++] = e);
+    }
+    /** @return remove and return last element */
+    public E pop( ) {
+        return _len==0 ? null : _es[--_len];
+    }
+    @Override public E removeLast() { return pop(); }
+
+
+    /** Add element in amortized constant time
+     *  @param e Element to add at end of list
+     *  @return true */
+    public boolean add( E e ) {
+        if( _len >= _es.length ) _es = Arrays.copyOf(_es,Math.max(1,_es.length<<1));
+        _es[_len++] = e;
+        return true;
+    }
+
+    /** Fast, constant-time, element removal.  Does not preserve order
+     *  @param i element to be removed
+     *  @return element removed */
+    public E del( int i ) {
+        range_check(i);
+        E tmp = _es[i];
+        _es[i]=_es[--_len];
+        return tmp;
+    }
+
+    /** Slow, linear-time, element removal.  Preserves order.
+     *  @param i element to be removed
+     *  @return element removed */
+    @Override public E remove( int i ) {
+        range_check(i);
+        E e = _es[i];
+        System.arraycopy(_es,i+1,_es,i,(--_len)-i);
+        return e;
+    }
+
+    /** Remove all elements */
+    public void clear( ) { _len=0; }
+
+    /** Set existing element
+     *  @param i element to set
+     *  @param e value to set
+     *  @return old value
+     *  @exception AIOOBE if !(0 <= i < _len)
+     */
+    public E set( int i, E e ) {
+        range_check(i);
+        E old = _es[i];
+        _es[i] = e;
+        return old;
+    }
+
+    /** Set existing element
+     *  @param i element to set
+     *  @param e value to set
+     *  @return old value
+     *  @exception AIOOBE if !(0 <= i < _len)
+     */
+    public E setX( int i, E e ) {
+        if( i >= _len ) {
+            while( i >= _es.length ) _es = Arrays.copyOf( _es, _es.length << 1 );
+            _len = i+1;
+        }
+        E old = _es[i];
+        _es[i] = e;
+        return old;
+    }
+
+    public Ary<E> setLen( int len ) {
+        if( len > _len )
+            while( len>= _es.length ) _es = Arrays.copyOf(_es,_es.length<<1);
+        _len = len;
+        while( _es.length > (len<<1) ) // Shrink if hugely too large
+            _es = Arrays.copyOf(_es,_es.length>>1);
+        Arrays.fill(_es,len,_es.length,null);
+        return this;
+    }
+
+    public E swap( int i, int j ) {
+        range_check(i);
+        range_check(j);
+        E tmp = _es[i];
+        if( i==j ) return tmp;
+        _es[i] = _es[j];
+        _es[j] = tmp;
+        return tmp;
+    }
+
+
+    /** @param c Collection to be added */
+    public boolean addAll( Collection<? extends E> c ) {
+        if( c==null ) return false;
+        for( E e : c ) add(e);
+        return true;
+    }
+    public Ary<E> addAll( Iterable<? extends E> it ) { for( E e : it ) add(e); return this; }
+
+    /** @param es Array to be added */
+    public <F extends E> Ary<E> addAll( F[] es ) {
+        if( es==null || es.length==0 ) return this;
+        while( _len+es.length > _es.length ) _es = Arrays.copyOf(_es,_es.length<<1);
+        System.arraycopy(es,0,_es,_len,es.length);
+        _len += es.length;
+        return this;
+    }
+
+    /** @param c Collection to be added */
+    public Ary<E> addAll( Ary<? extends E> c ) {
+        if( c==null || c._len==0 ) return this;
+        while( _len+c._len > _es.length ) _es = Arrays.copyOf(_es,_es.length<<1);
+        System.arraycopy(c._es,0,_es,_len,c._len);
+        _len += c._len;
+        return this;
+    }
+
+    /** @return compact array version */
+    public E[] asAry() { return Arrays.copyOf(_es,_len); }
+
+    /** Sorts in-place
+     *  @param c Comparator to sort by */
+    public void sort_update(Comparator<? super E> c ) { Arrays.sort(_es, 0, _len, c);  }
+
+    /** Find the first matching element using ==, or -1 if none.  Note that
+     *  most del calls shuffle the list, so the first element might be random.
+     *  @param e Element to find
+     *  @return index of first matching element, or -1 if none */
+    public int find( E e ) {
+        for( int i=0; i<_len; i++ )  if( _es[i]==e )  return i;
+        return -1;
+    }
+
+
+    /** @return an iterator */
+    @Override public Iterator<E> iterator() { return new Iter(); }
+    private class Iter implements Iterator<E> {
+        int _i=0;
+        @Override public boolean hasNext() { return _i<_len; }
+        @Override public E next() { return _es[_i++]; }
+    }
+
+    @Override public String toString() {
+        StringBuilder sb = new StringBuilder().append('{');
+        for( int i=0; i<_len; i++ ) {
+            if( i>0 ) sb.append(',');
+            if( _es[i] != null ) sb.append(_es[i].toString());
+        }
+        return sb.append('}').toString();
+    }
+
+    private void range_check( int i ) {
+        if( i < 0 || i>=_len )
+            throw new ArrayIndexOutOfBoundsException(""+i+" >= "+_len);
+    }
+
+    // Note that the hashCode() and equals() are not invariant to changes in the
+    // underlying array.  If the hashCode() is used (e.g., inserting into a
+    // HashMap) and the then the array changes, the hashCode() will change also.
+    @Override public boolean equals( Object o ) {
+        if( this==o ) return true;
+        if( !(o instanceof Ary ary) ) return false;
+        if( _len != ary._len ) return false;
+        if( _es == ary._es ) return true;
+        for( int i=0; i<_len; i++ )
+            if( !(_es[i]==null ? (ary._es[i] == null) : _es[i].equals(ary._es[i])) )
+                return false;
+        return true;
+    }
+    @Override public int hashCode( ) {
+        int sum=_len;
+        for( int i=0; i<_len; i++ )
+            sum += _es[i]==null ? 0 : _es[i].hashCode();
+        return sum;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/CodeGen.java b/chapter20/src/main/java/com/seaofnodes/simple/CodeGen.java
new file mode 100644
index 00000000..c48a4162
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/CodeGen.java
@@ -0,0 +1,288 @@
+ package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.node.cpus.x86_64_v2.MemOpX86;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.IdentityHashMap;
+
+public class CodeGen {
+    // Last created CodeGen as a global; used all over to avoid passing about a
+    // "context".
+    public static CodeGen CODE;
+
+    public enum Phase {
+        Parse,                  // Parse ASCII text into Sea-of-Nodes IR
+        Opto,                   // Run ideal optimizations
+        TypeCheck,              // Last check for bad programs
+        InstructionSelection,   // Convert to target hardware nodes
+        Schedule,               // Global schedule (code motion) nodes
+        LocalSched,             // Local schedule
+        RegAlloc;               // Register allocation
+    }
+    public enum CallingConv {
+        Win64,
+        SystemV
+    }
+    public Phase _phase;
+
+    // ---------------------------
+    // Compilation source code
+    public final String _src;
+    // Compile-time known initial argument type
+    public final TypeInteger _arg;
+    public CallingConv _callingConv;
+
+    // ---------------------------
+    public CodeGen( String src ) { this(src, TypeInteger.BOT, 123L ); }
+    public CodeGen( String src, TypeInteger arg, long workListSeed ) {
+        CODE = this;
+        _phase = null;
+        _callingConv = null;
+        _start = new StartNode(arg);
+        _stop = new StopNode(src);
+        _src = src;
+        _arg = arg;
+        _iter = new IterPeeps(workListSeed);
+        P = new Parser(this,arg);
+    }
+
+
+    // ---------------------------
+    /**
+     *  A counter, for unique node id generation.  Starting with value 1, to
+     *  avoid bugs confusing node ID 0 with uninitialized values.
+     */
+    private int _uid = 1;
+    public int UID() { return _uid; }
+    public int getUID() { return _uid++; }
+
+    // Next available memory alias number
+    private int _alias = 2; // 0 is for control, 1 for memory
+    public  int getALIAS() { return _alias++; }
+
+
+    // Popular visit bitset, declared here, so it gets reused all over
+    public final BitSet _visit = new BitSet();
+    public BitSet visit() { assert _visit.isEmpty(); return _visit; }
+
+    // Start and stop; end points of the generated IR
+    public StartNode _start;
+    public StopNode  _stop;
+
+    // Global Value Numbering.  Hash over opcode and inputs; hits in this table
+    // are structurally equal.
+    public final HashMap<Node,Node> _gvn = new HashMap<>();
+
+    // Compute "function indices": FIDX.
+    // Each new request at the same signature gets a new FIDX.
+    private final HashMap<TypeTuple,Integer> FIDXS = new HashMap<>();
+    public TypeFunPtr makeFun( TypeTuple sig, Type ret ) {
+        Integer i = FIDXS.get(sig);
+        int fidx = i==null ? 0 : i;
+        FIDXS.put(sig,fidx+1);  // Track count per sig
+        assert fidx<64;         // TODO: need a larger FIDX space
+        return TypeFunPtr.make((byte)2,sig,ret, 1L<<fidx );
+    }
+    // Signature for MAIN
+    public TypeFunPtr _main = makeFun(TypeTuple.MAIN,Type.BOTTOM);
+    // Reverse from a constant function pointer to the IR function being called
+    public FunNode link( TypeFunPtr tfp ) {
+        assert tfp.isConstant();
+        return _linker.get(tfp.makeFrom(Type.BOTTOM));
+    }
+
+    // Insert linker mapping from constant function signature to the function
+    // being called.
+    public void link(FunNode fun) {
+        _linker.put(fun.sig().makeFrom(Type.BOTTOM),fun);
+    }
+
+    // "Linker" mapping from constant TypeFunPtrs to heads of function.  These
+    // TFPs all have exact single fidxs and their return is wiped to BOTTOM (so
+    // the return is not part of the match).
+    private final HashMap<TypeFunPtr,FunNode> _linker = new HashMap<>();
+
+    // Parser object
+    public final Parser P;
+
+    // Parse ASCII text into Sea-of-Nodes IR
+    public CodeGen parse() {
+        assert _phase == null;
+        _phase = Phase.Parse;
+
+        P.parse();
+        JSViewer.show();
+        return this;
+    }
+
+
+    // ---------------------------
+    // Iterator peepholes.
+    public final IterPeeps _iter;
+    // Stop tracking deps while assertin
+    public boolean _midAssert;
+    // Statistics on peepholes
+    public int _iter_cnt, _iter_nop_cnt;
+    // Stat gathering
+    public void iterCnt() { if( !_midAssert ) _iter_cnt++; }
+    public void iterNop() { if( !_midAssert ) _iter_nop_cnt++; }
+
+    // Run ideal optimizations
+    public CodeGen opto() {
+        assert _phase == Phase.Parse;
+        _phase = Phase.Opto;
+
+        // Pessimistic peephole optimization on a worklist
+        _iter.iterate(this);
+
+        // TODO:
+        // Optimistic
+        // TODO:
+        // loop unroll, peel, RCE, etc
+        return this;
+    }
+    public <N extends Node> N add( N n ) { return (N)_iter.add(n); }
+    public void addAll( Ary<Node> ary ) { _iter.addAll(ary); }
+
+
+    // ---------------------------
+    // Last check for bad programs
+    public CodeGen typeCheck() {
+        // Demand phase Opto for cleaning up dead control flow at least,
+        // required for the following GCM.
+        assert _phase.ordinal() <= Phase.Opto.ordinal();
+        _phase = Phase.TypeCheck;
+
+        Parser.ParseException err = _stop.walk( Node::err );
+        if( err != null )
+            throw err;
+        return this;
+    }
+
+
+    // ---------------------------
+    // Code generation CPU target
+    public Machine _mach;
+
+    // Convert to target hardware nodes
+    public CodeGen instSelect( String cpu, String callingConv ) {
+        assert _phase.ordinal() <= Phase.TypeCheck.ordinal();
+        _phase = Phase.InstructionSelection;
+
+        _callingConv = switch(callingConv) {
+        case "SystemV" -> CallingConv.SystemV;
+        case "Win64"   -> CallingConv.Win64;
+        default -> throw Utils.TODO(); // Unknown calling convention
+        };
+
+        // Look for CPU in fixed named place:
+        //   com.seaofnodes.simple.node.cpus."cpu"."cpu.class"
+        String clzFile = "com.seaofnodes.simple.node.cpus."+cpu+"."+cpu;
+        try { _mach = ((Class<Machine>) Class.forName( clzFile )).getDeclaredConstructor().newInstance(); }
+        catch( Exception e ) { throw new RuntimeException(e); }
+
+        // Convert to machine ops
+        _uid = 1;               // All new machine nodes reset numbering
+        var map = new IdentityHashMap<Node,Node>();
+        _instSelect( _stop, map );
+        _stop  = ( StopNode)map.get(_stop );
+        _start = (StartNode)map.get(_start);
+        _instOuts(_stop,visit());
+        _visit.clear();
+        return this;
+    }
+
+    // Walk all ideal nodes, recursively mapping ideal to machine nodes, then
+    // make a machine node for "this".
+    private Node _instSelect( Node n, IdentityHashMap<Node,Node> map ) {
+        if( n==null ) return null;
+        Node x = map.get(n);
+        if( x !=null ) return x; // Been there, done that
+
+        // If n is a MachConcrete, then its part of a multi-node expansion.
+        // It does not need instruction selection (already selected!)
+        // but it does need its inputs walked.
+        if( n instanceof MachConcreteNode || n instanceof MemOpX86 ) {
+            for( int i=0; i < n.nIns(); i++ )
+                n._inputs.set(i, _instSelect(n.in(i),map) );
+            return n;
+        }
+
+        // Produce a machine node from n; map it to flag as done so stops cycles.
+        map.put(n, x=_mach.instSelect(n) );
+        // Walk machine op and replace inputs with mapped inputs
+        for( int i=0; i < x.nIns(); i++ )
+            x._inputs.set(i, _instSelect(x.in(i),map) );
+        if( x instanceof MachNode mach )
+            mach.postSelect();  // Post selection action
+
+        // Updates forward edges only.
+        n._outputs.clear();
+        return x;
+    }
+
+    // Walk all machine Nodes, and set their output edges
+    private void _instOuts( Node n, BitSet visit ) {
+        if( visit.get(n._nid) ) return;
+        visit.set(n._nid);
+        for( Node in : n._inputs )
+            if( in!=null ) {
+                in._outputs.push(n);
+                _instOuts(in,visit);
+            }
+    }
+
+
+    // ---------------------------
+    // Control Flow Graph in RPO order.
+    Ary<CFGNode> _cfg = new Ary<>(CFGNode.class);
+
+    // Global schedule (code motion) nodes
+    public CodeGen GCM() { return GCM(false); }
+    public CodeGen GCM( boolean show) {
+        assert _phase.ordinal() <= Phase.InstructionSelection.ordinal();
+        _phase = Phase.Schedule;
+
+        // Build the loop tree, fix never-exit loops
+        _start.buildLoopTree(_stop);
+        GlobalCodeMotion.buildCFG(this);
+        if( show )
+            System.out.println(new GraphVisualizer().generateDotOutput(_stop,null,null));
+        return this;
+    }
+
+    // ---------------------------
+    // Local (basic block) scheduler phase, a classic list scheduler
+    public CodeGen localSched() {
+        assert _phase == Phase.Schedule;
+        _phase = Phase.LocalSched;
+        ListScheduler.sched(this);
+        return this;
+     }
+
+
+    // ---------------------------
+    public String reg(Node n) {
+        if( _phase == Phase.RegAlloc ) throw Utils.TODO();
+        return "N"+ n._nid;
+    }
+
+
+    // ---------------------------
+    SB asm(SB sb) { return ASMPrinter.print(sb,this); }
+    String asm() { return asm(new SB()).toString(); }
+
+
+    // Testing shortcuts
+    Node ctrl() { return _stop.ret().ctrl(); }
+    Node expr() { return _stop.ret().expr(); }
+    String print() { return _stop.print(); }
+
+    // Debugging helper
+    @Override public String toString() { return _stop.p(9999); }
+
+    // Debugging helper
+    public Node f(int idx) { return _stop.find(idx); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java b/chapter20/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java
new file mode 100644
index 00000000..12dd9243
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java
@@ -0,0 +1,241 @@
+ package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.IterPeeps.WorkList;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.util.*;
+
+public abstract class GlobalCodeMotion {
+
+    // Arrange that the existing isCFG() Nodes form a valid CFG.  The
+    // Node.use(0) is always a block tail (either IfNode or head of the
+    // following block).  There are no unreachable infinite loops.
+    public static void buildCFG( CodeGen code ) {
+        Ary<CFGNode> rpo = new Ary<>(CFGNode.class);
+        _rpo_cfg(null, code._start, code.visit(), rpo);
+        // Reverse in-place
+        for( int i=0; i< rpo.size()>>1; i++ ) {
+            int j = rpo.size()-1-i;
+            CFGNode tmp = rpo.get(i);
+            rpo.set(i, rpo.get(j));
+            rpo.set(j, tmp);
+        }
+        // Set global CFG
+        code._cfg = rpo;
+
+        schedEarly(code);
+        code._visit.clear();
+        schedLate (code);
+    }
+
+    // Post-Order of CFG
+    private static void _rpo_cfg(CFGNode def, Node use, BitSet visit, Ary<CFGNode> rpo) {
+        if( !(use instanceof CFGNode cfg) || visit.get(cfg._nid) )
+            return;             // Been there, done that
+        if( def instanceof CallNode && cfg instanceof FunNode )
+            return;           // Ignore linked function calls
+        visit.set(cfg._nid);
+        for( Node useuse : cfg._outputs )
+            _rpo_cfg(cfg,useuse,visit,rpo);
+        rpo.add(cfg);
+    }
+
+    // ------------------------------------------------------------------------
+    // Visit all nodes in CFG Reverse Post-Order, essentially defs before uses
+    // (except at loops).  Since defs are visited first - and hoisted as early
+    // as possible, when we come to a use we place it just after its deepest
+    // input.
+    private static void schedEarly(CodeGen code) {
+        // Reverse Post-Order on CFG
+        for( CFGNode cfg : code._cfg ) {
+            cfg.loopDepth();
+            for( Node n : cfg._inputs )
+                _schedEarly(n,code._visit );
+            if( cfg instanceof RegionNode )
+                for( Node phi : cfg._outputs )
+                    if( phi instanceof PhiNode )
+                        _schedEarly(phi,code._visit );
+        }
+    }
+
+    private static void _schedEarly(Node n, BitSet visit) {
+        if( n==null || visit.get(n._nid) ) return; // Been there, done that
+        assert !(n instanceof CFGNode);
+        visit.set(n._nid);
+        // Schedule not-pinned not-CFG inputs before self.  Since skipping
+        // Pinned, this never walks the backedge of Phis (and thus spins around
+        // a data-only loop), eventually attempting relying on some pre-visited-
+        // not-post-visited data op with no scheduled control.
+        for( Node def : n._inputs )
+            if( def!=null && !(def instanceof PhiNode) )
+                _schedEarly(def,visit);
+
+        // If not-pinned (e.g. constants, projections, phi) and not-CFG
+        if( !n.isPinned() ) {
+            // Schedule at deepest input
+            CFGNode early = CodeGen.CODE._start; // Maximally early, lowest idepth
+            if( n.in(0) instanceof CFGNode cfg ) early = cfg;
+            for( int i=1; i<n.nIns(); i++ )
+                if( n.in(i)!=null && n.in(i).cfg0().idepth() > early.idepth() )
+                    early = n.in(i).cfg0(); // Latest/deepest input
+            n.setDef(0,early);
+        }
+    }
+
+    // ------------------------------------------------------------------------
+    private static void schedLate( CodeGen code ) {
+        CFGNode[] late = new CFGNode[code.UID()];
+        Node[] ns = new Node[code.UID()];
+        // Breadth-first scheduling
+        breadth(code._stop,ns,late);
+
+        // Copy the best placement choice into the control slot
+        for( int i=0; i<late.length; i++ )
+            if( ns[i] != null && !(ns[i] instanceof ProjNode) )
+                ns[i].setDef(0,late[i]);
+    }
+
+    private static void breadth(Node stop, Node[] ns, CFGNode[] late) {
+        // Things on the worklist have some (but perhaps not all) uses done.
+        WorkList<Node> work = new WorkList<>();
+        work.push(stop);
+        Node n;
+        outer:
+        while( (n = work.pop()) != null ) {
+            assert late[n._nid]==null; // No double visit
+            // These I know the late schedule of, and need to set early for loops
+            if( n instanceof CFGNode cfg ) late[n._nid] = cfg.blockHead() ? cfg : cfg.cfg(0);
+            else if( n instanceof PhiNode phi ) late[n._nid] = phi.region();
+            else if( n instanceof ProjNode && n.in(0) instanceof CFGNode cfg ) late[n._nid] = cfg;
+            else {
+
+                // All uses done?
+                for( Node use : n._outputs )
+                    if( use!=null && late[use._nid]==null )
+                        continue outer; // Nope, await all uses done
+
+                // Loads need their memory inputs' uses also done
+                if( n instanceof LoadNode ld )
+                    for( Node memuse : ld.mem()._outputs )
+                        if( late[memuse._nid]==null &&
+                            // New makes new memory, never crushes load memory
+                            !(memuse instanceof NewNode) &&
+                            // Load-use directly defines memory
+                            (memuse._type instanceof TypeMem ||
+                             // Load-use indirectly defines memory
+                             (memuse._type instanceof TypeTuple tt && tt._types[ld._alias] instanceof TypeMem)) )
+                            continue outer;
+
+                // All uses done, schedule
+                _doSchedLate(n,ns,late);
+            }
+
+            // Walk all inputs and put on worklist, as their last-use might now be done
+            for( Node def : n._inputs )
+                if( def!=null && late[def._nid]==null ) {
+                    work.push(def);
+                    // if the def has a load use, maybe the load can fire
+                    for( Node ld : def._outputs )
+                        if( ld instanceof LoadNode && late[ld._nid]==null )
+                            work.push(ld);
+                }
+        }
+    }
+
+    private static void _doSchedLate(Node n, Node[] ns, CFGNode[] late) {
+        // Walk uses, gathering the LCA (Least Common Ancestor) of uses
+        CFGNode early = n.in(0) instanceof CFGNode cfg ? cfg : n.in(0).cfg0();
+        assert early != null;
+        CFGNode lca = null;
+        for( Node use : n._outputs )
+            if( use != null )
+              lca = use_block(n,use, late)._idom(lca,null);
+
+        // Loads may need anti-dependencies, raising their LCA
+        if( n instanceof LoadNode load )
+            lca = find_anti_dep(lca,load,early,late);
+
+        // Walk up from the LCA to the early, looking for best place.  This is
+        // the lowest execution frequency, approximated by least loop depth and
+        // deepest control flow.
+        CFGNode best = lca;
+        lca = lca.idom();       // Already found best for starting LCA
+        for( ; lca != early.idom(); lca = lca.idom() )
+            if( better(lca,best) )
+                best = lca;
+        assert !(best instanceof IfNode);
+        ns  [n._nid] = n;
+        late[n._nid] = best;
+    }
+
+    // Block of use.  Normally from late[] schedule, except for Phis, which go
+    // to the matching Region input.
+    private static CFGNode use_block(Node n, Node use, CFGNode[] late) {
+        if( !(use instanceof PhiNode phi) )
+            return late[use._nid];
+        CFGNode found=null;
+        for( int i=1; i<phi.nIns(); i++ )
+            if( phi.in(i)==n )
+                found = phi.region().cfg(i)._idom(found,null);
+
+        assert found!=null;
+        return found;
+    }
+
+
+    // Least loop depth first, then largest idepth
+    private static boolean better( CFGNode lca, CFGNode best ) {
+        return lca.loopDepth() < best.loopDepth() ||
+                (lca.idepth() > best.idepth() || best instanceof IfNode);
+    }
+
+    private static CFGNode find_anti_dep(CFGNode lca, LoadNode load, CFGNode early, CFGNode[] late) {
+        // We could skip final-field loads here.
+        // Walk LCA->early, flagging Load's block location choices
+        for( CFGNode cfg=lca; early!=null && cfg!=early.idom(); cfg = cfg.idom() )
+            cfg._anti = load._nid;
+        // Walk load->mem uses, looking for Stores causing an anti-dep
+        for( Node mem : load.mem()._outputs ) {
+            switch( mem ) {
+            case StoreNode st:
+                assert late[st._nid]!=null;
+                lca = anti_dep(load,late[st._nid],st.cfg0(),lca,st);
+                break;
+            case CallNode st:
+                assert late[st._nid]!=null;
+                lca = anti_dep(load,late[st._nid],st.cfg0(),lca,st);
+                break;
+            case PhiNode phi:
+                // Repeat anti-dep for matching Phi inputs.
+                // No anti-dep edges but may raise the LCA.
+                for( int i=1; i<phi.nIns(); i++ )
+                    if( phi.in(i)==load.mem() )
+                        lca = anti_dep(load,phi.region().cfg(i),load.mem().cfg0(),lca,null);
+                break;
+            case NewNode st: break;
+            case LoadNode ld: break; // Loads do not cause anti-deps on other loads
+            case ReturnNode ret: break; // Load must already be ahead of Return
+            case MemMergeNode ret: break; // Mem uses now on ScopeMin
+            case NeverNode never: break;
+            default: throw Utils.TODO();
+            }
+        }
+        return lca;
+    }
+
+    //
+    private static CFGNode anti_dep( LoadNode load, CFGNode stblk, CFGNode defblk, CFGNode lca, Node st ) {
+        // Walk store blocks "reach" from its scheduled location to its earliest
+        for( ; stblk != defblk.idom(); stblk = stblk.idom() ) {
+            // Store and Load overlap, need anti-dependence
+            if( stblk._anti==load._nid ) {
+                lca = stblk._idom(lca,null); // Raise Loads LCA
+                if( lca == stblk && st != null && st._inputs.find(load) == -1 ) // And if something moved,
+                    st.addDef(load);   // Add anti-dep as well
+                return lca;            // Cap this stores' anti-dep to here
+            }
+        }
+        return lca;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/GraphVisualizer.java b/chapter20/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
new file mode 100644
index 00000000..30e25916
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
@@ -0,0 +1,288 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+
+import java.util.*;
+
+import static com.seaofnodes.simple.Utils.TODO;
+
+/**
+ * Simple visualizer that outputs GraphViz dot format.
+ * The dot output must be saved to a file and run manually via dot to generate the SVG output.
+ * Currently, this is done manually.
+ */
+public class GraphVisualizer {
+
+    /**
+     * If set to true we put the control nodes in a separate cluster from
+     * data nodes.
+     */
+    boolean _separateControlCluster = false;
+
+    public GraphVisualizer(boolean separateControlCluster) { this._separateControlCluster = separateControlCluster; }
+    public GraphVisualizer() { this(false); }
+
+    public String generateDotOutput(Parser parse) { return generateDotOutput(parse._code._stop,parse._scope,parse._xScopes); }
+    public String generateDotOutput(StopNode stop, Node scope, Stack<ScopeNode> xScopes) {
+
+        // Since the graph has cycles, we need to create a flat list of all the
+        // nodes in the graph.
+        Collection<Node> all = findAll(xScopes, stop, scope);
+        StringBuilder sb = new StringBuilder();
+        sb.append("digraph chapter18 {\n");
+        sb.append("/*\n");
+        sb.append(stop._src);
+        sb.append("\n*/\n");
+
+        // To keep the Scopes below the graph and pointing up into the graph we
+        // need to group the Nodes in a subgraph cluster, and the scopes into a
+        // different subgraph cluster.  THEN we can draw edges between the
+        // scopes and nodes.  If we try to cross subgraph cluster borders while
+        // still making the subgraphs DOT gets confused.
+        sb.append("\trankdir=BT;\n"); // Force Nodes before Scopes
+
+        // CNC - turned off Apr/8/2024, gives more flex in the layout and
+        // removes some of the more ludicrous layout choices.
+        // Preserve node input order
+        //sb.append("\tordering=\"in\";\n");
+
+        // Merge multiple edges hitting the same node.  Makes common shared
+        // nodes much prettier to look at.
+        sb.append("\tconcentrate=\"true\";\n");
+
+        // Force nested scopes to order
+        sb.append("\tcompound=\"true\";\n");
+
+        // Just the Nodes first, in a cluster no edges
+        nodes(sb, all);
+
+        // Now the scopes, in a cluster no edges
+        if( xScopes != null )
+            for( ScopeNode xscope : xScopes )
+                if( !xscope.isDead() )
+                    scope( sb, xscope );
+
+        // Walk the Node edges
+        nodeEdges(sb, all);
+
+        // Walk the active Scope edges
+        if( xScopes != null )
+            for( ScopeNode xscope : xScopes )
+                if( !xscope.isDead() )
+                    scopeEdges( sb, xscope );
+
+        sb.append("}\n");
+        return sb.toString();
+    }
+
+    private void nodesByCluster(StringBuilder sb, boolean doCtrl, Collection<Node> all) {
+        if (!_separateControlCluster && doCtrl) // all nodes in 1 cluster
+            return;
+        // Just the Nodes first, in a cluster no edges
+        sb.append(doCtrl ? "\tsubgraph cluster_Controls {\n" : "\tsubgraph cluster_Nodes {\n"); // Magic "cluster_" in the subgraph name
+        for (Node n : all) {
+            if (n instanceof ProjNode || n instanceof CProjNode || n instanceof MemMergeNode || n==Parser.XCTRL)
+                continue; // Do not emit, rolled into MultiNode or Scope cluster already
+            if( _separateControlCluster &&  doCtrl && !(n instanceof CFGNode) ) continue;
+            if( _separateControlCluster && !doCtrl &&  (n instanceof CFGNode) ) continue;
+            sb.append("\t\t").append(n.uniqueName()).append(" [ ");
+            String lab = n.glabel();
+            if (n instanceof MultiNode) {
+                // Make a box with the MultiNode on top, and all the projections on the bottom
+                sb.append("shape=plaintext label=<\n");
+                sb.append("\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\" CELLPADDING=\"4\">\n");
+                sb.append("\t\t\t<TR><TD BGCOLOR=\"yellow\">").append(lab).append("</TD></TR>\n");
+                sb.append("\t\t\t<TR>");
+                boolean doProjTable = false;
+                n._outputs.sort((x,y) -> x instanceof ProjNode xp && y instanceof ProjNode yp ? (xp._idx - yp._idx) : (x._nid - y._nid));
+                for (Node use : n._outputs) {
+                    if (use instanceof ProjNode proj) {
+                        if (!doProjTable) {
+                            doProjTable = true;
+                            sb.append("<TD>").append("\n");
+                            sb.append("\t\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">").append("\n");
+                            sb.append("\t\t\t\t<TR>");
+                        }
+                        sb.append("<TD PORT=\"p").append(proj._idx).append("\">").append(proj.glabel()).append("</TD>");
+                    }
+                    if (use instanceof CProjNode proj) {
+                        if (!doProjTable) {
+                            doProjTable = true;
+                            sb.append("<TD>").append("\n");
+                            sb.append("\t\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">").append("\n");
+                            sb.append("\t\t\t\t<TR>");
+                        }
+                        sb.append("<TD PORT=\"p").append(proj._idx).append("\" BGCOLOR=\"yellow\">").append(proj.glabel()).append("</TD>");
+                    }
+                }
+                if (doProjTable) {
+                    sb.append("</TR>").append("\n");
+                    sb.append("\t\t\t\t</TABLE>").append("\n");
+                    sb.append("\t\t\t</TD>");
+                }
+                sb.append("</TR>\n");
+                sb.append("\t\t\t</TABLE>>\n\t\t");
+
+            } else {
+                // control nodes have box shape
+                // other nodes are ellipses, i.e. default shape
+                if( n instanceof CFGNode ) sb.append("shape=box style=filled fillcolor=yellow ");
+                else if (n instanceof PhiNode) sb.append("style=filled fillcolor=lightyellow ");
+                sb.append("label=\"").append(lab).append("\" ");
+            }
+            sb.append("];\n");
+        }
+        if (!_separateControlCluster) {
+            // Force Region & Phis to line up
+            for (Node n : all) {
+                if (n instanceof RegionNode region) {
+                    sb.append("\t\t{ rank=same; ");
+                    sb.append(region.uniqueName()).append(";");
+                    for (Node phi : region._outputs)
+                        if (phi instanceof PhiNode) sb.append(phi.uniqueName()).append(";");
+                    sb.append("}\n");
+                }
+            }
+        }
+        sb.append("\t}\n");     // End Node cluster
+    }
+
+    private void nodes(StringBuilder sb, Collection<Node> all) {
+        nodesByCluster(sb, true, all);
+        nodesByCluster(sb, false, all);
+    }
+
+    // Build a nested scope display, walking the _prev edge
+    private void scope( StringBuilder sb, ScopeNode scope ) {
+        sb.append("\tnode [shape=plaintext];\n");
+        int last = scope.nIns();
+        int max = scope._lexSize.size();
+        for( int i = 0; i < max; i++ ) {
+            int level = max-i-1;
+            String scopeName = makeScopeName(scope, level);
+            sb.append("\tsubgraph cluster_").append(scopeName).append(" {\n"); // Magic "cluster_" in the subgraph name
+            // Special for memory ScopeMinNode
+            if( level==0 ) {
+                MemMergeNode n = scope.mem();
+                sb.append("\t\t").append(n.uniqueName()).append(" [label=\"").append(n.glabel()).append("\"];\n");
+            }
+            sb.append("\t\t").append(scopeName).append(" [label=<\n");
+            sb.append("\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">\n");
+            // Add the scope level
+            sb.append("\t\t\t<TR><TD BGCOLOR=\"cyan\">").append(level).append("</TD>");
+            int lexStart=scope._lexSize.at(level);
+            for( int j=lexStart; j<last; j++ ) {
+                var v = scope._vars.at(j);
+                sb.append("<TD PORT=\"").append(makePortName(scopeName, v._name)).append("\">").append(v._name).append("</TD>");
+            }
+            last = lexStart;
+            sb.append("</TR>\n");
+            sb.append("\t\t\t</TABLE>>];\n");
+        }
+        // Scope clusters nest, so the graphics shows the nested scopes, so
+        // they are not closed as they are printed; so they just keep nesting.
+        // We close them all at once here.
+        sb.append( "\t}\n".repeat( max ) ); // End all Scope clusters
+    }
+
+    private String makeScopeName(ScopeNode sn, int level) { return sn.uniqueName() + "_" + level; }
+    private String makePortName(String scopeName, String varName) { return scopeName + "_" + varName; }
+
+    // Walk the node edges
+    private void nodeEdges(StringBuilder sb, Collection<Node> all) {
+        // All them edge labels
+        sb.append("\tedge [ fontname=Helvetica, fontsize=8 ];\n");
+        for( Node n : all ) {
+            // Do not display the Constant->Start edge;
+            // ProjNodes handled by Multi;
+            // ScopeNodes are done separately
+            if( n instanceof ConstantNode || n instanceof ProjNode || n instanceof CProjNode || n instanceof ScopeNode || n==Parser.XCTRL )
+                continue;
+            for( int i=0; i<n.nIns(); i++ ) {
+                Node def = n.in(i);
+                if( n instanceof PhiNode && def instanceof RegionNode ) {
+                    // Draw a dotted use->def edge from Phi to Region.
+                    sb.append('\t').append(n.uniqueName());
+                    sb.append(" -> ");
+                    sb.append(def.uniqueName());
+                    sb.append(" [style=dotted taillabel=").append(i).append("];\n");
+                } else if( def != null ) {
+                    // Most edges land here use->def
+                    sb.append('\t').append(n.uniqueName()).append(" -> ");
+                    if( def instanceof CProjNode proj ) {
+                        String mname = proj.ctrl().uniqueName();
+                        sb.append(mname).append(":p").append(proj._idx);
+                    } else if( def instanceof ProjNode proj ) {
+                        String mname = proj.in(0).uniqueName();
+                        sb.append(mname).append(":p").append(proj._idx);
+                    } else sb.append(def.uniqueName());
+                    // Number edges, so we can see how they track
+                    sb.append("[taillabel=").append(i);
+                    // The edge from New to ctrl is just for anchoring the New
+                    if ( n instanceof NewNode )
+                        sb.append(" color=green");
+                    // control edges are colored red
+                    else if( def instanceof CFGNode )
+                        sb.append(" color=red");
+                    else if( def.isMem() )
+                        sb.append(" color=blue");
+                    // Backedges do not add a ranking constraint
+                    if( i==2 && (n instanceof PhiNode || n instanceof LoopNode) )
+                        sb.append(" constraint=false");
+                    sb.append("];\n");
+                }
+            }
+        }
+    }
+
+    // Walk the scope edges
+    private void scopeEdges( StringBuilder sb, ScopeNode scope ) {
+        sb.append("\tedge [style=dashed color=cornflowerblue];\n");
+        int level=0;
+        for( var v : scope._vars ) {
+            Node def = scope.in(v._idx);
+            while( def instanceof ScopeNode lazy )
+                def = lazy.in(v._idx);
+            if( def==null ) continue;
+            while( level < scope._lexSize.size() && v._idx >= scope._lexSize.at(level) )
+                level++;
+            String scopeName = makeScopeName(scope, level-1);
+            sb.append("\t")
+                .append(scopeName).append(":")
+                .append('"').append(makePortName(scopeName, v._name)).append('"') // wrap port name with quotes because $ctrl is not valid unquoted
+                .append(" -> ");
+            if( def instanceof CProjNode proj ) {
+                sb.append(def.in(0).uniqueName()).append(":p").append(proj._idx);
+            } else if( def instanceof ProjNode proj ) {
+                sb.append(def.in(0).uniqueName()).append(":p").append(proj._idx);
+            } else sb.append(def.uniqueName());
+            sb.append(";\n");
+        }
+    }
+
+    /**
+     * Finds all nodes in the graph.
+     */
+    public static Collection<Node> findAll(Stack<ScopeNode> ss, Node... ns) {
+        final HashMap<Integer, Node> all = new HashMap<>();
+        for( Node n : ns )
+            walk(all, n);
+        if( ss != null )
+            for( Node n : ss )
+                walk(all, n);
+        return all.values();
+    }
+
+    /**
+     * Walk a subgraph and populate distinct nodes in the all list.
+     */
+    private static void walk(HashMap<Integer,Node> all, Node n) {
+        if(n == null ) return;
+        if (all.get(n._nid) != null) return; // Been there, done that
+        all.put(n._nid, n);
+        for (Node c : n._inputs)
+            walk(all, c);
+        for( Node c : n._outputs )
+            walk(all, c);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/IRPrinter.java b/chapter20/src/main/java/com/seaofnodes/simple/IRPrinter.java
new file mode 100644
index 00000000..3cddacfd
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/IRPrinter.java
@@ -0,0 +1,279 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+
+public abstract class IRPrinter {
+
+    // Print a node on 1 line, columnar aligned, as:
+    // NNID NNAME DDEF DDEF  [[  UUSE UUSE  ]]  TYPE
+    // 1234 sssss 1234 1234 1234 1234 1234 1234 tttttt
+    public static SB printLine( Node n, SB sb ) {
+        sb.p("%4d %-7.7s ".formatted(n._nid,n.label()));
+        if( n._inputs==null )
+            return sb.p("DEAD\n");
+        for( Node def : n._inputs )
+            sb.p(def==null ? "____" : "%4d".formatted(def._nid))
+                // Lazy Phi indicator
+                .p(n instanceof MemMergeNode && def instanceof MemMergeNode ? "^" : " ");
+        for( int i = n._inputs.size(); i<4; i++ )
+            sb.p("     ");
+        sb.p(" [[  ");
+        for( Node use : n._outputs )
+            sb.p(use==null ? "____ " : "%4d ".formatted(use._nid));
+        int lim = 6 - Math.max(n._inputs.size(),4);
+        for( int i = n._outputs.size(); i<lim; i++ )
+            sb.p("     ");
+        sb.p(" ]]  ");
+        if( n._type!= null ) sb.p(n._type.str());
+        return sb.p("\n");
+    }
+
+
+    public static String prettyPrint(Node node, int depth) {
+        return CodeGen.CODE._phase.ordinal() > CodeGen.Phase.Schedule.ordinal()
+            ? _prettyPrintScheduled( node, depth )
+            : _prettyPrint( node, depth );
+    }
+
+    // Another bulk pretty-printer.  Makes more effort at basic-block grouping.
+    private static String _prettyPrint( Node node, int depth ) {
+        // First, a Breadth First Search at a fixed depth.
+        BFS bfs = new BFS(node,depth);
+        // Convert just that set to a post-order
+        ArrayList<Node> rpos = new ArrayList<>();
+        BitSet visit = new BitSet();
+        for( int i=bfs._lim; i< bfs._bfs.size(); i++ )
+            postOrd( bfs._bfs.get(i), null, rpos, visit, bfs._bs);
+        // Reverse the post-order walk
+        SB sb = new SB();
+        boolean gap=false;
+        for( int i=rpos.size()-1; i>=0; i-- ) {
+            Node n = rpos.get(i);
+            if( n instanceof CFGNode || n.isMultiHead() ) {
+                if( !gap ) sb.p("\n"); // Blank before multihead
+                if( n instanceof FunNode fun )
+                    fun.sig().print(sb.p("--- ").p(fun._name==null ? "" : fun._name).p(" "),false).p("----------------------\n");
+                printLine( n, sb );         // Print head
+                while( --i >= 0 ) {
+                    Node t = rpos.get(i);
+                    if( !t.isMultiTail() ) { i++; break; }
+                    printLine( t, sb );
+                }
+                if( n instanceof ReturnNode ret ) {
+                    FunNode fun = ret.fun();
+                    fun.sig().print(sb.p("--- ").p(fun._name==null ? "" : fun._name).p(" "),false).p("----------------------\n");
+                }
+                if( !(n instanceof CallNode) ) {
+                    sb.p("\n"); // Blank after multitail
+                    gap = true;
+                }
+            } else {
+                printLine( n, sb );
+                gap = false;
+            }
+        }
+        return sb.toString();
+    }
+
+    private static void postOrd(Node n, Node prior, ArrayList<Node> rpos, BitSet visit, BitSet bfs) {
+        if( !bfs.get(n._nid) )
+            return;  // Not in the BFS visit
+        if( n instanceof FunNode && !(prior instanceof StartNode) )
+            return;                     // Only visit Fun from Start
+        if( visit.get(n._nid) ) return; // Already post-order walked
+        visit.set(n._nid);
+        // First walk the CFG, then everything
+        if( n instanceof CFGNode ) {
+            for( Node use : n._outputs )
+                // Follow CFG, not across call/function borders, and not around backedges
+                if( use instanceof CFGNode && !(n instanceof CallNode && use instanceof FunNode) &&
+                    use.nOuts() >= 1 &&  !(use._outputs.get(0) instanceof LoopNode) )
+                    postOrd(use, n, rpos,visit,bfs);
+            for( Node use : n._outputs )
+                // Follow CFG, not across call/function borders
+                if( use instanceof CFGNode && !(n instanceof CallNode && use instanceof FunNode) )
+                    postOrd(use,n,rpos,visit,bfs);
+        }
+        // Follow all outputs
+        for( Node use : n._outputs )
+            if( use != null &&
+                !(n instanceof CallNode && use instanceof FunNode) &&
+                (n instanceof FunNode || !(use instanceof ParmNode)) )
+                postOrd(use, n, rpos,visit,bfs);
+        // Post-order
+        rpos.add(n);
+    }
+
+    // Breadth-first search, broken out in a class to keep in more independent.
+    // Maintains a root-set of Nodes at the limit (or past by 1 if MultiHead).
+    public static class BFS {
+        // A breadth first search, plus MultiHeads for any MultiTails
+        public final ArrayList<Node> _bfs;
+        public final BitSet _bs; // Visited members by node id
+        public final int _depth; // Depth limit
+        public final int _lim; // From here to _bfs._len can be roots for a reverse search
+        public BFS( Node base, int d ) {
+            _depth = d;
+            _bfs = new ArrayList<>();
+            _bs = new BitSet();
+
+            add(base);                 // Prime the pump
+            int idx=0, lim=1;          // Limit is where depth counter changes
+            while( idx < _bfs.size() ) { // Ran out of nodes below depth
+                Node n = _bfs.get(idx++);
+                for( Node def : n._inputs )
+                    if( def!=null && !_bs.get(def._nid) )
+                        add(def);
+                if( idx==lim ) {    // Depth counter changes at limit
+                    if( --d < 0 )
+                        break;      // Ran out of depth
+                    lim = _bfs.size();  // New depth limit
+                }
+            }
+            // Toss things past the limit except multi-heads
+            while( idx < _bfs.size() ) {
+                Node n = _bfs.get(idx);
+                if( n.isMultiHead() ) idx++;
+                else del(idx);
+            }
+            // Root set is any node with no inputs in the visited set
+            lim = _bfs.size();
+            for( int i=_bfs.size()-1; i>=0; i-- )
+                if( !any_visited(_bfs.get(i)) )
+                    swap( i,--lim);
+            _lim = lim;
+        }
+        void swap( int x, int y ) {
+            if( x==y ) return;
+            Node tx = _bfs.get(x);
+            Node ty = _bfs.get(y);
+            _bfs.set(x,ty);
+            _bfs.set(y,tx);
+        }
+        void add(Node n) {
+            _bfs.add(n);
+            _bs.set(n._nid);
+        }
+        void del(int idx) {
+            _bs.clear(_bfs.get(idx)._nid);
+            Utils.del(_bfs, idx);
+        }
+        boolean any_visited( Node n ) {
+            for( Node def : n._inputs )
+                if( def!=null && _bs.get(def._nid) )
+                    return true;
+            return false;
+        }
+    }
+
+    // Bulk pretty printer, knowing scheduling information is available
+    private static String _prettyPrintScheduled( Node node, int depth ) {
+        // Backwards DFS walk to depth.
+        HashMap<Integer,Integer> ds = new HashMap<>();
+        Ary<Node> ns = new Ary<>(Node.class);
+        _walk(ds,ns,node,depth);
+        // Remove data projections, these are force-printed behind their multinode head
+        for( int i=0; i<ns.size(); i++ ) {
+            if( ns.get(i) instanceof ProjNode proj && !(proj.in(0) instanceof CFGNode) ) {
+                ns.del(i--);
+                ds.remove(proj._nid);
+            }
+        }
+        // Print by block with least idepth
+        SB sb = new SB();
+        Ary<Node> bns = new Ary<>(Node.class);
+        while( !ds.isEmpty() ) {
+            CFGNode blk = null;
+            for( Node n : ns ) {
+                CFGNode cfg = n instanceof CFGNode cfg0 && cfg0.blockHead() ? cfg0 : n.cfg0();
+                if( blk==null || cfg.idepth() < blk.idepth() )
+                    blk = cfg;
+            }
+            Integer d = ds.remove(blk._nid);
+            ns.del(ns.find(blk));
+
+            // Print block header
+            sb.p("%-13.13s".formatted(label(blk)+":"));
+            sb.p( "     ".repeat(4) ).p(" [[  ");
+            if( blk instanceof StartNode ) ;
+            else if( blk instanceof RegionNode || blk instanceof StopNode )
+                for( int i=(blk instanceof StopNode ? 3 : 1); i<blk.nIns(); i++ )
+                    label(sb,blk.cfg(i));
+            else
+                label(sb,blk.cfg(0));
+            sb.p(" ]]  \n");
+            printLine(blk,sb);
+
+            // Collect block contents that are in the depth limit
+            bns.clear();
+            int xd = Integer.MAX_VALUE;
+            for( Node use : blk._outputs ) {
+                Integer i = ds.get(use._nid);
+                if( i!=null && !(use instanceof CFGNode cfg && cfg.blockHead()) ) {
+                    if( bns.find(use)==-1 )
+                        bns.add(use);
+                    xd = Math.min(xd,i);
+                }
+            }
+            // Print Phis up front, if any
+            for( int i=0; i<bns.size(); i++ )
+                if( bns.get(i) instanceof PhiNode phi )
+                    printLine( phi, sb,bns,i--,ds,ns);
+
+            // Print block contents in depth order, bumping depth until whole block printed
+            for( ; !bns.isEmpty(); xd++ )
+                for( int i=0; i<bns.size(); i++ ) {
+                    Node n = bns.get(i);
+                    if( ds.get(n._nid)==xd ) {
+                        printLine( n, sb, bns, i--, ds,ns );
+                        if( n instanceof MultiNode && !(n instanceof CFGNode) ) {
+                            for( Node use : n._outputs ) {
+                                printLine(use,sb,bns,bns.indexOf(use),ds,ns);
+                            }
+                        }
+                    }
+                }
+            sb.p("\n");
+        }
+        return sb.toString();
+    }
+
+    private static void _walk( HashMap<Integer,Integer> ds, Ary<Node> ns, Node node, int d ) {
+        Integer nd = ds.get(node._nid);
+        if( nd!=null && d <= nd ) return; // Been there, done that
+        Integer old = ds.put(node._nid,d) ;
+        if( old == null )
+          ns.add(node);
+        if( d == 0 ) return;    // Depth cutoff
+        for( Node def : node._inputs )
+            if( def != null &&
+                !(node instanceof LoopNode loop && loop.back()==def) &&
+                // Don't walk into or out of functions
+                !(node instanceof CallEndNode && def instanceof ReturnNode) &&
+                !(node instanceof FunNode && def instanceof CallNode) &&
+                !(node instanceof ParmNode && !(def instanceof FunNode))
+            )
+                _walk(ds,ns,def,d-1);
+    }
+
+    static String label( CFGNode blk ) {
+        if( blk instanceof StartNode ) return "START";
+        return (blk instanceof LoopNode ? "LOOP" : "L")+blk._nid;
+    }
+    static void label( SB sb, CFGNode blk ) {
+        if( !blk.blockHead() ) blk = blk.cfg(0);
+        sb.p( "%-9.9s ".formatted( label( blk ) ) );
+    }
+    static void printLine( Node n, SB sb, Ary<Node> bns, int i, HashMap<Integer,Integer> ds, Ary<Node> ns ) {
+        printLine( n, sb );
+        if( i != -1 ) bns.del(i);
+        ds.remove(n._nid);
+        int idx = ns.find(n);
+        if( idx!=-1 ) ns.del(idx);
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/IterPeeps.java b/chapter20/src/main/java/com/seaofnodes/simple/IterPeeps.java
new file mode 100644
index 00000000..265e0b21
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/IterPeeps.java
@@ -0,0 +1,196 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.Random;
+
+/**
+ * The IterPeeps runs after parsing. It iterates the peepholes to a fixed point
+ * so that no more peepholes apply.  This should be linear because peepholes rarely
+ * (never?)  increase code size.  The graph should monotonically reduce in some
+ * dimension, which is usually size.  It might also reduce in e.g. number of
+ * MulNodes or Load/Store nodes, swapping out more "expensive" Nodes for cheaper
+ * ones.
+ * <br>
+ * The theoretical overall worklist is mindless just grabbing the next thing and
+ * doing it.  If the graph changes, put the neighbors on the worklist.
+ * <br>
+ * Lather, Rinse, Repeat until the worklist runs dry.
+ * <p>
+ * The main issues we have to deal with:
+ *
+ * <ul>
+ * <li>Nodes have uses; replacing some set of Nodes with another requires more graph
+ *   reworking.  Not rocket science, but it can be fiddly.  Its helpful to have a
+ *   small set of graph munging utilities, and the strong invariant that the graph
+ *   is stable and correct between peepholes.  In our case `Node.subsume` does
+ *   most of the munging, building on our prior stable Node utilities.</li>
+ *
+ * <li>Changing a Node also changes the graph "neighborhood".  The neighbors need to
+ *   be checked to see if THEY can also peephole, and so on.  After any peephole
+ *   or graph update we put a Nodes uses and defs on the worklist.</li>
+ *
+ * <li>Our strong invariant is that for all Nodes, either they are on the worklist
+ *   OR no peephole applies.  This invariant is easy to check, although expensive.
+ *   Basically the normal "iterate peepholes to a fixed point" is linear, and this
+ *   check is linear at each peephole step... so quadratic overall.  Its a useful
+ *   assert, but one we can disable once the overall algorithm is stable - and
+ *   then turn it back on again when some new set of peepholes is misbehaving.
+ *   The code for this is turned on in `IterPeeps.iterate` as `assert
+ *   progressOnList(stop);`</li>
+ * </ul>
+ */
+public class IterPeeps {
+
+    private final WorkList<Node> _work;
+
+    IterPeeps( long seed ) { _work = new WorkList<>(seed); }
+
+    public <N extends Node> N add( N n ) { return (N)_work.push(n); }
+
+    public void addAll( Ary<Node> ary ) { _work.addAll(ary); }
+
+    /**
+     * Iterate peepholes to a fixed point
+     */
+    public void iterate( CodeGen code ) {
+        assert progressOnList(code);
+        int cnt=0;
+
+        Node n;
+        while( (n=_work.pop()) != null ) {
+            if( n.isDead() )  continue;
+            cnt++;              // Useful for debugging, searching which peephole broke things
+            Node x = n.peepholeOpt();
+            if( x != null ) {
+                if( x.isDead() ) continue;
+                // peepholeOpt can return brand-new nodes, needing an initial type set
+                if( x._type==null ) x.setType(x.compute());
+                // Changes require neighbors onto the worklist
+                if( x != n || !(x instanceof ConstantNode) ) {
+                    // All outputs of n (changing node) not x (prior existing node).
+                    for( Node z : n._outputs ) _work.push(z);
+                    // Everybody gets a free "go again" in case they didn't get
+                    // made in their final form.
+                    _work.push(x);
+                    // If the result is not self, revisit all inputs (because
+                    // there's a new user), and replace in the graph.
+                    if( x != n ) {
+                        for( Node z : n. _inputs ) _work.push(z);
+                        n.subsume(x);
+                    }
+                }
+                // If there are distant neighbors, move to worklist
+                n.moveDepsToWorklist();
+                JSViewer.show(); // Show again
+                assert progressOnList(code); // Very expensive assert
+            }
+            if( n.isUnused() && !(n instanceof StopNode) )
+                n.kill();       // Just plain dead
+        }
+
+    }
+
+    // Visit ALL nodes and confirm the invariant:
+    //   Either you are on the _work worklist OR running `iter()` makes no progress.
+
+    // This invariant ensures that no progress is missed, i.e., when the
+    // worklist is empty we have indeed done all that can be done.  To help
+    // with debugging, the {@code assert} is broken out in a place where it is easy to
+    // stop if a change is found.
+
+    // Also, the normal usage of `iter()` may attempt peepholes with distance
+    // neighbors and these should fail, but will then try to add dependencies
+    // {@link #Node.addDep} which is a side effect in an assert.  The {@link
+    // #midAssert} is used to stop this side effect.
+    private boolean progressOnList(CodeGen code) {
+        code._midAssert = true;
+        Node changed = code._stop.walk( n -> {
+                Node m = n;
+                if( n.compute().isa(n._type) && (!n.iskeep() || n._nid<=6) ) { // Types must be forwards, even if on worklist
+                    if( _work.on(n) ) return null;
+                    m = n.peepholeOpt();
+                    if( m==null ) return null;
+                }
+                System.err.println("BREAK HERE FOR BUG");
+                return m;
+            });
+        code._midAssert = false;
+        return changed==null;
+    }
+
+    /**
+     * Classic WorkList, with a fast add/remove, dup removal, random pull.
+     * The Node's nid is used to check membership in the worklist.
+     */
+    public static class WorkList<E extends Node> {
+
+        private Node[] _es;
+        private int _len;
+        private final BitSet _on;   // Bit set if Node._nid is on WorkList
+        private final Random _R;    // For randomizing pull from the WorkList
+        private final long _seed;
+
+        /* Useful stat - how many nodes are processed in the post parse iterative opt */
+        private long _totalWork = 0;
+
+        WorkList() { this(123); }
+        WorkList(long seed) {
+            _es = new Node[1];
+            _len=0;
+            _on = new BitSet();
+            _seed = seed;
+            _R = new Random();
+            _R.setSeed(_seed);
+        }
+
+        /**
+         * Pushes a Node on the WorkList, ensuring no duplicates
+         * If Node is null it will not be added.
+         */
+        public E push( E x ) {
+            if( x==null ) return null;
+            int idx = x._nid;
+            if( !_on.get(idx) ) {
+                _on.set(idx);
+                if( _len==_es.length )
+                    _es = Arrays.copyOf(_es,_len<<1);
+                _es[_len++] = x;
+                _totalWork++;
+            }
+            return x;
+        }
+
+        public void addAll( Ary<E> ary ) {
+            for( E n : ary )
+                push(n);
+        }
+
+        /**
+         * True if Node is on the WorkList
+         */
+        boolean on( E x ) { return _on.get(x._nid); }
+        boolean isEmpty() { return _len==0; }
+
+        /**
+         * Removes a random Node from the WorkList; null if WorkList is empty
+         */
+        E pop() {
+            if( _len == 0 ) return null;
+            int idx = _R.nextInt(_len);
+            E x = (E)_es[idx];
+            _es[idx] = _es[--_len]; // Compress array
+            _on.clear(x._nid);
+            return x;
+        }
+
+        public void clear() {
+            _len = 0;
+            _on.clear();
+            _R.setSeed(_seed);
+            _totalWork = 0;
+        }
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/JSViewer.java b/chapter20/src/main/java/com/seaofnodes/simple/JSViewer.java
new file mode 100644
index 00000000..fcb0c28a
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/JSViewer.java
@@ -0,0 +1,402 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.io.IOException;
+import java.util.Stack;
+import java.nio.file.Paths;
+import java.util.Collection;
+import static com.seaofnodes.simple.CodeGen.CODE;
+
+public class JSViewer implements AutoCloseable {
+    // Display programs in an endless loop
+    public static void main( String[] args ) throws Exception {
+        try(var js = new JSViewer()) {
+            js.run();
+        }
+    }
+
+    static boolean SHOW;
+
+    // WebSocket to the browser for display
+    static SimpleWebSocket SERVER;
+
+    static int N;               // Dot frames
+
+    JSViewer() throws Exception {
+        // Launch server; handshake
+        SERVER = new SimpleWebSocket(Paths.get("docs/index.html").toUri(),12345) ;
+    }
+
+    void run( ) throws Exception {
+        SERVER.put("!");
+        while( true ) {
+            String src = SERVER.get();
+            switch( src ) {
+            case null: return;
+            case "null": return;
+            case "+": break;    // Client requests more frames, but we send them all anyway
+            default:
+                System.out.println(src);
+                try {
+                    N=0;
+                    // Use parser scope, xscope when building views
+                    CodeGen code = new CodeGen(src);
+                    SHOW = true;
+                    show();
+                    // Parse program, generating views at every parse point
+                    code.parse();
+                    // No longer user parse internal state when building views
+                    code.opto();
+
+                    // Catch and ignore Parser errors
+                } catch(RuntimeException re) {
+                    System.err.println(re);
+                } finally {
+                    SHOW = false;
+                    SERVER.put("#"); // Final frame
+                }
+                break;
+            }
+        }
+    }
+
+    @Override public void close() throws IOException {
+        SERVER.close();
+        SERVER=null;
+    }
+
+    public static void show() { if( SERVER!=null && SHOW ) _show(); }
+    private static void _show() {
+        // Skip util we at least get the Parse object made
+        if( CODE._phase==null || CODE._phase.ordinal() < CodeGen.Phase.Parse.ordinal() )
+            return;
+        boolean midParse = CODE._phase == CodeGen.Phase.Parse;
+        Stack<ScopeNode> xScopes = midParse ? CODE.P._xScopes : null;
+
+        Collection<Node> all = GraphVisualizer.findAll(xScopes, CODE._stop, midParse ? CODE.P._scope: null);
+        SB sb = new SB();
+        sb.p("digraph view_").p(N++).p(" {\n").ii();
+        if( midParse )
+            sb.i().p("// POS: ").p(CODE.P.pos()).nl();
+
+        // To keep the Scopes below the graph and pointing up into the graph we
+        // need to group the Nodes in a subgraph cluster, and the scopes into a
+        // different subgraph cluster.  THEN we can draw edges between the
+        // scopes and nodes.  If we try to cross subgraph cluster borders while
+        // still making the subgraphs DOT gets confused.
+        sb.i().p("rankdir=BT;\n"); // Force Nodes before Scopes
+
+        // CNC - turned off Apr/8/2024, gives more flex in the layout and
+        // removes some of the more ludicrous layout choices.
+        // Preserve node input order
+        //sb.append("ordering=\"in\";\n");
+
+        // Merge multiple edges hitting the same node.  Makes common shared
+        // nodes much prettier to look at.
+        sb.i().p("concentrate=\"true\";\n");
+
+        // Force nested scopes to order
+        sb.i().p("compound=\"true\";\n");
+
+        // Just the Nodes first, in a cluster no edges
+        nodes(sb, all);
+
+        // Now the scopes, in a cluster no edges
+        if( midParse )
+            for( ScopeNode xscope : xScopes )
+                if( !xscope.isDead() )
+                    scope( sb, xscope );
+
+        // Walk the Node edges
+        nodeEdges(sb, midParse && !xScopes.empty() ? xScopes.peek() : null, all);
+
+        // Walk the active Scope edges
+        if( midParse )
+            for( ScopeNode xscope : xScopes )
+                if( !xscope.isDead() )
+                    scopeEdges( sb, xscope );
+
+
+        sb.p("}\n").di();
+        // Tell client another DOT frame
+        String dot = sb.toString();
+        System.out.println(dot);
+        try {
+            SERVER.put(dot);
+        } catch( IOException ioe ) {
+            try { SERVER.close();} catch( IOException ignored ){}
+        }
+    }
+
+
+    private static void nodes(SB sb, Collection<Node> all) {
+        // Just the Nodes first, in a cluster no edges
+        sb.i().p("subgraph cluster_Nodes {\n").ii(); // Magic "cluster_" in the subgraph name
+        for( Node n : all ) {
+            if( n instanceof ProjNode || n instanceof CProjNode || n instanceof MemMergeNode )
+                continue; // Do not emit, rolled into MultiNode or Scope cluster already
+            sb.i().p(n.uniqueName()).p(" [ ");
+            if( n instanceof MultiNode && !(n instanceof StartNode) ) {
+                // Make a box with the MultiNode on top, and all the projections on the bottom
+                sb.    p("shape=plaintext label=<\n").ii();
+                sb.i().p("<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\" CELLPADDING=\"4\">\n");
+                // Row over single cell for node label
+                cell(sb.i().p("<TR>"), n.glabel(), n, null).p("</TR>\n");
+                // Row over single cell, for nested table
+                sb.i().p("<TR><TD>\n").ii();
+                sb.i().p("<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">").p("\n");
+                sb.i().p("<TR>");
+                n._outputs.sort((x,y) -> x instanceof ProjNode xp && y instanceof ProjNode yp ? (xp._idx - yp._idx) : ((x==null ? 99999 : x._nid) - (y==null ? 99999 : y._nid)));
+                boolean empty_row=true;
+                for( Node use : n._outputs ) {
+                    int idx = idx(n);
+                    if( idx != -1 ) {
+                        cell(sb,use.glabel(),use,"p"+idx);
+                        empty_row=false;
+                    }
+                }
+                // At least one cell on row
+                if( empty_row )  sb.p("<TD></TD>");
+                sb.    p("</TR>").p("\n");
+                sb.i().p("</TABLE>").p("\n").di();
+                sb.i().p("</TD></TR>\n");
+                sb.i().p("</TABLE>>\n").di();
+                sb.i().p("];\n");
+
+            } else {
+                // control nodes have box shape
+                // other nodes are ellipses, i.e. default shape
+                //else if (n instanceof PhiNode) sb.p("style=filled fillcolor=lightyellow ");
+                node(sb,n.glabel(),n);
+                sb.p("];\n");
+            }
+        }
+        // Force Region & Phis to line up
+        for (Node n : all) {
+            if (n instanceof RegionNode region) {
+                sb.i().p("{ rank=same; ");
+                sb.p(region.uniqueName()).p(";");
+                for (Node phi : region._outputs)
+                    if (phi instanceof PhiNode) sb.p(phi.uniqueName()).p(";");
+                sb.p("}\n");
+            }
+        }
+        sb.di().i().p("}").nl();     // End Node cluster
+    }
+
+    // Build a nested scope display, walking the _prev edge
+    private static void scope( SB sb, ScopeNode scope ) {
+        sb.i().p("node [shape=plaintext];\n");
+        int last = scope.nIns();
+        int max = scope._lexSize.size()+1; // One more than lexsize
+        for( int i = 0; i < max; i++ ) {
+            int level = max-i-1;
+            String scopeName = makeScopeName(scope, level);
+            sb.i().p("subgraph cluster_").p(scopeName).p(" {\n").ii(); // Magic "cluster_" in the subgraph name
+            sb.i().p(scopeName).p(" [label=<\n").ii();
+            sb.i().p("<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">\n");
+            int lexStart = level==0 ? 0 : scope._lexSize.at(level-1);
+
+            // Special for memory ScopeMinNode
+            MemMergeNode n = scope.nIns()>1 ? scope.mem() : null;
+            if( level==0 && n!=null && n.nIns()>2 ) {
+                sb.i().p("<TR>");
+                for( int m=2; m<n.nIns(); m++ )
+                    cell(sb,"#"+m,n.alias(m),"m"+m);
+                sb.p("</TR>\n"); // End scope level
+            }
+
+            // Scope variables, empty if none
+            if( lexStart<last ) {
+                sb.i().p("<TR>\n");
+                for( int j=lexStart; j<last; j++ ) {
+                    if( scope.in(j)==null ) continue;
+                    var v = scope._vars.at(j);
+                    cell(sb.i(),v._name,scope.in(j),makePortName(scopeName, v._name)).nl();
+                }
+                last = lexStart;
+                sb.i().p("</TR>\n");
+            }
+            sb.i().p("</TABLE>>];\n").di();
+            // Scope label
+            sb.i().p(scopeName).p("A [label=\"").p(level).p("\" shape=doublecircle style=filled fillcolor=aqua fontsize=10 margin=0 width=0.2 ];\n");
+        }
+        // Scope clusters nest, so the graphics shows the nested scopes, so
+        // they are not closed as they are printed; so they just keep nesting.
+        // We close them all at once here.
+        for( int i=0; i<max; i++ )
+            sb.di().i().p("}\n");
+    }
+
+    // Append a cell, with color
+    private static SB cell(SB sb, String text, Node n, String port) {
+        sb.p("<TD");
+        String color = color(n);
+        sb.p(" BGCOLOR=\"").p(color).p("\"");
+        if( port!=null )  sb.p(" PORT=\"").p(port).p("\"");
+        return colorcell(sb.p(">"),text,n,dark(color)).p("</TD>");
+    }
+    private static SB node(SB sb, String text, Node n) {
+        String color = color(n);
+        sb.p("style=filled fillcolor=").p(color).p(" ");
+        String shape = switch( n ) {
+        case FunNode fun -> "shape=box peripheries=2";
+        case CFGNode cfg -> "shape=box";
+        default -> "";
+        };
+        sb.p(shape).p(" ");
+        return colorcell(sb.p("label=<"),text,n,dark(color)).p(">");
+    }
+
+    private static String color(Node n) {
+        return switch( n ) {
+        case CFGNode cfg  -> "yellow";
+        case NewNode nnn  -> "lightgreen";
+        case StructNode s -> "lightgreen";
+        default -> typeColor(n._type);
+        };
+    }
+    private static String typeColor(Type t) {
+        return t==null ? "white" : switch( t ) {
+        case TypeMem    mem -> "blue";
+        case TypeMemPtr tmp -> "green";
+        case TypeFunPtr tfp -> "orange";
+        case TypeRPC    rpc -> "antiquewhite";
+        case TypeInteger ti -> "lightblue";
+        case TypeFloat   tf -> "aqua";
+        case Type tn -> tn==Type.NIL ? "lightgray" : "red";
+        };
+    }
+    private static final String[] DARKS = new String[]{"blue","green","black"};
+    private static boolean dark(String color) { return Utils.find(DARKS,color) != -1; }
+
+
+
+    // Called with an open div
+    private static SB colorcell(SB sb, String text, Node n, boolean dark) {
+        if( dark ) sb.p("<font color=\"white\">");
+        sb.p(text);
+        if( n._type!=null ) {
+            sb.p("<br /><font point-size=\"10\">");
+            n._type.gprint(sb);
+            sb.p("</font>");
+        }
+        if( dark ) sb.p("</font>");
+        return sb;
+    }
+
+
+    private static String makeScopeName(ScopeNode sn, int level) { return sn.uniqueName() + "_" + level; }
+    private static String makePortName(String scopeName, String varName) { return scopeName + "_" + varName; }
+
+    // Walk the node edges
+    private static void nodeEdges(SB sb, ScopeNode scope, Collection<Node> all) {
+        // All them edge labels
+        String scopeName = scope!=null ? makeScopeName(scope, 0) : null;
+        sb.i().p("edge [ fontname=Helvetica, fontsize=8 ];\n");
+        for( Node n : all ) {
+            // Do not display the Constant->Start edge;
+            if( n instanceof ConstantNode ||
+                n instanceof XCtrlNode ||
+                // ProjNodes handled by Multi;
+                n instanceof ProjNode ||
+                n instanceof CProjNode ||
+                // ScopeNodes are done separately
+                n instanceof ScopeNode ||
+                n instanceof MemMergeNode
+                )
+                continue;
+            if( n.isDead() )
+                throw Utils.TODO();
+            // Normal edges
+            for( int i=0; i<n.nIns(); i++ ) {
+                Node def = n.in(i);
+                if( def==null ) continue;
+                sb.i().p(n.uniqueName()).p(" -> ");
+                if( n instanceof PhiNode && def instanceof RegionNode ) {
+                    // Draw a dotted use->def edge from Phi to Region.
+                    sb.p(def.uniqueName());
+                    sb.p(" [style=dotted taillabel=").p(i).p("];\n");
+                } else {
+                    // Most edges land here use->def
+                    if( def instanceof CProjNode proj ) {
+                        String mname = proj.ctrl().uniqueName();
+                        sb.p(mname).p(":p").p(proj._idx);
+                    } else if( def instanceof ProjNode proj ) {
+                        String mname = proj.in(0).uniqueName();
+                        sb.p(mname).p(":p").p(proj._idx);
+                    } else sb.p(def.uniqueName());
+                    // Number edges, so we can see how they track
+                    sb.p("[taillabel=").p(i);
+                    // Color the edge
+                    nodeEdgeColor(sb,def._type);
+                    // Backedges do not add a ranking constraint
+                    if( i==2 && (n instanceof PhiNode || n instanceof LoopNode) )
+                        sb.p(" constraint=false");
+                    sb.p("];\n");
+                }
+            }
+
+            // Bonus edge if hooked by parser
+            if( (n.iskeep() || n.isUnused()) && scopeName != null ) {
+                sb.i().p(scopeName).p(" -> ").p(n.uniqueName()).p(" [ style=dashed color=grey];\n");
+            }
+            // Force functions above return
+            if( n instanceof ReturnNode ret && ret.inProgress() && !ret.fun().isDead() )
+                sb.i().p(ret.ctrl().uniqueName()).p(" -> ").p(ret.fun().uniqueName()).p("[style=invis]\n");
+        }
+    }
+
+    private static void nodeEdgeColor(SB sb, Type t) {
+        sb.p(" color=").p(typeColor(t));
+    }
+
+    // Walk the scope edges
+    private static void scopeEdges( SB sb, ScopeNode scope ) {
+        sb.i().p("edge [style=dashed color=cornflowerblue];\n");
+        int level=0;
+        for( var v : scope._vars ) {
+            if( v._idx==1 ) continue; // Memory done separately
+            Node def = scope.in(v._idx);
+            while( def instanceof ScopeNode lazy )
+                def = lazy.in(v._idx);
+            if( def==null ) continue;
+            while( level < scope._lexSize.size() && v._idx >= scope._lexSize.at(level) )
+                level++;
+            String scopeName = makeScopeName(scope, level);
+            sb.i()
+                .p(scopeName).p(":")
+                .p('"').p(makePortName(scopeName, v._name)).p('"') // wrap port name with quotes because $ctrl is not valid unquoted
+                .p(" -> ");
+            defPort(sb,def).p(";\n");
+        }
+
+        // Memory
+        if( scope.nIns()>1 ) {
+            MemMergeNode n = scope.mem();
+            for( int i=2; i<n.nIns(); i++ ) {
+                Node def = n.in(i);
+                while( def instanceof ScopeNode lazy )
+                    def = lazy.in(i);
+                if( def==null ) continue;
+                String scopeName = makeScopeName(scope, 0);
+                sb.i().p(scopeName).p(":m").p(i).p(" -> ");
+                defPort(sb,def).p(";\n");
+            }
+        }
+
+    }
+
+    // (C)Projection index or -1
+    private static int idx(Node n) {
+        return n instanceof ProjNode p ? p._idx : (n instanceof CProjNode cp ? cp._idx : -1);
+    }
+
+    private static SB defPort(SB sb, Node def) {
+        int idx = idx(def);
+        return idx != -1
+            ? sb.p(def.in(0).uniqueName()).p(":p").p(idx)
+            : sb.p(def.uniqueName());
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/ListScheduler.java b/chapter20/src/main/java/com/seaofnodes/simple/ListScheduler.java
new file mode 100644
index 00000000..18055e19
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/ListScheduler.java
@@ -0,0 +1,231 @@
+ package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.IterPeeps.WorkList;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.util.*;
+
+public abstract class ListScheduler {
+
+    // eXtra per-node stuff for scheduling.
+    private static final IdentityHashMap<Node,XSched> XS = new IdentityHashMap<>();
+    private static class XSched {
+        static final Ary<XSched> FREE = new Ary<>(XSched.class);
+        static void alloc(CFGNode bb, Node n) {
+            XSched x = FREE.pop();
+            XS.put(n, (x==null ? new XSched() : x).init(bb,n));
+        }
+        void free() { _n = null; FREE.push(this); }
+
+        static XSched get(Node n) { return n==null ? null : XS.get(n); }
+
+        private XSched init(CFGNode bb, Node n) {
+            _n = n;
+            _bcnt = 0;
+            _ruse = _rdef = _single = false;
+
+            // Count block-locals and remote inputs
+            if( !(n instanceof PhiNode) )
+                for( Node def : n._inputs )
+                    if( def != null && def != bb ) {
+                        if( def.cfg0()==bb ) _bcnt++; // Raise block-local input count
+                        else                 _ruse = true;
+                    }
+            // Count remote outputs and allowed registers
+            if( n instanceof MultiNode )
+                for( Node use : n._inputs )
+                    computeSingleRDef(bb,use);
+            else
+                computeSingleRDef(bb,n);
+            return this;
+        }
+
+        private void computeSingleRDef(CFGNode bb, Node n) {
+            RegMaskRW rmask = n instanceof MachNode mach ? mach.outregmap().copy() : null;
+            for( Node use : n._outputs ) {
+                // Remote use, so this is a remote def
+                if( use!=null && use.cfg0()!=bb ) _rdef = true;
+                // And mask between n's def mask and all n's users masks'
+                if( use instanceof MachNode mach && rmask != null )
+                    for( int i=1; i<use.nIns(); i++ )
+                        if( use.in(i)==n )
+                            rmask.and(mach.regmap(i));
+            }
+            // Defines in a single register
+            _single = rmask!=null && rmask.size1();
+        }
+
+        // If _bcnt==0, declare ready; move user bcnts into rcnts.
+        boolean isReady() {
+            if( _bcnt > 0 || _rcnt > 0 ) return false;
+            if( _n instanceof MultiNode )
+                for( Node use : _n._outputs )
+                    if( use instanceof ProjNode ) readyUp(use);
+                    // anti-dep from a multireg directly
+                    else _readyUp(use);
+            else
+                readyUp(_n);
+            return true;
+        }
+        private static void readyUp(Node n) {
+            for( Node use : n._outputs )
+                _readyUp(use);
+        }
+        private static void _readyUp(Node use) {
+            XSched xs = get(use);
+            if( xs!=null && !(use instanceof PhiNode) )
+                { assert xs._bcnt>0; xs._bcnt--; xs._rcnt++; }
+        }
+
+        boolean decIsReady() {
+            assert _rcnt > 0;
+            _rcnt--;
+            return isReady();
+        }
+
+        Node _n;         // Node this extra is for
+        int _bcnt;       // Not-ready not-scheduled inputs
+        int _rcnt;       // Ready not-scheduled inputs
+        boolean _ruse;   // Node IS a "remote use", uses a other-block value
+        boolean _rdef;   // Node IS a "remote def" of a value used in other block
+        boolean _single; // Defines a single register, likely to conflict
+    }
+
+
+    // List schedule every block
+    public static void sched( CodeGen code ) {
+        XS.clear();
+        for( CFGNode bb : code._cfg )
+            if( bb.blockHead() )
+                local(bb);
+    }
+
+    // Classic list scheduler
+    private static void local( CFGNode bb ) {
+        assert XS.isEmpty();
+        int len = bb.nOuts();
+
+        // Count block-locals, remote inputs and outputs
+        for( int i=0; i<len; i++ )
+            XSched.alloc(bb,bb.out(i));
+
+        // Nodes are ready if they are not used by other nodes in this block.
+        // Move ready up front.
+        int ready = 0;
+        for( int i=0; i<len; i++ )
+            if( XSched.get(bb.out(i)).isReady() ) // No block-local inputs?
+                bb._outputs.swap(ready++,i);      // Move into ready set
+        assert len==0 || ready > 0;
+
+        // Classic list scheduler.  Behind sched is scheduled.  Between sched
+        // and ready have zero counts and are ready to schedule.  Ahead of
+        // ready is undefined.
+        //
+        // As nodes are scheduled, the nodes they use decrement their bcnts[]. Once
+        // that gets to 0, all the nodes using it are scheduled, so it's ready.
+        int sched = 0;
+        while( sched < len ) {
+            assert sched < ready;
+            int  pick = best(bb._outputs,sched,ready);  // Pick best
+            Node best = bb._outputs.swap(pick,sched++); // Swap best to head of ready and move into the scheduled set
+            // Lower ready count of users, and since projections are ready as
+            // soon as their multi is ready, lower those now too.
+            for( Node use : best._outputs )
+                if( use instanceof ProjNode )
+                    for( Node useuse : use._outputs )
+                        ready = ready(bb,useuse,ready);
+                else
+                    ready = ready(bb,use,ready);
+        }
+
+        // Reset for next block
+        for( XSched x : XS.values() )
+            x.free();
+        XS.clear();
+    }
+
+    private static int ready(CFGNode bb, Node use, int ready) {
+        if( use!=null && !(use instanceof PhiNode) && use.in(0)==bb && XSched.get(use).decIsReady() )
+            bb._outputs.set(ready++, use); // Became ready, move into ready set
+            //bb._outputs.swap(ready++,use);  // Became ready, move into ready set
+        return ready;
+    }
+
+
+    // Pick best between sched and ready.
+    private static int best( Ary<Node> blk, int sched, int ready ) {
+        int pick = sched;
+        int score = score(blk.at(pick));
+        for( int i=sched+1; i<ready; i++ ) {
+            int nscore = score(blk.at(i));
+            if( nscore > score )
+                { score = nscore; pick = i; }
+        }
+        return pick;
+    }
+
+    // Highest score wins.  Max at 1000, min at 10, except specials.
+    private static final int[] CNT = new int[3];
+    static int score( Node n ) {
+        if( n instanceof  ProjNode     ) return 1001; // Pinned at block entry
+        if( n instanceof CProjNode     ) return 1001; // Pinned at block entry
+        if( n instanceof   PhiNode     ) return 1000;
+        if( n instanceof CFGNode       ) return    1; // Pinned at block exit
+
+        int score = 500;
+        // Ideal nodes ignore register pressure scheduling
+        if( !(n instanceof MachNode) )
+            return score;
+
+        // Register pressure local scheduling: avoid overlapping specialized
+        // registers usages.
+
+        // Subtract 10 if this op forces a live range to exist that cannot be
+        // resolved immediately; i.e., live count goes up.  Scale to 20 if
+        // multi-def.
+
+        // Subtract 100 if this op forces a single-def live range to exist
+        // which might conflict on the same register with other live ranges.
+        // Defines a single register based on def & uses, and the output is not
+        // ready.  Scale to 200 for multi-def.
+        CNT[1]=CNT[2]=0;
+        XSched xn = XSched.get(n);
+        if( xn._rdef ) score = 200; // If defining a remote value, just generically stall alot
+        if( n instanceof MultiNode ) {
+            for( Node use : n._outputs )
+                singleUseNotReady( use, xn._single );
+        } else if( n.nOuts() == 1 )
+            singleUseNotReady( n, xn._single );
+        score +=  -10 * Math.min( CNT[1], 2 );
+        score += -100 * Math.min( CNT[2], 2 );
+
+        // Add 10 if this op ends a single-def live range, add 20 for 2 or more.
+        // Scale to 100,200 if the single-def is also single-register.
+        CNT[1]=CNT[2]=0;
+        for( int i=1; i<n.nIns(); i++ ) {
+            XSched xd = XSched.get( n.in(i) );
+            if( xd != null && xd._n.nOuts()==1 )
+                CNT[xd._single || ((MachNode)n).regmap(i).size1() ? 2 : 1]++;
+        }
+        score +=   10 * Math.min( CNT[1], 2 );
+        score +=  100 * Math.min( CNT[2], 2 );
+
+        //// Nothing special
+        //if( n instanceof Pe            ) return  500; // RISC want to go after PE
+        //if( n instanceof Risc          ) return  400; // RISC want to go after PE
+        assert 10 <= score && score <= 990;
+        return score;
+    }
+
+    // Single use, and that use is not ready to fire once this one does.
+    // If true, stalling 'n' might reduce 'n's lifetime.
+    // Return 0 for false, 1 if true, 10 if also single register
+    private static void singleUseNotReady( Node n, boolean single ) {
+        if( n.nOuts() != 1 ) return;
+        XSched xu = XSched.get(n.out(0));
+        if( xu !=null && xu._bcnt==0 )
+            return;
+        CNT[single ? 2 : 1]++;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/Machine.java b/chapter20/src/main/java/com/seaofnodes/simple/Machine.java
new file mode 100644
index 00000000..b29e9aba
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/Machine.java
@@ -0,0 +1,21 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.node.CFGNode;
+import com.seaofnodes.simple.node.IfNode;
+import com.seaofnodes.simple.node.Node;
+
+abstract public class Machine {
+    // Human readable machine name.  Something like "x86-64" or "arm" or "risc5"
+    public abstract String name();
+    // Human-readable name for a register number, e.g. "RAX" or "R0"
+    public abstract String reg( int reg );
+    // Create a split op; any register to any register, including stack slots
+    public abstract Node split();
+    // Return a MachNode unconditional branch
+    public abstract CFGNode jump();
+    // Break an infinite loop
+    public abstract IfNode never( CFGNode ctrl );
+    // Instruction select from ideal nodes
+    public abstract Node instSelect( Node n );
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/Parser.java b/chapter20/src/main/java/com/seaofnodes/simple/Parser.java
new file mode 100644
index 00000000..61a53d68
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/Parser.java
@@ -0,0 +1,1729 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.text.ParseException;
+import java.util.*;
+
+/**
+ * The Parser converts a Simple source program to the Sea of Nodes intermediate
+ * representation directly in one pass.  There is no intermediate Abstract
+ * Syntax Tree structure.
+ * <p>
+ * This is a simple recursive descent parser. All lexical analysis is done here as well.
+ */
+public class Parser {
+
+    public static ConstantNode ZERO; // Very common node, cached here
+    public static ConstantNode NIL;  // Very common node, cached here
+    public static XCtrlNode XCTRL;   // Very common node, cached here
+
+    // Compile driver
+    public final CodeGen _code;
+
+    // The Lexer.  Thin wrapper over a byte[] buffer with a cursor.
+    private final Lexer _lexer;
+
+    /**
+     * Current ScopeNode - ScopeNodes change as we parse code, but at any point of time
+     * there is one current ScopeNode. The reason the current ScopeNode can change is to do with how
+     * we handle branching. See {@link #parseIf()}.
+     * <p>
+     * Each ScopeNode contains a stack of lexical scopes, each scope is a symbol table that binds
+     * variable names to Nodes.  The top of this stack represents current scope.
+     * <p>
+     * We keep a list of all ScopeNodes so that we can show them in graphs.
+     * @see #parseIf()
+     * @see #_xScopes
+     */
+    public ScopeNode _scope;
+
+    /**
+     * List of keywords disallowed as identifiers
+     */
+    public static final HashSet<String> KEYWORDS = new HashSet<>(){{
+            add("bool");
+            add("break");
+            add("byte");
+            add("continue");
+            add("else");
+            add("f32");
+            add("f64");
+            add("false");
+            add("flt");
+            add("i16");
+            add("i32");
+            add("i64");
+            add("i8");
+            add("if");
+            add("int");
+            add("new");
+            add("null");
+            add("return");
+            add("struct");
+            add("true");
+            add("u1");
+            add("u16");
+            add("u32");
+            add("u8");
+            add("while");
+        }};
+
+    /**
+     * We clone ScopeNodes when control flows branch; it is useful to have
+     * a list of all active ScopeNodes for purposes of visualization of the SoN graph
+     */
+    public final Stack<ScopeNode> _xScopes = new Stack<>();
+
+    ScopeNode _continueScope;
+    ScopeNode _breakScope;      // Merge all the while-breaks here
+    FunNode _fun;               // Current function being parsed
+
+    // Mapping from a type name to a Type.  The string name matches
+    // `type.str()` call.  No TypeMemPtrs are in here, because Simple does not
+    // have C-style '*ptr' references.
+    public static HashMap<String, Type> TYPES;
+
+    // Mapping from a type name to the constructor for a Type.
+    public final HashMap<String, StructNode> INITS;
+
+
+    public Parser(CodeGen code, TypeInteger arg) {
+        _code = code;
+        _lexer = new Lexer(code._src);
+        _scope = new ScopeNode();
+        _continueScope = _breakScope = null;
+        ZERO  = con(TypeInteger.ZERO).keep();
+        NIL  = con(Type.NIL).keep();
+        XCTRL= new XCtrlNode().peephole().keep();
+        TYPES = defaultTypes();
+        INITS = new HashMap<>();
+    }
+
+    @Override
+    public String toString() { return _lexer.toString(); }
+
+    public static HashMap<String, Type> defaultTypes() {
+        return new HashMap<>() {{
+            put("bool",TypeInteger.U1 );
+            put("byte",TypeInteger.U8 );
+            put("f32" ,TypeFloat  .F32);
+            put("f64" ,TypeFloat  .F64);
+            put("flt" ,TypeFloat  .F64);
+            put("i16" ,TypeInteger.I16);
+            put("i32" ,TypeInteger.I32);
+            put("i64" ,TypeInteger.BOT);
+            put("i8"  ,TypeInteger.I8 );
+            put("int" ,TypeInteger.BOT);
+            put("u1"  ,TypeInteger.U1 );
+            put("u16" ,TypeInteger.U16);
+            put("u32" ,TypeInteger.U32);
+            put("u8"  ,TypeInteger.U8 );
+            put("val" ,Type.TOP);    // Marker type, indicates type inference
+            put("var" ,Type.BOTTOM); // Marker type, indicates type inference
+        }};
+    }
+
+    // Debugging utility to find a Node by index
+    public Node f(int nid) { return _code.f(nid); }
+
+    private Node ctrl() { return _scope.ctrl(); }
+    private <N extends Node> N ctrl(N n) { return _scope.ctrl(n); }
+
+    public void parse() { parse(false); }
+    public void parse(boolean show) {
+        _xScopes.push(_scope);
+        _scope.define(ScopeNode.CTRL, Type.CONTROL   , false, null, _lexer);
+        _scope.define(ScopeNode.MEM0, TypeMem.BOT    , false, null, _lexer);
+        _scope.define(ScopeNode.ARG0, TypeInteger.BOT, false, null, _lexer);
+
+        ctrl(XCTRL);
+        _scope.mem(new MemMergeNode(false));
+
+        // Parse whole program, as-if function header "{ int arg -> body }"
+        parseFunctionBody(_code._main,loc(),"arg");
+        _code.link(_code._main)._name = "main";
+
+        if( !_lexer.isEOF() ) throw _errorSyntax("unexpected");
+
+        // Clean up and reset
+        _xScopes.pop();
+        _scope.kill();
+        for( StructNode init : INITS.values() )
+            init.unkeep().kill();
+        INITS.clear();
+        _code._stop.peephole();
+        if( show ) showGraph();
+    }
+
+    /**
+     *  Parses a function body, assuming the header is parsed.
+     */
+    private ReturnNode parseFunctionBody(TypeFunPtr sig, Lexer loc, String... ids) {
+        // Stack parser state on the local Java stack, and unstack it later
+        Node oldctrl = ctrl().keep();
+        Node oldmem  = _scope.mem().keep();
+        FunNode oldfun  = _fun;
+        ScopeNode breakScope = _breakScope; _breakScope = null;
+        ScopeNode continueScope = _continueScope; _continueScope = null;
+
+        FunNode fun = _fun = (FunNode)peep(new FunNode(loc(),sig,null,_code._start));
+        // Once the function header is available, install in linker table -
+        // allowing recursive functions.  Linker matches on declared args and
+        // exact fidx, and ignores the return (because the fidx will only match
+        // the exact single function).
+        _code.link(fun);
+
+        Node rpc = new ParmNode("$rpc",0,TypeRPC.BOT,fun,con(TypeRPC.BOT)).peephole();
+
+        // Build a multi-exit return point for all function returns
+        RegionNode r = new RegionNode((Lexer)null,null,null).init();
+        assert r.inProgress();
+        PhiNode rmem = new PhiNode(ScopeNode.MEM0,TypeMem.BOT,r,null).init();
+        PhiNode rrez = new PhiNode(ScopeNode.ARG0,Type.BOTTOM,r,null).init();
+        ReturnNode ret = new ReturnNode(r, rmem, rrez, rpc, fun).init();
+        fun.setRet(ret);
+        assert ret.inProgress();
+        _code._stop.addDef(ret);
+
+        // Pre-call the function from Start, with worse-case arguments.  This
+        // represents all the future, yet-to-be-parsed functions calls and
+        // external calls.
+        _scope.push(ScopeNode.Kind.Function);
+        ctrl(fun);              // Scope control from function
+        // Private mem alias tracking per function
+        MemMergeNode mem = new MemMergeNode(true);
+        mem.addDef(null);       // Alias#0
+        mem.addDef(new ParmNode(ScopeNode.MEM0,1,TypeMem.BOT,fun,con(TypeMem.BOT)).peephole()); // All aliases
+        _scope.mem(mem);
+        // All args, "as-if" called externally
+        for( int i=0; i<ids.length; i++ ) {
+            Type t = sig.arg(i);
+            _scope.define(ids[i], t, false, new ParmNode(ids[i],i+2,t,fun,con(t)).peephole(), loc);
+        }
+
+        // Parse the body
+        Node last=ZERO;
+        while (!peek('}') && !_lexer.isEOF())
+            last = parseStatement();
+
+        // Last expression is the return
+        if( ctrl()._type==Type.CONTROL )
+            fun.addReturn(ctrl(), _scope.mem().merge(), last);
+
+        // Pop off the inProgress node on the multi-exit Region merge
+        assert r.inProgress();
+        r   ._inputs.pop();
+        rmem._inputs.pop();
+        rrez._inputs.pop();
+        r._loc = loc();         // Final position
+        assert !r.inProgress();
+
+        // Force peeps, which have been avoided due to inProgress
+        ret.setDef(1,rmem.peephole());
+        ret.setDef(2,rrez.peephole());
+        ret.setDef(0,r.peephole());
+        ret = (ReturnNode)ret.peephole();
+
+        // Function scope ends
+        _scope.pop();
+        _fun = oldfun;
+        _breakScope = breakScope;
+        _continueScope = continueScope;
+        // Reset control and memory to pre-function parsing days
+        ctrl(oldctrl.unkeep());
+        _scope.mem(oldmem.unkeep());
+
+        return ret;
+    }
+
+    /**
+     * Parses a block
+     *
+     * <pre>
+     *     '{' statements '}'
+     * </pre>
+     * Does not parse the opening or closing '{}'
+     * @return a {@link Node} or {@code null}
+     */
+    private Node parseBlock(ScopeNode.Kind kind) {
+        // Enter a new scope
+        _scope.push(kind);
+        Node last = ZERO;
+        while (!peek('}') && !_lexer.isEOF())
+            last = parseStatement();
+        // Exit scope
+        last.keep();
+        _scope.pop();
+        return last.unkeep();
+    }
+
+    /**
+     * Parses a statement
+     *
+     * <pre>
+     *     returnStatement | declStatement | blockStatement | ifStatement | expressionStatement
+     * </pre>
+     * @return a {@link Node} or {@code null}
+     */
+    private Node parseStatement() {
+        if( false ) return null;
+        else if (matchx("return")  ) return parseReturn();
+        else if (matchx("if")      ) return parseIf();
+        else if (matchx("while")   ) return parseWhile();
+        else if (matchx("for")     ) return parseFor();
+        else if (matchx("break")   ) return parseBreak();
+        else if (matchx("continue")) return parseContinue();
+        else if (matchx("struct")  ) return parseStruct();
+        else if (matchx("#showGraph")) return require(showGraph(),";");
+        else if (matchx(";")       ) return null; // Empty statement
+        // Break ambiguity around leading function types and starting a block
+        else if (peek('{') && !isTypeFun() ) {
+            match("{");
+            return require(parseBlock(ScopeNode.Kind.Block),"}");
+        }
+        // Declaration or normal assignment/expression
+        else return parseDeclarationStatement();
+    }
+
+    /**
+     * Parses a while statement
+     *
+     * <pre>
+     *     while ( expression ) statement
+     * </pre>
+     * @return a {@link Node}, never {@code null}
+     */
+    private Node parseWhile() {
+        require("(");
+        return parseLooping(false);
+    }
+
+
+    /**
+     * Parses a for statement
+     *
+     * <pre>
+     *     for( var x=init; test; incr ) body
+     * </pre>
+     * @return a {@link Node}, never {@code null}
+     */
+    private Node parseFor() {
+        // {   var x=init,y=init,...;
+        //     while( test ) {
+        //         body;
+        //         next;
+        //     }
+        // }
+        require("(");
+        _scope.push(ScopeNode.Kind.Block); // Scope for the index variables
+        if( !match(";") )       // Can be empty init "for(;test;next) body"
+            parseDeclarationStatement(); // Non-empty init
+        Node rez = parseLooping(true);
+        _scope.pop();           // Exit index variable scope
+        return rez;
+    }
+
+    // Shared by `for` and `while`
+    private Node parseLooping( boolean doFor ) {
+
+        var savedContinueScope = _continueScope;
+        var savedBreakScope    = _breakScope;
+
+        // Loop region has two control inputs, the first is the entry
+        // point, and second is back edge that is set after loop is parsed
+        // (see end_loop() call below).  Note that the absence of back edge is
+        // used as an indicator to switch off peepholes of the region and
+        // associated phis; see {@code inProgress()}.
+
+        ctrl(new LoopNode(loc(),ctrl()).peephole()); // Note we set back edge to null here
+
+        // At loop head, we clone the current Scope (this includes all
+        // names in every nesting level within the Scope).
+        // We create phis eagerly for all the names we find, see dup().
+
+        // Save the current scope as the loop head
+        ScopeNode head = _scope.keep();
+        // Clone the head Scope to create a new Scope for the body.
+        // Create phis eagerly as part of cloning
+        _xScopes.push(_scope = _scope.dup(true)); // The true argument triggers creating phis
+
+        // Parse predicate
+        var pred = peek(';') ? con(1) : parseAsgn();
+        require( doFor ? ";" : ")" );
+
+        // IfNode takes current control and predicate
+        Node ifNode = new IfNode(ctrl(), pred.keep()).peephole();
+        // Setup projection nodes
+        Node ifT = new CProjNode(ifNode.  keep(), 0, "True" ).peephole().keep();
+        Node ifF = new CProjNode(ifNode.unkeep(), 1, "False").peephole();
+
+        // for( ;;next ) body
+        int nextPos = -1, nextEnd = -1;
+        if( doFor ) {
+            // Skip the next expression and parse it later
+            nextPos = pos();
+            skipAsgn();
+            nextEnd = pos();
+            require(")");
+        }
+
+        // Clone the body Scope to create the break/exit Scope which accounts for any
+        // side effects in the predicate.  The break/exit Scope will be the final
+        // scope after the loop, and its control input is the False branch of
+        // the loop predicate.  Note that body Scope is still our current scope.
+        ctrl(ifF);
+        _xScopes.push(_breakScope = _scope.dup());
+        _breakScope.addGuards(ifF,pred,true); // Up-cast predicate
+
+        // No continues yet
+        _continueScope = null;
+
+        // Parse the true side, which corresponds to loop body
+        // Our current scope is the body Scope
+        ctrl(ifT.unkeep());     // set ctrl token to ifTrue projection
+        _scope.addGuards(ifT,pred.unkeep(),false); // Up-cast predicate
+        parseStatement();       // Parse loop body
+        _scope.removeGuards(ifT);
+
+        // Merge the loop bottom into other continue statements
+        if (_continueScope != null) {
+            _continueScope = jumpTo(_continueScope);
+            _scope.kill();
+            _scope = _continueScope;
+        }
+
+        // Now append the next code onto the body code
+        if( doFor ) {
+            int old = pos(nextPos);
+            if( !peek(')') )
+              parseAsgn();
+            if( pos() != nextEnd )
+                throw errorSyntax( "Unexpected code after expression" );
+            pos(old);
+        }
+
+        // The true branch loops back, so whatever is current _scope.ctrl gets
+        // added to head loop as input.  endLoop() updates the head scope, and
+        // goes through all the phis that were created earlier.  For each phi,
+        // it sets the second input to the corresponding input from the back
+        // edge.  If the phi is redundant, it is replaced by its sole input.
+        var exit = _breakScope;
+        head.endLoop(_scope, exit);
+        head.unkeep().kill();
+
+        _xScopes.pop();       // Cleanup
+        _xScopes.pop();       // Cleanup
+
+        _continueScope = savedContinueScope;
+        _breakScope = savedBreakScope;
+
+        // At exit the false control is the current control, and
+        // the scope is the exit scope after the exit test.
+        _xScopes.pop();
+        _xScopes.push(exit);
+        _scope = exit;
+        return ZERO;
+    }
+
+    private ScopeNode jumpTo(ScopeNode toScope) {
+        ScopeNode cur = _scope.dup();
+        ctrl(XCTRL); // Kill current scope
+        // Prune nested lexical scopes that have depth > than the loop head
+        // We use _breakScope as a proxy for the loop head scope to obtain the depth
+        while( cur._lexSize.size() > _breakScope._lexSize.size() )
+            cur.pop();
+        // If this is a continue then first time the target is null
+        // So we just use the pruned current scope as the base for the
+        // "continue"
+        if( toScope == null )
+            return cur;
+        // toScope is either the break scope, or a scope that was created here
+        assert toScope._lexSize.size() <= _breakScope._lexSize.size();
+        toScope.ctrl(toScope.mergeScopes(cur,loc()).peephole());
+        return toScope;
+    }
+
+    private void checkLoopActive() { if (_breakScope == null) throw error("No active loop for a break or continue"); }
+
+    private Node parseContinue() { checkLoopActive(); _continueScope = require(jumpTo( _continueScope ),";"); return ZERO; }
+    private Node parseBreak   () {
+        checkLoopActive();
+        // At the time of the break, and loop-exit conditions are only valid if
+        // they are ALSO valid at the break.  It is the intersection of
+        // conditions here, not the union.
+        _breakScope.removeGuards(_breakScope.ctrl());
+        _breakScope = require(jumpTo(_breakScope ),";");
+        _breakScope.addGuards(_breakScope.ctrl(), null, false);
+        return ZERO;
+    }
+
+    // Look for an unbalanced `)`, skipping balanced
+    private void skipAsgn() {
+        int paren=0;
+        while( true )
+            // Next X char handles skipping complex comments
+            switch( _lexer.nextXChar() ) {
+            case Character.MAX_VALUE:
+                throw Utils.TODO();
+            case ')':
+                if( --paren<0 ) {
+                    posT( pos() - 1 );
+                    return; // Leave the `)` behind
+                }
+                break;
+            case '(': paren ++; break;
+            default: break;
+            }
+    }
+
+
+    /**
+     * Parses a statement
+     *
+     * <pre>
+     *     if ( expression ) statement [else statement]
+     * </pre>
+     * @return a {@link Node}, never {@code null}
+     */
+    private Node parseIf() {
+        // Parse predicate
+        require("(");
+        var pred = require(parseAsgn(), ")");
+        return parseTrinary(pred,true,"else");
+    }
+
+    // Parse a conditional expression, merging results.
+    private Node parseTrinary( Node pred, boolean stmt, String fside ) {
+        pred.keep();
+
+        // IfNode takes current control and predicate
+        Node ifNode = new IfNode(ctrl(), pred).peephole();
+        // Setup projection nodes
+        Node ifT = new CProjNode(ifNode.  keep(), 0, "True" ).peephole().keep();
+        Node ifF = new CProjNode(ifNode.unkeep(), 1, "False").peephole().keep();
+        // In if true branch, the ifT proj node becomes the ctrl
+        // But first clone the scope and set it as current
+        ScopeNode fScope = _scope.dup(); // Duplicate current scope
+        _xScopes.push(fScope); // For graph visualization we need all scopes
+
+        // Parse the true side
+        ctrl(ifT.unkeep());     // set ctrl token to ifTrue projection
+        _scope.addGuards(ifT,pred,false); // Up-cast predicate
+        Node lhs = (stmt ? parseStatement() : parseAsgn()).keep(); // Parse true-side
+        _scope.removeGuards(ifT);
+
+        // See if a one-sided def was made: "if(pred) int x = 1;" and throw.
+        // See if any forward-refs were made, and copy them to the other side:
+        // "pred ? n*fact(n-1) : 1"
+        fScope.balanceIf(_scope);
+
+        ScopeNode tScope = _scope;
+
+        // Parse the false side
+        _scope = fScope;        // Restore scope, then parse else block if any
+        ctrl(ifF.unkeep());     // Ctrl token is now set to ifFalse projection
+        // Up-cast predicate, even if not else clause, because predicate can
+        // remain true if the true clause exits: `if( !ptr ) return 0; return ptr.fld;`
+        _scope.addGuards(ifF,pred,true);
+        boolean doRHS = match(fside);
+        Node rhs = (doRHS
+            ? (stmt ? parseStatement() : parseAsgn())
+            : con(lhs._type.makeZero())).keep();
+        _scope.removeGuards(ifF);
+        if( doRHS )
+            fScope = _scope;
+        pred.unkeep();
+
+        // Check the trinary widening int/flt
+        if( !stmt ) {
+            rhs = widenInt( rhs.unkeep(), lhs._type ).keep();
+            lhs = widenInt( lhs.unkeep(), rhs._type ).keep();
+        }
+
+        _scope = tScope;
+        _xScopes.pop();       // Discard pushed from graph display
+        // See if a one-sided def was made: "if(pred) int x = 1;" and throw.
+        // See if any forward-refs were made, and copy them to the other side:
+        // "pred ? n*fact(n-1) : 1"
+        tScope.balanceIf(fScope);
+
+        // Merge results
+        RegionNode r = ctrl(tScope.mergeScopes(fScope,loc()));
+        Node ret = peep(new PhiNode("",lhs._type.meet(rhs._type),r,lhs.unkeep(),rhs.unkeep()));
+        // Immediately fail e.g. `arg ? 7 : ptr`
+        ParseException err;
+        if( !stmt && (err=ret.err()) !=null )  throw err;
+        r.peephole();
+        return ret;
+    }
+
+    /**
+     * Parses a return statement; "return" already parsed.
+     * The $ctrl edge is killed.
+     *
+     * <pre>
+     *     'return' expr ;
+     * </pre>
+     * @return an expression {@link Node}, never {@code null}
+     */
+    private Node parseReturn() {
+        var expr = require(parseAsgn(), ";");
+        // Need default memory, since it can be lazy, need to force
+        // a non-lazy Phi
+        _fun.addReturn(ctrl(), _scope.mem().merge(), expr);
+        ctrl(XCTRL);            // Kill control
+        return expr;
+    }
+
+    /**
+     * Dumps out the node graph
+     * @return {@code null}
+     */
+    Node showGraph() {
+        System.out.println(new GraphVisualizer().generateDotOutput(_code._stop,_scope,_xScopes));
+        return null;
+    }
+
+    /** Parse: [name '='] expr
+     */
+    private Node parseAsgn() {
+        int old = pos();
+        String name = _lexer.matchId();
+        // Just a plain expression, no assignment.
+        // Distinguish `var==expr` from `var=expr`
+        if( name==null || KEYWORDS.contains(name) || !matchOpx('=','=') )
+            {  pos(old);  return parseExpression();  }
+
+        // Parse assignment expression
+        Node expr = parseAsgn();
+
+        // Final variable to update
+        Var def = _scope.lookup(name);
+        if( def==null )
+            throw error("Undefined name '" + name + "'");
+
+        // TOP fields are for late-initialized fields; these have never
+        // been written to, and this must be the final write.  Other writes
+        // outside the constructor need to check the final bit.
+        if( _scope.in(def._idx)._type!=Type.TOP && def._final &&
+            // Inside a constructor, final assign is OK, outside nope
+            !(_scope.inCon() && def._idx >= _scope._lexSize.last()) )
+            throw error("Cannot reassign final '"+name+"'");
+
+        // Lift expression, based on type
+        Node lift = liftExpr(expr.keep(), def.type(), def._final);
+        // Update
+        _scope.update(name,lift);
+        // Return un-lifted expr
+        return expr.unkeep();
+    }
+
+    // Make finals deep; widen ints to floats; narrow wide int types.
+    // Early error if types do not match variable.
+    private Node liftExpr( Node expr, Type t, boolean xfinal ) {
+        assert !(expr._type instanceof TypeMemPtr tmp) || !tmp.isFRef();
+        // Final is deep on ptrs
+        if( xfinal && t instanceof TypeMemPtr tmp ) {
+            t = tmp.makeRO();
+            expr = peep(new ReadOnlyNode(expr));
+        }
+        // Auto-widen int to float
+        expr = widenInt( expr, t );
+        // Auto-narrow wide ints to narrow ints
+        expr = zsMask(expr,t);
+        // Type is sane
+        if( expr._type!=Type.BOTTOM && !expr._type.shallowISA(t) )
+            throw error("Type " + expr._type.str() + " is not of declared type " + t.str());
+        return expr;
+    }
+
+    private Node widenInt( Node expr, Type t ) {
+        return (expr._type instanceof TypeInteger || expr._type==Type.NIL) && t instanceof TypeFloat
+            ? peep(new ToFloatNode(expr)) : expr;
+    }
+
+    /**
+     * Parse declaration or expression statement
+     * declStmt = type var['=' exprAsgn][, var['=' exprAsgn]]* ';' | exprAsgn ';'
+     * <p>
+     * exprAsgn = var '=' exprAsgn | expr
+     */
+    private Node parseDeclarationStatement() {
+        Type t = type();
+        if( t == null )
+            return require(parseAsgn(),";");
+
+        // now parse var['=' asgnexpr] in a loop
+        Node n = parseDeclaration(t);
+        while( match(",") )
+            n = parseDeclaration(t);
+        return require(n,";");
+    }
+
+    /** Parse final: [!]var['=' asgn]
+     */
+    private Node parseDeclaration(Type t) {
+        assert t!=null;
+        // Has var/val instead of a user-declared type
+        boolean inferType = t==Type.TOP || t==Type.BOTTOM;
+        boolean hasBang = match("!");
+        Lexer loc = loc();
+        String name = requireId();
+        // Optional initializing expression follows
+        boolean xfinal = false;
+        Node expr;
+        if( match("=") ) {
+            expr = parseAsgn();
+            // TOP means val and val is always final
+            xfinal = (t==Type.TOP) ||
+                // BOTTOM is var and var is always not-final
+                (t!=Type.BOTTOM &&
+                 // no Bang AND
+                 !hasBang &&
+                 // not-null (expecting null to be set to not-null)
+                 expr._type != Type.NIL &&
+                 // Pointers are final by default; int/flt are not-final by default.
+                 (t instanceof TypeNil));
+            // var/val, then type comes from expression
+            if( inferType ) {
+                if( expr._type==Type.NIL )
+                    throw error("a not-null/non-zero expression");
+                t = expr._type;
+                if( !xfinal ) t = t.glb();  // Widen if not final
+            }
+            if( t instanceof TypeFunPtr && expr._type instanceof TypeFunPtr tfp && tfp.isConstant() )
+                _code.link(tfp)._name = name;
+
+        } else {
+            // Need an expression to infer the type.
+            // Also, if not-null then need an initializing expression.
+            // Allowed in a class def, because type/init will happen in the constructor.
+            if( (inferType || (t instanceof TypeNil tn && !tn.nullable() )) && !_scope.inCon() )
+                throw errorSyntax("=expression");
+            // Initial value for uninitialized struct fields.
+            expr = switch( t ) {
+                // Nullable pointers get a NIL; not-null get a TOP which
+                // signals that they *must* be initialized in the constructor.
+            case TypeNil tn -> tn.nullable() ? NIL : con(Type.TOP);
+            case TypeInteger ti -> ZERO;
+            case TypeFloat tf -> con(TypeFloat.FZERO);
+            // Bottom signals type inference: they must be initialized in
+            // the constructor and that's when we'll discover the type.
+            case Type tt -> { assert tt==Type.BOTTOM; yield con(tt); }
+            };
+        }
+
+        // Lift expression, based on type
+        Node lift = liftExpr(expr, t, xfinal);
+
+        if( xfinal && t instanceof TypeMemPtr tmp )
+            t = tmp.makeRO();
+
+        // Lift type to the declaration.  This will report as an error later if
+        // we cannot lift the type.
+        if( !lift._type.isa(t) )
+            lift = peep(new CastNode(t,null,lift));
+        // Define a new name
+        if( !_scope.define(name,t,xfinal,lift, loc) )
+            throw error("Redefining name '" + name + "'", loc);
+        return lift;
+    }
+
+
+
+    /**
+     * Parse a struct declaration, and return the following statement.
+     * Only allowed in top level scope.
+     * Structs cannot be redefined.
+     *
+     * @return The statement following the struct
+     */
+    private Node parseStruct() {
+        if (_xScopes.size() > 1) throw error("struct declarations can only appear in top level scope");
+        String typeName = requireId();
+        Type t = TYPES.get(typeName);
+        if( t!=null && !(t instanceof TypeMemPtr tmp && tmp.isFRef() ) )
+            throw error("struct '" + typeName + "' cannot be redefined");
+
+        // A Block scope parse, and inspect the scope afterward for fields.
+        _scope.push(ScopeNode.Kind.Constructor);
+        require("{");
+        while (!peek('}') && !_lexer.isEOF())
+            parseStatement();
+
+        // Grab the declarations and build fields and a Struct
+        int lexlen = _scope._lexSize.last();
+        int varlen = _scope._vars._len;
+        StructNode s = new StructNode();
+        Ary<Field> fs = new Ary<>(Field.class);
+        for( int i=lexlen; i<varlen; i++ ) {
+            s.addDef(_scope.in(i));
+            Var v = _scope._vars.at(i);
+            if( !v.isFRef() )  // Promote to outer scope, not defined here
+                fs.push(Field.make(v._name,v.type(),_code.getALIAS(),v._final));
+        }
+        TypeStruct ts = s._ts = TypeStruct.make(typeName, fs.asAry());
+        TYPES.put(typeName, TypeMemPtr.make(ts));
+        INITS.put(typeName,s.peephole().keep());
+        // Done with struct/block scope
+        require("}");
+        require(";");
+        _scope.pop();
+        return ZERO;
+    }
+
+
+    // Parse and return a type or null.  Valid types always are followed by an
+    // 'id' which the caller must parse.  This lets us distinguish forward ref
+    // types (which ARE valid here) from local vars in an (optional) forward
+    // ref type position.
+
+    // t = int|i8|i16|i32|i64|u8|u16|u32|u64|byte|bool | flt|f32|f64 | val | var | struct[?]
+    private Type type() {
+        int old1 = pos();
+        // Only type with a leading `{` is a function pointer...
+        if( peek('{') ) return typeFunPtr();
+
+        // Otherwise you get a type name
+        String tname = _lexer.matchId();
+        if( tname==null ) return null;
+
+        // Convert the type name to a type.
+        Type t0 = TYPES.get(tname);
+        // No new types as keywords
+        if( t0 == null && KEYWORDS.contains(tname) )
+            return posT(old1);
+        if( t0 == Type.BOTTOM || t0 == Type.TOP ) return t0; // var/val type inference
+        Type t1 = t0 == null ? TypeMemPtr.make(TypeStruct.makeFRef(tname)) :t0; // Null: assume a forward ref type
+        // Nest arrays and '?' as needed
+        Type t2 = t1;
+        while( true ) {
+            if( match("?") ) {
+                if( !(t2 instanceof TypeMemPtr tmp) )
+                    throw error("Type "+t0+" cannot be null");
+                if( tmp.nullable() ) throw error("Type "+t2+" already allows null");
+                t2 = tmp.makeNullable();
+            } else if( match("[]") ) {
+                t2 = typeAry(t2);
+            } else
+                break;
+        }
+
+        // Check no forward ref
+        if( t0 != null ) return t2;
+        // Check valid forward ref, after parsing all the type extra bits.
+        // Cannot check earlier, because cannot find required 'id' until after "[]?" syntax
+        int old2 = pos();
+        match("!");
+        String id = _lexer.matchId();
+        if( !(peek(',') || peek(';') || match("->")) )
+            return posT(old1);
+        pos(old2);              // Reset lexer to reparse
+        if( id==null )
+            return posT(old1);  // Reset lexer to reparse
+        // Yes a forward ref, so declare it
+        TYPES.put(tname,t1);
+        return t2;
+    }
+
+    // Make an array type of t
+    private TypeMemPtr typeAry( Type t ) {
+        if( t instanceof TypeMemPtr tmp && tmp.notNull()  )
+            throw error("Arrays of reference types must always be nullable");
+        String tname = "["+t.str()+"]";
+        Type ta = TYPES.get(tname);
+        if( ta != null ) return (TypeMemPtr)ta;
+        // Need make an array type.
+        TypeStruct ts = TypeStruct.makeAry(TypeInteger.U32,_code.getALIAS(),t,_code.getALIAS());
+        assert ts.str().equals(tname);
+        TypeMemPtr tary = TypeMemPtr.make(ts);
+        TYPES.put(tname,tary);
+        return tary;
+    }
+
+    // A function type is `{ type... -> type }` or `{ type }`.
+    private Type typeFunPtr() {
+        int old = pos();        // Record lexer position
+        match("{");             // Skip already-peeked '{'
+        Type t0 = type();       // Either return or first arg
+        if( t0==null ) return posT(old); // Not a function
+        if( match("}") )                 // No-arg function { -> type }
+            return TypeFunPtr.make(match("?"),TypeTuple.BOT,t0);
+        Ary<Type> ts = new Ary<>(Type.class);
+        ts.push(t0);            // First argument
+        while( true ) {
+            if( match("->") ) { // End of arguments, parse return
+                Type ret = type();
+                if( ret==null || !match("}") )
+                    return posT(old); // Not a function
+                return TypeFunPtr.make(match("?"),TypeTuple.make(ts.asAry()),ret);
+            }
+            Type t1 = type();
+            if( t1==null ) return posT(old); // Not a function
+            ts.push(t1);
+        }
+    }
+
+    // True if a TypeFunPtr, without advancing parser
+    private boolean isTypeFun() {
+        int old = pos();
+        if( typeFunPtr()==null ) return false;
+        pos(old);
+        return true;
+    }
+
+    /**
+     * Parse an expression of the form:
+     *
+     * <pre>
+     *     expr : bitwise [? expr [: expr]]
+     * </pre>
+     * @return an expression {@link Node}, never {@code null}
+     */
+    private Node parseExpression() {
+        Node expr = parseBitwise();
+        return match("?") ? parseTrinary(expr,false,":") : expr;
+    }
+
+    /**
+     * Parse an bitwise expression
+     *
+     * <pre>
+     *     bitwise : compareExpr (('&' | '|' | '^') compareExpr)*
+     * </pre>
+     * @return a bitwise expression {@link Node}, never {@code null}
+     */
+    private Node parseBitwise() {
+        Node lhs = parseComparison();
+        while( true ) {
+            if( false ) ;
+            else if( match("&") ) lhs = new AndNode(loc(),lhs,null);
+            else if( match("|") ) lhs = new  OrNode(loc(),lhs,null);
+            else if( match("^") ) lhs = new XorNode(loc(),lhs,null);
+            else break;
+            lhs.setDef(2,parseComparison());
+            lhs = peep(lhs);
+        }
+        return lhs;
+    }
+
+    /**
+     * Parse an expression of the form:
+     *
+     * <pre>
+     *     expr : additiveExpr op additiveExpr
+     * </pre>
+     * @return an comparator expression {@link Node}, never {@code null}
+     */
+    private Node parseComparison() {
+        var lhs = parseShift();
+        while( true ) {
+            int idx=0;  boolean negate=false;
+            // Test for any local nodes made, and "keep" lhs during peepholes
+            if( false ) ;
+            else if( match("==") ) { idx=2;  lhs = new BoolNode.EQ(lhs, null); }
+            else if( match("!=") ) { idx=2;  lhs = new BoolNode.EQ(lhs, null); negate=true; }
+            else if( match("<=") ) { idx=2;  lhs = new BoolNode.LE(lhs, null); }
+            else if( match("<" ) ) { idx=2;  lhs = new BoolNode.LT(lhs, null); }
+            else if( match(">=") ) { idx=1;  lhs = new BoolNode.LE(null, lhs); }
+            else if( match(">" ) ) { idx=1;  lhs = new BoolNode.LT(null, lhs); }
+            else break;
+            // Peepholes can fire, but lhs is already "hooked", kept alive
+            lhs.setDef(idx,parseShift());
+            lhs = peep(lhs.widen());
+            if( negate )        // Extra negate for !=
+                lhs = peep(new NotNode(lhs));
+        }
+        return lhs;
+    }
+
+    /**
+     * Parse an additive expression
+     *
+     * <pre>
+     *     shiftExpr : additiveExpr (('<<' | '>>' | '>>>') additiveExpr)*
+     * </pre>
+     * @return a shift expression {@link Node}, never {@code null}
+     */
+    private Node parseShift() {
+        Node lhs = parseAddition();
+        while( true ) {
+            if( false ) ;
+            else if( match("<<") ) lhs = new ShlNode(loc(),lhs,null);
+            else if( match(">>>")) lhs = new ShrNode(loc(),lhs,null);
+            else if( match(">>") ) lhs = new SarNode(loc(),lhs,null);
+            else break;
+            lhs.setDef(2,parseAddition());
+            ParseException err;
+            if( (err=lhs.err()) != null )
+                throw err;
+            lhs = peep(lhs.widen());
+        }
+        return lhs;
+    }
+
+    /**
+     * Parse an additive expression
+     *
+     * <pre>
+     *     additiveExpr : multiplicativeExpr (('+' | '-') multiplicativeExpr)*
+     * </pre>
+     * @return an add expression {@link Node}, never {@code null}
+     */
+    private Node parseAddition() {
+        Node lhs = parseMultiplication();
+        while( true ) {
+            if( false ) ;
+            else if( match("+") ) lhs = new AddNode(lhs,null);
+            else if( match("-") ) lhs = new SubNode(lhs,null);
+            else break;
+            lhs.setDef(2,parseMultiplication());
+            lhs = peep(lhs.widen());
+        }
+        return lhs;
+    }
+
+    /**
+     * Parse an multiplicativeExpr expression
+     *
+     * <pre>
+     *     multiplicativeExpr : unaryExpr (('*' | '/') unaryExpr)*
+     * </pre>
+     * @return a multiply expression {@link Node}, never {@code null}
+     */
+    private Node parseMultiplication() {
+        var lhs = parseUnary();
+        while( true ) {
+            if( false ) ;
+            else if( match("*") ) lhs = new MulNode(lhs,null);
+            else if( match("/") ) lhs = new DivNode(lhs,null);
+            else break;
+            lhs.setDef(2,parseUnary());
+            lhs = peep(lhs.widen());
+        }
+        return lhs;
+    }
+
+    /**
+     * Parse a unary minus expression.
+     *
+     * <pre>
+     *     unaryExpr : ('-') unaryExpr | '!') unaryExpr | postfixExpr | primaryExpr | '--' Id | '++' Id
+     * </pre>
+     * @return a unary expression {@link Node}, never {@code null}
+     */
+    private Node parseUnary() {
+        // Pre-dec/pre-inc
+        int old = pos();
+        if( match("--") || match("++") ) {
+            int delta = _lexer.peek(-1)=='+' ? 1 : -1; // Pre vs post
+            String name = _lexer.matchId();
+            if( name!=null ) {
+                Var n = _scope.lookup(name);
+                if( n != null && !(n.type() instanceof TypeMemPtr) ) {
+                    if( n._final )
+                        throw error("Cannot reassign final '"+n._name+"'");
+                    Node expr = n.type() instanceof TypeFloat
+                        ?        peep(new AddFNode(_scope.in(n),con(TypeFloat.constant(delta))))
+                        : zsMask(peep(new  AddNode(_scope.in(n),con(delta))),n.type());
+                    _scope.update(n,expr);
+                    return expr;
+                }
+            }
+            // Reset, try again
+            pos(old);
+        }
+        if (match("-")) return peep(new MinusNode(parseUnary()).widen());
+        if (match("!")) return peep(new   NotNode(parseUnary()));
+        return parsePostfix(parsePrimary());
+    }
+
+    /**
+     * Parse a primary expression:
+     *
+     * <pre>
+     *     primaryExpr : integerLiteral | true | false | null | new Type | '(' expression ')' | Id['++','--']
+     * </pre>
+     * @return a primary {@link Node}, never {@code null}
+     */
+    private Node parsePrimary() {
+        if( _lexer.isNumber(_lexer.peek()) ) return parseLiteral();
+        if( matchx("true" ) ) return con(1);
+        if( matchx("false") ) return ZERO;
+        if( matchx("null" ) ) return NIL;
+        if( match ("("    ) ) return require(parseAsgn(), ")");
+        if( matchx("new"  ) ) return alloc();
+        if( match ("{"    ) ) return require(func(),"}");
+        // Expect an identifier now
+        Var n = requireLookupId();
+        Node rvalue = _scope.in(n);
+        if( rvalue._type == Type.BOTTOM )
+            if( rvalue instanceof FRefNode ) return rvalue;
+            else throw error("Cannot read uninitialized field '"+n._name+"'");
+        // Check for assign-update, x += e0;
+        char ch = _lexer.matchOperAssign();
+        if( ch==0  ) return rvalue;
+        Node op = opAssign(ch,rvalue,n._final,n.type(),n._name);
+        _scope.update(n,op);
+        return postfix(ch) ? rvalue.unkeep() : op;
+    }
+
+    // Check for assign-update, "x += e0".
+    // Returns "x + e0"; the caller assigns value.
+    // if ch is postfix, then lhs is kept and caller will unkeep and return it.
+    private Node opAssign(char ch, Node lhs, boolean xfinal, Type t, String name ) {
+        if( xfinal )
+            throw error("Cannot reassign final '"+name+"'");
+        // RHS of the update.
+        lhs.keep();             // Alive across parseAsgn
+        Node rhs =
+            (byte)ch ==  1 ? con( 1) : // var++
+            (byte)ch == -1 ? con(-1) : // var--
+            parseAsgn();               // var op= rhs
+        if( !postfix(ch) ) lhs.unkeep();   // Allow to die in next peep
+        // 4 cases:
+        // int + int ==>> narrow int
+        // int + flt ==>> error, caller must fail assigning flt into int
+        // flt + int ==>> use float op, wrap toFloat()
+        // flt + flt ==>> use float op
+        Node op = switch(ch) {
+        case 1, (char)-1,
+             '+' -> new AddNode(lhs,rhs);
+        case '-' -> new SubNode(lhs,rhs);
+        case '*' -> new MulNode(lhs,rhs);
+        case '/' -> new DivNode(lhs,rhs);
+        default  -> throw Utils.TODO();
+        };
+        // Convert to float ops, or narrow int types; error if not declared type.
+        // Also, if postfix LHS is still keep()
+        return liftExpr(peep(op.widen()),t,false);
+    }
+
+
+    // Expect an ID here.  If not found, assume a forward reference function
+    Var requireLookupId() {
+        String id = _lexer.matchId();
+        if( id == null || KEYWORDS.contains(id) )
+            throw errorSyntax("an identifier or expression");
+        Var n = _scope.lookup(id);
+        // If missing, assume a forward reference
+        if( n==null ) {
+            _scope.define(id, FRefNode.FREF_TYPE, true, XCTRL, loc());
+            n = _scope.lookup(id);
+        } else {
+            // Lookup worked on an out-of-function value.
+            if( _scope.outOfFunction(n) ) {
+                // No closures, so this has to be a final constant (which
+                // includes forward refs)
+                Node def = _scope.in(n._idx);
+                if( !(def instanceof FRefNode) && !(n._final && def._type.isConstant()) )
+                    throw error("Variable '"+n._name+"' is out of function scope and must be a final constant");
+            }
+        }
+        return n;
+    }
+
+    /**
+       Parse an allocation
+     */
+    private Node alloc() {
+        Type t = type();
+        if( t==null ) throw error("Expected a type");
+        // Parse ary[ length_expr ]
+        if( match("[") ) {
+            if( !t.makeZero().isa(t) )
+                throw error("Cannot allocate a non-nullable, since arrays always zero/null fill");
+            Node len = parseAsgn();
+            if( !(len._type instanceof TypeInteger) )
+                throw error("Cannot allocate an array with length "+len._type);
+            require("]");
+            TypeMemPtr tmp = typeAry(t);
+            return newArray(tmp._obj,len);
+        }
+
+        if( !(t instanceof TypeMemPtr tmp) )
+            throw error("Cannot allocate a "+t.str());
+
+        // Parse new struct { default_initialization }
+        StructNode s = INITS.get(tmp._obj._name);
+        if( s==null ) throw error("Unknown struct type '" + tmp._obj._name + "'");
+
+        Field[] fs = s._ts._fields;
+        // if the object is fully initialized, we can skip a block here.
+        // Check for constructor block:
+        boolean hasConstructor = match("{");
+        Ary<Node> init=s._inputs;  int idx=0;
+        if( hasConstructor ) {
+            idx = _scope.nIns();
+            // Push a scope, and pre-assign all struct fields.
+            _scope.push(ScopeNode.Kind.Block);
+            Lexer loc = loc();
+            for( int i=0; i<fs.length; i++ )
+                _scope.define(fs[i]._fname, fs[i]._type, fs[i]._final, s.in(i)._type==Type.TOP ? con(Type.BOTTOM) : s.in(i), loc);
+            // Parse the constructor body
+            require(parseBlock(ScopeNode.Kind.Constructor),"}");
+            init = _scope._inputs;
+        }
+        // Check that all fields are initialized
+        for( int i=idx; i<init.size(); i++ )
+            if( init.at(i)._type == Type.TOP || init.at(i)._type == Type.BOTTOM )
+                throw error("'"+tmp._obj._name+"' is not fully initialized, field '" + fs[i-idx]._fname + "' needs to be set in a constructor");
+        Node ptr = newStruct(tmp._obj, con(tmp._obj.offset(fs.length)), idx, init );
+        if( hasConstructor )
+            _scope.pop();
+        return ptr;
+    }
+
+
+    /**
+     * Return a NewNode initialized memory.
+     * @param obj is the declared type, with GLB fields
+     * @param init is a collection of initialized fields
+     */
+    private Node newStruct( TypeStruct obj, Node size, int idx, Ary<Node> init ) {
+        Field[] fs = obj._fields;
+        if( fs==null )
+            throw error("Unknown struct type '" + obj._name + "'");
+        int len = fs.length;
+        Node[] ns = new Node[2+len];
+        ns[0] = ctrl();         // Control in slot 0
+        // Total allocated length in bytes
+        ns[1] = size;
+        // Memory aliases for every field
+        for( int i = 0; i < len; i++ )
+            ns[2+i] = memAlias(fs[i]._alias);
+        Node nnn = new NewNode(TypeMemPtr.make(obj), ns).peephole().keep();
+        for( int i = 0; i < len; i++ )
+            memAlias(fs[i]._alias, new ProjNode(nnn,i+2,memName(fs[i]._alias)).peephole());
+        Node ptr = new ProjNode(nnn.unkeep(),1,obj._name).peephole().keep();
+
+        // Initial nonzero values for every field
+        for( int i = 0; i < len; i++ ) {
+            Node val = init.get( i + idx );
+            if( val._type != val._type.makeZero() ) {
+                Node mem = memAlias(fs[i]._alias);
+                Node st = new StoreNode(loc(),fs[i]._fname,fs[i]._alias,fs[i]._type,mem,ptr,con(obj.offset(i)),val,true).peephole();
+                memAlias(fs[i]._alias,st);
+            }
+        }
+
+        return ptr.unkeep();
+    }
+
+    private static final Ary<Node> ALTMP = new Ary<>(Node.class);
+    private Node newArray(TypeStruct ary, Node len) {
+        int base = ary.aryBase ();
+        int scale= ary.aryScale();
+        Node size = peep(new AddNode(con(base),peep(new ShlNode(null,len.keep(),con(scale)))));
+        ALTMP.clear();  ALTMP.add(len.unkeep()); ALTMP.add(con(ary._fields[1]._type.makeZero()));
+        return newStruct(ary,size,0,ALTMP);
+    }
+
+    // We set up memory aliases by inserting special vars in the scope these
+    // variables are prefixed by $ so they cannot be referenced in Simple code.
+    // Using vars has the benefit that all the existing machinery of scoping
+    // and phis work as expected
+    private Node memAlias(int alias         ) { return _scope.mem(alias    ); }
+    private void memAlias(int alias, Node st) {        _scope.mem(alias, st); }
+    public static String memName(int alias) { return ("$"+alias).intern(); }
+
+    /**
+     * Parse postfix expression; this can be a field expression, an array
+     * lookup or a postfix operator like '#'
+     *
+     * <pre>
+     *     expr ('.' FIELD)* [ = expr ]       // Field reference
+     *     expr '#'                           // Postfix unary read operator
+     *     expr ['++' | '--' ]                // Postfix unary write operator
+     *     expr ('[' expr ']')* = [ = expr ]  // Array reference
+     *     expr '(' [args,]* ')'              // Function call
+     * </pre>
+     */
+    private Node parsePostfix(Node expr) {
+        String name;
+        if( match(".") )      name = requireId();
+        else if( match("#") ) name = "#";
+        else if( match("[") ) name = "[]";
+        else if( match("(") ) return parsePostfix(require(functionCall(expr),")"));
+        else return expr;       // No postfix
+
+        if( expr._type==Type.NIL )
+            throw error("Accessing unknown field '" + name + "' from 'null'");
+
+        // Sanity check expr for being a reference
+        if( !(expr._type instanceof TypeMemPtr ptr) ) {
+            throw error( "Expected "+(name=="#" || name=="[]" ? "array" : "reference")+" but found " + expr._type.str() );
+        }
+
+        // Sanity check field name for existing
+        TypeMemPtr tmp = (TypeMemPtr)TYPES.get(ptr._obj._name);
+        if( tmp == null ) throw error("Accessing unknown field '" + name + "' from '" + ptr + "'");
+        TypeStruct base = tmp._obj;
+        int fidx = base.find(name);
+        if( fidx == -1 ) throw error("Accessing unknown field '" + name + "' from '" + ptr.str() + "'");
+
+        // Get field type and layout offset from base type and field index fidx
+        Field f = base._fields[fidx];  // Field from field index
+        Type tf = f._type;
+        if( tf instanceof TypeMemPtr ftmp && ftmp.isFRef() )
+            tf = ftmp.makeFrom(((TypeMemPtr)(TYPES.get(ftmp._obj._name)))._obj);
+
+        // Field offset; fixed for structs, computed for arrays
+        Node off = (name.equals("[]")       // If field is an array body
+            // Array index math
+            ? peep(new AddNode(con(base.aryBase()),peep(new ShlNode(null,require(parseAsgn(),"]"),con(base.aryScale())))))
+            // Struct field offsets are hardwired
+            : con(base.offset(fidx))).keep();
+
+        // Disambiguate "obj.fld==x" boolean test from "obj.fld=x" field assignment
+        if( matchOpx('=','=') ) {
+            Node val = parseAsgn().keep();
+            Node lift = liftExpr( val, tf, f._final );
+
+            Node st = new StoreNode(loc(), name, f._alias, tf, memAlias(f._alias), expr, off.unkeep(), lift, false);
+            // Arrays include control, as a proxy for a safety range check.
+            // Structs don't need this; they only need a NPE check which is
+            // done via the type system.
+            if( base.isAry() )  st.setDef(0,ctrl());
+            memAlias(f._alias, st.peephole());
+            return val.unkeep();        // "obj.a = expr" returns the expression while updating memory
+        }
+
+        Node load = new LoadNode(loc(),name, f._alias, tf, memAlias(f._alias), expr.keep(), off);
+        // Arrays include control, as a proxy for a safety range check
+        // Structs don't need this; they only need a NPE check which is
+        // done via the type system.
+        if( base.isAry() && !name.equals("#") ) load.setDef(0,ctrl());
+        load = peep(load);
+
+        // Check for assign-update, "ptr.fld += expr" or "ary[idx]++"
+        char ch = _lexer.matchOperAssign();
+        if( ch!=0 ) {
+            Node op = opAssign(ch,load,f._final,tf,name);
+            Node st = new StoreNode(loc(), name, f._alias, tf, memAlias(f._alias), expr.unkeep(), off, op, false);
+            // Arrays include control, as a proxy for a safety range check.
+            // Structs don't need this; they only need a NPE check which is
+            // done via the type system.
+            if( base.isAry() )  st.setDef(0,ctrl());
+            memAlias(f._alias, peep(st));
+            load = postfix(ch) ? load.unkeep() : op;
+            // And use the original loaded value as the result
+        } else expr.unkill();
+        off.unkill();
+
+        return parsePostfix(load);
+    }
+
+
+    // zero/sign extend.  "i" is limited to either classic unsigned (min==0) or
+    // classic signed (min=minus-power-of-2); max=power-of-2-minus-1.
+    private Node zsMask(Node val, Type t ) {
+        if( !(val._type instanceof TypeInteger tval && t instanceof TypeInteger t0 && !tval.isa(t0)) ) {
+            if( !(val._type instanceof TypeFloat tval && t instanceof TypeFloat t0 && !tval.isa(t0)) )
+                return val;
+            // Float rounding
+            return peep(new RoundF32Node(val));
+        }
+        if( t0._min==0 )        // Unsigned
+            return peep(new AndNode(null,val,con(t0._max)));
+        // Signed extension
+        int shift = Long.numberOfLeadingZeros(t0._max)-1;
+        Node shf = con(shift);
+        if( shf._type==TypeInteger.ZERO )
+            return val;
+        return peep(new SarNode(null,peep(new ShlNode(null,val,shf.keep())),shf.unkeep()));
+    }
+
+    /**
+     * Parse a function body; the caller will parse the surrounding "{}"
+     *
+     * <pre>
+     *     { [type arg,]* -> expr }
+     *     { expr } // The no-argument function
+     * </pre>
+     */
+    private Node func() {
+        Ary<Type> ts = new Ary<>(Type.class);
+        Ary<String> ids = new Ary<>(String.class);
+        _lexer.skipWhiteSpace();
+        Lexer loc = loc();      // First argument location
+        while( true ) {
+            Type t = type();    // Arg type
+            if( t==null ) break;
+            String id = requireId();
+            ts .push(t );       // Push type/arg pairs
+            ids.push(id);
+            match(",");
+        }
+        require("->");
+        // Make a concrete function type, with a fidx
+        TypeFunPtr tfp = _code.makeFun(TypeTuple.make(ts.asAry()),Type.BOTTOM);
+        ReturnNode ret = parseFunctionBody(tfp,loc,ids.asAry());
+        return con(ret._fun.sig());
+    }
+
+    /**
+     *  Parse function call arguments; caller will parse the surrounding "()"
+     * <pre>
+     *   ( arg* )
+     * </pre>
+     */
+    private Node functionCall(Node expr) {
+        if( expr._type == Type.NIL )
+            throw error("Calling a null function pointer");
+        if( !(expr instanceof FRefNode) && !expr._type.isa(TypeFunPtr.BOT) )
+            throw error("Expected a function but got "+expr._type.glb().str());
+        expr.keep();            // Keep while parsing args
+
+        Ary<Node> args = new Ary<Node>(Node.class);
+        args.push(null);        // Space for ctrl,mem
+        args.push(null);
+        while( !peek(')') ) {
+            Node arg = parseAsgn();
+            if( arg==null ) break;
+            args.push(arg.keep());
+            if( !match(",") ) break;
+        }
+        // Control & memory after parsing args
+        args.set(0,ctrl().keep());
+        args.set(1,_scope.mem().merge().keep());
+        args.push(expr);        // Function pointer
+        // Unkeep them all
+        for( Node arg : args )
+            arg.unkeep();
+        // Dead into the call?  Skip all the node gen
+        if( ctrl()._type == Type.XCONTROL ) {
+            for( Node arg : args )
+                if( arg.isUnused() )
+                    arg.kill();
+            return con(Type.TOP);
+        }
+
+        // Into the call
+        CallNode call = (CallNode)new CallNode(loc(), args.asAry()).peephole();
+
+        // Post-call setup
+        CallEndNode cend = (CallEndNode)new CallEndNode(call).peephole();
+        // Control from CallEnd
+        ctrl(new CProjNode(cend,0,ScopeNode.CTRL).peephole());
+        // Memory from CallEnd
+        MemMergeNode mem = new MemMergeNode(true);
+        mem.addDef(null);       // Alias#0
+        mem.addDef(new ProjNode(cend,1,ScopeNode.MEM0).peephole());
+        _scope.mem(mem);
+        // Call result
+        return new ProjNode(cend,2,null).peephole();
+    }
+
+    /**
+     * Parse integer literal
+     *
+     * <pre>
+     *     integerLiteral: [1-9][0-9]* | [0]
+     *     floatLiteral: [digits].[digits]?[e [digits]]?
+     * </pre>
+     */
+    private ConstantNode parseLiteral() { return con(_lexer.parseNumber()); }
+    public static Node con( long con ) { return con==0 ? ZERO : con(TypeInteger.constant(con));  }
+    public static ConstantNode con( Type t ) { return (ConstantNode)new ConstantNode(t).peephole();  }
+    public Node peep( Node n ) {
+        // Peephole, then improve with lexically scoped guards
+        return _scope.upcastGuard(n.peephole());
+    }
+
+    //////////////////////////////////
+    // Utilities for lexical analysis
+
+    // Return true and skip if "syntax" is next in the stream.
+    private boolean match (String syntax) { return _lexer.match (syntax); }
+    // Match must be "exact", not be followed by more id letters
+    private boolean matchx(String syntax) { return _lexer.matchx(syntax); }
+    private boolean matchOpx(char c0, char c1) { return _lexer.matchOpx(c0,c1);  }
+    // Return true and do NOT skip if 'ch' is next
+    private boolean peek(char ch) { return _lexer.peek(ch); }
+    private boolean peekIsId() { return _lexer.peekIsId(); }
+
+    // ch is +/- 1, means oper++ or oper-- means postfix
+    private static boolean postfix(char ch) {
+        return (byte)ch== 1 || (byte)ch== -1;
+    }
+
+    public int pos() { return _lexer._position; }
+    private int pos(int pos) {
+        int old = _lexer._position;
+        _lexer._position = pos;
+        return old;
+    }
+    private Type posT(int pos) { _lexer._position = pos; return null; }
+    // Source code location
+    Lexer loc() { return new Lexer(_lexer); }
+
+
+    // Require and return an identifier
+    private String requireId() {
+        String id = _lexer.matchId();
+        if (id != null && !KEYWORDS.contains(id) ) return id.intern();
+        throw error("Expected an identifier, found '"+id+"'");
+    }
+
+    private String matchId() {
+        int old = pos();
+        String id = _lexer.matchId();
+        if( id==null ) return null;
+        if( !KEYWORDS.contains(id) ) return id;
+        pos(old);
+        return null;
+    }
+
+    // Require an exact match
+    private Parser require(String syntax) { require(null, syntax); return this; }
+    private <N> N require(N n, String syntax) {
+        if (match(syntax)) return n;
+        throw errorSyntax(syntax);
+    }
+
+    ////////////////////////////////////
+    // Lexer components
+
+    // Lexer provides low level access to the raw file bytes, peeks and matches
+    // short strings, parses numbers, skips comments and whitespace, tracks
+    // line numbers, allows the parse position to be saved and restored, and
+    // serves as a location indicator for errors.
+
+    public static class Lexer {
+
+        // Input buffer; an array of text bytes read from a file or a string
+        private final byte[] _input;
+        // Tracks current position in input buffer
+        private int _position = 0;
+
+        //
+        private int _line_number = 1;
+        // Start of current line
+        private int _line_start = 0;
+
+        /**
+         * Record the source text for lexing
+         */
+        public Lexer(String source) {
+            this(source.getBytes());
+        }
+
+        /**
+         * Direct from disk file source
+         */
+        public Lexer(byte[] buf) {
+            _input = buf;
+        }
+
+        /**
+         *  Copy a lexer from a lexer
+         */
+        private Lexer(Lexer l) {
+            _input = l._input;
+            _position = l._position;
+            _line_number = l._line_number;
+            _line_start = l._line_start;
+        }
+
+        // Very handy in the debugger, shows the unparsed program
+        @Override
+        public String toString() {
+            return new String(_input, _position, _input.length - _position);
+        }
+
+        // True if at EOF
+        private boolean isEOF() {
+            return _position >= _input.length;
+        }
+
+        // Peek next character, or report EOF
+        private char peek() {
+            return isEOF() ? Character.MAX_VALUE   // Special value that causes parsing to terminate
+                    : (char) _input[_position];
+        }
+        // Just crash if misused
+        public byte peek(int off) { return _input[_position+off]; }
+
+        private void inc() {
+            if( _position++ < _input.length && _input[_position-1] == '\n' ) {
+                _line_number++;
+                _line_start = _position;
+            }
+        }
+        // Does not honor LF, so caller must roll back position on a LF
+        private char nextChar() {
+            char ch = peek();
+            inc();
+            return ch;
+        }
+
+        // True if a white space
+        private boolean isWhiteSpace() {
+            return peek() <= ' '; // Includes all the use space, tab, newline, CR
+        }
+
+        /**
+         * Return the next non-white-space character
+         */
+        private void skipWhiteSpace() {
+            while( true ) {
+                if( isWhiteSpace() ) inc();
+                // Skip // to end of line
+                else if( _position+2 < _input.length &&
+                         _input[_position  ] == '/' &&
+                         _input[_position+1] == '/') {
+                    inc(); inc();
+                    while( !isEOF() && _input[_position] != '\n' ) inc();
+                } else break;
+            }
+        }
+
+        // Next non-white-space character, or EOF
+        public char nextXChar() { skipWhiteSpace(); return nextChar(); }
+
+        // Return true, if we find "syntax" after skipping white space; also
+        // then advance the cursor past syntax.
+        // Return false otherwise, and do not advance the cursor.
+        boolean match(String syntax) {
+            assert syntax.indexOf('\n')==-1; // No newlines in match
+            skipWhiteSpace();
+            int len = syntax.length();
+            if (_position + len > _input.length) return false;
+            for (int i = 0; i < len; i++)
+                if ((char) _input[_position + i] != syntax.charAt(i))
+                    return false;
+            _position += len;
+            return true;
+        }
+
+        // Match must be exact and not followed by more ID characters.
+        // Prevents identifier "ifxy" from matching an "if" statement.
+        boolean matchx(String syntax) {
+            if( !match(syntax) ) return false;
+            if( !isIdLetter(peek()) ) return true;
+            _position -= syntax.length();
+            return false;
+        }
+        boolean matchOpx(char c0, char c1) {
+            skipWhiteSpace();
+            if( _position+1 >= _input.length || _input[_position]!=c0 || _input[_position+1]==c1 )
+                return false;
+            inc();
+            return true;
+        }
+
+        private boolean peek(char ch) {
+            skipWhiteSpace();
+            return peek()==ch;
+        }
+
+        boolean peekIsId() {
+            skipWhiteSpace();
+            return isIdStart(peek());
+        }
+
+        // Return an identifier or null
+        String matchId() {
+            return peekIsId() ? parseId() : null;
+        }
+
+        // Used for errors
+        String getAnyNextToken() {
+            if (isEOF()) return "";
+            if (isIdStart(peek())) return parseId();
+            if (isNumber(peek())) return parseNumberString();
+            if (isPunctuation(peek())) return parsePunctuation();
+            return String.valueOf(peek());
+        }
+
+
+        boolean isNumber(char ch) {return Character.isDigit(ch);}
+
+        // Return a constant Type, either TypeInteger or TypeFloat
+        private Type parseNumber() {
+            int old = _position;
+            int len = isLongOrDouble();
+            if( len > 0 ) {
+                if( len > 1 && _input[old]=='0' )
+                    throw error("Syntax error: integer values cannot start with '0'",this);
+                long i = Long.parseLong(new String(_input,old,len));
+                return TypeInteger.constant(i);
+            }
+            return TypeFloat.constant(Double.parseDouble(new String(_input,old,-len)));
+        }
+        private String parseNumberString() {
+            int old = _position;
+            int len = Math.abs(isLongOrDouble());
+            return new String(_input,old,len);
+        }
+
+        // Return +len that ends a long
+        // Return -len that ends a double
+        private int isLongOrDouble() {
+            int old = _position;
+            char c;
+            while( Character.isDigit(c=nextChar()) ) ;
+            if( !(c=='e' || c=='.') )
+                return --_position - old;
+            while( Character.isDigit(c=nextChar()) || c=='e' || c=='.' ) ;
+            return -(--_position - old);
+        }
+
+        // First letter of an identifier
+        private boolean isIdStart(char ch) {
+            return Character.isAlphabetic(ch) || ch == '_';
+        }
+
+        // All characters of an identifier, e.g. "_x123"
+        private boolean isIdLetter(char ch) {
+            return Character.isLetterOrDigit(ch) || ch == '_';
+        }
+
+        private String parseId() {
+            int start = _position;
+            while (isIdLetter(nextChar())) ;
+            return new String(_input, start, --_position - start);
+        }
+
+        //
+        private boolean isPunctuation(char ch) {
+            return "=;[]<>()+-/*&|^".indexOf(ch) != -1;
+        }
+
+        private String parsePunctuation() {
+            int start = _position;
+            return new String(_input, start, 1);
+        }
+
+        // Next oper= character, or 0.
+        // As a convenience, mark "++" as a char 1 and "--" as char -1 (65535)
+        public char matchOperAssign() {
+            skipWhiteSpace();
+            if( _position+2 >= _input.length ) return 0;
+            char ch0 = (char)_input[_position];
+            if( "+-/*&|^".indexOf(ch0) == -1 ) return 0;
+            char ch1 = (char)_input[_position+1];
+            if(               ch1 == '=' ) { _position += 2; return ch0; }
+            if( isIdLetter((char)_input[_position+2]) ) return 0;
+            if( ch0 == '+' && ch1 == '+' ) { _position += 2; return (char) 1; }
+            if( ch0 == '-' && ch1 == '-' ) { _position += 2; return (char)-1; }
+            return 0;
+        }
+    }
+
+    ParseException errorSyntax(String syntax) { return _errorSyntax("expected "+syntax);  }
+    private ParseException _errorSyntax(String msg) {
+        return error("Syntax error, "+msg+": " + _lexer.getAnyNextToken());
+    }
+    ParseException error(String msg) { return error(msg,_lexer); }
+    public static ParseException error(String msg, Lexer loc) { return new ParseException(msg,loc); }
+
+    public static class ParseException extends RuntimeException {
+        public final Lexer _loc;
+        // file:line:charoff err
+        //String msg = "src:"+_line_number+":"+(_position-_line_start)+" "+errorMessage;
+        ParseException( String msg, Lexer loc ) { super(msg);  _loc = loc; assert loc!=null; }
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/RegMask.java b/chapter20/src/main/java/com/seaofnodes/simple/RegMask.java
new file mode 100644
index 00000000..20be7157
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/RegMask.java
@@ -0,0 +1,39 @@
+package com.seaofnodes.simple;
+
+import java.util.BitSet;
+
+// A "register mask" - 1 bit set for each allowed register.  In addition "stack
+// slot" registers may be allowed, effectively making the set infinite.
+public class RegMask {
+
+    public static final RegMask EMPTY = new RegMask();
+
+    final BitSet _bits;
+
+    public RegMask(long   x ) { _bits = BitSet.valueOf(new long[]{x}); }
+    public RegMask(long[] xs) { _bits = BitSet.valueOf(           xs); }
+    // Internal constructor
+    RegMask() { _bits = new BitSet(); }
+    RegMask(BitSet bs) { _bits = bs; }
+
+    public boolean get(int r) { return _bits.get(r); }
+
+    // Defensive writable copy
+    public RegMaskRW copy() { return new RegMaskRW( (BitSet)_bits.clone() ); }
+
+    boolean size1() { return _bits.cardinality()==1; }
+}
+
+class RegMaskRW extends RegMask {
+    public RegMaskRW() { super(); }
+    public RegMaskRW(long x) { super(new long[]{x}); }
+    public RegMaskRW(long[] xs) { super(xs); }
+    public RegMaskRW(BitSet bs) { super(bs); }
+    public void set(int r) { _bits.set(r); }
+    public void clr(int r) { _bits.clear(r); }
+    public void set(int r, boolean b) { _bits.set(r,b); }
+    public RegMaskRW and( RegMask r ) {
+        _bits.and(r._bits);
+        return this;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/SB.java b/chapter20/src/main/java/com/seaofnodes/simple/SB.java
new file mode 100644
index 00000000..7d580c21
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/SB.java
@@ -0,0 +1,91 @@
+package com.seaofnodes.simple;
+
+/** Tight/tiny StringBuilder wrapper.
+ *  Short short names on purpose; so they don't obscure the printing.
+ *  Can't believe this wasn't done long, long ago. */
+public final class SB {
+  private final StringBuilder _sb;
+  private int _indent = 0;
+  public SB(        ) { _sb = new StringBuilder( ); }
+  public SB(String s) { _sb = new StringBuilder(s); }
+  public SB p( String s ) { _sb.append(s); return this; }
+  public SB p( float  s ) {
+    if( Float.isNaN(s) )
+      _sb.append( "Float.NaN");
+    else if( Float.isInfinite(s) ) {
+      _sb.append(s > 0 ? "Float.POSITIVE_INFINITY" : "Float.NEGATIVE_INFINITY");
+    } else _sb.append(s);
+    return this;
+  }
+  public SB p( double s ) {
+    if( Double.isNaN(s) )
+      _sb.append("Double.NaN");
+    else if( Double.isInfinite(s) ) {
+      _sb.append(s > 0 ? "Double.POSITIVE_INFINITY" : "Double.NEGATIVE_INFINITY");
+    } else _sb.append(s);
+    return this;
+  }
+  public SB p( char   s ) { _sb.append(s); return this; }
+  public SB p( int    s ) { _sb.append(s); return this; }
+  public SB p( long   s ) { _sb.append(s); return this; }
+  public SB p( boolean s) { _sb.append(s); return this; }
+  // 4 hex digits
+  public SB hex4(int s) {
+    assert (s>>4*4)==0; // Fits in 16 bits
+    for( int i=0; i<4; i++ ) {
+      int digit = (s>>((3-i)*4)) & 0xf;
+      _sb.append((char)((digit <= 9 ? '0' : ('A'-10))+digit));
+    }
+    return this;
+  }
+  // Fixed width field
+  public SB fix( int sz, String s ) {
+    assert sz >=0;
+    for( int i=0; i<sz; i++ )
+      _sb.append( i < s.length() ? s.charAt(i) : ' ');
+    return this;
+  }
+
+  // Not spelled "p" on purpose: too easy to accidentally say "p(1.0)" and
+  // suddenly call the autoboxed version.
+  public SB pobj( Object s ) { _sb.append(s.toString()); return this; }
+  public SB i( int d ) { for( int i=0; i<d+_indent; i++ ) p("  "); return this; }
+  public SB i( ) { return i(0); }
+  public SB ip(String s) { return i().p(s); }
+  public SB s() { _sb.append(' '); return this; }
+
+  // Increase indentation
+  public SB ii( int i) { _indent += i; return this; }
+  public SB ii() { return ii(1); }
+  // Decrease indentation
+  public SB di( int i) { _indent -= i; return this; }
+  public SB di() { return di(1); }
+
+  public SB nl( ) { return p(System.lineSeparator()); }
+  // Last printed a nl
+  public boolean was_nl() {
+    int len = _sb.length();
+    String nl = System.lineSeparator();
+    int nlen = nl.length();
+    if( len < nlen ) return false;
+    for( int i=0; i<nlen; i++ )
+      if( _sb.charAt(len-nlen+i)!=nl.charAt(i) )
+        return false;
+    return true;
+  }
+
+  // Delete last char.  Useful when doing string-joins and JSON printing and an
+  // extra separater char needs to be removed:
+  //
+  //   sb.p('[');
+  //   for( Foo foo : foos )
+  //     sb.p(foo).p(',');
+  //   sb.unchar().p(']');  // remove extra trailing comma
+  //
+  public SB unchar() { return unchar(1); }
+  public SB unchar(int x) { _sb.setLength(_sb.length()-x); return this; }
+
+  public SB clear() { _sb.setLength(0); return this; }
+  public int len() { return _sb.length(); }
+  @Override public String toString() { return _sb.toString(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/SimpleWebSocket.java b/chapter20/src/main/java/com/seaofnodes/simple/SimpleWebSocket.java
new file mode 100644
index 00000000..1ce766ff
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/SimpleWebSocket.java
@@ -0,0 +1,148 @@
+package com.seaofnodes.simple;
+
+import java.io.*;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.net.URI;
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Base64;
+
+// Why-Oh-Why is this needed?
+
+// Pass in a URI and a port.
+// Opens the client; client has to open a websocket at the given port.
+// Connects, handshakes.
+// Thereafter you can call get/put to swap frames with client.
+
+class SimpleWebSocket extends ServerSocket {
+    final  InputStream _in;
+    final OutputStream _out;
+
+    SimpleWebSocket(URI uri, int port) throws IOException, NoSuchAlgorithmException {
+        super(port);
+        // Launch client
+        java.awt.Desktop.getDesktop().browse(uri);
+        // Look for client; get in/out streams
+        Socket sock = accept();
+        _in  = sock. getInputStream();
+        _out = sock.getOutputStream();
+
+
+        // Establish web socket with handshake; easier with a buffered reader
+        BufferedReader br = new BufferedReader(new InputStreamReader(_in));
+        String key = null;
+        while( br.ready() ) {
+            String line = br.readLine();
+            if( line.startsWith("Sec-WebSocket-Key: ") )
+                key = line.substring(19);
+        }
+        assert key!=null;
+        // Magic handshake
+        byte[] response = ("HTTP/1.1 101 Switching Protocols\r\n"
+                           + "Connection: Upgrade\r\n"
+                           + "Upgrade: websocket\r\n"
+                           + "Sec-WebSocket-Accept: "
+                           + Base64.getEncoder().encodeToString(MessageDigest.getInstance("SHA-1").digest((key + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11").getBytes( StandardCharsets.UTF_8 )))
+                           + "\r\n\r\n").getBytes( StandardCharsets.UTF_8 );
+        _out.write(response,0,response.length);
+    }
+
+    final byte[] _ins = new byte[1024];
+    final byte[] _str = new byte[1024];
+    final byte[] _key = new byte[4];
+    int _x, _len;
+    private int rawget() { assert _x<_len; return _ins[_x++]&0xFF; }
+
+    // TODO: Flip to Direct Byte Buffer, this is just a poor-mans version
+    private void flipRead() throws IOException {
+        // Move _x to _len to offset 0
+        System.arraycopy(_ins,_x,_ins,0,(_len-_x));
+        _len = _len-_x;
+        _x=0;
+        // Read more
+        int len = _in.read(_ins,_len,_ins.length-_len);
+        if( len == -1 )
+            throw Utils.TODO(); // EOF
+        _len += len;
+    }
+    // Block until you read at least len
+    private void atLeast(int len) throws IOException {
+        if( _x+len <= _len ) return;
+        flipRead();
+    }
+
+
+    // Classic read from browser client.  Encoded, so decoded here
+    public String get() throws IOException {
+        atLeast(1);             // Need 1 byte for opcode
+        int op = rawget();
+        if( (op&0x80)!=0x80 )   // FIN bit not set?
+            throw Utils.TODO( "Multi-part from client: " + op ); // Multipart message
+        op &= 0x7F;             // Strip FIN bit
+        switch( op&15) {
+        case 1: {
+            atLeast(5);         // Min message length
+            // Message length
+            int len = rawget()-128;
+            if( len > 125 ) {
+                if( len > 126 )
+                    throw Utils.TODO(); // Multi-byte length
+                len = (rawget()<<8) | rawget();
+            }
+            atLeast(len+4);     // Rest of message
+            // Encoding key
+            _key[0] = (byte)rawget();
+            _key[1] = (byte)rawget();
+            _key[2] = (byte)rawget();
+            _key[3] = (byte)rawget();
+
+            // Decode bytes
+            for( int i=0; i<len; i++ )
+                _str[i] = (byte)(rawget() ^ _key[i & 3]);
+
+            return new String(_str,0,len);
+        }
+            // Client closes
+        case 8: return null;
+            // Ping
+        case 9:
+            // Send a PONG back.  TODO: echo PING data in the PONG
+            _out.write(0x8A); // FIN + PONG
+            _out.write(0x00); // LENGTH==0
+            return get();
+            // Not (yet) implemented: continuation frames, ping/pong
+        default:
+            throw Utils.TODO("Unexpected op from client: "+op); // Multi-part message
+        }
+    }
+
+    // Classic put to browser client.  No encoding.
+    public void put(String msg) throws IOException {
+        int len = msg.length();
+        if( len <= 125 ) {
+            _out.write(129); // FIN, opcode 1 - whole text message
+            _out.write(len);
+            for( int i=0; i<msg.length(); i++ )
+                _out.write(msg.charAt(i));
+            return;
+        }
+        if( len > 65535 )
+            throw Utils.TODO("MOAR LENGTH");
+        _out.write(129);        // FIN, opcode 1 - whole text message
+        _out.write(126);        // Length is 16b
+        _out.write(len>>>8);
+        _out.write(len&255);
+        for( int i=0; i<msg.length(); i++ )
+            _out.write(msg.charAt(i));
+    }
+
+    @Override public void close() throws IOException {
+        if( _out != null ) {
+            _out.write(0b10001000);
+            _out.flush();
+        }
+        super.close();
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/Utils.java b/chapter20/src/main/java/com/seaofnodes/simple/Utils.java
new file mode 100644
index 00000000..1346c3ea
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/Utils.java
@@ -0,0 +1,53 @@
+package com.seaofnodes.simple;
+
+import java.util.ArrayList;
+
+public class Utils {
+    public static RuntimeException TODO() { return TODO("Not yet implemented"); }
+    public static RuntimeException TODO(String msg) { return new RuntimeException(msg); }
+
+    /**
+     *  Fast, constant-time, element removal.  Does not preserve order
+     *
+     *  @param array ArrayList to modify
+     *  @param i element to be removed
+     *  @return element removed
+     */
+    public static <E> void del(ArrayList<E> array, int i) {
+        E last = array.removeLast();
+        if (i < array.size()) array.set(i, last);
+    }
+
+    /**
+     * Search a list for an element by reference
+     *
+     * @param ary List to search in
+     * @param x Object to be searched
+     * @return >= 0 on success, -1 on failure
+     */
+    public static <E> int find( ArrayList<E> ary, E x ) {
+        for( int i=0; i<ary.size(); i++ )
+            if( ary.get(i)==x )
+                return i;
+        return -1;
+    }
+    /**
+     * Search a list for an element by reference
+     *
+     * @param ary List to search in
+     * @param x Object to be searched
+     * @return >= 0 on success, -1 on failure
+     */
+    public static <E> int find( E[] ary, E x ) {
+        for( int i=0; i<ary.length; i++ )
+            if( ary[i]==x )
+                return i;
+        return -1;
+    }
+
+    // Rotate a long, nice for hashes
+    public static long rot( long x, int n ) { return (x<<n) | (x>>>n); }
+
+    // Fold a 64bit hash into 32 bits
+    public static int fold( long x ) { return (int)((x>>32) ^ x); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/Var.java b/chapter20/src/main/java/com/seaofnodes/simple/Var.java
new file mode 100644
index 00000000..e71d7ef2
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/Var.java
@@ -0,0 +1,55 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.type.*;
+
+
+/**
+ *  The tracked fields are now complex enough to deserve a array-of-structs layout
+ */
+public class Var {
+
+    public final String _name;   // Declared name
+    public int _idx;             // index in containing scope
+    private Type _type;          // Declared type
+    public boolean _final;       // Final field
+    public Parser.Lexer _loc;    // Source location
+    public boolean _fref;        // Forward ref
+
+    public Var(int idx, String name, Type type, boolean xfinal, Parser.Lexer loc ) {
+        this(idx,name,type,xfinal,loc,false);
+    }
+    public Var(int idx, String name, Type type, boolean xfinal, Parser.Lexer loc, boolean fref) {
+        _idx = idx;
+        _name = name;
+        _type = type;
+        _final = xfinal;
+        _loc = loc;
+        _fref = fref;
+    }
+    public Type type() {
+        if( !_type.isFRef() ) return _type;
+        // Update self to no longer use the forward ref type
+        Type def = Parser.TYPES.get(((TypeMemPtr)_type)._obj._name);
+        return (_type=_type.meet(def));
+    }
+    public Type lazyGLB() {
+        Type t = type();
+        return t instanceof TypeMemPtr ? t : t.glb();
+    }
+
+    // Forward reference variables (not types) must be BOTTOM and
+    // distinct from inferred variables
+    public boolean isFRef() { return _fref; }
+
+    public void defFRef( Type type, boolean xfinal, Parser.Lexer loc ) {
+        assert isFRef() && xfinal;
+        _type = type;
+        _final = true;
+        _loc = loc;
+        _fref = false;
+    }
+
+    @Override public String toString() {
+        return _type.toString()+(_final ? " ": " !")+_name;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/AddFNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/AddFNode.java
new file mode 100644
index 00000000..7d4e2910
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/AddFNode.java
@@ -0,0 +1,44 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class AddFNode extends Node {
+    public AddFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "AddF"; }
+
+    @Override public String glabel() { return "+"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("+"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0 &&
+            in(2)._type instanceof TypeFloat i1) {
+            if (i0.isConstant() && i1.isConstant())
+                return TypeFloat.constant(i0.value()+i1.value());
+        }
+        return in(1)._type.meet(in(2)._type);
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Type t2 = in(2)._type;
+
+        // Add of 0.
+        if ( t2.isConstant() && t2 instanceof TypeFloat i && i.value()==0 )
+            return lhs;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new AddFNode(lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/AddNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/AddNode.java
new file mode 100644
index 00000000..6b7f2418
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/AddNode.java
@@ -0,0 +1,190 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.*;
+
+import java.util.BitSet;
+
+import static com.seaofnodes.simple.Parser.con;
+
+public class AddNode extends Node {
+    public AddNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "Add"; }
+
+    @Override public String glabel() { return "+"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("+"), visited);
+        return sb.append(")");
+    }
+
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i1 &&
+            t2 instanceof TypeInteger i2 ) {
+            if (i1.isConstant() && i2.isConstant())
+                return TypeInteger.constant(i1.value()+i2.value());
+            // Fold ranges like {0-1} + {2-3} into {2-4}.
+            if( !overflow(i1._min,i2._min) &&
+                !overflow(i1._max,i2._max) )
+                return TypeInteger.make(i1._min+i2._min,i1._max+i2._max);
+        }
+        return TypeInteger.BOT;
+    }
+
+    static boolean overflow( long x, long y ) {
+        if( (x ^    y ) < 0 ) return false; // unequal signs, never overflow
+        return (x ^ (x + y)) < 0; // sum has unequal signs, so overflow
+    }
+    @Override
+    public Node idealize () {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t2 = rhs._type;
+
+        // Add of 0.  We do not check for (0+x) because this will already
+        // canonicalize to (x+0)
+        if( t2 == TypeInteger.ZERO )
+            return lhs;
+
+        // Add of same to a multiply by 2
+        if( lhs==rhs )
+            return new ShlNode(null,lhs,con(1));
+
+        // Goal: a left-spine set of adds, with constants on the rhs (which then fold).
+
+        // Move non-adds to RHS
+        if( !(lhs instanceof AddNode) && rhs instanceof AddNode )
+            return swap12();
+
+        // x+(-y) becomes x-y
+        if( rhs instanceof MinusNode minus )
+            return new SubNode(lhs,minus.in(1));
+
+        // Now we might see (add add non) or (add non non) or (add add add) but never (add non add)
+
+        // Do we have  x + (y + z) ?
+        // Swap to    (x + y) + z
+        // Rotate (add add add) to remove the add on RHS
+        if( rhs instanceof AddNode add )
+            return new AddNode(new AddNode(lhs,add.in(1)).peephole(), add.in(2));
+
+        // Now we might see (add add non) or (add non non) but never (add non add) nor (add add add)
+        if( !(lhs instanceof AddNode) )
+            // Rotate; look for (add (phi cons) con/(phi cons))
+            return spine_cmp(lhs,rhs,this) ? swap12() : phiCon(this,true);
+
+        // Now we only see (add add non)
+
+        // Dead data cycle; comes about from dead infinite loops.  Do nothing,
+        // the loop will peep as dead after a bit.
+        if( lhs.in(1) == lhs )
+            return null;
+
+        // Do we have (x + con1) + con2?
+        // Replace with (x + (con1+con2) which then fold the constants
+        // lhs.in(2) is con1 here
+        // If lhs.in(2) is not a constant, we add ourselves as a dependency
+        // because if it later became a constant then we could make this
+        // transformation.
+        if( lhs.in(2).addDep(this)._type.isConstant() && rhs._type.isConstant() )
+            return new AddNode(lhs.in(1),new AddNode(lhs.in(2),rhs).peephole());
+
+
+        // Do we have ((x + (phi cons)) + con) ?
+        // Do we have ((x + (phi cons)) + (phi cons)) ?
+        // Push constant up through the phi: x + (phi con0+con0 con1+con1...)
+        Node phicon = phiCon(this,true);
+        if( phicon!=null ) return phicon;
+
+        // Now we sort along the spine via rotates, to gather similar things together.
+
+        // Do we rotate (x + y) + z
+        // into         (x + z) + y ?
+        if( spine_cmp(lhs.in(2),rhs,this) )
+            return new AddNode(new AddNode(lhs.in(1),rhs).peephole(),lhs.in(2));
+
+        return null;
+    }
+
+    // Rotation is only valid for associative ops, e.g. Add, Mul, And, Or, Xor.
+    // Do we have ((phi cons)|(x + (phi cons)) + con|(phi cons)) ?
+    // Push constant up through the phi: x + (phi con0+con0 con1+con1...)
+    static Node phiCon(Node op, boolean rotate) {
+        Node lhs = op.in(1);
+        Node rhs = op.in(2);
+        if( rhs._type==TypeInteger.TOP ) return null;
+        // LHS is either a Phi of constants, or another op with Phi of constants
+        PhiNode lphi = pcon(lhs,op);
+        if( rotate && lphi==null && lhs.nIns() > 2 ) {
+            // Only valid to rotate constants if both are same associative ops
+            if( lhs.getClass() != op.getClass() ) return null;
+            lphi = pcon(lhs.in(2),op); // Will rotate with the Phi push
+        }
+        if( lphi==null ) return null;
+        if( lphi.region().nIns() <=2 ) return null; // Phi is collapsing
+
+        // RHS is a constant or a Phi of constants
+        if( !(rhs instanceof ConstantNode) && pcon(rhs,op)==null )
+            return null;
+
+        // If both are Phis, must be same Region
+        if( rhs instanceof PhiNode && lphi.in(0) != rhs.in(0) )
+            return null;
+
+        // Note that this is the exact reverse of Phi pulling a common op down
+        // to reduce total op-count.  We don't get in an endless push-up
+        // push-down peephole cycle because the constants all fold first.
+        Node[] ns = new Node[lphi.nIns()];
+        ns[0] = lphi.in(0);
+        // Push constant up through the phi: x + (phi con0+con0 con1+con1...)
+        for( int i=1; i<ns.length; i++ )
+            ns[i] = op.copy(lphi.in(i), rhs instanceof PhiNode ? rhs.in(i) : rhs).peephole();
+        String label = lphi._label + (rhs instanceof PhiNode rphi ? rphi._label : "");
+        Node phi = new PhiNode(label,lphi._declaredType,ns).peephole();
+        // Rotate needs another op, otherwise just the phi
+        return lhs==lphi ? phi : op.copy(lhs.in(1),phi);
+    }
+
+    /**
+     * Tests if the op is a phi and has all constant inputs.
+     * If not, returns null.
+     * If op is a phi, but its inputs are not all constants, then dep is added as
+     * a dependency to the phi's non-const input, because if later the input turn into a constant
+     * dep can make progress.
+     */
+    static PhiNode pcon(Node op, Node dep) {
+        return op instanceof PhiNode phi && phi.allCons(dep) ? phi : null;
+    }
+
+    // Compare two off-spine nodes and decide what order they should be in.
+    // Do we rotate ((x + hi) + lo) into ((x + lo) + hi) ?
+    // Generally constants always go right, then Phi-of-constants, then muls, then others.
+    // Ties with in a category sort by node ID.
+    // TRUE if swapping hi and lo.
+    static boolean spine_cmp( Node hi, Node lo, Node dep ) {
+        if( lo._type.isConstant() ) return false;
+        if( hi._type.isConstant() ) return true ;
+
+        if( lo instanceof PhiNode lphi && lphi.region()._type==Type.XCONTROL ) return false;
+        if( hi instanceof PhiNode hphi && hphi.region()._type==Type.XCONTROL ) return false;
+
+        if( lo instanceof PhiNode && lo.allCons(dep) ) return false;
+        if( hi instanceof PhiNode && hi.allCons(dep) ) return true ;
+
+        if( lo instanceof PhiNode && !(hi instanceof PhiNode) ) return true;
+        if( hi instanceof PhiNode && !(lo instanceof PhiNode) ) return false;
+
+        // Same category of "others"
+        return lo._nid > hi._nid;
+    }
+
+    @Override Node copy(Node lhs, Node rhs) { return new AddNode(lhs,rhs); }
+    @Override Node copyF() { return new AddFNode(null,null); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/AndNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/AndNode.java
new file mode 100644
index 00000000..36e3a949
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/AndNode.java
@@ -0,0 +1,58 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.util.BitSet;
+
+public class AndNode extends LogicalNode {
+    public AndNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "And"; }
+    @Override public String op() { return "&"; }
+
+    @Override public String glabel() { return "&"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1 ) {
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()&i1.value());
+            // Sharpen allowed bits if either value is narrowed
+            long mask = i0.mask() & i1.mask();
+            return mask < 0 ? TypeInteger.BOT : TypeInteger.make(0,mask);
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // And of -1.  We do not check for (-1&x) because this will already
+        // canonicalize to (x&-1)
+        if( t2.isConstant() && t2 instanceof TypeInteger i && i.value()==-1 )
+            return lhs;
+
+        // Move constants to RHS: con*arg becomes arg*con
+        if ( t1.isConstant() && !t2.isConstant() )
+            return swap12();
+
+        // Do we have ((x & (phi cons)) & con) ?
+        // Do we have ((x & (phi cons)) & (phi cons)) ?
+        // Push constant up through the phi: x & (phi con0&con0 con1&con1...)
+        Node phicon = AddNode.phiCon(this,true);
+        if( phicon!=null ) return phicon;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new AndNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/BoolNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/BoolNode.java
new file mode 100644
index 00000000..84be11a9
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/BoolNode.java
@@ -0,0 +1,134 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+import static com.seaofnodes.simple.type.TypeInteger.*;
+
+abstract public class BoolNode extends Node {
+
+    public BoolNode(Node lhs, Node rhs) {
+        super(null, lhs, rhs);
+    }
+
+    abstract public String op(); // String opcode name
+
+    @Override
+    public String label() { return getClass().getSimpleName(); }
+
+    @Override
+    public String glabel() { return op(); }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append(op()), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public TypeInteger compute() {
+        Type t1 = in(1)._type;
+        Type t2 = in(2)._type;
+        // Exactly equals?
+        if( t1.isHigh() || t2.isHigh() )
+            return BOOL.dual();
+        if( in(1)==in(2) )
+            // LT fails, both EQ and LE succeed
+            return this instanceof LT ? FALSE : TRUE;
+        if( t1 instanceof TypeInteger i1 &&
+            t2 instanceof TypeInteger i2 )
+            return doOp(i1,i2);
+        if( t1 instanceof TypeFloat f1 &&
+            t2 instanceof TypeFloat f2 &&
+            f1.isConstant() && f2.isConstant() )
+            return doOp(f1.value(), f2.value()) ? TRUE : FALSE;
+        return BOOL;
+    }
+
+    TypeInteger doOp(TypeInteger t1, TypeInteger t2) { throw Utils.TODO(); }
+    boolean doOp(double lhs, double rhs) { throw Utils.TODO(); }
+    Node copyF(Node lhs, Node rhs) { return null; }
+
+    @Override
+    public Node idealize() {
+        // Compare of same
+        if( in(1)==in(2) )
+            return this instanceof LT ? Parser.ZERO : new ConstantNode(TRUE);
+
+        // Equals pushes constant to the right; 5==X becomes X==5.
+        if( this instanceof EQ ) {
+            if( !(in(2) instanceof ConstantNode) ) {
+                // con==noncon becomes noncon==con
+                if( in(1) instanceof ConstantNode || in(1)._nid > in(2)._nid )
+                // Equals sorts by NID otherwise: non.high == non.low becomes non.low == non.high
+                    return in(1)._type instanceof TypeFloat ? new EQF(in(2),in(1)) : new EQ(in(2),in(1));
+            }
+            // Equals X==0 becomes a !X
+            if( (in(2)._type == ZERO || in(2)._type == Type.NIL) )
+                return new NotNode(in(1));
+        }
+
+        // Do we have ((x * (phi cons)) * con) ?
+        // Do we have ((x * (phi cons)) * (phi cons)) ?
+        // Push constant up through the phi: x * (phi con0*con0 con1*con1...)
+        Node phicon = AddNode.phiCon(this,this instanceof EQ);
+        if( phicon!=null ) return phicon;
+
+        return null;
+    }
+
+    public static class EQ extends BoolNode {
+        public EQ(Node lhs, Node rhs) { super(lhs,rhs); }
+        public String op() { return "=="; }
+        TypeInteger doOp(TypeInteger i1, TypeInteger i2) {
+            if( i1==i2 && i1.isConstant() ) return TRUE;
+            if( i1._max < i2._min || i1._min > i2._max ) return FALSE;
+            return BOOL;
+        }
+        Node copy(Node lhs, Node rhs) { return new EQ(lhs,rhs); }
+        Node copyF() { return new EQF(null,null); }
+    }
+    public static class LT extends BoolNode {
+        public LT(Node lhs, Node rhs) { super(lhs,rhs); }
+        public String op() { return "<" ; }
+        public String glabel() { return "&lt;"; }
+        TypeInteger doOp(TypeInteger i1, TypeInteger i2) {
+            if( i1._max <  i2._min ) return TRUE;
+            if( i1._min >= i2._max ) return FALSE;
+            return BOOL;
+        }
+        Node copy(Node lhs, Node rhs) { return new LT(lhs,rhs); }
+        Node copyF() { return new LTF(null,null); }
+    }
+    public static class LE extends BoolNode {
+        public LE(Node lhs, Node rhs) { super(lhs,rhs); }
+        public String op() { return "<="; }
+        public String glabel() { return "&lt;="; }
+        TypeInteger doOp(TypeInteger i1, TypeInteger i2) {
+            if( i1._max <= i2._min ) return TRUE;
+            if( i1._min >  i2._max ) return FALSE;
+            return BOOL;
+        }
+        Node copy(Node lhs, Node rhs) { return new LE(lhs,rhs); }
+        Node copyF() { return new LEF(null,null); }
+    }
+
+    public static class EQF extends EQ { public EQF(Node lhs, Node rhs) { super(lhs,rhs); } boolean doOp(double lhs, double rhs) { return lhs == rhs; } }
+    public static class LTF extends LT { public LTF(Node lhs, Node rhs) { super(lhs,rhs); } boolean doOp(double lhs, double rhs) { return lhs <  rhs; } }
+    public static class LEF extends LE { public LEF(Node lhs, Node rhs) { super(lhs,rhs); } boolean doOp(double lhs, double rhs) { return lhs <= rhs; } }
+
+    // Unsigned less that, for range checks.  Not directly user writable.
+    public static class ULT extends BoolNode {
+        public ULT(Node lhs, Node rhs) { super(lhs,rhs); }
+        public String op() { return "u<" ; }
+        public String glabel() { return "u&lt;"; }
+        TypeInteger doOp(TypeInteger i1, TypeInteger i2) {
+            if( Long.compareUnsigned(i1._max,i2._min) <  0 ) return TRUE;
+            if( Long.compareUnsigned(i1._min,i2._max) >= 0 ) return FALSE;
+            return BOOL;
+        }
+        Node copy(Node lhs, Node rhs) { return new ULT(lhs,rhs); }
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CFGNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CFGNode.java
new file mode 100644
index 00000000..174725f5
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CFGNode.java
@@ -0,0 +1,162 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Ary;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.HashSet;
+
+/** Control Flow Graph Nodes
+ * <p>
+ *  CFG nodes have a immediate dominator depth (idepth) and a loop nesting
+ *  depth(loop_depth).
+ * <p>
+ *  idepth is computed lazily upon first request, and is valid even in the
+ *  Parser, and is used by peepholes during parsing and afterward.
+ * <p>
+ *  loop_depth is computed after optimization as part of scheduling.
+ *
+ */
+public abstract class CFGNode extends Node {
+
+    public CFGNode(Node...   nodes) { super(nodes); }
+    public CFGNode(CFGNode cfg) {
+        super(cfg);
+        _idepth = cfg._idepth;
+        _ltree = cfg._ltree;
+        _pre = cfg._pre;
+    }
+
+    public CFGNode cfg(int idx) { return (CFGNode)in(idx); }
+
+    // Block head is Start, Region, CProj, but not e.g. If, Return, Stop
+    public boolean blockHead() { return false; }
+
+    // Get the one control following; error to call with more than one e.g. an
+    // IfNode or other multi-way branch.
+    public CFGNode uctrl() {
+        CFGNode c = null;
+        for( Node n : _outputs )
+            if( n instanceof CFGNode cfg )
+                {  assert c==null;  c = cfg; }
+        return c;
+    }
+
+
+    // ------------------------------------------------------------------------
+    /**
+     * Immediate dominator tree depth, used to approximate a real IDOM during
+     * parsing where we do not have the whole program, and also peepholes
+     * change the CFG incrementally.
+     * <p>
+     * See {@link <a href="https://en.wikipedia.org/wiki/Dominator_(graph_theory)">...</a>}
+     */
+    public int _idepth;
+    public int idepth() { return _idepth==0 ? (_idepth=idom().idepth()+1) : _idepth; }
+
+    // Return the immediate dominator of this Node and compute dom tree depth.
+    public CFGNode idom(Node dep) { return cfg(0); }
+    public final CFGNode idom() { return idom(null); }
+
+    // Return the LCA of two idoms
+    public CFGNode _idom(CFGNode rhs, Node dep) {
+        if( rhs==null ) return this;
+        CFGNode lhs = this;
+        while( lhs != rhs ) {
+            var comp = lhs.idepth() - rhs.idepth();
+            if( comp >= 0 ) lhs = ((CFGNode)lhs.addDep(dep)).idom();
+            if( comp <= 0 ) rhs = ((CFGNode)rhs.addDep(dep)).idom();
+        }
+        return lhs;
+    }
+
+    // Anti-dependence field support
+    public int _anti;           // Per-CFG field to help find anti-deps
+
+    // ------------------------------------------------------------------------
+    // Loop nesting
+    public LoopNode loop() { return _ltree._head; }
+    public int loopDepth() { return _ltree==null ? 0 : _ltree.depth(); }
+
+    LoopTree _ltree;
+    int _pre;                   // Pre-order numbers for loop tree finding
+    private static class LoopTree {
+        LoopTree _par;
+        final LoopNode _head;
+        int _depth;
+        LoopTree(LoopNode head) { _head = head; }
+        @Override public String toString() { return "LOOP"+_head._nid; }
+        int depth() {
+            return _depth==0 ? (_par==null ? 0 : (_depth = _par.depth()+1)) : _depth;
+        }
+    }
+
+    // ------------------------------------------------------------------------
+    // Tag all CFG Nodes with their containing LoopNode; LoopNodes themselves
+    // also refer to *their* containing LoopNode, as well as have their depth.
+    // Start is a LoopNode which contains all at depth 1.
+    public void buildLoopTree(StopNode stop) {
+        _ltree = stop._ltree = Parser.XCTRL._ltree = new LoopTree((StartNode)this);
+        _bltWalk(2,null,stop, new BitSet());
+    }
+    int _bltWalk( int pre, FunNode fun, StopNode stop, BitSet post ) {
+        // Pre-walked?
+        if( _pre!=0 ) return pre;
+        _pre = pre++;
+        // Pre-walk
+        for( Node use : _outputs )
+            if( use instanceof CFGNode usecfg && !skip( usecfg ) )
+                pre = usecfg._bltWalk( pre, use instanceof FunNode fuse ? fuse : fun, stop, post );
+
+        // Post-order work: find innermost loop
+        LoopTree inner = null, ltree;
+        for( Node use : _outputs ) {
+            if( !(use instanceof CFGNode usecfg) ) continue;
+            if( skip(usecfg) ) continue;
+            if( usecfg._type == Type.XCONTROL ||       // Do not walk dead control
+                usecfg._type == TypeTuple.IF_NEITHER ) // Nor dead IFs
+                continue;
+            // Child visited but not post-visited?
+            if( !post.get(usecfg._nid) ) {
+                // Must be a backedge to a LoopNode then
+                ltree = usecfg._ltree = new LoopTree((LoopNode)usecfg);
+            } else {
+                // Take child's loop choice, which must exist
+                ltree = usecfg._ltree;
+                // If falling into a loop, use the target loop's parent instead
+                if( ltree._head == usecfg ) {
+                    if( ltree._par == null )
+                        // This loop never had an If test choose to take its
+                        // exit, i.e. it is a no-exit infinite loop.
+                        ltree._par = ltree._head.forceExit(fun,stop)._ltree;
+                    ltree = ltree._par;
+                }
+            }
+            // Sort inner loops.  The decision point is some branch far removed
+            // from either loop head OR either backedge so requires pre-order
+            // numbers to figure out innermost.
+            if( inner == null ) { inner = ltree; continue; }
+            if( inner == ltree ) continue; // No change
+            LoopTree outer = ltree._head._pre > inner._head._pre ? inner : ltree;
+            inner =          ltree._head._pre > inner._head._pre ? ltree : inner;
+            inner._par = outer;
+        }
+        // Set selected loop
+        if( inner!=null )
+            _ltree = inner;
+        // Tag as post-walked
+        post.set(_nid);
+        return pre;
+    }
+
+    boolean skip(CFGNode usecfg) {
+        // Only walk control users that are alive.
+        // Do not walk from a Call to linked Fun's.
+        return usecfg instanceof XCtrlNode ||
+                (this instanceof CallNode && usecfg instanceof FunNode) ||
+                (this instanceof ReturnNode && usecfg instanceof CallEndNode);
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CProjNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CProjNode.java
new file mode 100644
index 00000000..690ef590
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CProjNode.java
@@ -0,0 +1,62 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMem;
+import com.seaofnodes.simple.type.TypeTuple;
+import java.util.BitSet;
+
+public class CProjNode extends CFGNode {
+
+    // Which slice of the incoming multipart value
+    public final int _idx;
+
+    // Debugging label
+    public final String _label;
+
+    public CProjNode(Node ctrl, int idx, String label) {
+        super(ctrl);
+        _idx = idx;
+        _label = label;
+    }
+    public CProjNode(CProjNode c) { super(c); _idx = c._idx; _label = c._label; }
+
+    @Override public String label() { return _label; }
+
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append(_label); }
+
+    @Override public boolean isMultiTail() { return in(0).isMultiHead(); }
+    @Override public boolean blockHead() { return true; }
+
+    public CFGNode ctrl() { return cfg(0); }
+
+    @Override
+    public Type compute() {
+        Type t = ctrl()._type;
+        return t instanceof TypeTuple tt ? tt._types[_idx] : Type.BOTTOM;
+    }
+
+    @Override
+    public Node idealize() {
+        if( ctrl()._type instanceof TypeTuple tt ) {
+            if( tt._types[_idx]==Type.XCONTROL )
+                return Parser.XCTRL; // We are dead
+            if( ctrl() instanceof IfNode && tt._types[1-_idx]==Type.XCONTROL ) // Only true for IfNodes
+                return ctrl().in(0);               // We become our input control
+        }
+
+        // Flip a negating if-test, to remove the not
+        if( ctrl() instanceof IfNode iff && iff.pred().addDep(this) instanceof NotNode not )
+            return new CProjNode(new IfNode(iff.ctrl(),not.in(1)).peephole(),1-_idx,_idx==0 ? "False" : "True");
+
+        // Copy of some other input
+        return ((MultiNode)ctrl()).pcopy(_idx);
+    }
+
+    @Override
+    boolean eq( Node n ) { return _idx == ((CProjNode)n)._idx; }
+
+    @Override
+    int hash() { return _idx; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CallEndNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
new file mode 100644
index 00000000..4e50c1fc
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
@@ -0,0 +1,90 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+/**
+ *  CallEnd
+ */
+public class CallEndNode extends CFGNode implements MultiNode {
+
+    // When set true, this Call/CallEnd/Fun/Return is being trivially inlined
+    private boolean _folding;
+
+    public CallEndNode(CallNode call) { super(new Node[]{call}); }
+    public CallEndNode(CallEndNode cend) { super(cend); }
+
+    @Override
+    public String label() { return "CallEnd"; }
+    @Override public boolean isMultiHead() { return true; }
+    @Override public boolean blockHead() { return true; }
+
+    CallNode call() { return (CallNode)in(0); }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("cend( ");
+        sb.append( in(0) instanceof CallNode ? "Call, " : "----, ");
+        for( int i=1; i<nIns()-1; i++ )
+            in(i)._print0(sb,visited).append(",");
+        sb.setLength(sb.length()-1);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if( !(in(0) instanceof CallNode call) )
+            return TypeTuple.RET.dual();
+        Type ret = call.fptr().addDep(this)._type instanceof TypeFunPtr tfp ? tfp.ret() : Type.BOTTOM;
+        return TypeTuple.make(call._type,TypeMem.BOT,ret);
+    }
+
+    @Override
+    public Node idealize() {
+
+        // Trivial inlining: call site calls a single function; single function
+        // is only called by this call site.
+        if( !_folding && nIns()==2 && in(0) instanceof CallNode call ) {
+            Node fptr = call.fptr();
+            if( fptr.nOuts() == 1 && // Only user is this call
+                fptr instanceof ConstantNode && // We have an immediate call
+                // Function is being called, and its not-null
+                fptr._type instanceof TypeFunPtr tfp && tfp.notNull() &&
+                // Arguments are correct
+                call.err()==null ) {
+                ReturnNode ret = (ReturnNode)in(1);
+                FunNode fun = ret.fun();
+                // Expecting Start, and the Call
+                if( fun.nIns()==3 ) {
+                    assert fun.in(1) instanceof StartNode && fun.in(2)==call;
+                    // Disallow self-recursive inlining (loop unrolling by another name)
+                    CFGNode idom = call;
+                    while( !(idom instanceof FunNode fun2) )
+                        idom = idom.idom();
+                    if( idom != fun ) {
+                        // Trivial inline: rewrite
+                        _folding = true;
+                        // Rewrite Fun so the normal RegionNode ideal collapses
+                        fun._folding = true;
+                        fun.setDef(1,Parser.XCTRL); // No default/unknown StartNode caller
+                        fun.setDef(2,call.ctrl());  // Bypass the Call;
+                        fun.ret().setDef(3,null);   // Return is folding also
+                        CodeGen.CODE.addAll(fun._outputs);
+                        return this;
+                    }
+                } else {
+                    fun.addDep(this);
+                }
+            } else { // Function ptr has multiple users (so maybe multiple call sites)
+                fptr.addDep(this);
+            }
+        }
+
+        return null;
+    }
+
+    @Override public Node pcopy(int idx) {
+        return _folding ? in(1).in(idx) : null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CallNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CallNode.java
new file mode 100644
index 00000000..a9ca852c
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CallNode.java
@@ -0,0 +1,146 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.IterPeeps;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.util.BitSet;
+
+/**
+ *  Call
+ */
+public class CallNode extends CFGNode {
+
+    // Source location for late reported errors
+    public final Parser.Lexer _loc;
+
+    public CallNode(Parser.Lexer loc, Node... nodes) { super(nodes); _loc = loc; }
+    public CallNode(CallNode call) { super(call); _loc = call._loc; }
+
+    @Override
+    public String label() { return "Call"; }
+
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        String fname = name();
+        if( fname == null ) fptr()._print0(sb,visited);
+        else sb.append(fname);
+        sb.append("( ");
+        for( int i=2; i<nIns()-1; i++ )
+            in(i)._print0(sb,visited).append(",");
+        sb.setLength(sb.length()-1);
+        return sb.append(")");
+    }
+    public String name() {
+        if( fptr()._type instanceof TypeFunPtr tfp && tfp.isConstant() )
+            return CodeGen.CODE.link(tfp)._name;
+        return null;
+    }
+
+
+
+    Node ctrl() { return in(0); }
+    Node mem () { return in(1); }
+    // Args mapped 1-to-1 on inputs, so conceptually start at 2
+    Node arg(int idx) { return in(idx); }
+    // Same arg accounting as TFPs, although the numbering starts at 2
+    int nargs() { return nIns()-3; } // Minus control, memory, fptr
+    // args from input 2 to last; last is function input
+    public Node fptr() { return _inputs.last(); }
+
+    // Find the Call End from the Call
+    public CallEndNode cend() {
+        // Always in use slot 0
+        if( nOuts()>0 && out(0) instanceof CallEndNode cend ) {
+            assert _cend()==cend;
+            return cend;
+        } else {
+            assert _cend()==null;
+            return null;
+        }
+    }
+    private CallEndNode _cend() {
+        CallEndNode cend=null;
+        for( Node n : _outputs )
+            if( n instanceof CallEndNode cend0 )
+                { assert cend == null; cend = cend0; }
+        return cend;
+    }
+
+    // Get the one control following; error to call with more than one e.g. an
+    // IfNode or other multi-way branch.
+    @Override public CFGNode uctrl() { return cend(); }
+
+
+    @Override
+    public Type compute() {
+        return ctrl()._type;
+    }
+
+    @Override
+    public Node idealize() {
+        CallEndNode cend = cend();
+        if( cend==null ) return null; // Still building
+
+        // Link: call calls target function.  Linking makes the target FunNode
+        // point to this Call, and all his Parms point to the call arguments;
+        // also the CallEnd points to the Return.
+        if( fptr()._type instanceof TypeFunPtr tfp && tfp.nargs() == nargs() ) {
+            // If fidxs is negative, then infinite unknown functions
+            long fidxs = tfp.fidxs();
+            if( fidxs > 0 ) {
+                // Wipe out the return which matching in the linker table
+                // Walk the (63 max) bits and link
+                for( ; fidxs!=0; fidxs = TypeFunPtr.nextFIDX(fidxs) ) {
+                    int fidx = Long.numberOfTrailingZeros(fidxs);
+                    TypeFunPtr tfp0 = tfp.makeFrom(fidx);
+                    FunNode fun = CodeGen.CODE.link(tfp0);
+                    if( fun!=null && !fun._folding && !linked(fun) )
+                        link(fun);
+                }
+            }
+        }
+
+        return null;
+    }
+
+    // True if Fun is linked to this Call
+    boolean linked( FunNode fun ) {
+        for( Node n : fun._inputs )
+            if( n == this )
+                return true;
+        return false;
+    }
+
+
+    // Link so this calls fun
+    private void link( FunNode fun ) {
+        assert !linked(fun);
+        fun.addDef(this);
+        for( Node use : fun._outputs )
+            if( use instanceof ParmNode parm )
+                parm.addDef(parm._idx==0 ? cend() : arg(parm._idx));
+        // Call end points to function return
+        CodeGen.CODE.add(cend()).addDef(fun.ret());
+        assert linked(fun);
+    }
+
+    @Override
+    public Parser.ParseException err() {
+        if( !(fptr()._type instanceof TypeFunPtr tfp) )
+            throw Utils.TODO();
+        if( !tfp.notNull() )
+            return Parser.error( "Might be null calling "+tfp, _loc);
+        if( nargs() != tfp.nargs() )
+            return Parser.error( "Expecting "+tfp.nargs()+" arguments, but found "+nargs(), _loc);
+
+        // Check for args
+        for( int i=0; i<tfp.nargs(); i++ )
+            if( !arg(i+2)._type.isa(tfp.arg(i)) )
+                return Parser.error( "Argument #"+i+" isa "+arg(i+2)._type+", but must be a "+tfp.arg(i), _loc);
+
+        return null;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CastNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CastNode.java
new file mode 100644
index 00000000..d8a968c1
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CastNode.java
@@ -0,0 +1,58 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+// Upcast (join) the input to a t.  Used after guard test to lift an input.
+// Can also be used to make a type-assertion if ctrl is null.
+public class CastNode extends Node {
+    private final Type _t;
+    public CastNode(Type t, Node ctrl, Node in) {
+        super(ctrl, in);
+        _t = t;
+        setType(compute());
+    }
+
+    @Override public String label() { return "("+_t.str()+")"; }
+
+    @Override
+    public String uniqueName() { return "Cast_" + _nid; }
+
+    @Override public boolean isPinned() { return true; }
+    @Override public boolean isConst() { return true; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return in(1)._print0(sb.append(label()), visited);
+    }
+
+    @Override
+    public Type compute() {
+        return in(1)._type.join(_t);
+    }
+
+    @Override
+    public Node idealize() {
+        return in(1)._type.isa(_t) ? in(1) : null;
+    }
+
+    @Override
+    boolean eq(Node n) {
+        CastNode cast = (CastNode)n; // Contract
+        return _t==cast._t;
+    }
+
+    @Override
+    int hash() { return _t.hashCode(); }
+
+    @Override
+    public Parser.ParseException err() {
+        // Has a condition to test, so OK
+        if( in(0) != null ) return null;
+        // No condition to test, so this must optimize away
+        throw Utils.TODO();
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ConstantNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
new file mode 100644
index 00000000..d788cff7
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
@@ -0,0 +1,70 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.util.BitSet;
+
+/**
+ * A Constant node represents a constant value.  At present, the only constants
+ * that we allow are integer literals; therefore Constants contain an integer
+ * value.  As we add other types of constants, we will refactor how we represent
+ * Constants.
+ * <p>
+ * Constants have no semantic inputs. However, we set Start as an input to
+ * Constants to enable a forward graph walk.  This edge carries no semantic
+ * meaning, and it is present <em>solely</em> to allow visitation.
+ * <p>
+ * The Constant's value is the value stored in it.
+ */
+
+public class ConstantNode extends Node {
+    public final Type _con;
+    public ConstantNode( Type type ) {
+        super(new Node[]{CodeGen.CODE._start});
+        _con = _type = type;
+    }
+    public ConstantNode( ConstantNode con ) { super(con);  _con = con._type;  }
+
+    public static Node make( Type type ) {
+        if( type==Type. CONTROL ) return new CtrlNode();
+        if( type==Type.XCONTROL ) return new XCtrlNode();
+        return new ConstantNode(type);
+    }
+
+    @Override public String  label() { return "#"+_con; }
+    @Override public String glabel() { return _con.gprint(new SB().p("#")).toString(); }
+
+    @Override
+    public String uniqueName() { return "Con_" + _nid; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        if( _con instanceof TypeFunPtr tfp ) {
+            FunNode fun = CodeGen.CODE.link(tfp);
+            if( fun._name != null )
+                return sb.append("{ ").append(fun._name).append("}");
+        }
+        return sb.append(_con.print(new SB()));
+    }
+
+    @Override public boolean isMultiTail() { return true; }
+    @Override public boolean isConst() { return true; }
+
+    @Override
+    public Type compute() { return _con; }
+
+    @Override
+    public Node idealize() { return null; }
+
+    @Override
+    boolean eq(Node n) {
+        ConstantNode con = (ConstantNode)n; // Contract
+        return _con==con._con;
+    }
+
+    @Override
+    int hash() { return _con.hashCode(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/CtrlNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/CtrlNode.java
new file mode 100644
index 00000000..0ea060bd
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/CtrlNode.java
@@ -0,0 +1,15 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import java.util.BitSet;
+
+public class CtrlNode extends CFGNode {
+    public CtrlNode() { super(CodeGen.CODE._start); }
+    @Override public String label() { return "Ctrl"; }
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Cctrl"); }
+    @Override public boolean isConst() { return true; }
+    @Override  public Type compute() { return Type.CONTROL; }
+    @Override public Node idealize() { return null; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/DivFNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/DivFNode.java
new file mode 100644
index 00000000..36fd4524
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/DivFNode.java
@@ -0,0 +1,46 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class DivFNode extends Node {
+    public DivFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "DivF"; }
+
+    @Override public String glabel() { return "/"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("/"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0 &&
+            in(2)._type instanceof TypeFloat i1) {
+            if (i0.isConstant() && i1.isConstant())
+                return TypeFloat.constant(i0.value()/i1.value());
+        }
+        return in(1)._type.meet(in(2)._type);
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // Div of 1.  
+        if ( t2.isConstant() && t2 instanceof TypeFloat i && i.value()==1 )
+            return lhs;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new DivFNode(lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/DivNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/DivNode.java
new file mode 100644
index 00000000..0d5ed297
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/DivNode.java
@@ -0,0 +1,46 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class DivNode extends Node {
+    public DivNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "Div"; }
+
+    @Override public String glabel() { return "//"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("/"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i1 &&
+            t2 instanceof TypeInteger i2 ) {
+            if (i1.isConstant() && i2.isConstant())
+                return i2.value() == 0
+                    ? TypeInteger.ZERO
+                    : TypeInteger.constant(i1.value()/i2.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        // Div of 1.
+        if( in(2)._type == TypeInteger.TRUE )
+            return in(1);
+        return null;
+    }
+
+    @Override Node copy(Node lhs, Node rhs) { return new DivNode(lhs,rhs); }
+    @Override Node copyF() { return new DivFNode(null,null); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/FRefNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/FRefNode.java
new file mode 100644
index 00000000..f0c4045d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/FRefNode.java
@@ -0,0 +1,35 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Var;
+import com.seaofnodes.simple.type.Type;
+import java.util.BitSet;
+
+/**
+ *  A Forward Reference.  Its any final constant, including functions.  When
+ *  the Def finally appears its plugged into the forward reference, which then
+ *  peepholes to the Def.
+ */
+public class FRefNode extends ConstantNode {
+    public static final Type FREF_TYPE = Type.BOTTOM;
+    public final Var _n;
+    public FRefNode( Var n ) { super(FREF_TYPE); _n = n; }
+
+    @Override public String label() { return "FRef"+_n; }
+
+    @Override public String uniqueName() { return "FRef_" + _nid; }
+
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return sb.append("FRef_").append(_n);
+    }
+
+    @Override public Node idealize() {
+        // When FRef finds its definition, idealize to it
+        return nIns()==1 ? null : in(1);
+    }
+
+    public Parser.ParseException err() { return Parser.error("Undefined name '"+_n._name+"'",_n._loc); }
+
+    @Override boolean eq(Node n) { return this==n; }
+    @Override int hash() { return _n._idx; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/FunNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/FunNode.java
new file mode 100644
index 00000000..506e7758
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/FunNode.java
@@ -0,0 +1,149 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.util.BitSet;
+import static com.seaofnodes.simple.CodeGen.CODE;
+
+public class FunNode extends RegionNode {
+
+    // When set true, this Call/CallEnd/Fun/Return is being trivially inlined
+    boolean _folding;
+
+    private TypeFunPtr _sig;    // Initial signature
+    private ReturnNode _ret;    // Return pointer
+
+    public String _name;        // Debug name
+
+    public FunNode( Parser.Lexer loc, TypeFunPtr sig, Node... nodes ) { super(loc,nodes); _sig = sig; }
+    public FunNode( FunNode fun ) { super( fun, fun._loc ); _sig = fun.sig(); _name = fun._name; }
+
+    @Override
+    public String label() { return _name == null ? "$fun" : _name; }
+
+    // Find the one CFG user from Fun.  It's not always the Return, but always
+    // the Return *is* a CFG user of Fun.
+    @Override public CFGNode uctrl() {
+        for( Node n : _outputs )
+            if( n instanceof CFGNode cfg &&
+                (cfg instanceof RegionNode || cfg.cfg0()==this) )
+                return cfg;
+        return null;
+    }
+
+    public ParmNode rpc() {
+        ParmNode rpc = null;
+        for( Node n : _outputs )
+            if( n instanceof ParmNode parm && parm._idx==0 )
+                { assert rpc==null; rpc=parm; }
+        return rpc;
+    }
+
+    // Cannot create the Return and Fun at the same time; one has to be first.
+    // So setting the return requires a second step.
+    public void setRet(ReturnNode ret) { _ret=ret; }
+    ReturnNode ret() { assert _ret!=null; return _ret; }
+
+    // Signature can improve over time
+    public TypeFunPtr sig() { return _sig; }
+    void setSig( TypeFunPtr sig ) {
+        assert sig.isa(_sig);
+        if( _sig != sig ) {
+            CODE.add(this);
+            _sig = sig;
+        }
+    }
+
+    @Override
+    public Type compute() {
+        // Only dead if no callers after SCCP
+        return Type.CONTROL;
+    }
+
+    @Override
+    public Node idealize() {
+
+        // Some linked path dies
+        Node progress = deadPath();
+        if( progress!=null ) {
+            if( nIns()==3 && in(2) instanceof CallNode call )
+                CODE.add(call.cend()); // If Start and one call, check for inline
+            return progress;
+        }
+
+        // When can we assume no callers?  Or no other callers (except main)?
+        // In a partial compilation, we assume Start gets access to any/all
+        // top-level public structures and recursively what they point to.
+        // This in turn is valid arguments to every callable function.
+        //
+        // In a total compilation, we can start from Start and keep things
+        // more contained.
+
+        // If no default/unknown caller, use the normal RegionNode ideal rules
+        // to collapse
+        if( unknownCallers() ) return null;
+
+        // If down to a single input, become that input
+        if( nIns()==2 && !hasPhi() ) {
+            CODE.add( CODE._stop ); // Stop will remove dead path
+            CODE.add( _ret );       // Return will compute to TOP control
+            return in(1); // Collapse if no Phis; 1-input Phis will collapse on their own
+        }
+
+        return null;
+    }
+
+    // Bypass Region idom, always assume depth == 1, one more than Start
+    @Override public int idepth() { return (_idepth=1); }
+    // Bypass Region idom, always assume idom is Start
+    @Override public CFGNode idom(Node dep) { return cfg(1); }
+
+    // Always in-progress until we run out of unknown callers
+    public boolean unknownCallers() { return in(1) instanceof StartNode; }
+
+    @Override public boolean inProgress() { return unknownCallers(); }
+
+    // Add a new function exit point.
+    public void addReturn(Node ctrl, Node mem, Node rez) {  _ret.addReturn(ctrl,mem,rez);  }
+
+    // Build the function body
+    public BitSet body() {
+
+        // Reverse up (stop to start) CFG only, collect bitmap.
+        BitSet cfgs = new BitSet();
+        cfgs.set(_nid);
+        walkUp(ret(),cfgs );
+
+        // Top down (start to stop) all flavors.  CFG limit to bitmap.
+        // If data use bottoms out in wrong CFG, returns false - but tries all outputs.
+        // If any output hits an in-CFG use (e.g. phi), then keep node.
+        BitSet body = new BitSet();
+        walkDown(this, cfgs, body, new BitSet());
+        return body;
+    }
+
+    private static void walkUp(CFGNode n, BitSet cfgs) {
+        if( cfgs.get(n._nid) ) return;
+        cfgs.set(n._nid);
+        if( n instanceof RegionNode r )
+            for( int i=1; i<n.nIns(); i++ )
+                walkUp(n.cfg(i),cfgs);
+        else walkUp(n.cfg0(),cfgs);
+    }
+
+    private static boolean walkDown( Node n, BitSet cfgs, BitSet body, BitSet visit ) {
+        if( visit.get(n._nid) ) return body.get(n._nid);
+        visit.set(n._nid);
+
+        if( n instanceof CFGNode && !cfgs.get(n._nid) )
+            return false;
+        if( n.in(0)!=null && !cfgs.get(n.in(0)._nid) )
+            return false;
+        boolean in = n.in(0)!=null || n instanceof CFGNode;
+        for( Node use : n._outputs )
+            in |= walkDown(use,cfgs,body,visit);
+        if( in ) body.set(n._nid);
+        return in;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/IfNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/IfNode.java
new file mode 100644
index 00000000..9e6d2dff
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/IfNode.java
@@ -0,0 +1,69 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.IterPeeps;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+import java.util.HashSet;
+
+public class IfNode extends CFGNode implements MultiNode {
+
+    public IfNode(Node ctrl, Node pred) {
+        super(ctrl, pred);
+        CodeGen.CODE.add(this); // Because idoms are complex, just add it
+    }
+    public IfNode(IfNode iff) { super(iff); }
+
+    @Override
+    public String label() { return "If"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("if( ");
+        return in(1)._print0(sb, visited).append(" )");
+    }
+
+    @Override public boolean isMultiHead() { return true; }
+
+    public Node ctrl() { return in(0); }
+    public Node pred() { return in(1); }
+
+    // No one unique control follows
+    @Override public CFGNode uctrl() { return null; }
+
+    @Override
+    public Type compute() {
+        // If the If node is not reachable then neither is any following Proj
+        if (ctrl()._type != Type.CONTROL && ctrl()._type != Type.BOTTOM )
+            return TypeTuple.IF_NEITHER;
+        Node pred = pred();
+        Type t = pred._type;
+        // High types mean NEITHER side is reachable.
+        // Wait until the type falls to decide which way to go.
+        if( t.isHigh() )
+            return TypeTuple.IF_NEITHER;
+        // If constant is 0 then false branch is reachable
+        // Else true branch is reachable
+        if( t.isConstant() )
+            return (t==Type.NIL || t==TypeInteger.ZERO || (t instanceof TypeFunPtr tfp && tfp._fidxs==0) ) ? TypeTuple.IF_FALSE : TypeTuple.IF_TRUE;
+        // If adding a zero makes a difference, the predicate must not have a zero/null
+        if( !t.makeZero().isa(t) )
+            return TypeTuple.IF_TRUE;
+
+        return TypeTuple.IF_BOTH;
+    }
+
+    @Override
+    public Node idealize() {
+        // Hunt up the immediate dominator tree.  If we find an identical if
+        // test on either the true or false branch, that side wins.
+        if( !pred()._type.isHighOrConst() )
+            for( CFGNode dom = idom(), prior=this; dom!=null;  prior = dom, dom = dom.idom() )
+                if( dom.addDep(this) instanceof IfNode iff && iff.pred().addDep(this)==pred() && prior instanceof CProjNode prj ) {
+                    setDef(1,con( prj._idx==0 ? 1 : 0 ));
+                    return this;
+                }
+        return null;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/LoadNode.java
new file mode 100644
index 00000000..6c74042b
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -0,0 +1,210 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+/**
+ * Load represents extracting a value from inside a memory object,
+ * in chapter 10 this means Struct fields.
+ */
+public class LoadNode extends MemOpNode {
+
+    /**
+     * Load a value from a ptr.field.
+     *
+     * @param name  The field we are loading
+     * @param mem   The memory alias node - this is updated after a Store
+     * @param ptr   The ptr to the struct base from where we load a field
+     * @param off   The offset inside the struct base
+     */
+    public LoadNode(Parser.Lexer loc, String name, int alias, Type glb, Node mem, Node ptr, Node off) {
+        super(loc, name, alias, glb, mem, ptr, off);
+    }
+
+    // GraphVis DOT code (must be valid Java identifiers) and debugger labels
+    @Override public String  label() { return "ld_"+mlabel(); }
+    // GraphVis node-internal labels
+    @Override public String glabel() { return "." +_name; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append(".").append(_name); }
+
+    @Override
+    public Type compute() {
+        if( mem()._type instanceof TypeMem mem ) {
+            // Update declared forward ref to the actual
+            if( _declaredType.isFRef() && mem._t instanceof TypeMemPtr tmp && !tmp.isFRef() )
+                _declaredType = tmp;
+            // No lifting if ptr might null-check
+            if( err()==null )
+                return _declaredType.join(mem._t);
+        }
+        return _declaredType;
+    }
+
+    @Override
+    public Node idealize() {
+        Node ptr = ptr();
+        Node mem = mem();
+
+        // Simple Load-after-Store on same address.
+        if( mem instanceof StoreNode st &&
+            ptr == st.ptr() && off() == st.off() ) { // Must check same object
+            assert _name.equals(st._name); // Equiv class aliasing is perfect
+            return extend(st.val());
+        }
+
+        // Simple Load-after-New on same address.
+        if( mem instanceof ProjNode p && p.in(0) instanceof NewNode nnn &&
+            ptr == nnn.proj(1) ) // Must check same object
+            return zero(nnn);   // Load zero from new
+
+        // Uplift control to a prior dominating load.
+        for( Node memuse : mem._outputs )
+            // Find a prior load, has same mem,ptr,off but higher ctrl
+            if( memuse != this && memuse instanceof LoadNode ld && ptr==ld.ptr() && off()==ld.off() &&
+                cfg0()!=null && cfg0()._idom(ld.cfg0(),this) == ld.cfg0() ) // Higher control means load is legal earlier
+                return ld;
+
+        // Load-after-Store on same address, but bypassing provably unrelated
+        // stores.  This is a more complex superset of the above two peeps.
+        // "Provably unrelated" is really weak.
+        if( ptr instanceof ReadOnlyNode ro )
+            ptr = ro.in(1);
+        outer:
+        while( true ) {
+            switch( mem ) {
+            case StoreNode st:
+                if( ptr == st.ptr().addDep(this) && off() == st.off() )
+                    return extend(castRO(st.val())); // Proved equal
+                // Can we prove unequal?  Offsets do not overlap?
+                if( !off()._type.join(st.off()._type).isHigh() && // Offsets overlap
+                    !neverAlias(ptr,st.ptr()) )                   // And might alias
+                    break outer; // Cannot tell, stop trying
+                // Pointers cannot overlap
+                mem = st.mem(); // Proved never equal
+                break;
+            case PhiNode phi:
+                // Assume related
+                phi.addDep(this);
+                break outer;
+            case ConstantNode top: break outer;  // Assume shortly dead
+            case ProjNode mproj: // Memory projection
+                switch( mproj.in(0) ) {
+                case NewNode nnn1:
+                    if( ptr instanceof ProjNode pproj && pproj.in(0) == mproj.in(0) )
+                        return zero(nnn1);
+                    if( !(ptr instanceof ProjNode pproj && pproj.in(0) instanceof NewNode) )
+                        break outer; // Cannot tell, ptr not related to New
+                    mem = nnn1.in(nnn1.findAlias(_alias));// Bypass unrelated New
+                    break;
+                case StartNode  start: break outer;
+                case CallEndNode cend: break outer; // TODO: Bypass no-alias call
+                default: throw Utils.TODO();
+                }
+                break;
+            case MemMergeNode merge:  mem = merge.alias(_alias);  break;
+
+            default:
+                throw Utils.TODO();
+            }
+        }
+
+        // Push a Load up through a Phi, as long as it collapses on at least
+        // one arm.  If at a Loop, the backedge MUST collapse - else we risk
+        // spinning the same transform around the loop indefinitely.
+        //   BEFORE (2 Sts, 1 Ld):          AFTER (1 St, 0 Ld):
+        //   if( pred ) ptr.x = e0;         val = pred ? e0
+        //   else       ptr.x = e1;                    : e1;
+        //   val = ptr.x;                   ptr.x = val;
+        if( mem() instanceof PhiNode memphi && memphi.region()._type == Type.CONTROL && memphi.nIns()== 3 &&
+            // Offset can be hoisted
+            off() instanceof ConstantNode &&
+            // Pointer can be hoisted
+            hoistPtr(ptr,memphi)  ) {
+
+            // Profit on RHS/Loop backedge
+            if( profit(memphi,2) ||
+                // Else must not be a loop to count profit on LHS.
+                (!(memphi.region() instanceof LoopNode) && profit(memphi,1)) ) {
+                Node ld1 = ld(1);
+                Node ld2 = ld(2);
+                return new PhiNode(_name,_declaredType,memphi.region(),ld1,ld2);
+            }
+        }
+
+        return null;
+    }
+
+    // Load a flavored zero from a New
+    private Node zero(NewNode nnn) {
+        TypeStruct ts = nnn._ptr._obj;
+        Type zero = ts._fields[ts.findAlias(_alias)]._type.makeZero();
+        return castRO(new ConstantNode(zero).peephole());
+    }
+
+    private Node ld( int idx ) {
+        Node mem = mem(), ptr = ptr();
+        return new LoadNode(_loc,_name,_alias,_declaredType,mem.in(idx),ptr instanceof PhiNode && ptr.in(0)==mem.in(0) ? ptr.in(idx) : ptr, off()).peephole();
+    }
+
+    private static boolean neverAlias( Node ptr1, Node ptr2 ) {
+        return ptr1.in(0) != ptr2.in(0) &&
+            // Unrelated allocations
+            ptr1 instanceof ProjNode && ptr1.in(0) instanceof NewNode &&
+            ptr2 instanceof ProjNode && ptr2.in(0) instanceof NewNode;
+    }
+
+    private static boolean hoistPtr(Node ptr, PhiNode memphi ) {
+        // Can I hoist ptr above the Region?
+        if( !(memphi.region() instanceof RegionNode r) )
+            return false;       // Dead or dying Region/Phi
+        // If ptr from same Region, then yes, just use hoisted split pointers
+        if( ptr instanceof PhiNode pphi && pphi.region() == r )
+            return true;
+
+        // No, so can we lift this ptr?
+        CFGNode cptr = ptr.cfg0();
+        if( cptr != null )
+            // Pointer is controlled high
+            // TODO: Really needs to be the LCA of all inputs is high
+            return cptr.idepth() <= r.idepth();
+
+        // Dunno without a longer walk
+        return false;
+    }
+
+    // Profitable if we find a matching Store on this Phi arm.
+    private boolean profit(PhiNode phi, int idx) {
+        Node px = phi.in(idx);
+        if( px==null ) return false;
+        if( px._type instanceof TypeMem mem && mem._t.isHighOrConst() ) return true;
+        if( px instanceof StoreNode st1 && ptr()==st1.ptr() && off()==st1.off() ) return true;
+        px.addDep(this);
+        return false;
+    }
+
+    // Read-Only is a deep property, and cannot be cast-away
+    private Node castRO(Node rez) {
+        if( ptr()._type.isFinal() && !rez._type.isFinal() )
+            return new ReadOnlyNode(rez).peephole();
+        return rez;
+    }
+
+    // When a load bypasses a store, the store might truncate bits - and the
+    // load will need to zero/sign-extend.
+    private Node extend(Node val) {
+        if( !(_declaredType instanceof TypeInteger ti) ) return val;
+        if( ti._min==0 )        // Unsigned
+            return new AndNode(null,val,con(ti._max));
+        // Signed extension
+        int shift = Long.numberOfLeadingZeros(ti._max)-1;
+        Node shf = con(shift);
+        if( shf._type==TypeInteger.ZERO )
+            return val;
+        //return peep(new SarNode(null,peep(new ShlNode(null,val,shf.keep())),shf.unkeep()));
+        throw Utils.TODO();
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/LogicalNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/LogicalNode.java
new file mode 100644
index 00000000..ccc1f6b5
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/LogicalNode.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public abstract class LogicalNode extends Node {
+    // Source location for late reported errors
+    Parser.Lexer _loc;
+
+    public LogicalNode(Parser.Lexer loc, Node lhs, Node rhs) { super(null, lhs, rhs); _loc = loc; }
+    abstract String op();
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append(op()), visited);
+        return sb.append(")");
+    }
+
+
+    @Override public Parser.ParseException err() {
+        if( in(1)._type.isHigh() || in(2)._type.isHigh() ) return null;
+        if( !(in(1)._type instanceof TypeInteger) ) return Parser.error("Cannot '"+op()+"' " + in(1)._type.glb(),_loc);
+        if( !(in(2)._type instanceof TypeInteger) ) return Parser.error("Cannot '"+op()+"' " + in(2)._type.glb(), _loc);
+        return null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/LoopNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/LoopNode.java
new file mode 100644
index 00000000..d2b0e36c
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/LoopNode.java
@@ -0,0 +1,86 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMem;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+import java.util.HashSet;
+
+public class LoopNode extends RegionNode {
+    public LoopNode( Parser.Lexer loc, Node entry ) { super(loc,null,entry,null); }
+    public LoopNode( LoopNode loop ) { super(loop); }
+
+    public CFGNode entry() { return cfg(1); }
+    public CFGNode back () { return cfg(2); }
+
+    @Override
+    public String label() { return "Loop"; }
+
+    @Override
+    public Type compute() {
+        if( inProgress() ) return Type.CONTROL;
+        return entry()._type;
+    }
+
+    // Bypass Region idom, same as the default idom() using use in(1) instead of in(0)
+    @Override public int idepth() { return _idepth==0 ? (_idepth=idom().idepth()+1) : _idepth; }
+    // Bypass Region idom, same as the default idom() using use in(1) instead of in(0)
+    @Override public CFGNode idom(Node dep) { return entry(); }
+
+    // If this is an unreachable loop, it may not have an exit.  If it does not
+    // (i.e., infinite loop), force an exit to make it reachable.
+    public StopNode forceExit( FunNode fun, StopNode stop ) {
+        // Walk the backedge, then immediate dominator tree util we hit this
+        // Loop again.  If we ever hit a CProj from an If (as opposed to
+        // directly on the If) we found our exit.
+        CFGNode x = back();
+        while( x != this ) {
+            if( x instanceof CProjNode exit && exit.in(0) instanceof IfNode iff ) {
+                CFGNode other = iff.cproj(1-exit._idx);
+                if( other!=null && other.loopDepth() < loopDepth() )
+                    return stop; // Found an exit, not an infinite loop
+            }
+            x = x.idom();
+        }
+        // Found a no-exit loop.  Insert an exit
+        NeverNode iff = new NeverNode(back());
+        for( Node use : _outputs )
+            if( use instanceof PhiNode )
+                iff.addDef(use);
+        CProjNode t = new CProjNode(iff,0,"True" ).init();
+        CProjNode f = new CProjNode(iff,1,"False").init();
+        setDef(2,f);
+
+        // Now fold control into the exit.  Might have 1 valid exit, or an
+        // XCtrl or a bunch of prior NeverNode exits.
+        Node top = new ConstantNode(Type.TOP).peephole();
+        ReturnNode ret = fun.ret();
+        Node ctrl = ret.ctrl(), mem = ret.mem(), expr = ret.expr();
+        if( ctrl._type != Type.XCONTROL ) {
+            // Perfect aligned exit?
+            if( !(ctrl instanceof RegionNode r &&
+                  mem  instanceof PhiNode pmem && pmem.region()==r &&
+                  expr instanceof PhiNode prez && prez.region()==r ) ) {
+                // Nope, insert an aligned exit layer
+                ctrl = new RegionNode(_loc,null,ctrl).init();
+                mem  = new    PhiNode((RegionNode)ctrl,mem ).init();
+                expr = new    PhiNode((RegionNode)ctrl,expr).init();
+            }
+            // Append new Never exit
+            ctrl.addDef(t  );
+            mem .addDef(top);
+            expr.addDef(top);
+        } else {
+            ctrl = t;
+            mem  = top;
+            expr = top;
+        }
+        ret.setDef(0,ctrl);
+        ret.setDef(1,mem );
+        ret.setDef(2,expr);
+
+        return stop;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java
new file mode 100644
index 00000000..0c49fc64
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java
@@ -0,0 +1,27 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.Utils;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+
+// Generic machine-specific class, has a few Node implementations that have to
+// exist (abstract) but are not useful past the optimizer.
+public abstract class MachConcreteNode extends Node implements MachNode{
+
+    public MachConcreteNode(Node node) { super(node); }
+    public MachConcreteNode(Node[]nodes) { super(nodes); }
+
+    @Override public String label() { return op(); }
+    @Override public Type compute () { throw Utils.TODO(); }
+    @Override public Node idealize() { throw Utils.TODO(); }
+
+    @Override public StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("(").append(op()).append(",");
+        for( int i=1; i<nIns(); i++ )
+            (in(i)==null ? sb.append(" ---") :  in(i)._print0(sb, visited)).append(",");
+        sb.setLength(sb.length()-1);
+        return sb.append(")");
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MachNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MachNode.java
new file mode 100644
index 00000000..9f2fee85
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MachNode.java
@@ -0,0 +1,49 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import java.io.ByteArrayOutputStream;
+
+public interface MachNode {
+
+    // Easy access to the abstract Machine
+    default Machine machine() { return CodeGen.CODE._mach; }
+
+    // Run a post-instruction-selection action
+    default void postSelect() { }
+
+    // Register mask allowed on input i.  0 for no register.
+    abstract public RegMask regmap(int i);
+    // Register mask allowed as a result.  0 for no register.
+    abstract public RegMask outregmap();
+    // Multi-reg-defining machine op; idx comes from Proj.
+    // Sometimes these Projs have no uses, and just exist to kill a register.
+    default RegMask outregmap(int idx) { throw Utils.TODO(); }
+
+    // If this op updates the same register as input 'idx', e.g. many X86 "R1 +=
+    // R2" style ops.  This forces the output live range to equal the input live
+    // range, so they both get the same register.
+
+    // This can hold true for projections, if the instruction updates many
+    // registers that it also takes in.  Note that ops also use the same
+    // registers for both inputs and outputs but these are pinned and without any
+    // choices (e.g. always RCX for both an input and output) and are better
+    // served with just declaring as a fixed register.
+
+    // Returns either 0 for not-two-adr or the updated input; for projections
+    // this is their Multi's updated input.
+    default int twoAddress( ) { return 0; }
+
+    // Instructions cheaper to recreate than to spill, such as loading small constants
+    default boolean isClone() { return false; }
+    // Encoding is appended into the byte array; size is returned
+    abstract public int encoding(ByteArrayOutputStream bytes);
+
+    // Human-readable form appended to the SB.  Things like the encoding,
+    // indentation, leading address or block labels not printed here.
+    // Just something like "R17=[R18+12] // Load array base".
+    // General form: "dst=src+src".
+    default void asm(CodeGen code, SB sb) { throw Utils.TODO(); }
+
+    // Human readable opcode; e.g. "ld4" or "call".
+    default String op() { throw Utils.TODO(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
new file mode 100644
index 00000000..5363bb6f
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
@@ -0,0 +1,154 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.*;
+import java.util.*;
+
+/**
+ *  Memory Merge - a merge of many aliases into a "fat memory".  All aliases
+ *  are here, but most will be lazy - take the default fat memory.
+ */
+public class MemMergeNode extends Node {
+
+    /*
+     *  In-Progress means this is being used by the Parser to track memory
+     *  aliases.  No optimizations are allowed.  When no longer "in progress"
+     *  normal peeps work.
+     */
+    public final boolean _inProgress;
+
+    public MemMergeNode( boolean inProgress) { _type = TypeMem.BOT; _inProgress = inProgress; }
+    public MemMergeNode(MemMergeNode mem) { super(mem); _inProgress = false; }
+
+
+    // If being used by a Scope, this is "in progress" from the Parser.
+    // Otherwise, it's a memory merge
+    boolean inProgress() { return _inProgress; }
+
+    @Override public String label() { return "ALLMEM"; }
+    @Override public boolean isMem() { return true; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append(_inProgress ? "Merge[" : "MEM[ ");
+        for( int j=2; j<nIns(); j++ ) {
+            sb.append(j);
+            sb.append(":");
+            Node n = in(j);
+            while( n instanceof ScopeNode loop ) {
+                sb.append("Lazy_");
+                n = loop.mem(j);
+            }
+            if( n==null ) sb.append("___ ");
+            else n._print0(sb, visited).append(" ");
+        }
+        sb.setLength(sb.length()-1);
+        return sb.append("]");
+    }
+
+    // Make a memory merge: no longer a Scope really, tracking memory state but
+    // not related to the parser in any way.
+    public Node merge() {
+        // Force default memory to not be lazy
+        MemMergeNode merge = new MemMergeNode(false);
+        for( Node n : _inputs )
+            merge.addDef(n);
+        merge._mem(1,null);
+        return merge.peephole();
+    }
+
+
+    @Override public Type compute() { return TypeMem.BOT; }
+
+    @Override public Node idealize() {
+        if( inProgress() ) return null;
+
+        // If not merging any memory (all memory is just the default)
+        if( nIns()==2 )
+            return in(1);       // Become default memory
+
+        return null;
+    }
+
+    public Node in( Var v ) { return in(v._idx); }
+
+    public Node alias( int alias ) {
+        return in(alias<nIns() && in(alias)!=null ? alias : 1);
+    }
+
+    Node alias( int alias, Node st ) {
+        while( alias >= nIns() ) addDef(null);
+        return setDef(alias,st);
+    }
+
+    // Read or update from memory.
+    // A shared implementation allows us to create lazy phis both during
+    // lookups and updates; the lazy phi creation is part of chapter 8.
+    Node _mem( int alias, Node st ) {
+        // Memory projections are made lazily; if one does not exist
+        // then it must be START.proj(1)
+        Node old = alias(alias);
+        if( old instanceof ScopeNode loop ) {
+            MemMergeNode loopmem = loop.mem();
+            Node memdef = loopmem.alias(alias);
+            // Lazy phi!
+            old = memdef instanceof PhiNode phi && loop.ctrl()==phi.region()
+                // Loop already has a real Phi, use it
+                ? memdef
+                // Set real Phi in the loop head
+                // The phi takes its one input (no backedge yet) from a recursive
+                // lookup, which might have insert a Phi in every loop nest.
+                : loopmem.alias(alias, new PhiNode(Parser.memName(alias), TypeMem.BOT,loop.ctrl(),loopmem._mem(alias,null),null).peephole() );
+            alias(alias,old);
+        }
+        // Memory projections are made lazily; expand as needed
+        return st==null ? old : alias(alias,st); // Not lazy, so this is the answer
+    }
+
+
+    void _merge( MemMergeNode that, RegionNode r) {
+        int len = Math.max(nIns(),that.nIns());
+        for( int i = 2; i < len; i++)
+            if( alias(i) != that.alias(i) ) { // No need for redundant Phis
+                // If we are in lazy phi mode we need to a lookup
+                // by alias as it will trigger a phi creation
+                Node lhs = this._mem(i,null);
+                Node rhs = that._mem(i,null);
+                alias(i, new PhiNode(Parser.memName(i), lhs._type.glb().meet(rhs._type.glb()), r, lhs, rhs).peephole());
+            }
+    }
+
+    // Fill in the backedge of any inserted Phis
+    void _endLoopMem( ScopeNode scope, MemMergeNode back, MemMergeNode exit ) {
+        Node exit_def = exit.alias(1);
+        for( int i=1; i<nIns(); i++ ) {
+            if( in(i) instanceof PhiNode phi && phi.region()==scope.ctrl() ) {
+                assert phi.in(2)==null;
+                phi.setDef(2,back.in(i)==scope ? phi : back.in(i)); // Fill backedge
+            }
+            if( exit_def == scope ) // Replace a lazy-phi on the exit path also
+                exit.alias(i,in(i));
+        }
+    }
+
+    // Now one-time do a useless-phi removal
+    void _useless( ) {
+        for( int i=2; i<nIns(); i++ ) {
+            if( in(i) instanceof PhiNode phi ) {
+                // Do an eager useless-phi removal
+                Node in = phi.peephole();
+                CodeGen.CODE.addAll(phi._outputs);
+                phi.moveDepsToWorklist();
+                if( in != phi ) {
+                    if( !phi.iskeep() ) // Keeping phi around for parser elsewhere
+                        phi.subsume(in);
+                    setDef(i,in); // Set the update back into Scope
+                }
+            }
+        }
+    }
+
+    @Override boolean eq( Node n ) {
+        return this==n || !_inProgress;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MemOpNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
new file mode 100644
index 00000000..d9ab6b89
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
@@ -0,0 +1,74 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMemPtr;
+import java.lang.StringBuilder;
+import java.util.BitSet;
+
+/**
+ * Convenience common base for Load and Store.
+ */
+public abstract class MemOpNode extends Node {
+
+    public final String _name;
+    public final int _alias;
+    // Declared type; not final because it might be a forward-reference
+    // which will be lazily improved when the reference is declared.
+    public Type _declaredType;
+    // Source location for late reported errors
+    public final Parser.Lexer _loc;
+
+    public MemOpNode(Parser.Lexer loc, String name, int alias, Type glb, Node mem, Node ptr, Node off) {
+        super(null, mem, ptr, off);
+        _name  = name;
+        _alias = alias;
+        _declaredType = glb;
+        _loc = loc;
+    }
+    public MemOpNode(Parser.Lexer loc, String name, int alias, Type glb, Node mem, Node ptr, Node off, Node value) {
+        this(loc,name, alias, glb, mem, ptr, off);
+        addDef(value);
+    }
+    public MemOpNode( Node mach, MemOpNode mop ) {
+        super(mach);
+        _name  = mop._name;
+        _alias = mop._alias;
+        _declaredType = mop._declaredType;
+        _loc = mop._loc;
+    }
+
+    //
+    static String mlabel(String name) { return name.equals("[]") ? "ary" : (name.equals("#") ? "len" : name); }
+    String mlabel() { return mlabel(_name); }
+
+    public Node mem() { return in(1); }
+    public Node ptr() { return in(2); }
+    public Node off() { return in(3); }
+
+    @Override StringBuilder _print1( StringBuilder sb, BitSet visited ) { return _printMach(sb,visited);  }
+    public StringBuilder _printMach( StringBuilder sb, BitSet visited ) { throw Utils.TODO(); }
+
+
+    @Override
+    boolean eq(Node n) {
+        MemOpNode mem = (MemOpNode)n; // Invariant
+        return _alias==mem._alias;    // When comparing types error to use "equals"; always use "=="
+    }
+
+    @Override
+    int hash() { return _alias; }
+
+    @Override
+    public Parser.ParseException err() {
+        Type ptr = ptr()._type;
+        // Already an error, but better error messages come from elsewhere
+        if( ptr == Type.BOTTOM ) return null;
+        if( ptr.isHigh() ) return null; // Assume it will fall to not-null
+        // Better be a not-nil TMP
+        if( ptr instanceof TypeMemPtr tmp && tmp.notNull() )
+            return null;
+        return Parser.error( "Might be null accessing '" + _name + "'",_loc);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MinusFNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MinusFNode.java
new file mode 100644
index 00000000..2b749ba3
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MinusFNode.java
@@ -0,0 +1,36 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class MinusFNode extends Node {
+    public MinusFNode(Node in) { super(null, in); }
+
+    @Override public String label() { return "MinusF"; }
+
+    @Override public String glabel() { return "-"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("(-"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0)
+            return i0.isConstant() ? TypeFloat.constant(-i0.value()) : i0;
+        return TypeFloat.F64;
+    }
+
+    @Override
+    public Node idealize() {
+        // -(-x) is x
+        if( in(1) instanceof MinusFNode minus )
+            return minus.in(1);
+
+        return null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MinusNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MinusNode.java
new file mode 100644
index 00000000..dd2cbd26
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MinusNode.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import com.seaofnodes.simple.Utils;
+
+import java.util.BitSet;
+
+public class MinusNode extends Node {
+    public MinusNode(Node in) { super(null, in); }
+
+    @Override public String label() { return "Minus"; }
+
+    @Override public String glabel() { return "-"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("(-"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if( in(1)._type.isHigh() ) return TypeInteger.TOP;
+        if( in(1)._type instanceof TypeInteger i0 &&
+            !(i0==TypeInteger.BOT || i0._min == Long.MIN_VALUE || i0._max == Long.MIN_VALUE) )
+            return TypeInteger.make(-i0._max,-i0._min);
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        // -(-x) is x
+        if( in(1) instanceof MinusNode minus )
+            return minus.in(1);
+
+        return null;
+    }
+    @Override Node copyF() { return new MinusFNode(null); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MulFNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MulFNode.java
new file mode 100644
index 00000000..2d44a9fb
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MulFNode.java
@@ -0,0 +1,51 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class MulFNode extends Node {
+    public MulFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "MulF"; }
+
+    @Override public String glabel() { return "*"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("*"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0 &&
+            in(2)._type instanceof TypeFloat i1) {
+            if (i0.isConstant() && i1.isConstant())
+                return TypeFloat.constant(i0.value()*i1.value());
+        }
+        return in(1)._type.meet(in(2)._type);
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // Mul of 1.  We do not check for (1*x) because this will already
+        // canonicalize to (x*1)
+        if ( t2.isConstant() && t2 instanceof TypeFloat i && i.value()==1 )
+            return lhs;
+
+        // Move constants to RHS: con*arg becomes arg*con
+        if ( t1.isConstant() && !t2.isConstant() )
+            return swap12();
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new MulFNode(lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MulNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MulNode.java
new file mode 100644
index 00000000..4fdf987d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MulNode.java
@@ -0,0 +1,81 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class MulNode extends Node {
+    public MulNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "Mul"; }
+
+    @Override public String glabel() { return "*"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("*"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i1 &&
+            t2 instanceof TypeInteger i2 ) {
+            if( i1==TypeInteger.ZERO || i2==TypeInteger.ZERO)
+                return TypeInteger.ZERO;
+            if (i1.isConstant() && i2.isConstant())
+                return TypeInteger.constant(i1.value()*i2.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // Move constants to RHS: con*arg becomes arg*con
+        if ( t1.isConstant() && !t2.isConstant() )
+            return swap12();
+
+        // Multiply by constant
+        if ( t2.isConstant() && t2 instanceof TypeInteger i ) {
+            // Mul of 1.  We do not check for (1*x) because this will already
+            // canonicalize to (x*1)
+            long c = i.value();
+            if( c==1 )  return lhs;
+            if( c==0 )  return Parser.ZERO;
+            // Mul by a power of 2, +/-1.  Bit patterns more complex than this
+            // are unlikely to win on an X86 vs the normal "imul", and so
+            // become machine-specific.
+            if( (c & (c-1)) == 0 )
+                return new ShlNode(null,lhs,con(Long.numberOfTrailingZeros(c)));
+            // 2**n + 1, e.g. 9
+            long d = c-1;
+            if( (d & (d-1)) == 0 )
+                return new AddNode(new ShlNode(null,lhs,con(Long.numberOfTrailingZeros(d))).peephole(),lhs);
+            // 2**n - 1, e.g. 31
+            long e = c+1;
+            if( (e & (e-1)) == 0 )
+                return new SubNode(new ShlNode(null,lhs,con(Long.numberOfTrailingZeros(e))).peephole(),lhs);
+
+        }
+
+        // Do we have ((x * (phi cons)) * con) ?
+        // Do we have ((x * (phi cons)) * (phi cons)) ?
+        // Push constant up through the phi: x * (phi con0*con0 con1*con1...)
+        Node phicon = AddNode.phiCon(this,true);
+        if( phicon!=null ) return phicon;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new MulNode(lhs,rhs); }
+    @Override Node copyF() { return new MulFNode(null,null); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/MultiNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/MultiNode.java
new file mode 100644
index 00000000..17d00881
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/MultiNode.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Ary;
+
+
+public interface MultiNode {
+
+    abstract Ary<Node> outs();
+
+    // Find a projection by index
+    default ProjNode proj( int idx ) {
+        for( Node out : outs() )
+            if( out instanceof ProjNode prj && prj._idx==idx )
+                return prj;
+        return null;
+    }
+
+    // Find a projection by index
+    default CProjNode cproj( int idx ) {
+        for( Node out : outs() )
+            if( out instanceof CProjNode prj && prj._idx==idx )
+                return prj;
+        return null;
+    }
+
+    // Return not-null if this projection index is a ideal copy.
+    // Called by ProjNode ideal and used to collapse Multis.
+    default Node pcopy(int idx) { return null; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/NeverNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/NeverNode.java
new file mode 100644
index 00000000..e77ed653
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/NeverNode.java
@@ -0,0 +1,21 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.TypeInteger;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeTuple;
+
+import java.util.BitSet;
+
+// "Never true" for infinite loop exits
+public class NeverNode extends IfNode {
+    public NeverNode(Node ctrl) { super(ctrl,Parser.ZERO); }
+
+    @Override public String label() { return "Never"; }
+
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Never"); }
+
+    @Override public Type compute() { return TypeTuple.IF_BOTH; }
+
+    @Override public Node idealize() { return null; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/NewNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/NewNode.java
new file mode 100644
index 00000000..80545d66
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/NewNode.java
@@ -0,0 +1,83 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.*;
+import com.seaofnodes.simple.Utils;
+import java.util.BitSet;
+
+/**
+ *  Allocation!  Allocate a chunk of memory, and pre-zero it.
+ *  The inputs include control and size, and ALL aliases being set.
+ *  The output is large tuple, one for every alias plus the created pointer.
+ *  New is expected to be followed by projections for every alias.
+ */
+public class NewNode extends Node implements MultiNode {
+
+    public final TypeMemPtr _ptr;
+    public final int _len;
+
+    public NewNode(TypeMemPtr ptr, Node... nodes) {
+        super(nodes);
+        assert !ptr.nullable();
+        _ptr = ptr;
+        _len = ptr._obj._fields.length;
+        // Control in slot 0
+        assert nodes[0]._type==Type.CONTROL || nodes[0]._type == Type.XCONTROL;
+        // Malloc-length in slot 1
+        assert nodes[1]._type instanceof TypeInteger || nodes[1]._type==Type.NIL;
+        for( int i=0; i<_len; i++ )
+            // Memory slices for all fields.
+            assert nodes[2+i]._type.isa(TypeMem.BOT);
+    }
+
+    public NewNode(NewNode nnn) { super(nnn); _ptr = nnn._ptr; _len = nnn._len; }
+
+    public Node mem (int idx) { return in(idx+2); }
+
+    @Override public String label() { return "new_"+glabel(); }
+    @Override public String glabel() {
+        return _ptr._obj.isAry() ? "ary_"+_ptr._obj._fields[1]._type.str() : _ptr._obj.str();
+    }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("new ");
+        return sb.append(_ptr._obj.str());
+    }
+
+    int findAlias(int alias) {
+        int idx = _ptr._obj.findAlias(alias);
+        assert idx!= -1;        // Error, caller should be calling
+        return idx+2;           // Skip ctrl, size
+    }
+
+    // 0 - ctrl
+    // 1 - byte size
+    // 2-len+2 - aliases, one per field
+    // len+2 - 2*len+2 - initial values, one per field
+    public Node size() { return in(1); }
+
+    @Override
+    public TypeTuple compute() {
+        Field[] fs = _ptr._obj._fields;
+        Type[] ts = new Type[fs.length+2];
+        ts[0] = Type.CONTROL;
+        ts[1] = _ptr;
+        for( int i=0; i<fs.length; i++ ) {
+            Type mt = in(i+2)._type;
+            TypeMem mem = mt==Type.TOP ? TypeMem.TOP : (TypeMem)mt;
+            Type tfld = mem._t.meet(mem._t.makeZero());
+            Type tfld2 = tfld.join(fs[i]._type);
+            ts[i+2] = TypeMem.make(fs[i]._alias,tfld2);
+        }
+        return TypeTuple.make(ts);
+    }
+
+    @Override
+    public Node idealize() { return null; }
+
+    @Override
+    boolean eq(Node n) { return this == n; }
+
+    @Override
+    int hash() { return _ptr.hashCode(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter20/src/main/java/com/seaofnodes/simple/node/Node.java
new file mode 100644
index 00000000..bbf1ebe9
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -0,0 +1,640 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.*;
+import java.util.function.Function;
+import static com.seaofnodes.simple.CodeGen.CODE;
+
+/**
+ * All Nodes in the Sea of Nodes IR inherit from the Node class.
+ * The Node class provides common functionality used by all subtypes.
+ * Subtypes of Node specialize by overriding methods.
+ */
+public abstract class Node {
+
+    /**
+     * Each node has a unique dense Node ID within a compilation context
+     * The ID is useful for debugging, for using as an offset in a bitvector,
+     * as well as for computing equality of nodes (to be implemented later).
+     */
+    public final int _nid;
+
+    /**
+     * Inputs to the node. These are use-def references to Nodes.
+     * <p>
+     * Generally fixed length, ordered, nulls allowed, no unused trailing space.
+     * Ordering is required because e.g. "a/b" is different from "b/a".
+     * The first input (offset 0) is often a {@link CFGNode} node.
+     */
+    public final Ary<Node> _inputs;
+
+    /**
+     * Outputs reference Nodes that are not null and have this Node as an
+     * input.  These nodes are users of this node, thus these are def-use
+     * references to Nodes.
+     * <p>
+     * Outputs directly match inputs, making a directed graph that can be
+     * walked in either direction.  These outputs are typically used for
+     * efficient optimizations but otherwise have no semantics meaning.
+     */
+    public final Ary<Node> _outputs;
+
+
+    /**
+     * Current computed type for this Node.  This value changes as the graph
+     * changes and more knowledge is gained about the program.
+     */
+    public Type _type;
+
+
+    Node(Node... inputs) {
+        _nid = CODE.getUID(); // allocate unique dense ID
+        _inputs = new Ary<>(Node.class);
+        Collections.addAll(_inputs,inputs);
+        _outputs = new Ary<>(Node.class);
+        for( Node n : _inputs )
+            if( n != null )
+                n.addUse( this );
+    }
+
+    // Make a Node using the existing arrays of nodes.
+    // Used by any pass rewriting all Node classes but not the edges.
+    Node( Node n ) {
+        assert CodeGen.CODE._phase == CodeGen.Phase.InstructionSelection;
+        _nid = CODE.getUID(); // allocate unique dense ID
+        _inputs  = new Ary<>(n._inputs.asAry());
+        _outputs = new Ary<>(Node.class);
+        _type = n._type;
+        _deps = null;
+        _hash = 0;
+    }
+
+    // Easy reading label for debugger, e.g. "Add" or "Region" or "EQ"
+    public abstract String label();
+
+    // Unique label for graph visualization, e.g. "Add12" or "Region30" or "EQ99"
+    public String uniqueName() {
+        // Get rid of $ as graphviz doesn't like it
+        String label = label().replaceAll("\\$", "");
+        return label + _nid;
+    }
+
+    // Graphical label, e.g. "+" or "Region" or "=="
+    public String glabel() { return label(); }
+
+    // Extra fun stuff, for assembly printing.  Jump labels, parser locations,
+    // variable types, etc.
+    public String comment() { return null; }
+
+    // ------------------------------------------------------------------------
+
+    // Debugger Printing.
+
+    // {@code toString} is what you get in the debugger.  It has to print 1
+    // line (because this is what a debugger typically displays by default) and
+    // has to be robust with broken graph/nodes.
+    @Override
+    public final String toString() {  return print(); }
+
+    // This is a *deep* print.  We print with a mutually recursive tik-tok
+    // style; the common _print0 calls the per-Node _print1, which calls back
+    // to _print0;
+    public final String print() {
+        return _print0(new StringBuilder(), new BitSet()).toString();
+    }
+
+    // This is the common print: check for repeats, check for DEAD and print
+    // "DEAD" else call the per-Node print1.
+    final StringBuilder _print0(StringBuilder sb, BitSet visited) {
+        if (visited.get(_nid) && !(this instanceof ConstantNode) )
+            return sb.append(label());
+        visited.set(_nid);
+        return isDead()
+            ? sb.append(uniqueName()).append(":DEAD")
+            : _print1(sb, visited);
+    }
+    // Every Node implements this; a partial-line recursive print
+    abstract StringBuilder _print1(StringBuilder sb, BitSet visited);
+
+    public String p(int depth) { return IRPrinter.prettyPrint(this,depth); }
+
+    public boolean isMultiHead() { return false; }
+    public boolean isMultiTail() { return false; }
+    public boolean isConst    () { return false; }
+
+    // ------------------------------------------------------------------------
+    // Graph Node & Edge manipulation
+
+    /**
+     * Gets the ith input node
+     * @param i Offset of the input node
+     * @return Input node or null
+     */
+    public Node in(int i) { return _inputs.get(i); }
+    public Node out(int i) { return _outputs.get(i); }
+    public final Ary<Node> outs() { return _outputs; }
+
+    public int nIns() { return _inputs.size(); }
+
+    public int nOuts() { return _outputs.size(); }
+
+    public boolean isUnused() { return nOuts() == 0; }
+
+    public CFGNode cfg0() { return (CFGNode)in(0); }
+
+    /**
+     * Change a <em>def</em> into a Node.  Keeps the edges correct, by removing
+     * the corresponding <em>use->def</em> edge.  This may make the original
+     * <em>def</em> go dead.  This function is co-recursive with {@link #kill}.
+     * <p>
+
+     * This method is the normal path for altering a Node, because it does the
+     * proper default edge maintenance.  It also <em>immediately</em> kills
+     * Nodes that lose their last use; at times care must be taken to avoid
+     * killing Nodes that are being used without having an output Node.  This
+     * definitely happens in the middle of recursive {@link #peephole} calls.
+     *
+     * @param idx which def to set
+     * @param new_def the new definition
+     * @return new_def for flow coding
+     */
+    public <N extends Node> N setDef(int idx, N new_def ) {
+        unlock();
+        Node old_def = in(idx);
+        if( old_def == new_def ) return new_def; // No change
+        // If new def is not null, add the corresponding def->use edge
+        // This needs to happen before removing the old node's def->use edge as
+        // the new_def might get killed if the old node kills it recursively.
+        if( new_def != null )
+            new_def.addUse(this);
+        // Set the new_def over the old (killed) edge
+        _inputs.set(idx,new_def);
+        if( old_def != null ) {        // If the old def exists, remove a def->use edge
+            if( old_def.delUse(this) ) // If we removed the last use, the old def is now dead
+                old_def.kill();        // Kill old def
+            else CODE.add(old_def);    // Else old lost a use, so onto worklist
+        }
+        moveDepsToWorklist();
+        // Return new_def for easy flow-coding
+        return new_def;
+    }
+
+    // Remove the numbered input, compressing the inputs in-place.  This
+    // shuffles the order deterministically - which is suitable for Region and
+    // Phi, but not for every Node.  If the def goes dead, it is recursively
+    // killed, which may include 'this' Node.
+    Node delDef(int idx) {
+        unlock();
+        Node old_def = in(idx);
+        _inputs.del(idx);
+        if( old_def.delUse(this) ) // If we removed the last use, the old def is now dead
+            old_def.kill();     // Kill old def
+        old_def.moveDepsToWorklist();
+        return this;
+    }
+
+    // Insert the numbered input, sliding other inputs to the right
+    Node insertDef(int idx, Node new_def) {
+        _inputs.add(idx,null);
+        return setDef(idx,new_def);
+    }
+
+
+    /**
+     * Add a new def to an existing Node.  Keep the edges correct by
+     * adding the corresponding <em>def->use</em> edge.
+     *
+     * @param new_def the new definition, appended to the end of existing definitions
+     * @return new_def for flow coding
+     */
+    public Node addDef(Node new_def) {
+        unlock();
+        // Add use->def edge
+        _inputs.add(new_def);
+        // If new def is not null, add the corresponding def->use edge
+        if( new_def != null )
+            new_def.addUse(this);
+        return new_def;
+    }
+
+    // Breaks the edge invariants, used temporarily
+    protected <N extends Node> N addUse(Node n) { _outputs.add(n); return (N)this; }
+
+    // Remove node 'use' from 'def's (i.e. our) output list, by compressing the list in-place.
+    // Return true if the output list is empty afterward.
+    // Error is 'use' does not exist; ok for 'use' to be null.
+    protected boolean delUse( Node use ) {
+        _outputs.del(_outputs.find(use));
+        return _outputs.isEmpty();
+    }
+
+    // Shortcut for "popping" until n nodes.  A "pop" is basically a
+    // setDef(last,null) followed by lowering the nIns() count.
+    void popUntil(int n) {
+        unlock();
+        while( nIns() > n ) {
+            Node old_def = _inputs.pop();
+            if( old_def != null &&     // If it exists and
+                old_def.delUse(this) ) // If we removed the last use, the old def is now dead
+                old_def.kill();        // Kill old def
+        }
+    }
+
+    /**
+     * Kill a Node with no <em>uses</em>, by setting all of its <em>defs</em>
+     * to null.  This may recursively kill more Nodes, and is basically dead
+     * code elimination.
+     */
+    public void kill( ) {
+        unlock();
+        moveDepsToWorklist();
+        assert isUnused();      // Has no uses, so it is dead
+        _type=null;             // Flag as dead
+        while( nIns()>0 ) { // Set all inputs to null, recursively killing unused Nodes
+            Node old_def = _inputs.removeLast();
+            // Revisit neighbor because removed use
+            if( old_def != null && CODE.add(old_def).delUse(this) )
+                old_def.kill(); // If we removed the last use, the old def is now dead
+        }
+        assert isDead();        // Really dead now
+    }
+
+    // Mostly used for asserts and printing.
+    public boolean isDead() { return isUnused() && nIns()==0 && _type==null; }
+
+    // Shortcuts to stop DCE mid-parse
+    // Add bogus null use to keep node alive
+    public <N extends Node> N keep() { return addUse(null); }
+    // Remove bogus null.
+    public <N extends Node> N unkeep() {
+        delUse(null);
+        return (N)this;
+    }
+    // Test "keep" status
+    public boolean iskeep() { return _outputs.find(null) != -1; }
+    public void unkill() {
+        if( unkeep().isUnused() )
+            kill();
+    }
+
+
+    // Replace self with nnn in the graph, making 'this' go dead
+    public void subsume( Node nnn ) {
+        assert nnn!=this;
+        while( nOuts() > 0 ) {
+            Node n = _outputs.removeLast();
+            n.unlock();
+            int idx = n._inputs.find(this);
+            n._inputs.set(idx,nnn);
+            nnn.addUse(n);
+            CODE.addAll(n._outputs);
+        }
+        kill();
+    }
+
+    // ------------------------------------------------------------------------
+    // Graph-based optimizations
+
+    /**
+     * Try to peephole at this node and return a better replacement Node.
+     * Always returns some not-null Node (often this).
+     */
+    public final Node peephole( ) {
+        if( _type==null )       // Brand-new node, never peeped before
+            JSViewer.show();
+        Node n = peepholeOpt();
+        if( n!=null )           // Made progress?
+            JSViewer.show();    // Show again
+        return n==null ? this : deadCodeElim(n._nid >= _nid ? n.peephole() : n); // Cannot return null for no-progress
+    }
+
+    /**
+     * Try to peephole at this node and return a better replacement Node if
+     * possible.  We compute a {@link Type} and then check and replace:
+     * <ul>
+     * <li>if the Type {@link Type#isConstant}, we replace with a {@link ConstantNode}</li>
+     * <li>in a future chapter we will look for a
+     * <a href="https://en.wikipedia.org/wiki/Common_subexpression_elimination">Common Subexpression</a>
+     * to eliminate.</li>
+     * <li>we ask the Node for a better replacement.  The "better replacement"
+     * is things like {@code (1+2)} becomes {@code 3} and {@code (1+(x+2))} becomes
+     * {@code (x+(1+2))}.  By canonicalizing expressions we fold common addressing
+     * math constants, remove algebraic identities and generally simplify the
+     * code. </li>
+     *
+     * Unlike peephole above, this explicitly returns null for no-change, or not-null
+     * for a better replacement (which can be this).
+     * </ul>
+     */
+    public final Node peepholeOpt( ) {
+        CODE.iterCnt();
+        // Compute initial or improved Type
+        Type old = setType(compute());
+
+        // Replace constant computations from non-constants with a constant
+        // node.  If peeps are disabled, still allow high Phis to collapse;
+        // they typically come from dead Regions, and we want the Region to
+        // collapse, which requires the Phis to die first.
+        if( _type.isHighOrConst() && !isConst() )
+            return ConstantNode.make(_type).peephole();
+
+        // Global Value Numbering
+        if( _hash==0 ) {
+            Node n = CODE._gvn.get(this); // Will set _hash as a side effect
+            if( n==null )
+                CODE._gvn.put(this,this);  // Put in table now
+            else {
+                // Because of random worklist ordering, the two equal nodes
+                // might have different types.  Because of monotonicity, both
+                // types are valid.  To preserve monotonicity, the resulting
+                // shared Node has to have the best of both types.
+                n.setType(n._type.join(_type));
+                _hash = 0; // Clear, since it never went in the table
+                return deadCodeElim(n);// Return previous; does Common Subexpression Elimination
+            }
+        }
+
+        // Ask each node for a better replacement
+        Node n = idealize();
+        if( n != null )         // Something changed
+            return n;           // Report progress
+
+        if( old!=_type ) return this; // Report progress;
+        CODE.iterNop();
+        return null;            // No progress
+    }
+
+    // m is the new Node, self is the old.
+    // Return 'm', which may have zero uses but is alive nonetheless.
+    // If self has zero uses (and is not 'm'), {@link #kill} self.
+    private Node deadCodeElim(Node m) {
+        // If self is going dead and not being returned here (Nodes returned
+        // from peephole commonly have no uses (yet)), then kill self.
+        if( m != this && isUnused() && !isDead() ) {
+            // Killing self - and since self recursively kills self's inputs we
+            // might end up killing 'm', which we are returning as a live Node.
+            // So we add a bogus extra null output edge to stop kill().
+            m.keep();      // Keep m alive
+            kill();        // Kill self because replacing with 'm'
+            m.unkeep();    // Okay to peephole m
+        }
+        return m;
+    }
+
+    /**
+     * This function needs to be
+     * <a href="https://en.wikipedia.org/wiki/Monotonic_function">Monotonic</a>
+     * as it is part of a Monotone Analysis Framework.
+     * <a href="https://www.cse.psu.edu/~gxt29/teaching/cse597s21/slides/08monotoneFramework.pdf">See for example this set of slides</a>.
+     * <p>
+     * For Chapter 2, all our Types are really integer constants, and so all
+     * the needed properties are trivially true, and we can ignore the high
+     * theory.  Much later on, this will become important and allow us to do
+     * many fancy complex optimizations trivially... because theory.
+     * <p>
+     * {@link #compute()} needs to be stand-alone, and cannot recursively call compute
+     * on its inputs, because programs are cyclic (have loops!) and this will just
+     * infinitely recurse until stack overflow.  Instead, compute typically
+     * computes a new type from the {@link #_type} field of its inputs.
+     */
+    public abstract Type compute();
+
+    // Set the type.  Assert monotonic progress.
+    // If changing, add users to worklist.
+    public Type setType(Type type) {
+        Type old = _type;
+        assert old==null || type.isa(old); // Since _type not set, can just re-run this in assert in the debugger
+        if( old == type ) return old;
+        _type = type;       // Set _type late for easier assert debugging
+        CODE.addAll(_outputs);
+        moveDepsToWorklist();
+        return old;
+    }
+
+    public <N extends Node> N init() { _type = compute(); return (N)this; }
+
+    /**
+     * This function rewrites the current Node into a more "idealized" form.
+     * This is the bulk of our peephole rewrite rules, and we use this to
+     * e.g. turn arbitrary collections of adds and multiplies with mixed
+     * constants into a normal form that's easy for hardware to implement.
+     * Example: An array addressing expression:
+     * <pre>   ary[idx+1]</pre>
+     * might turn into Sea-of-Nodes IR:
+     * <pre>   (ary+12)+((idx+1) * 4)</pre>
+     * This expression can then be idealized into:
+     * <pre>   ary + ((idx*4) + (12 + (1*4)))</pre>
+     * And more folding:
+     * <pre>   ary + ((idx<<2) + 16)</pre>
+     * And during code-gen:
+     * <pre>   MOV4 Rary,[Ridx<<2 +16] // or some such hardware-specific notation </pre>
+     * <p>
+     * {@link #idealize} has a very specific calling convention:
+     * <ul>
+     * <li>If NO change is made, return {@code null}
+     * <li>If ANY change is made, return not-null; this can be {@code this}
+     * <li>The returned Node does NOT call {@link #peephole} on itself; the {@link #peephole} call will recursively peephole it.
+     * <li>Any NEW nodes that are not directly returned DO call {@link #peephole}.
+     * </ul>
+     * <p>
+     * Examples:
+     * <table border="3">
+     * <tr><th>    before       </th><th>       after     </th><th>return </th><th>comment  </th></tr>
+     * <tr><td>{@code (x+5)    }</td><td>{@code   (x+5)  }</td><td>{@code null  }</td><td>No change</td></tr>
+     * <tr><td>{@code (5+x)    }</td><td>{@code   (x+5)  }</td><td>{@code this  }</td><td>Swapped arguments</td></tr>
+     * <tr><td>{@code ((x+1)+2)}</td><td>{@code (x+(1+2))}</td><td>{@code (x+_) }</td><td>Returns 2 new Nodes</td></tr>
+     * </table>
+     *
+     * The last entry deserves more discussion.  The new Node {@code (1+2)}
+     * created in {@link #idealize} calls {@link #peephole} (which then folds
+     * into a constant).  The other new Node {@code (x+3)} does not call
+     * peephole, because it is returned and peephole itself will recursively
+     * call peephole.
+     * <p>
+     * Since idealize calls peephole and peephole calls idealize, you must be
+     * careful that all idealizations are <em>monotonic</em>: all transforms
+     * remove some feature, so that the set of available transforms always
+     * shrinks.  If you don't, you risk an infinite peephole loop!
+     *
+     * @return Either a new or changed node, or null for no changes.
+     */
+    public abstract Node idealize();
+
+
+    // Some of the peephole rules get complex, and search further afield than
+    // just the nearest neighbor.  These peepholes can fail the pattern match
+    // on a node some distance away, and if that node ever changes we should
+    // retry the peephole.  Track a set of Nodes dependent on `this`, and
+    // revisit them if `this` changes.
+    Ary<Node> _deps;
+
+    /**
+     * Add a node to the list of dependencies.  Only add it if its not an input
+     * or output of this node, that is, it is at least one step away.  The node
+     * being added must benefit from this node being peepholed.
+     */
+    Node addDep( Node dep ) {
+        // Running peepholes during the big assert cannot have side effects
+        // like adding dependencies.
+        if( CODE._midAssert ) return this;
+        if( dep == null ) return this;
+        if( _deps==null ) _deps = new Ary<>(Node.class);
+        if( _deps   .find(dep) != -1 ) return this; // Already on list
+        if( _inputs .find(dep) != -1 ) return this; // No need for deps on immediate neighbors
+        if( _outputs.find(dep) != -1 ) return this;
+        _deps.add(dep);
+        return this;
+    }
+
+    // Move the dependents onto a worklist, and clear for future dependents.
+    public void moveDepsToWorklist( ) {
+        if( _deps==null ) return;
+        CODE.addAll(_deps);
+        _deps.clear();
+    }
+
+
+    // Two nodes are equal if they have the same inputs and the same "opcode"
+    // which means the same Java class, plus same internal parts.
+    @Override public final boolean equals( Object o ) {
+        if( o==this ) return true;
+        if( o.getClass() != getClass() ) return false;
+        Node n = (Node)o;
+        int len = _inputs.size();
+        if( len != n._inputs.size() ) return false;
+        for( int i=0; i<len; i++ )
+            if( in(i) != n.in(i) )
+                return false;
+        return eq(n);
+    }
+    // Subclasses add extra checks (such as ConstantNodes have same constant),
+    // and can assume "this!=n" and has the same Java class.
+    boolean eq( Node n ) { return true; }
+
+
+    // Cached hash.  If zero, then not computed AND this Node is NOT in the GVN
+    // table - and can have its edges hacked (which will change his hash
+    // anyway).  If Non-Zero then this Node is IN the GVN table, or is being
+    // probed to see if it can be inserted.  His edges are "locked", because
+    // hacking his edges will change his hash.
+    int _hash;
+
+    // If the _hash is set, then the Node is in the GVN table; remove it.
+    void unlock() {
+        if( _hash==0 ) return;
+        Node old = CODE._gvn.remove(this); // Pull from table
+        assert old==this;
+        _hash=0;                // Out of table now
+    }
+
+
+    // Hash of opcode and inputs
+    @Override public final int hashCode() {
+        if( _hash != 0 ) return _hash;
+        int hash = hash();
+        for( Node n : _inputs )
+            if( n != null )
+                hash = hash ^ (hash<<17) ^ (hash>>13) ^ n._nid;
+        if( hash==0 ) hash = 0xDEADBEEF; // Bad hash, so use some junky thing
+        return (_hash=hash);
+    }
+    // Subclasses add extra hash info (such as ConstantNodes constant)
+    int hash() { return 0; }
+
+    // ------------------------------------------------------------------------
+    //
+
+    /** Is this Node Memory related */
+    public boolean isMem() { return false; }
+
+    /** Pinned in the schedule; these are data nodes whose input#0 is not allowed to change */
+    public boolean isPinned() { return false; }
+
+    // Semantic change to the graph (so NOT a peephole), used by the Parser.
+    // If any input is a float, flip to a float-flavored opcode and widen any
+    // non-float input.
+    public final Node widen() {
+        if( !hasFloatInput() ) return this;
+        Node flt = copyF();
+        if( flt==null ) return this;
+        for( int i=1; i<nIns(); i++ )
+            flt.setDef(i, in(i)._type instanceof TypeFloat ? in(i) : new ToFloatNode(in(i)).peephole());
+        kill();
+        return flt;
+    }
+    private boolean hasFloatInput() {
+        for( int i=1; i<nIns(); i++ )
+            if( in(i)._type instanceof TypeFloat )
+                return true;
+        return false;
+    }
+    Node copyF() { return null; }
+
+
+    // ------------------------------------------------------------------------
+    // Peephole utilities
+
+    // Swap inputs without letting either input go dead during the swap.
+    Node swap12() {
+        unlock();               // Hash is order dependent
+        _inputs.swap(1,2);
+        return this;
+    }
+
+    /**
+     * Does this node contain all constants?  Ignores in(0), as is usually
+     * control.  In an input is not a constant, we add dep as a dependency to
+     * it because dep can make progress if the input becomes a constant later.
+     * It is sufficient for one of the non-const inputs to have the dependency,
+     * so we don't bother checking the rest.
+     */
+    boolean allCons(Node dep) {
+        for( int i=1; i<nIns(); i++ )
+            if( !(in(i)._type.isConstant()) ) {
+                in(i).addDep(dep); // If in(i) becomes a constant later, will trigger some peephole
+                return false;
+            }
+        return true;
+    }
+
+
+    // Make a shallow copy (same class) of this Node, with given inputs and
+    // empty outputs and a new Node ID.  The original inputs are ignored.
+    // Does not need to be implemented in isCFG() nodes.
+    Node copy(Node lhs, Node rhs) { throw Utils.TODO("Binary ops need to implement copy"); }
+
+    // Report any post-optimize errors
+    public Parser.ParseException err() { return null; }
+
+    // Common integer constants
+    public static ConstantNode con(long x) { return (ConstantNode)(new ConstantNode(TypeInteger.constant(x)).peephole()); }
+
+    // Utility to walk the entire graph applying a function; return the first
+    // not-null result.
+    final public <E> E walk( Function<Node,E> pred ) {
+        assert CODE._visit.isEmpty();
+        E rez = _walk(pred);
+        CODE._visit.clear();
+        return rez;
+    }
+
+    private <E> E _walk( Function<Node,E> pred ) {
+        if( CODE._visit.get(_nid) ) return null; // Been there, done that
+        CODE._visit.set(_nid);
+        E x = pred.apply(this);
+        if( x != null ) return x;
+        for( Node def : _inputs  )  if( def != null && (x = def._walk(pred)) != null ) return x;
+        for( Node use : _outputs )  if( use != null && (x = use._walk(pred)) != null ) return x;
+        return null;
+    }
+
+    /**
+     * Debugging utility to find a Node by index
+     */
+    public Node find(int nid) {
+        return walk( n -> n._nid==nid ? n : null );
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/NotNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/NotNode.java
new file mode 100644
index 00000000..b454de66
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/NotNode.java
@@ -0,0 +1,32 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+public class NotNode extends Node {
+    public NotNode(Node in) { super(null, in); }
+
+    @Override public String label() { return "Not"; }
+
+    @Override public String glabel() { return "!"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("(!"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public TypeInteger compute() {
+        Type t0 = in(1)._type;
+        if( t0.isHigh() )  return TypeInteger.BOOL.dual();
+        if( t0 == Type.NIL || t0 == TypeInteger.ZERO ) return TypeInteger.TRUE;
+        if( t0 instanceof TypeNil tn && tn.notNull() ) return TypeInteger.FALSE;
+        if( t0 instanceof TypeInteger i && (i._min > 0 || i._max < 0) ) return TypeInteger.FALSE;
+        return TypeInteger.BOOL;
+    }
+
+    @Override
+    public Node idealize() { return null; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/OrNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/OrNode.java
new file mode 100644
index 00000000..9b03dc5d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/OrNode.java
@@ -0,0 +1,55 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.util.BitSet;
+
+public class OrNode extends LogicalNode {
+    public OrNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "Or"; }
+    @Override public String op() { return "|"; }
+
+    @Override public String glabel() { return "|"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1 ) {
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()|i1.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // Or of 0.  We do not check for (0|x) because this will already
+        // canonicalize to (x|0)
+        if( t2.isConstant() && t2 instanceof TypeInteger i && i.value()==0 )
+            return lhs;
+
+        // Move constants to RHS: con*arg becomes arg*con
+        if ( t1.isConstant() && !t2.isConstant() )
+            return swap12();
+
+        // Do we have ((x | (phi cons)) | con) ?
+        // Do we have ((x | (phi cons)) | (phi cons)) ?
+        // Push constant up through the phi: x | (phi con0|con0 con1|con1...)
+        Node phicon = AddNode.phiCon(this,true);
+        if( phicon!=null ) return phicon;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new OrNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ParmNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ParmNode.java
new file mode 100644
index 00000000..8d7c4205
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ParmNode.java
@@ -0,0 +1,48 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import java.util.BitSet;
+
+public class ParmNode extends PhiNode {
+
+    // Argument indices are mapped one-to-one on CallNode inputs
+    public final int _idx;             // Argument index
+
+    public ParmNode(String label, int idx, Type declaredType, Node... inputs) {
+        super(label,declaredType,inputs);
+        _idx = idx;
+    }
+    public ParmNode(ParmNode parm) { super(parm, parm._label, parm._declaredType); _idx = parm._idx; }
+
+    @Override public String label() { return MemOpNode.mlabel(_label); }
+
+    @Override public String glabel() { return _label; }
+
+    public FunNode fun() { return (FunNode)in(0); }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        if( "main".equals(fun()._name) && _label.equals("arg") )
+            return sb.append("arg");
+        sb.append("Parm_").append(_label).append("(");
+        for( Node in : _inputs ) {
+            if (in == null) sb.append("____");
+            else in._print0(sb, visited);
+            sb.append(",");
+        }
+        sb.setLength(sb.length()-1);
+        sb.append(")");
+        return sb;
+    }
+
+
+    @Override
+    public Node idealize() {
+        if( inProgress() ) return null;
+        return super.idealize();
+    }
+
+    // Always in-progress until we run out of unknown callers
+    @Override public boolean inProgress() { return fun().inProgress(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/PhiNode.java
new file mode 100644
index 00000000..17748afe
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -0,0 +1,201 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+public class PhiNode extends Node {
+
+    public final String _label;
+
+    // The Phi type we compute must stay within the domain of the Phi.
+    // Example Int stays Int, Ptr stays Ptr, Control stays Control, Mem stays Mem.
+    final Type _declaredType;
+
+    public PhiNode(String label, Type declaredType, Node... inputs) { super(inputs); _label = label;  assert declaredType!=null; _declaredType = declaredType; }
+    public PhiNode(PhiNode phi, String label, Type declaredType) { super(phi); _label = label; _declaredType = declaredType; }
+    public PhiNode(PhiNode phi) { super(phi); _label = phi._label; _declaredType = phi._declaredType;  }
+
+    public PhiNode(RegionNode r, Node sample) {
+        super(new Node[]{r});
+        _label = "";
+        _declaredType = sample._type;
+        while( nIns() < r.nIns() )
+            addDef(sample);
+    }
+
+    @Override public String label() { return "Phi_"+MemOpNode.mlabel(_label); }
+
+    @Override public String glabel() { return "&phi;_"+_label; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        if( !(region() instanceof RegionNode r) || r.inProgress() )
+            sb.append("Z");
+        sb.append("Phi(");
+        for( Node in : _inputs ) {
+            if (in == null) sb.append("____");
+            else in._print0(sb, visited);
+            sb.append(",");
+        }
+        sb.setLength(sb.length()-1);
+        sb.append(")");
+        return sb;
+    }
+
+    public CFGNode region() { return (CFGNode)in(0); }
+    @Override public boolean isMultiTail() { return true; }
+    @Override public boolean isMem() { return _declaredType instanceof TypeMem; }
+    @Override public boolean isPinned() { return true; }
+
+    @Override
+    public Type compute() {
+        if( !(region() instanceof RegionNode r) )
+            return region()._type==Type.XCONTROL ? (_type instanceof TypeMem ? TypeMem.TOP : Type.TOP) : _type;
+        // During parsing Phis have to be computed type pessimistically.
+        if( r.inProgress() ) return _declaredType;
+        // Set type to local top of the starting type
+        Type t = _declaredType.glb().dual();//Type.TOP;
+        for (int i = 1; i < nIns(); i++)
+            // If the region's control input is live, add this as a dependency
+            // to the control because we can be peeped should it become dead.
+            if( r.in(i).addDep(this)._type != Type.XCONTROL )
+                t = t.meet(in(i)._type);
+        return t;
+    }
+
+    @Override
+    public Node idealize() {
+        if( !(region() instanceof RegionNode r ) )
+            return in(1);       // Input has collapse to e.g. starting control.
+        if( r.inProgress() || r.nIns()<=1 )
+            return null;        // Input is in-progress
+
+        // If we have only a single unique input, become it.
+        Node live = singleUniqueInput();
+        if (live != null)
+            return live;
+
+        // No bother if region is going to fold dead paths soon
+        for( int i=1; i<nIns(); i++ )
+            if( r.in(i)._type == Type.XCONTROL )
+                return null;
+
+        // Pull "down" a common data op.  One less op in the world.  One more
+        // Phi, but Phis do not make code.
+        //   Phi(op(A,B),op(Q,R),op(X,Y)) becomes
+        //     op(Phi(A,Q,X), Phi(B,R,Y)).
+        Node op = in(1);
+        if( !isMem() && op.nIns()==3 && op.in(0)==null && same_op() ) {
+            assert !(op instanceof CFGNode);
+            Node[] lhss = new Node[nIns()];
+            Node[] rhss = new Node[nIns()];
+            lhss[0] = rhss[0] = in(0); // Set Region
+            for( int i=1; i<nIns(); i++ ) {
+                lhss[i] = in(i).in(1);
+                rhss[i] = in(i).in(2);
+            }
+            Node phi_lhs = new PhiNode(_label, _declaredType,lhss).peephole();
+            Node phi_rhs = new PhiNode(_label, _declaredType,rhss).peephole();
+            Node down = op.copy(phi_lhs,phi_rhs);
+            // Test not running backwards, which can happen for e.g. And's
+            if( down.compute().isa(compute()) )
+                return down;
+            down.kill();
+        }
+
+        // If merging Phi(N, cast(N)) - we are losing the cast JOIN effects, so just remove.
+        if( nIns()==3 ) {
+            if( in(1) instanceof CastNode cast && cast.in(1).addDep(this)==in(2) ) return in(2);
+            if( in(2) instanceof CastNode cast && cast.in(1).addDep(this)==in(1) ) return in(1);
+        }
+        // If merging a null-checked null and the checked value, just use the value.
+        // if( val ) ..; phi(Region,False=0/null,True=val);
+        // then replace with plain val.
+        if( nIns()==3 ) {
+            int nullx = -1;
+            if( in(1)._type == in(1)._type.makeZero() ) nullx = 1;
+            if( in(2)._type == in(2)._type.makeZero() ) nullx = 2;
+            if( nullx != -1 ) {
+                Node val = in(3-nullx);
+                if( val instanceof CastNode cast )
+                    val = cast.in(1);
+                if( r.idom(this).addDep(this) instanceof IfNode iff && iff.pred().addDep(this)==val ) {
+                    // Must walk the idom on the null side to make sure we hit False.
+                    CFGNode idom = (CFGNode)r.in(nullx);
+                    while( idom != null && idom.nIns() > 0 && idom.in(0) != iff ) idom = idom.idom();
+                    if( idom instanceof CProjNode proj && proj._idx==1 )
+                        return val;
+                }
+            }
+        }
+
+        return null;
+    }
+
+    private boolean same_op() {
+        for( int i=2; i<nIns(); i++ )
+            if( in(1).getClass() != in(i).getClass() )
+                return false;
+        return true;
+    }
+
+    /**
+     * If only single unique input, return it
+     */
+    private Node singleUniqueInput() {
+        if( region() instanceof LoopNode loop && loop.entry()._type == Type.XCONTROL )
+            return null;    // Dead entry loops just ignore and let the loop collapse
+        Node live = null;
+        for( int i=1; i<nIns(); i++ ) {
+            // If the region's control input is live, add this as a dependency
+            // to the control because we can be peeped should it become dead.
+            if( region().in(i).addDep(this)._type != Type.XCONTROL && in(i) != this )
+                if( live == null || live == in(i) ) live = in(i);
+                else return null;
+        }
+        return live;
+    }
+
+    @Override
+    boolean allCons(Node dep) {
+        if( !(region() instanceof RegionNode r) ) return false;
+        // When the region completes (is no longer in progress) the Phi can
+        // become a "all constants" Phi, and the "dep" might make progress.
+        addDep(dep);
+        if( r.inProgress() ) return false;
+        return super.allCons(dep);
+    }
+
+    // True if last input is null
+    public boolean inProgress() {
+        return in(nIns()-1) == null;
+    }
+
+    // Never equal if inProgress
+    @Override boolean eq( Node n ) {
+        return !inProgress();
+    }
+
+    @Override
+    public Parser.ParseException err() {
+        if( _type != Type.BOTTOM ) return null;
+
+        // BOTTOM means we mixed e.g. int and ptr
+        for( int i=1; i<nIns(); i++ )
+            // Already an error, but better error messages come from elsewhere
+            if( in(i)._type == Type.BOTTOM )
+                return null;
+
+        // Gather a minimal set of types that "cover" all the rest
+        boolean ti=false, tf=false, tp=false, tn=false;
+        for( int i=1; i<nIns(); i++ ) {
+            Type t = in(i)._type;
+            ti |= t instanceof TypeInteger x;
+            tf |= t instanceof TypeFloat   x;
+            tp |= t instanceof TypeMemPtr  x;
+            tn |= t==Type.NIL;
+        }
+        return ReturnNode.mixerr(ti,tf,tp,tn, ((RegionNode)region())._loc);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ProjNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ProjNode.java
new file mode 100644
index 00000000..ef7b17e4
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ProjNode.java
@@ -0,0 +1,55 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMem;
+import com.seaofnodes.simple.type.TypeTuple;
+
+import java.util.BitSet;
+
+public class ProjNode extends Node {
+
+    // Which slice of the incoming multipart value
+    public final int _idx;
+
+    // Debugging label
+    public final String _label;
+
+    public ProjNode(Node ctrl, int idx, String label) {
+        super(new Node[]{ctrl});
+        _idx = idx;
+        _label = label;
+    }
+    public ProjNode(ProjNode p) { super(p); _idx = p._idx; _label = p._label; }
+
+    @Override public String label() { return _label; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        if( _label != null )  return sb.append(_label);
+        if( in(0) instanceof CallEndNode cend && cend.call()!=null )
+            return cend.call()._print0(sb,visited);
+        return sb.append("LONELY PROJ");
+    }
+
+    @Override public CFGNode cfg0() {
+        return in(0) instanceof CFGNode cfg ? cfg : in(0).cfg0();
+    }
+
+    @Override public boolean isMultiTail() { return in(0).isMultiHead(); }
+    @Override public boolean isMem() { return _type instanceof TypeMem; }
+    @Override public boolean isPinned() { return true; }
+
+    @Override
+    public Type compute() {
+        Type t = in(0)._type;
+        return t instanceof TypeTuple tt ? tt._types[_idx] : Type.BOTTOM;
+    }
+
+    @Override public Node idealize() { return ((MultiNode)in(0)).pcopy(_idx); }
+
+    @Override
+    boolean eq( Node n ) { return _idx == ((ProjNode)n)._idx; }
+
+    @Override
+    int hash() { return _idx; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
new file mode 100644
index 00000000..b755af3f
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
@@ -0,0 +1,30 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMemPtr;
+
+import java.util.BitSet;
+
+/**
+ * Cast a pointer to read-only
+ */
+public class ReadOnlyNode extends Node {
+    public ReadOnlyNode( Node n ) { super(null,n); }
+    public ReadOnlyNode( ReadOnlyNode n ) { super(n); }
+    @Override public String label() { return "ReadOnly"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return in(1)._print0(sb.append("(const)"),visited);
+    }
+    @Override public Type compute() {
+        Type t = in(1)._type;
+        return t instanceof TypeMemPtr tmp ? tmp.makeRO() : t;
+    }
+
+    @Override public Node idealize() {
+        if( in(1)._type instanceof TypeMemPtr tmp && tmp.isFinal() )
+            return in(1);
+        return null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/RegionNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/RegionNode.java
new file mode 100644
index 00000000..5d3db5c6
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/RegionNode.java
@@ -0,0 +1,126 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.Type;
+import java.util.*;
+
+public class RegionNode extends CFGNode {
+    // Source location for late discovered errors
+    public Parser.Lexer _loc;
+
+    public RegionNode(Parser.Lexer loc, Node...   nodes) { super(nodes); _loc = loc; }
+    public RegionNode(RegionNode r, Parser.Lexer loc) { super(r); _loc = loc; }
+    public RegionNode(RegionNode r) { super(r); _loc = r._loc; }
+
+    @Override
+    public String label() { return "Region"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return sb.append(label());
+    }
+
+    @Override public boolean isMultiHead() { return true; }
+    @Override public boolean blockHead() { return true; }
+
+    @Override
+    public Type compute() {
+        if( inProgress() ) return Type.CONTROL;
+        Type t = Type.XCONTROL;
+        for (int i = 1; i < nIns(); i++)
+            t = t.meet(in(i)._type);
+        return t;
+    }
+
+    @Override
+    public Node idealize() {
+        if( inProgress() ) return null;
+
+        Node progress = deadPath();
+        if( progress!=null ) return progress;
+
+        // If down to a single input, become that input
+        if( nIns()==2 && !hasPhi() )
+            return in(1);       // Collapse if no Phis; 1-input Phis will collapse on their own
+
+        // If a CFG diamond with no merging, delete: "if( pred ) {} else {};"
+        if( !hasPhi() &&         // No Phi users, just a control user
+            in(1) instanceof CProjNode p1 &&
+            in(2) instanceof CProjNode p2 &&
+            p1.in(0).addDep(this)==p2.in(0).addDep(this) &&
+            p1.in(0) instanceof IfNode iff ) {
+            // Replace with the iff.ctrl directly
+            if( nIns()==3 ) return iff.ctrl();
+            // Just delete the path for fat Regions
+            setDef(1,iff.ctrl());
+            return delDef(2);
+        }
+
+        return null;
+    }
+
+    Node deadPath() {
+        // Delete dead paths into a Region
+        int path = findDeadInput();
+        if( path==0 ) return null;
+        // Do not delete the entry path of a loop (ok to remove the back edge
+        // and make the loop a single-entry Region which folds away the Loop).
+        // Folding the entry path confused the loop structure, moving the
+        // backedge to the entry point.
+        if( this instanceof LoopNode loop && loop.entry()==in(path) )
+            return null;
+        // Cannot use the obvious output iterator here, because a Phi deleting
+        // an input might recursively delete *itself*.  This shuffles the
+        // output array, and we might miss iterating an unrelated Phi. So on
+        // rare occasions we repeat the loop to get all the Phis.
+        int nouts = 0;
+        while( nouts != nOuts() ) {
+            nouts = nOuts();
+            for( int i=0; i<nOuts(); i++ )
+                if( out(i) instanceof PhiNode phi && phi.nIns()==nIns() )
+                    CodeGen.CODE.addAll(phi.delDef(path)._outputs);
+        }
+        return isDead() ? Parser.XCTRL : delDef(path);
+    }
+
+
+    private int findDeadInput() {
+        for( int i=1; i<nIns(); i++ )
+            if( in(i)._type==Type.XCONTROL )
+                return i;
+        return 0;               // All inputs alive
+    }
+
+    boolean hasPhi() {
+        for( Node phi : _outputs )
+            if( phi instanceof PhiNode )
+                return true;
+        return false;
+    }
+
+    // Immediate dominator of Region is a little more complicated.
+    @Override public int idepth() {
+        if( _idepth!=0 ) return _idepth;
+        int d=0;
+        for( Node n : _inputs )
+            if( n!=null )
+                d = Math.max(d,((CFGNode)n).idepth()+1);
+        return _idepth=d;
+    }
+
+    @Override public CFGNode idom(Node dep) {
+        CFGNode lca = null;
+        // Walk the LHS & RHS idom trees in parallel until they match, or either fails.
+        // Because this does not cache, it can be linear in the size of the program.
+        for( int i=1; i<nIns(); i++ )
+            lca = cfg(i)._idom(lca,dep);
+        return lca;
+    }
+
+    // True if last input is null
+    public boolean inProgress() { return nIns()>1 && in(nIns()-1) == null; }
+
+    // Never equal if inProgress
+    @Override boolean eq( Node n ) { return !inProgress(); }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ReturnNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
new file mode 100644
index 00000000..20b6c7b9
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
@@ -0,0 +1,129 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+/**
+ * The Return node has two inputs.  The first input is a control node and the
+ * second is the data node that supplies the return value.
+ * <p>
+ * In this presentation, Return functions as a Stop node, since multiple <code>return</code> statements are not possible.
+ * The Stop node will be introduced in Chapter 6 when we implement <code>if</code> statements.
+ * <p>
+ * The Return's output is the value from the data node.
+ */
+public class ReturnNode extends CFGNode {
+
+    public FunNode _fun;
+
+    public ReturnNode(Node ctrl, Node mem, Node data, Node rpc, FunNode fun ) {
+        super(ctrl, mem, data, rpc);
+        _fun = fun;
+    }
+    public ReturnNode( ReturnNode ret, FunNode fun ) { super(ret);  _fun = fun;  }
+
+    public Node ctrl() { return in(0); }
+    public Node mem () { return in(1); }
+    public Node expr() { return in(2); }
+    public Node rpc () { return in(3); }
+    public FunNode fun() { return _fun; }
+
+    @Override
+    public String label() { return "Return"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("return ");
+        expr()._print0(sb, visited);
+        return sb.append(";");
+    }
+
+    // No one unique control follows; can be many call end sites
+    @Override public CFGNode uctrl() { return null; }
+
+    @Override
+    public Type compute() {
+        if( inProgress () ) return TypeTuple.RET; // In progress
+        if( _fun.isDead() ) return TypeTuple.RET.dual(); // Dead another way
+        return TypeTuple.make(ctrl()._type,mem()._type,expr()._type);
+    }
+
+    @Override public Node idealize() {
+        if( inProgress () ) return null;
+        if( _fun.isDead() ) return null;
+
+        // Upgrade signature based on return type
+        Type ret = expr()._type;
+        TypeFunPtr fcn = _fun.sig();
+        assert ret.isa(fcn.ret());
+        if( ret != fcn.ret() )
+            _fun.setSig(fcn.makeFrom(ret));
+
+        // If dead (cant be reached; infinite loop), kill the exit values
+        if( ctrl()._type==Type.XCONTROL &&
+            !(mem() instanceof ConstantNode && expr() instanceof ConstantNode) ) {
+            Node top = new ConstantNode(Type.TOP).peephole();
+            setDef(1,top);
+            setDef(2,top);
+            return this;
+        }
+
+        return null;
+    }
+
+    public boolean inProgress() {
+        return ctrl().getClass() == RegionNode.class && ((RegionNode)ctrl()).inProgress();
+    }
+
+    // Gather parse-time return types for error reporting
+    private Type mt = Type.TOP;
+    private boolean ti=false, tf=false, tp=false, tn=false;
+
+    // Add a return exit to the current parsing function
+    void addReturn( Node ctrl, Node rmem, Node expr ) {
+        assert inProgress();
+
+        // Gather parse-time return types for error reporting
+        Type t = expr._type;
+        mt = mt.meet(t);
+        ti |= t instanceof TypeInteger x;
+        tf |= t instanceof TypeFloat   x;
+        tp |= t instanceof TypeMemPtr  x;
+        tn |= t==Type.NIL;
+
+        // Merge path into the One True Return
+        RegionNode r = (RegionNode)ctrl();
+        // Assert that the Phis are in particular outputs; not reordered or shuffled
+        PhiNode mem = (PhiNode)r.out(0); assert mem._declaredType == TypeMem.BOT;
+        PhiNode rez = (PhiNode)r.out(1); assert rez._declaredType == Type.BOTTOM;
+        // Pop "inProgress" null off
+        r  ._inputs.pop();
+        mem._inputs.pop();
+        rez._inputs.pop();
+        // Add new return point
+        r  .addDef(ctrl);
+        mem.addDef(rmem);
+        rez.addDef(expr);
+        // Back to being inProgress
+        r  .addDef(null);
+        mem.addDef(null);
+        rez.addDef(null);
+    }
+
+    @Override public Parser.ParseException err() {
+        return expr()._type/*mt*/==Type.BOTTOM ? mixerr(ti,tf,tp,tn,_fun._loc) : null;
+    }
+
+    static Parser.ParseException mixerr( boolean ti, boolean tf, boolean tp, boolean tn, Parser.Lexer loc ) {
+        if( !ti && !tf && !tp && !tn )
+            return Parser.error("No defined return type", loc);
+        SB sb = new SB().p("No common type amongst ");
+        if( ti ) sb.p("int and ");
+        if( tf ) sb.p("f64 and ");
+        if( tp || tn ) sb.p("reference and ");
+        return Parser.error(sb.unchar(5).toString(),loc);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java b/chapter20/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java
new file mode 100644
index 00000000..44d3a587
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java
@@ -0,0 +1,38 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class RoundF32Node extends Node {
+    public RoundF32Node(Node lhs) { super(null, lhs); }
+
+    @Override public String label() { return "RoundF32"; }
+
+    @Override public String glabel() { return "(f32)"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return in(1)._print0(sb.append("((f32)"), visited).append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0 && i0.isConstant() )
+            return TypeFloat.constant((float)i0.value());
+        return in(1)._type;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Type t1 = lhs._type;
+
+        // RoundF32 of float
+        if( t1 instanceof TypeFloat tf && tf._sz==32 )
+            return lhs;
+
+        return null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/SarNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/SarNode.java
new file mode 100644
index 00000000..4a71ec06
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/SarNode.java
@@ -0,0 +1,50 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class SarNode extends LogicalNode {
+    public SarNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "Sar"; }
+    @Override public String op() { return ">>"; }
+
+    @Override public String glabel() { return "&gt;&gt;"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if (t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1) {
+            if( i0 == TypeInteger.ZERO )
+                return TypeInteger.ZERO;
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()>>i1.value());
+            if( i1.isConstant() ) {
+                int log = (int)i1.value();
+                return TypeInteger.make(-1L<<(63-log),(1L<<(63-log))-1);
+            }
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t2 = rhs._type;
+
+        // Sar of 0.
+        if( t2.isConstant() && t2 instanceof TypeInteger i && (i.value()&63)==0 )
+            return lhs;
+
+        // TODO: x >> 3 >> (y ? 1 : 2) ==> x >> (y ? 4 : 5)
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new SarNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
new file mode 100644
index 00000000..1208ff63
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -0,0 +1,428 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.*;
+import java.util.*;
+
+/**
+ * The Scope node is purely a parser helper - it tracks names to nodes with a
+ * stack of variables.
+ */
+public class ScopeNode extends MemMergeNode {
+
+    /**
+     * The control is a name that binds to the currently active control
+     * node in the graph
+     */
+    public static final String CTRL = "$ctrl";
+    public static final String ARG0 = "arg";
+    public static final String MEM0 = "$mem";
+
+    // All active/live variables in all nested scopes, all run together
+    public final Ary<Var> _vars;
+
+    // Size of each nested lexical scope
+    public final Ary<Integer> _lexSize;
+
+    // Lexical scope is one of normal Block, constructor or function
+    public enum Kind { Block, Constructor, Function };
+    public final Ary<Kind> _kinds;
+
+    // Extra guards; tested predicates and casted results
+    private final Ary<Node> _guards;
+
+    // A new ScopeNode
+    public ScopeNode() {
+        super(true);
+        _vars   = new Ary<>(Var    .class);
+        _lexSize= new Ary<>(Integer.class);
+        _kinds  = new Ary<>(Kind   .class);
+        _guards = new Ary<>(Node   .class);
+    }
+
+    @Override public String label() { return "Scope"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        sb.append("Scope[ ");
+        int j=1;
+        for( int i=0; i<nIns(); i++ ) {
+            if( j < _lexSize._len && i == _lexSize.at(j) ) { sb.append("| "); j++; }
+            Var v = _vars.get(i);
+            sb.append(v.type().print(new SB()));
+            sb.append(" ");
+            if( v._final ) sb.append("!");
+            sb.append(v._name);
+            sb.append("=");
+            Node n = in(i);
+            while( n instanceof ScopeNode loop ) {
+                sb.append("Lazy_");
+                n = loop.in(i);
+            }
+            if( n==null ) sb.append("___");
+            else n._print0(sb, visited);
+            sb.append(", ");
+        }
+        sb.setLength(sb.length()-2);
+        return sb.append("]");
+    }
+
+
+    public Node ctrl() { return in(0); }
+    public MemMergeNode mem() { return (MemMergeNode)in(1); }
+
+    /**
+     * The ctrl of a ScopeNode is always bound to the currently active
+     * control node in the graph, via a special name '$ctrl' that is not
+     * a valid identifier in the language grammar and hence cannot be
+     * referenced in Simple code.
+     *
+     * @param n The node to be bound to '$ctrl'
+     *
+     * @return Node that was bound
+     */
+    public <N extends Node> N ctrl(N n) { return setDef(0,n); }
+    public Node mem(Node n) { return setDef(1,n); }
+
+    public void push(Kind kind) {
+        assert _lexSize._len==_kinds._len;
+        _lexSize.push(_vars.size());
+        _kinds  .push(kind);
+    }
+
+    // Pop a lexical scope
+    public void pop() {
+        assert _lexSize._len==_kinds._len;
+        promote();
+        int n = _lexSize.pop();
+        _kinds.pop();
+        popUntil(n);
+        _vars.setLen(n);
+    }
+
+
+    // Look for forward references in the last lexical scope and promote to the
+    // next outer lexical scope.  At the last scope declare them an error.
+    public void promote() {
+        int n = _lexSize.last();
+        for( int i=n; i<nIns(); i++ ) {
+            Var v = _vars.at(i);
+            if( !v.isFRef() ) continue;
+            if( _lexSize._len==1 )
+                throw Parser.error("Undefined name '" + v._name + "'",v._loc);
+            _vars.swap(n,i);
+            _inputs.swap(n,i);
+            v._idx = n;
+            n++;
+            _lexSize.set(_lexSize._len-1,n);
+        }
+    }
+
+
+    public boolean inCon() { return _kinds.last() == Kind.Constructor; }
+
+    // Is v outside any current function scope?
+    public boolean outOfFunction( Var v ) {
+        for( int i=_lexSize._len-1; i>=0 && v._idx<_lexSize.at(i); i-- )
+            if( _kinds.at(i)==Kind.Function )
+                return true;
+        return false;
+    }
+
+
+    // Find name in reverse, return an index into _vars or -1.  Linear scan
+    // instead of hashtable, but probably doesn't matter until the scan
+    // typically hits many dozens of variables.
+    int find( String name ) {
+        for( int i=_vars.size()-1; i>=0; i-- )
+            if( _vars.at(i)._name.equals(name) )
+                return i;
+        return -1;
+    }
+
+    /**
+     * Create a new variable name in the current scope
+     */
+    public boolean define( String name, Type declaredType, boolean xfinal, Node init, Parser.Lexer loc ) {
+        assert _lexSize.isEmpty() || name.charAt(0)!='$' ; // Later scopes do not define memory
+        if( _lexSize._len > 0 )
+            for( int i=_vars.size()-1; i>=_lexSize.last(); i-- ) {
+                Var n = _vars.at(i);
+                if( n._name.equals(name) ) {
+                    if( !n.isFRef() ) return false;       // Double define
+                    FRefNode fref = (FRefNode)in(n._idx); // Get forward ref
+                    if( !xfinal || !declaredType.isConstant() ) throw fref.err();  // Must be a final constant
+                    n.defFRef(declaredType,xfinal,loc);   // Declare full correct type, final, source location
+                    setDef(n._idx,fref.addDef(init));     // Set FRef to defined; tell parser also
+                }
+            }
+        Var v = new Var(nIns(),name,declaredType,xfinal,loc,init==Parser.XCTRL);
+        _vars.add(v);
+        // Creating a forward reference
+        if( init==Parser.XCTRL )
+            init = new FRefNode(v).init();
+        addDef(init);
+        return true;
+    }
+
+    // Read from memory
+    public Node mem( int alias ) { return mem()._mem(alias,null); }
+    // Write to memory
+    public void mem( int alias, Node st ) { mem()._mem(alias,st); }
+
+
+    /**
+     * Lookup a name in all scopes starting from most deeply nested.
+     *
+     * @param name Name to be looked up
+     * @return null if not found, or the implementing Node
+     */
+    public Var lookup( String name ) {
+        int idx = find(name);
+        // -1 is missed in all scopes, not found
+        return idx == -1 ? null : update(_vars.at(idx),null);
+    }
+
+    /**
+     * If the name is present in any scope, then redefine else null
+     *
+     * @param name Name being redefined
+     * @param n    The node to bind to the name
+     */
+    public void update( String name, Node n ) {
+        int idx = find(name);
+        assert idx>=0;
+        update(_vars.at(idx),n);
+    }
+
+    public Var update( Var v, Node st ) {
+        Node old = in(v._idx);
+        if( old instanceof ScopeNode loop ) {
+            // Lazy Phi!
+            Node def = loop.in(v._idx);
+            old = def instanceof PhiNode phi && loop.ctrl()==phi.region()
+                // Loop already has a real Phi, use it
+                ? def
+                // Set real Phi in the loop head
+                // The phi takes its one input (no backedge yet) from a recursive
+                // lookup, which might have insert a Phi in every loop nest.
+                : loop.setDef(v._idx,new PhiNode(v._name, v.lazyGLB(), loop.ctrl(), loop.in(loop.update(v,null)._idx),null).peephole());
+            setDef(v._idx,old);
+        }
+        assert !v._final || st==null;
+        if( st!=null ) setDef(v._idx,st); // Set new value
+        return v;
+    }
+
+    /**
+     * Duplicate a ScopeNode; including all levels, up to Nodes.  So this is
+     * neither shallow (would dup the Scope but not the internal HashMap
+     * tables), nor deep (would dup the Scope, the HashMap tables, but then
+     * also the program Nodes).
+     * <p>
+     * If the {@code loop} flag is set, the edges are filled in as the original
+     * Scope, as an indication of Lazy Phis at loop heads.  The goal here is to
+     * not make Phis at loop heads for variables which are never touched in the
+     * loop body.
+     * <p>
+     * The new Scope is a full-fledged Node with proper use<->def edges.
+     */
+    public ScopeNode dup() { return dup(false); }
+    public ScopeNode dup(boolean loop) {
+        ScopeNode dup = new ScopeNode();
+        // Our goals are:
+        // 1) duplicate the name bindings of the ScopeNode across all stack levels
+        // 2) Make the new ScopeNode a user of all the nodes bound
+        // 3) Ensure that the order of defs is the same to allow easy merging
+        dup._vars   .addAll(_vars   );
+        dup._lexSize.addAll(_lexSize);
+        dup._kinds  .addAll(_kinds  );
+        dup._guards .addAll(_guards );
+        // The dup'd guards all need dup'd keepers, to keep proper accounting
+        // when later removing all guards
+        for( Node n : _guards )
+            if( !(n instanceof CFGNode) )
+                n.keep();
+        dup.addDef(ctrl());     // Control input is just copied
+
+        // Memory input is a shallow copy
+        MemMergeNode memdup = new MemMergeNode(true), mem = mem();
+        memdup.addDef(null);
+        memdup.addDef(loop ? this : mem.in(1));
+        for( int i=2; i<mem.nIns(); i++ )
+            // For lazy phis on loops we use a sentinel
+            // that will trigger phi creation on update
+            memdup.addDef(loop ? this : mem.in(i));
+        dup.addDef(memdup);
+
+        // Copy of other inputs
+        for( int i=2; i<nIns(); i++ )
+            // For lazy phis on loops we use a sentinel
+            // that will trigger phi creation on update
+            dup.addDef(loop && !_vars.at(i)._final ? this : in(i));
+        return dup;
+    }
+
+    /**
+     * Merges the names whose node bindings differ, by creating Phi node for such names
+     * The names could occur at all stack levels, but a given name can only differ in the
+     * innermost stack level where the name is bound.
+     *
+     * @param that The ScopeNode to be merged into this
+     * @return A new node representing the merge point
+     */
+    public RegionNode mergeScopes(ScopeNode that, Parser.Lexer loc) {
+        RegionNode r = ctrl(new RegionNode(loc,null,ctrl(), that.ctrl()).keep());
+        mem()._merge(that.mem(),r);
+        this ._merge(that      ,r);
+        that.kill();            // Kill merged scope
+        CodeGen.CODE.add(r);
+        return r.unkeep();
+    }
+
+    private void _merge(ScopeNode that, RegionNode r) {
+        for( int i = 2; i < nIns(); i++)
+            if( in(i) != that.in(i) ) { // No need for redundant Phis
+                // If we are in lazy phi mode we need to a lookup
+                // by name as it will trigger a phi creation
+                Var v = _vars.at(i);
+                Node lhs = this.in(this.update(v,null));
+                Node rhs = that.in(that.update(v,null));
+                setDef(i, new PhiNode(v._name, v.type(), r, lhs, rhs).peephole());
+            }
+    }
+
+    // Balance arms of an IF.  Extra lonely defs are thrown: "if(pred) int x;".
+    // Forward refs are copied to the other side, "as if" they were there all along.
+    public void balanceIf( ScopeNode scope ) {
+        for( int i = nIns(); i < scope.nIns(); i++ ) {
+            Var n = scope._vars.at(i);
+            if( n.isFRef() ) {  // RHS has forward refs
+                _vars.add(n);   // Copy to LHS
+                addDef(scope.in(i));
+            } else
+                throw Parser.error("Cannot define a '"+n._name+"' on one arm of an if",n._loc);
+        }
+    }
+
+
+    // peephole the backedge scope into this loop head scope
+    // We set the second input to the phi from the back edge (i.e. loop body)
+    public void endLoop(ScopeNode back, ScopeNode exit ) {
+        Node ctrl = ctrl();
+        assert ctrl instanceof LoopNode loop && loop.inProgress();
+        ctrl.setDef(2,back.ctrl());
+
+        mem()._endLoopMem( this, back.mem(), exit.mem() );
+        this ._endLoop   ( this, back      , exit       );
+        back.kill();            // Loop backedge is dead
+        // Now one-time do a useless-phi removal
+        mem()._useless();
+        this ._useless();
+
+        // The exit mem's lazy default value had been the loop top,
+        // now it goes back to predating the loop.
+        exit.mem().setDef(1,mem().in(1));
+    }
+
+    // Fill in the backedge of any inserted Phis
+    void _endLoop( ScopeNode scope, Node back, Node exit ) {
+        for( int i=2; i<nIns(); i++ ) {
+            if( _vars.at(i)._final ) continue; // Final vars did not get modified in the loop
+            if( _vars.at(i).type().isHighOrConst() ) continue; // Cannot lift higher than a constant, so no Phi
+            if( back.in(i) != scope ) {
+                PhiNode phi = (PhiNode)in(i);
+                assert phi.region()==scope.ctrl() && phi.in(2)==null;
+                phi.setDef(2,back.in(i)); // Fill backedge
+            }
+            if( exit.in(i) == scope ) // Replace a lazy-phi on the exit path also
+                exit.setDef(i,in(i));
+        }
+    }
+
+
+    // Up-casting: using the results of an If to improve a value.
+    // E.g. "if( ptr ) ptr.field;" is legal because ptr is known not-null.
+    public void addGuards( Node ctrl, Node pred, boolean invert ) {
+        assert ctrl instanceof CFGNode;
+        _guards.add(ctrl);      // Marker to distinguish 0,1,2 guards
+        // add pred & its cast to the normal input list, with special Vars
+        if( pred==null || pred.isDead() )
+            return;           // Dead, do not add any guards
+        // Invert the If conditional
+        if( invert )
+            pred = pred instanceof NotNode not ? not.in(1) : CodeGen.CODE.add(new NotNode(pred).peephole());
+        // This is a zero/null test.
+        // Compute the positive test type.
+        Type tnz = pred._type.nonZero();
+        if( tnz!=null )
+            _addGuard(tnz,ctrl,pred);
+
+        // Compute the negative test type.
+        if( pred instanceof NotNode not ) {
+            Node npred = not.in(1);
+            Type tzero = npred._type.makeZero();
+            _addGuard(tzero,ctrl,npred);
+        }
+    }
+
+    private void _addGuard(Type guard, Node ctrl, Node pred) {
+        Type tcast = guard.join(pred._type);
+        if( tcast != pred._type && !tcast.isHigh() ) {
+            Node cast = new CastNode(tcast,ctrl,pred.keep()).peephole().keep();
+            _guards.add(pred);
+            _guards.add(cast);
+            replace(pred,cast);
+        }
+    }
+
+
+    // Remove matching pred/cast pairs from this guarded region.
+    public ScopeNode removeGuards( Node ctrl ) {
+        assert ctrl instanceof CFGNode;
+        // 0,1 or 2 guards
+        while( true ) {
+            Node g = _guards.pop();
+            if( g == ctrl ) break;
+            if( g instanceof CFGNode ) continue;
+            g            .unkill(); // Pop/kill cast
+            _guards.pop().unkill(); // Pop/kill pred
+        }
+        return this;
+    }
+
+    // If we find a guarded instance of pred, replace with the upcasted version
+    public Node upcastGuard( Node pred ) {
+        // If finding an instanceof pred, replace with cast.
+        // Otherwise, just pred itself.
+        int i = _guards._len;
+        while( i > 0 ) {
+            Node  cast = _guards.at(--i);
+            if( cast instanceof CFGNode ) continue; // Marker between guard sets
+            Node xpred = _guards.at(--i);
+            if( xpred == pred )
+                return cast;
+        }
+        return pred;
+    }
+
+    // Kill guards also
+    @Override public void kill() {
+        for( Node n : _guards )
+            if( !(n instanceof CFGNode) )
+                n.unkill();
+        _guards.clear();
+        // Can have lazy uses remaining
+        if( isUnused() )
+            super.kill();
+    }
+
+
+    private void replace( Node old, Node cast ) {
+        assert old!=null && old!=cast;
+        for( int i=0; i<nIns(); i++ )
+            if( in(i)==old )
+                setDef(i,cast);
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ShlNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ShlNode.java
new file mode 100644
index 00000000..21dbd503
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ShlNode.java
@@ -0,0 +1,53 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class ShlNode extends LogicalNode {
+    public ShlNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "Shl"; }
+    @Override public String op() { return "<<"; }
+
+    @Override public String glabel() { return "&lt;&lt;"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if (t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1 ) {
+            if( i0 == TypeInteger.ZERO )
+                return TypeInteger.ZERO;
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()<<i1.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+
+        if( rhs._type instanceof TypeInteger shl && shl.isConstant() ) {
+            // Shl of 0.
+            if( (shl.value()&63)==0 )
+                return lhs;
+            // (x + c) << i  =>  (x << i) + (c << i)
+            if( lhs instanceof AddNode add && add.addDep(this).in(2)._type instanceof TypeInteger c && c.isConstant() ) {
+                long sum = c.value() << shl.value();
+                if( Integer.MIN_VALUE <= sum  && sum <= Integer.MAX_VALUE )
+                    return new AddNode(new ShlNode(_loc,add.in(1),rhs).peephole(), Parser.con(sum) );
+            }
+        }
+
+        // TODO: x << 3 << (y ? 1 : 2) ==> x << (y ? 4 : 5)
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new ShlNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ShrNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ShrNode.java
new file mode 100644
index 00000000..789fb8a8
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ShrNode.java
@@ -0,0 +1,46 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class ShrNode extends LogicalNode {
+    public ShrNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "Shr"; }
+    @Override public String op() { return ">>>"; }
+
+    @Override public String glabel() { return "&gt;&gt;&gt;"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if (t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1 ) {
+            if( i0 == TypeInteger.ZERO )
+                return TypeInteger.ZERO;
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()>>>i1.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t2 = rhs._type;
+
+        // Shr of 0.
+        if( t2.isConstant() && t2 instanceof TypeInteger i && (i.value()&63)==0 )
+            return lhs;
+
+        // TODO: x >>> 3 >>> (y ? 1 : 2) ==> x >>> (y ? 4 : 5)
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new ShrNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/StartNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/StartNode.java
new file mode 100644
index 00000000..26e08535
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/StartNode.java
@@ -0,0 +1,58 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.*;
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.HashSet;
+import static com.seaofnodes.simple.Utils.TODO;
+
+/**
+ * The Start node represents the start of the function.
+ *
+ * Start initially has 1 input (arg) from outside and the initial control.
+ * In ch10 we also add mem aliases as structs get defined; each field in struct
+ * adds a distinct alias to Start's tuple.
+ */
+public class StartNode extends LoopNode implements MultiNode {
+
+    final Type _arg;
+
+    public StartNode(Type arg) { super((Parser.Lexer)null,null); _arg = arg; _type = compute(); }
+    public StartNode(StartNode start) { super(start); _arg = start._arg; }
+
+    @Override public String label() { return "Start"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+      return sb.append(label());
+    }
+
+    @Override public boolean isMultiHead() { return true; }
+    @Override public boolean blockHead() { return true; }
+    @Override public CFGNode cfg0() { return null; }
+
+    // Get the one control following; error to call with more than one e.g. an
+    // IfNode or other multi-way branch.  For Start, its "main"
+    @Override public CFGNode uctrl() {
+        // Find "main", its the start.
+        CFGNode C = null;
+        for( Node use : _outputs )
+            if( use instanceof FunNode fun && fun.sig().isa(CodeGen.CODE._main) )
+                { assert C==null; C = fun; }
+        return C;
+    }
+
+
+    @Override public TypeTuple compute() {
+        return TypeTuple.make(Type.CONTROL,TypeMem.TOP,_arg);
+    }
+
+    @Override public Node idealize() { return null; }
+
+    // No immediate dominator, and idepth==0
+    @Override public int idepth() { return 0; }
+    @Override public CFGNode idom(Node dep) { return null; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/StopNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/StopNode.java
new file mode 100644
index 00000000..6aaba3b3
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/StopNode.java
@@ -0,0 +1,64 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.type.Type;
+import java.util.BitSet;
+
+public class StopNode extends CFGNode {
+
+    public final String _src;
+
+    public StopNode(String src) {
+        super();
+        _src = src;
+        _type = compute();
+    }
+    public StopNode(StopNode stop) { super(stop);  _src = stop._src; }
+
+    @Override
+    public String label() {
+        return "Stop";
+    }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        // For the sake of many old tests, and single value prints as "return val"
+        if( ret()!=null ) return ret()._print0(sb,visited);
+        sb.append("Stop[ ");
+        for( Node ret : _inputs )
+            ret._print0(sb, visited).append(" ");
+        return sb.append("]");
+    }
+
+    @Override public boolean blockHead() { return true; }
+
+
+    // If a single Return, return it.
+    // Otherwise, null because ambiguous.
+    public ReturnNode ret() {
+        return nIns()==1 && in(0) instanceof ReturnNode ret ? ret : null;
+    }
+
+    @Override
+    public Type compute() {
+        return Type.BOTTOM;
+    }
+
+    @Override
+    public Node idealize() {
+        int len = nIns();
+        for( int i=0; i<nIns(); i++ )
+            if( ((ReturnNode)in(i)).fun().isDead() )
+                delDef(i--);
+        if( len != nIns() ) return this;
+        return null;
+    }
+
+    @Override public int idepth() {
+        if( _idepth!=0 ) return _idepth;
+        int d=0;
+        for( Node ret : _inputs )
+            d = Math.max(d,((ReturnNode)ret).idepth()+1);
+        return _idepth=d;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/StoreNode.java
new file mode 100644
index 00000000..93294dba
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -0,0 +1,113 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+/**
+ * Store represents setting a value to a memory based object, in chapter 10
+ * this means a field inside a struct.
+ */
+public class StoreNode extends MemOpNode {
+
+    private final boolean _init; // Initializing writes are allowed to write null
+
+    /**
+     * @param name  The struct field we are assigning to
+     * @param mem   The memory alias node - this is updated after a Store
+     * @param ptr   The ptr to the struct base where we will store a value
+     * @param off   The offset inside the struct base
+     * @param value Value to be stored
+     */
+    public StoreNode(Parser.Lexer loc, String name, int alias, Type glb, Node mem, Node ptr, Node off, Node value, boolean init) {
+        super(loc, name, alias, glb, mem, ptr, off, value);
+        _init = init;
+    }
+
+    // GraphVis DOT code and debugger labels
+    @Override public String  label() { return "st_"+mlabel(); }
+    // GraphVis node-internal labels
+    @Override public String glabel() { return "." +_name+"="; }
+    @Override public boolean isMem() { return true; }
+
+    public Node val() { return in(4); }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return sb.append(".").append(_name).append("=").append( val()).append(";");
+    }
+
+    @Override
+    public Type compute() {
+        Type val = val()._type;
+        TypeMem mem = (TypeMem)mem()._type; // Invariant
+        if( mem == TypeMem.TOP ) return TypeMem.TOP;
+        Type t = Type.BOTTOM;               // No idea on field contents
+        // Same alias, lift val to the declared type and then meet into other fields
+        if( mem._alias == _alias ) {
+            // Update declared forward ref to the actual
+            if( _declaredType.isFRef() && val instanceof TypeMemPtr tmp && !tmp.isFRef() )
+                _declaredType = tmp;
+            val = val.join(_declaredType);
+            t = val.meet(mem._t);
+        }
+        return TypeMem.make(_alias,t);
+    }
+
+    @Override
+    public Node idealize() {
+
+        // Simple store-after-store on same address.  Should pick up the
+        // required init-store being stomped by a first user store.
+        if( mem() instanceof StoreNode st &&
+            ptr()==st.ptr() &&  // Must check same object
+            off()==st.off() &&  // And same offset (could be "same alias" but this handles arrays to same index)
+            ptr()._type instanceof TypeMemPtr && // No bother if weird dead pointers
+            // Must have exactly one use of "this" or you get weird
+            // non-serializable memory effects in the worse case.
+            checkOnlyUse(st) ) {
+            assert _name.equals(st._name); // Equiv class aliasing is perfect
+            setDef(1,st.mem());
+            return this;
+        }
+
+        // Value is automatically truncated by narrow store
+        if( val() instanceof AndNode and && and.in(2)._type.isConstant()  ) {
+            int log = _declaredType.log_size();
+            if( log<3 ) {       // And-mask vs narrow store
+                long mask = ((TypeInteger)and.in(2)._type).value();
+                long bits = (1L<<(8<<log))-1;
+                // Mask does not mask any of the stored bits
+                if( (bits&mask)==bits )
+                    // So and-mask is already covered by the store
+                    { setDef(4,and.in(1)); return this; }
+            }
+        }
+
+
+        return null;
+    }
+
+    // Check that "mem" has no uses except "this"
+    private boolean checkOnlyUse(Node mem) {
+        if( mem.nOuts()==1 ) return true;
+        // Add deps on the other uses (can be e.g. ScopeNode mid-parse) so that
+        // when the other uses go away we can retry.
+        for( Node use : mem._outputs )
+            if( use != this )
+                use.addDep(this);
+        return false;
+    }
+
+    @Override
+    public Parser.ParseException err() {
+        Parser.ParseException err = super.err();
+        if( err != null ) return err;
+        TypeMemPtr tmp = (TypeMemPtr)ptr()._type;
+        if( tmp._obj.field(_name)._final && !_init )
+            return Parser.error("Cannot modify final field '"+_name+"'",_loc);
+        Type t = val()._type;
+        //return _init || t.isa(_declaredType) ? null : Parser.error("Cannot store "+t+" into field "+_declaredType+" "+_name,_loc);
+        return null;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/StructNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/StructNode.java
new file mode 100644
index 00000000..076b342a
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/StructNode.java
@@ -0,0 +1,46 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+
+/**
+ * Build a compound object
+ */
+public class StructNode extends Node {
+
+    public TypeStruct _ts;
+
+    @Override public String label() { return _ts==null ? "STRUCT?" : _ts.str(); }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        if( _ts==null ) return sb.append("STRUCT?");
+        sb.append(_ts._name).append(" {");
+        for( int i=0; i<nIns(); i++ ) {
+            sb.append(_ts._fields[i]._fname).append(":");
+            sb.append((in(i)==null ? Type.BOTTOM : in(i)._type).print(new SB()));
+            sb.append("; ");
+        }
+        sb.setLength(sb.length()-2);
+        return sb.append("}");
+    }
+
+    @Override
+    public TypeStruct compute() {
+        if( _ts==null ) return TypeStruct.BOT;
+        Field[] fs = new Field[_ts._fields.length];
+        for( int i=0; i<fs.length; i++ )
+            fs[i] = _ts._fields[i].makeFrom(in(i)==null ? Type.TOP : in(i)._type);
+        return TypeStruct.make(_ts._name,fs);
+    }
+
+    @Override
+    public Node idealize() { return null; }
+
+    @Override
+    boolean eq(Node n) { return _ts == ((StructNode)n)._ts; }
+
+    @Override
+    int hash() { return _ts==null ? 0 : _ts.hashCode(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/SubFNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/SubFNode.java
new file mode 100644
index 00000000..b591718d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/SubFNode.java
@@ -0,0 +1,44 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+
+import java.util.BitSet;
+
+public class SubFNode extends Node {
+    public SubFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "SubF"; }
+
+    @Override public String glabel() { return "-"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("-"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        if (in(1)._type instanceof TypeFloat i0 &&
+            in(2)._type instanceof TypeFloat i1) {
+            if (i0.isConstant() && i1.isConstant())
+                return TypeFloat.constant(i0.value()-i1.value());
+        }
+        return in(1)._type.meet(in(2)._type);
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Type t2 = in(2)._type;
+
+        // Sub of 0.
+        if ( t2.isConstant() && t2 instanceof TypeFloat i && i.value()==0 )
+            return lhs;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new SubFNode(lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/SubNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/SubNode.java
new file mode 100644
index 00000000..339c65ca
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/SubNode.java
@@ -0,0 +1,59 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class SubNode extends Node {
+    public SubNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
+
+    @Override public String label() { return "Sub"; }
+
+    @Override public String glabel() { return "-"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        in(1)._print0(sb.append("("), visited);
+        in(2)._print0(sb.append("-"), visited);
+        return sb.append(")");
+    }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        // Sub of same is 0
+        if( in(1)==in(2) )
+            return TypeInteger.ZERO;
+        if( t1 instanceof TypeInteger i1 &&
+            t2 instanceof TypeInteger i2 ) {
+            if (i1.isConstant() && i2.isConstant())
+                return TypeInteger.constant(i1.value()-i2.value());
+            // Fold ranges like {2-3} - {0-1} into {1-3}.
+            if( !AddNode.overflow(i1._min,-i2._max) &&
+                !AddNode.overflow(i1._max,-i2._min) &&
+                i2._min != Long.MIN_VALUE  )
+                return TypeInteger.make(i1._min-i2._max,i1._max-i2._min);
+        }
+
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        // x - (-y) is x+y
+        if( in(2) instanceof MinusNode minus )
+            return new AddNode(in(1),minus.in(1));
+
+        // (-x) - y is -(x+y)
+        if( in(1) instanceof MinusNode minus )
+            return new MinusNode(new AddNode(minus.in(1),in(2)).peephole());
+
+        return null;
+    }
+
+    @Override Node copy(Node lhs, Node rhs) { return new SubNode(lhs,rhs); }
+    @Override Node copyF() { return new SubFNode(null,null); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java
new file mode 100644
index 00000000..1f4d67e0
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java
@@ -0,0 +1,34 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFloat;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.util.BitSet;
+
+public class ToFloatNode extends Node {
+    public ToFloatNode(Node lhs) { super(null, lhs); }
+
+    @Override public String label() { return "ToFloat"; }
+
+    @Override public String glabel() { return "(flt)"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return in(1)._print0(sb.append("(flt)"), visited);
+    }
+
+    @Override
+    public Type compute() {
+        if( in(1)._type == Type.NIL ) return TypeFloat.FZERO;
+        if (in(1)._type instanceof TypeInteger i0 ) {
+            if( i0.isHigh() ) return TypeFloat.F64.dual();
+            if( i0.isConstant() )
+                return TypeFloat.constant(i0.value());
+        }
+        return TypeFloat.F64;
+    }
+
+    @Override public Node idealize() { return null; }
+    @Override Node copy(Node lhs, Node rhs) { return new ToFloatNode(lhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java
new file mode 100644
index 00000000..9b4245c7
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java
@@ -0,0 +1,16 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import java.util.BitSet;
+
+public class XCtrlNode extends CFGNode {
+    public XCtrlNode() { super(new Node[]{CodeGen.CODE._start}); }
+    @Override public String label() { return "Xctrl"; }
+    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Xctrl"); }
+    @Override public boolean isConst() { return true; }
+    @Override public boolean isMultiTail() { return true; }
+    @Override  public Type compute() { return Type.XCONTROL; }
+    @Override public Node idealize() { return null; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/XorNode.java b/chapter20/src/main/java/com/seaofnodes/simple/node/XorNode.java
new file mode 100644
index 00000000..37d7147d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/XorNode.java
@@ -0,0 +1,54 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.BitSet;
+
+public class XorNode extends LogicalNode {
+    public XorNode(Parser.Lexer loc, Node lhs, Node rhs) { super(loc, lhs, rhs); }
+
+    @Override public String label() { return "Xor"; }
+    @Override public String op() { return "^"; }
+
+    @Override public String glabel() { return "^"; }
+
+    @Override
+    public Type compute() {
+        Type t1 = in(1)._type, t2 = in(2)._type;
+        if( t1.isHigh() || t2.isHigh() )
+            return TypeInteger.TOP;
+        if( t1 instanceof TypeInteger i0 &&
+            t2 instanceof TypeInteger i1 ) {
+            if( i0.isConstant() && i1.isConstant() )
+                return TypeInteger.constant(i0.value()^i1.value());
+        }
+        return TypeInteger.BOT;
+    }
+
+    @Override
+    public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        // Xor of 0.  We do not check for (0^x) because this will already
+        // canonicalize to (x^0)
+        if( t2.isConstant() && t2 instanceof TypeInteger i && i.value()==0 )
+            return lhs;
+
+        // Move constants to RHS: con*arg becomes arg*con
+        if ( t1.isConstant() && !t2.isConstant() )
+            return swap12();
+
+        // Do we have ((x ^ (phi cons)) ^ con) ?
+        // Do we have ((x ^ (phi cons)) ^ (phi cons)) ?
+        // Push constant up through the phi: x ^ (phi con0^con0 con1^con1...)
+        Node phicon = AddNode.phiCon(this,true);
+        if( phicon!=null ) return phicon;
+
+        return null;
+    }
+    @Override Node copy(Node lhs, Node rhs) { return new XorNode(_loc,lhs,rhs); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFMemX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFMemX86.java
new file mode 100644
index 00000000..4f75edcd
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFMemX86.java
@@ -0,0 +1,33 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.*;
+
+public class AddFMemX86 extends MemOpX86 {
+    AddFMemX86( AddFNode add, LoadNode ld , Node base, Node idx, int off, int scale, Node val ) {
+        super(add,ld, base, idx, off, scale, 0, val );
+    }
+
+    @Override public RegMask regmap(int i) {
+        if( i==1 ) return RegMask.EMPTY;    // Memory
+        if( i==2 ) return x86_64_v2.RMASK;  // base
+        if( i==3 ) return x86_64_v2.RMASK;  // index
+        if( i==4 ) return x86_64_v2.XMASK;  // value
+        throw Utils.TODO();
+    }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+
+
+    // General form: "add  dst = src + [base + idx<<2 + 12]"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ");
+        sb.p(val()==null ? "#"+_imm : code.reg(val())).p(" + ");
+        asm_address(code,sb);
+    }
+    @Override public String op() { return "addf"+_sz; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFX86.java
new file mode 100644
index 00000000..a3f5c7b3
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddFX86.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class AddFX86 extends MachConcreteNode implements MachNode {
+    AddFX86( Node addf ) { super(addf); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.XMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "addf  dst += src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" + ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "addf"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddIX86.java
new file mode 100644
index 00000000..6a332ff5
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddIX86.java
@@ -0,0 +1,39 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class AddIX86 extends MachConcreteNode implements MachNode {
+    final TypeInteger _ti;
+    AddIX86( Node add, TypeInteger ti ) {
+        super(add);
+        _inputs.pop();
+         _ti = ti;
+    }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) {
+        // assert i== i;
+        return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "addi  dst += #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" + #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() {
+        return _ti.value() == 1  ? "inc" : (_ti.value() == -1 ? "dec" : "addi");
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddMemX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddMemX86.java
new file mode 100644
index 00000000..7d45d757
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddMemX86.java
@@ -0,0 +1,25 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.*;
+
+public class AddMemX86 extends MemOpX86 {
+    AddMemX86( AddNode add, LoadNode ld , Node base, Node idx, int off, int scale, int imm, Node val ) {
+        super(add,ld, base, idx, off, scale, imm, val );
+    }
+
+    @Override public String op() { return "add"+_sz; }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // General form: "add  dst = src + [base + idx<<2 + 12]"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ");
+        sb.p(val()==null ? "#"+_imm : code.reg(val())).p(" + ");
+        asm_address(code,sb);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddX86.java
new file mode 100644
index 00000000..61aa5a9e
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AddX86.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class AddX86 extends MachConcreteNode implements MachNode {
+    AddX86( Node add ) { super(add); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "add  dst += src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" + ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "add"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AndIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AndIX86.java
new file mode 100644
index 00000000..f2ee1c66
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/AndIX86.java
@@ -0,0 +1,42 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+import java.lang.StringBuilder;
+
+public class AndIX86 extends MachConcreteNode implements MachNode {
+    final TypeInteger _ti;
+    AndIX86(Node and, TypeInteger ti) {
+    super(and);
+    _inputs.pop();
+    _ti = ti;
+    }
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "andi  dst & #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" & #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "andi"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallRX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallRX86.java
new file mode 100644
index 00000000..31d303ed
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallRX86.java
@@ -0,0 +1,31 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.io.ByteArrayOutputStream;
+
+public class CallRX86 extends CallNode implements MachNode {
+    CallRX86( CallNode call ) { super(call); }
+
+    @Override public String label() { return op(); }
+    @Override public RegMask regmap(int i) {
+        return i==_inputs._len
+            ? x86_64_v2.WMASK          // Function call target
+            : x86_64_v2.callInMask(i); // Normal argument
+    }
+    @Override public RegMask outregmap() { return x86_64_v2.RET_MASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(fptr()));
+    }
+
+    @Override public String op() { return "callr"; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallX86.java
new file mode 100644
index 00000000..9c246c24
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CallX86.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+
+public class CallX86 extends CallNode implements MachNode {
+    final TypeFunPtr _tfp;
+    final String _name;
+    CallX86( CallNode call, TypeFunPtr tfp ) {
+        super(call);
+        _inputs.pop(); // Pop constant target
+        assert tfp.isConstant();
+        _tfp = tfp;
+        _name = CodeGen.CODE.link(tfp)._name;
+    }
+
+    @Override public String label() { return op(); }
+    @Override public RegMask regmap(int i) {
+        return x86_64_v2.callInMask(i); // Normal argument
+    }
+    @Override public RegMask outregmap() { return x86_64_v2.RET_MASK; }
+
+    @Override public String name() { return _name; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(_name);
+    }
+
+    @Override public String op() { return "call"; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpIX86.java
new file mode 100644
index 00000000..2fa7fbb1
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpIX86.java
@@ -0,0 +1,43 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+// Compare immediate.  Sets flags.
+public class CmpIX86 extends MachConcreteNode implements MachNode {
+    final int _imm;
+    final String _bop;
+    CmpIX86( BoolNode bool, TypeInteger ti ) {
+        super(bool);
+        _inputs.pop(); // Toss ideal ConstantNode away, embedded into machine op
+        _bop = bool.op();       // One of <,<=,==
+        _imm = (int)ti.value();
+        assert _imm == ti.value();
+    }
+    CmpIX86( Node cmp, double ignore ) {
+        super(cmp);
+        _bop = "==";
+        _imm = 0;
+    }
+
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.RMASK; }
+    @Override public RegMask outregmap() { return x86_64_v2.FLAGS_MASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    @Override public void asm(CodeGen code, SB sb) {
+        String dst = code.reg(this);
+        if( dst!="FLAGS" )  sb.p(dst).p(" = ");
+        sb.p(code.reg(in(1)));
+        if( _imm != 0 ) sb.p(", #").p(_imm);
+    }
+
+    @Override public String op() { return _imm==0 ? "test" : "cmp"; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpMemX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpMemX86.java
new file mode 100644
index 00000000..873ca9df
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpMemX86.java
@@ -0,0 +1,33 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.*;
+
+public class CmpMemX86 extends MemOpX86 {
+    final boolean _invert;      // Op switched LHS, RHS
+    CmpMemX86( BoolNode bool, LoadNode ld , Node base, Node idx, int off, int scale, int imm, Node val, boolean invert ) {
+        super(bool,ld, base, idx, off, scale, imm, val );
+        _invert = invert;
+    }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.FLAGS_MASK; }
+
+    // General form: "cmp  dst = src, [base + idx<<2 + 12]"
+    @Override public void asm(CodeGen code, SB sb) {
+        String dst = code.reg(this);
+        if( dst!="FLAGS" )  sb.p(dst).p(" = ");
+        if( _invert ) asm_address(code,sb).p(",");
+        if( val()==null ) {
+            if( _imm!=0 )  sb.p("#").p(_imm);
+        } else {
+            sb.p(code.reg(val()));
+        }
+        if( !_invert ) asm_address(code,sb.p(", "));
+    }
+
+    @Override public String op() { return ((val()==null && _imm==0) ? "test" : "cmp") + _sz; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpX86.java
new file mode 100644
index 00000000..6b502249
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/CmpX86.java
@@ -0,0 +1,27 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class CmpX86 extends MachConcreteNode implements MachNode {
+    CmpX86( Node cmp ) { super(cmp); }
+
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.RMASK; }
+    @Override public RegMask outregmap() { return x86_64_v2.FLAGS_MASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "add  dst += src"
+    @Override public void asm(CodeGen code, SB sb) {
+        String dst = code.reg(this);
+        if( dst!="FLAGS" )  sb.p(dst).p(" = ");
+        sb.p(code.reg(in(1))).p(", ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "cmp"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivFX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivFX86.java
new file mode 100644
index 00000000..d73bfd5b
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivFX86.java
@@ -0,0 +1,33 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class DivFX86 extends MachConcreteNode implements MachNode {
+    DivFX86( Node divf) { super(divf); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.XMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() {  return x86_64_v2.XMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+
+    // General form: "divf  dst /= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" / ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() {
+        // 8 bytes = 64 bits
+        return "divf";
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivX86.java
new file mode 100644
index 00000000..1dc20017
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/DivX86.java
@@ -0,0 +1,31 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class DivX86 extends MachConcreteNode implements MachNode {
+    DivX86( Node div ) { super(div); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) {
+        assert i==1 || i==2;
+        return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "div  dst /= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" / ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "div"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FltX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FltX86.java
new file mode 100644
index 00000000..21529f7b
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FltX86.java
@@ -0,0 +1,36 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.ConstantNode;
+import com.seaofnodes.simple.node.MachNode;
+
+import java.io.ByteArrayOutputStream;
+
+public class FltX86 extends ConstantNode implements MachNode {
+    FltX86(ConstantNode con ) { super(con); }
+
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // General int registers
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // Human-readable form appended to the SB.  Things like the encoding,
+    // indentation, leading address or block labels not printed here.
+    // Just something like "ld4\tR17=[R18+12] // Load array base".
+    // General form: "op\tdst=src+src"
+    @Override public void asm(CodeGen code, SB sb) {
+        _con.print(sb.p(code.reg(this)).p(" #"));
+    }
+
+    @Override public String op() {
+        return "fld";           // Some fancier encoding
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java
new file mode 100644
index 00000000..f969fae4
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java
@@ -0,0 +1,21 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.FunNode;
+import com.seaofnodes.simple.node.MachNode;
+import java.io.ByteArrayOutputStream;
+
+public class FunX86 extends FunNode implements MachNode {
+    FunX86( FunNode fun ) { super(fun); }
+
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/I2f8X86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/I2f8X86.java
new file mode 100644
index 00000000..983f817d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/I2f8X86.java
@@ -0,0 +1,28 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class I2f8X86 extends MachConcreteNode implements MachNode {
+    I2f8X86(Node i2f8 ) { super(i2f8); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "i2f8 (flt)int_value"
+
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p("(flt)").p(code.reg(in(1)));
+    }
+
+    @Override public String op() { return "i2f8"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/IntX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/IntX86.java
new file mode 100644
index 00000000..2cd27c14
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/IntX86.java
@@ -0,0 +1,45 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.ConstantNode;
+import com.seaofnodes.simple.node.MachNode;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.io.ByteArrayOutputStream;
+
+// Integer constants
+public class IntX86 extends ConstantNode implements MachNode {
+
+    IntX86( ConstantNode con ) {
+        super(con);
+    }
+
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // General int registers
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // Human-readable form appended to the SB.  Things like the encoding,
+    // indentation, leading address or block labels not printed here.
+    // Just something like "ld4\tR17=[R18+12] // Load array base".
+    // General form: "op\tdst=src+src"
+    @Override public void asm(CodeGen code, SB sb) {
+        String reg = code.reg(this);
+        if( _con == Type.NIL || _con == TypeInteger.ZERO )
+            sb.p(reg).p(",").p(reg);
+        else
+            _con.print(sb.p(reg).p(" #"));
+    }
+
+    @Override public String op() {
+        if( _con == Type.NIL || _con == TypeInteger.ZERO )
+            return "xor";
+        return "ldi";           // Some fancier encoding
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java
new file mode 100644
index 00000000..7cf4444c
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java
@@ -0,0 +1,46 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+// Jump on flags, uses flags
+public class JmpX86 extends IfNode implements MachNode {
+    final String _bop;
+    JmpX86( IfNode iff, String bop ) {
+        super(iff);
+        _bop = bop;
+    }
+
+    @Override public String label() { return op(); }
+
+    @Override public void postSelect() {
+        Node set = in(1);
+        Node cmp = set.in(1);
+        // Bypass an expected Set and just reference the cmp directly
+        if( set instanceof SetX86 && (cmp instanceof CmpX86 || cmp instanceof CmpIX86 || cmp instanceof CmpMemX86) )
+            _inputs.set(1,cmp);
+        else
+            throw Utils.TODO();
+    }
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.FLAGS_MASK; }
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    @Override public void asm(CodeGen code, SB sb) {
+        String src = code.reg(in(1));
+        if( src!="FLAGS" )  sb.p(src);
+    }
+
+    @Override public String op() { return "j"+_bop; }
+
+    @Override public String comment() {
+        return "L"+cproj(1)._nid+", L"+cproj(0)._nid;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LeaX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LeaX86.java
new file mode 100644
index 00000000..a49b8d7f
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LeaX86.java
@@ -0,0 +1,42 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class LeaX86 extends MachConcreteNode implements MachNode {
+    final int _scale;
+    final long _offset;
+    LeaX86( Node add, Node base, Node idx, int scale, long offset ) {
+        super(add);
+        assert scale==1 || scale==2 || scale==4 || scale==8;
+        _inputs.pop();
+        _inputs.pop();
+        _inputs.push(base);
+        _inputs.push(idx);
+        _scale = scale;
+        _offset = offset;
+    }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "lea  dst = base + 4*idx + 12"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ");
+        if( in(1) != null )
+            sb.p(code.reg(in(1))).p(" + ");
+        sb.p(code.reg(in(2))).p("*").p(_scale);
+        if( _offset!=0 ) sb.p(" + #").p(_offset);
+    }
+
+    @Override public String op() { return "lea"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LoadX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LoadX86.java
new file mode 100644
index 00000000..02a9a4fe
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/LoadX86.java
@@ -0,0 +1,25 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.LoadNode;
+import com.seaofnodes.simple.node.Node;
+
+public class LoadX86 extends MemOpX86 {
+    LoadX86( LoadNode ld, Node base, Node idx, int off, int scale ) {
+        super(ld,ld, base, idx, off, scale, 0);
+    }
+
+    @Override public String op() { return "ld"+_sz; }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // General form: "ldN  dst,[base + idx<<2 + 12]"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(",");
+        asm_address(code,sb);
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemAddX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemAddX86.java
new file mode 100644
index 00000000..418f63f3
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemAddX86.java
@@ -0,0 +1,28 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.*;
+
+public class MemAddX86 extends MemOpX86 {
+    MemAddX86( StoreNode st, Node base, Node idx, int off, int scale, int imm, Node val ) {
+        super(st, st, base, idx, off, scale, imm, val );
+    }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+
+    // General form: "add  [base + idx<<2 + 12] += src"
+    @Override public void asm(CodeGen code, SB sb) {
+        asm_address(code,sb);
+        if( val()==null ) {
+            if( _imm != 1 && _imm != -1 ) sb.p(" += #").p(_imm);
+        } else sb.p(" += ").p(code.reg(val()));
+    }
+
+    @Override public String op() {
+        return (_imm == 1 ? "inc" : (_imm == -1 ? "dec" : "add")) + _sz;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java
new file mode 100644
index 00000000..1e678a0b
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java
@@ -0,0 +1,87 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.io.ByteArrayOutputStream;
+import java.lang.StringBuilder;
+import java.util.BitSet;
+
+// Generic X86 memory operand base.
+// inputs:
+//   ctrl     - will appear for possibly RCE (i.e. array ops)
+//   mem      - memory dependence edge
+//   base     - Basic object pointer
+//   idx/null - Scaled index offset, or null if none
+//   val/null - Value to store, as part of a op-to-mem or op-from-mem.  Null for loads, or if an immediate is being used
+// Constants:
+//   offset   - offset added to base.  Can be zero.
+//   scale    - scale on index; only 0,1,2,4,8 allowed, 0 is only when index is null
+//   imm      - immediate value to store or op-to-mem, and only when val is null
+public abstract class MemOpX86 extends MemOpNode implements MachNode {
+    final int _off;             // Limit 32 bits
+    final int _scale;           // Limit 0,1,2,3
+    final int _imm;             // Limit 32 bits
+    final char _sz = (char)('0'+(1<<_declaredType.log_size()));
+    MemOpX86( Node op, MemOpNode mop, Node base, Node idx, int off, int scale, int imm ) {
+        super(op,mop);
+        assert base._type instanceof TypeMemPtr && !(base instanceof AddNode);
+        assert (idx==null && scale==0) || (idx!=null && 0<= scale && scale<=3);
+
+        // Copy memory parts from eg the LoadNode over the opcode, e.g. an Add
+        if( op != mop ) {
+            _inputs.set(0,mop.in(0)); // Control from mem op
+            _inputs.set(1,mop.in(1)); // Memory  from mem op
+            _inputs.set(2,base);      // Base handed in
+        }
+
+        assert ptr() == base;
+        _inputs.setX(3,idx);
+        _off = off;
+        _scale = scale;
+        _imm = imm;
+    }
+
+    // Store-based flavors have a value edge
+    MemOpX86( Node op, MemOpNode mop, Node base, Node idx, int off, int scale, int imm, Node val ) {
+        this(op,mop,base,idx,off,scale,imm);
+        _inputs.setX(4,val);
+    }
+
+    Node idx() { return in(3); }
+    Node val() { return in(4); }
+
+    @Override public  StringBuilder _printMach(StringBuilder sb, BitSet visited) { return sb.append(".").append(_name); }
+
+    @Override public String label() { return op(); }
+    @Override public Type compute() { throw Utils.TODO(); }
+    @Override public Node idealize() { throw Utils.TODO(); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) {
+        if( i==1 ) return RegMask.EMPTY;    // Memory
+        if( i==2 ) return x86_64_v2.RMASK;  // base
+        if( i==3 ) return x86_64_v2.RMASK;  // index
+        if( i==4 ) return x86_64_v2.RMASK;  // value
+        throw Utils.TODO();
+    }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { throw Utils.TODO(); }
+
+    @Override public int encoding(ByteArrayOutputStream bytes) { throw Utils.TODO(); }
+
+
+    // "[base + idx<<2 + 12]"
+    SB asm_address(CodeGen code, SB sb) {
+        sb.p("[").p(code.reg(ptr()));
+        if( idx() != null ) {
+            sb.p("+").p(code.reg(idx()));
+            if( _scale != 0 )
+                sb.p("<<").p(_scale);
+        }
+        if( _off != 0 )
+            sb.p("+").p(_off);
+        return sb.p("]");
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulFX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulFX86.java
new file mode 100644
index 00000000..aef813e1
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulFX86.java
@@ -0,0 +1,30 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeFloat;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class MulFX86 extends MachConcreteNode implements MachNode {
+    MulFX86( Node mulf) { super(mulf); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.XMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "mulf  dst *= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" * ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "mulf"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulIX86.java
new file mode 100644
index 00000000..7508cf4c
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulIX86.java
@@ -0,0 +1,36 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class MulIX86 extends MachConcreteNode  implements MachNode {
+    final TypeInteger _ti;
+    MulIX86(Node mul, TypeInteger ti) {super(mul); _inputs.pop(); _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        // assert i==1;
+        return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+    // General form
+    // General form: "muli  dst * #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" * #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "muli"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulX86.java
new file mode 100644
index 00000000..15fd9496
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MulX86.java
@@ -0,0 +1,30 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class MulX86 extends MachConcreteNode implements MachNode {
+
+    MulX86( Node mul ) { super(mul); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "mul  dst *= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" * ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "mul"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/NewX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/NewX86.java
new file mode 100644
index 00000000..4396a917
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/NewX86.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import java.io.ByteArrayOutputStream;
+
+public class NewX86 extends NewNode implements MachNode {
+
+    // A pre-zeroed chunk of memory.
+    NewX86( NewNode nnn ) {  super(nnn); }
+
+    // Register mask allowed on input i, the size
+    @Override public RegMask regmap(int i) {
+        // Size
+        if( i==1 ) return x86_64_v2.RDI_MASK;
+        // All the memory alias edges
+        return RegMask.EMPTY;
+    }
+    @Override public RegMask outregmap() { throw Utils.TODO(); }
+
+    // Register mask allowed as a result.  Pointer result in standard calling
+    // convention.
+    @Override public RegMask outregmap(int i) {
+        if( i == 1 ) return x86_64_v2.RET_MASK;
+        // All the memory aliases edges
+        return RegMask.EMPTY;
+    }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "alloc #bytes"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(size()));
+    }
+
+    @Override public String op() { return "alloc"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/OrIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/OrIX86.java
new file mode 100644
index 00000000..513962c2
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/OrIX86.java
@@ -0,0 +1,44 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.MachConcreteNode;
+import com.seaofnodes.simple.node.MachNode;
+import com.seaofnodes.simple.node.Node;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.io.ByteArrayOutputStream;
+
+public class OrIX86  extends MachConcreteNode implements MachNode {
+
+    final TypeInteger _ti;
+    OrIX86(Node or, TypeInteger ti) {super(or);  _inputs.pop(); _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        //assert i==1;
+        return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "ori  ori | #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" | #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "ori"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ParmX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ParmX86.java
new file mode 100644
index 00000000..8a439644
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ParmX86.java
@@ -0,0 +1,24 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.ParmNode;
+import com.seaofnodes.simple.node.MachNode;
+import java.io.ByteArrayOutputStream;
+
+public class ParmX86 extends ParmNode implements MachNode {
+    final RegMask _rmask;
+    ParmX86( ParmNode parm ) {
+        super(parm);
+        _rmask = x86_64_v2.callInMask(_idx);
+    }
+
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // Register mask allowed as a result.  Calling convention register
+    @Override public RegMask outregmap() { return _rmask; }
+
+    // Encoding is appended into the byte array.  Returns size
+    @Override public int encoding(ByteArrayOutputStream bytes) { return 0; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ProjX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ProjX86.java
new file mode 100644
index 00000000..2849b232
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ProjX86.java
@@ -0,0 +1,23 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.ProjNode;
+import com.seaofnodes.simple.node.MachNode;
+import java.io.ByteArrayOutputStream;
+
+public class ProjX86 extends ProjNode implements MachNode {
+
+    ProjX86( ProjNode p ) { super(p); }
+
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/RetX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/RetX86.java
new file mode 100644
index 00000000..e6219ff4
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/RetX86.java
@@ -0,0 +1,48 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.FunNode;
+import com.seaofnodes.simple.node.ReturnNode;
+import com.seaofnodes.simple.node.MachNode;
+import java.io.ByteArrayOutputStream;
+
+// Return
+public class RetX86 extends ReturnNode implements MachNode {
+    RetX86( ReturnNode ret, FunNode fun ) { super(ret, fun); fun.setRet(this); }
+
+    // Correct Nodes outside the normal edges
+    @Override public void postSelect() {
+        FunNode fun = (FunNode)rpc().in(0);
+        _fun = fun;
+        fun.setRet(this);
+    }
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        return switch( i ) {
+        case 0 -> RegMask.EMPTY;
+        case 1 -> RegMask.EMPTY;
+        case 2 -> x86_64_v2.RET_MASK;
+        case 3 -> RegMask.EMPTY; // RPC is always on stack
+        default -> throw Utils.TODO();
+        };
+    }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // Human-readable form appended to the SB.  Things like the encoding,
+    // indentation, leading address or block labels not printed here.
+    // Just something like "ld4\tR17=[R18+12] // Load array base".
+    // General form: "op\tdst=src+src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "ret"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SarX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SarX86.java
new file mode 100644
index 00000000..3d907eef
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SarX86.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+import java.lang.StringBuilder;
+
+
+public class SarX86 extends MachConcreteNode implements MachNode {
+    final TypeInteger _ti;
+    SarX86(Node sar, TypeInteger ti) {super(sar); _inputs.pop();  _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        // assert i==1;
+        return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "sari  dst << #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" >> #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "sari"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SetX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SetX86.java
new file mode 100644
index 00000000..25367e03
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SetX86.java
@@ -0,0 +1,39 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+// Compare immediate.  Sets flags.
+// Corresponds to the x86 instruction "sete && setne".
+// Use result of comparison without jump.
+public class SetX86 extends MachConcreteNode implements MachNode {
+    final String _bop;          // One of <,<=,==
+    // Constructor expects input is an X86 and not an Ideal node.
+    SetX86( Node cmp, String bop ) {
+        super(cmp);
+        _inputs.setLen(1);   // Pop the cmp inputs
+        // Replace with the matched cmp
+        _inputs.push(cmp);
+        _bop = bop;
+    }
+
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.FLAGS_MASK; }
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this));
+        String src = code.reg(in(1));
+        if( src!="FLAGS" )  sb.p(" = ").p(src);
+    }
+
+    @Override public String op() { return "set"+_bop; }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShlIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShlIX86.java
new file mode 100644
index 00000000..61e0d262
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShlIX86.java
@@ -0,0 +1,38 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+
+public class ShlIX86 extends MachConcreteNode implements MachNode{
+    final TypeInteger _ti;
+    ShlIX86(Node shl, TypeInteger ti) {super(shl); _inputs.pop(); _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        //assert i==1;
+        return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "shli  dst << #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" << #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "shli"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShrIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShrIX86.java
new file mode 100644
index 00000000..08cae93e
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/ShrIX86.java
@@ -0,0 +1,39 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+import java.util.BitSet;
+import java.lang.StringBuilder;
+
+public class ShrIX86 extends MachConcreteNode implements MachNode{
+    final TypeInteger _ti;
+    ShrIX86(Node shr, TypeInteger ti) {super(shr); _inputs.pop(); _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) {
+        //assert i==1;
+        return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "shri  dst >>> #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" >>> #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "shri"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/StoreX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/StoreX86.java
new file mode 100644
index 00000000..c9191b87
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/StoreX86.java
@@ -0,0 +1,30 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.node.Node;
+import com.seaofnodes.simple.node.StoreNode;
+import java.util.BitSet;
+
+public class StoreX86 extends MemOpX86 {
+    StoreX86( StoreNode st, Node base, Node idx, int off, int scale, int imm, Node val ) {
+        super(st,st, base, idx, off, scale, imm, val);
+    }
+
+    @Override public String op() { return "st"+_sz; }
+
+    @Override public StringBuilder _printMach(StringBuilder sb, BitSet visited) {
+        return sb.append(".").append(_name).append("=").append(val()==null ? _imm : val()).append(";");
+    }
+
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return RegMask.EMPTY; }
+
+    // General form: "stN  [base + idx<<2 + 12],val"
+    @Override public void asm(CodeGen code, SB sb) {
+        asm_address(code,sb).p(",");
+        if( val()==null ) sb.p("#").p(_imm);
+        else sb.p(code.reg(val()));
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubFX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubFX86.java
new file mode 100644
index 00000000..ed19ad79
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubFX86.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import java.io.ByteArrayOutputStream;
+
+public class SubFX86 extends MachConcreteNode implements MachNode {
+    SubFX86( Node subf) {  super(subf); }
+
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.XMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.XMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "subf  dst -= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" - ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "subf"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubX86.java
new file mode 100644
index 00000000..cac59d3b
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SubX86.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.ByteArrayOutputStream;
+
+public class SubX86 extends MachConcreteNode implements MachNode {
+    SubX86( Node sub ) { super(sub); }
+
+    // Register mask allowed on input i.
+    @Override public RegMask regmap(int i) { assert i==1 || i==2; return x86_64_v2.RMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form: "sub  dst -= src"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" - ").p(code.reg(in(2)));
+    }
+
+    @Override public String op() { return "sub"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/TFPX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/TFPX86.java
new file mode 100644
index 00000000..bd88011f
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/TFPX86.java
@@ -0,0 +1,41 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.*;
+import com.seaofnodes.simple.node.ConstantNode;
+import com.seaofnodes.simple.node.MachNode;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeFunPtr;
+
+import java.io.ByteArrayOutputStream;
+
+// Function constants
+public class TFPX86 extends ConstantNode implements MachNode {
+    TFPX86( ConstantNode con ) {  super(con); }
+    // Register mask allowed on input i.  0 for no register.
+    @Override public RegMask regmap(int i) { return RegMask.EMPTY; }
+    // General int registers
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // Human-readable form appended to the SB.  Things like the encoding,
+    // indentation, leading address or block labels not printed here.
+    // Just something like "ld4\tR17=[R18+12] // Load array base".
+    // General form: "op\tdst=src+src"
+    @Override public void asm(CodeGen code, SB sb) {
+        String reg = code.reg(this);
+        if( _con == Type.NIL )
+            sb.p(reg).p(",").p(reg);
+        else
+            _con.print(sb.p(reg).p(" #"));
+    }
+
+    @Override public String op() {
+        if( _con == Type.NIL )
+            return "xor";
+        return "ldx";           // Some fancier encoding
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/XorIX86.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/XorIX86.java
new file mode 100644
index 00000000..795fa814
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/XorIX86.java
@@ -0,0 +1,42 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.MachConcreteNode;
+import com.seaofnodes.simple.node.MachNode;
+import com.seaofnodes.simple.node.Node;
+import com.seaofnodes.simple.type.TypeInteger;
+
+import java.io.ByteArrayOutputStream;
+
+public class XorIX86  extends MachConcreteNode implements MachNode {
+
+    final TypeInteger _ti;
+    XorIX86(Node xor, TypeInteger ti) {super(xor); _inputs.pop(); _ti = ti;}
+
+    // Register mask allowed on input i.
+    // This is the normal calling convention
+    @Override public RegMask regmap(int i) { assert i==1; return x86_64_v2.WMASK; }
+    // Register mask allowed as a result.  0 for no register.
+    @Override public RegMask outregmap() { return x86_64_v2.WMASK; }
+
+
+    // Output is same register as input#1
+    @Override public int twoAddress() { return 1; }
+
+    // Encoding is appended into the byte array; size is returned
+    @Override public int encoding(ByteArrayOutputStream bytes) {
+        throw Utils.TODO();
+    }
+
+    // General form
+    // General form: "ori  xori ^ #imm"
+    @Override public void asm(CodeGen code, SB sb) {
+        sb.p(code.reg(this)).p(" = ").p(code.reg(in(1))).p(" ^ #");
+        _ti.print(sb);
+    }
+
+    @Override public String op() { return "xori"; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
new file mode 100644
index 00000000..45ae19dc
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
@@ -0,0 +1,418 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.Machine;
+import com.seaofnodes.simple.RegMask;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+
+public class x86_64_v2 extends Machine {
+    // X86-64 V2.  Includes e.g. SSE4.2 and POPCNT.
+    @Override public String name() { return "x86_64_v2"; }
+
+    public static int RAX =  0, RCX =  1, RDX =  2, RBX =  3, RSP =  4, RBP =  5, RSI =  6, RDI =  7;
+    public static int R08 =  8, R09 =  9, R10 = 10, R11 = 11, R12 = 12, R13 = 13, R14 = 14, R15 = 15;
+    public static int FLAGS = 32;
+
+    public static int XMM0  = 16, XMM1  = 17, XMM2  = 18, XMM3  = 19, XMM4  = 20, XMM5  = 21, XMM6  = 22, XMM7  = 23;
+    public static int XMM8  = 24, XMM9  = 25, XMM10 = 26, XMM11 = 27, XMM12 = 28, XMM13 = 29, XMM14 = 30, XMM15 = 31;
+
+    // General purpose register mask: pointers and ints, not floats
+    public static RegMask RMASK = new RegMask(0b1111111111111111);
+    // No RSP in the *write* general set.
+    public static RegMask WMASK = new RegMask(0b1111111111101111);
+    // Xmm register mask
+    public static RegMask XMASK = new RegMask( 0b1111111111111111L << XMM0);
+
+    public static RegMask FLAGS_MASK = new RegMask(1L<<FLAGS);
+
+    // Return single int/ptr register
+    public static RegMask RET_MASK = new RegMask(RAX);
+
+    public static RegMask RDI_MASK = new RegMask(1L<<RDI);
+    public static RegMask RCX_MASK = new RegMask(1L<<RCX);
+    public static RegMask RDX_MASK = new RegMask(1L<<RDX);
+    public static RegMask R08_MASK = new RegMask(1L<<R08);
+    public static RegMask R09_MASK = new RegMask(1L<<R09);
+    public static RegMask RSI_MASK = new RegMask(1L<<RSI);
+
+    // Calling conv metadata
+    public int GPR_COUNT_CONV_WIN64 = 4; // RCX, RDX, R9, R9
+    public int XMM_COUNT_CONV_WIN64 = 4; // XMM0L, XMM1L, XMM2L, XMM3L
+
+    public int GPR_COUNT_CONV_SYSTEM_V = 6; // RDI, RSI, RDX, RCX, R8, R9
+    public int XMM_COUNT_CONV_SYSTEM_V = 4; // XMM0, XMM1, XMM2, XMM3 ....
+    // Human-readable name for a register number, e.g. "RAX".
+    // Hard crash for bad register number, fix yer bugs!
+    public static final String[] REGS = new String[] {
+        "rax" , "rcx" , "rdx"  , "rbx"  , "rsp"  , "rbp"  , "rsi"  , "rdi"  ,
+        "r8"  , "r9"  , "r10"  , "r11"  , "r12"  , "r13"  , "r14"  , "r15"  ,
+        "xmm0", "xmm1", "xmm2" , "xmm3" , "xmm4" , "xmm5" , "xmm6" , "xmm7" ,
+        "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15",
+    };
+    @Override public String reg( int reg ) { return REGS[reg]; }
+
+    // Calling convention; returns a machine-specific register
+    // for incoming argument idx.
+    // index 0 for control, 1 for memory, real args start at index 2
+    static int callInArg( int idx ) {
+        return switch( CodeGen.CODE._callingConv ) {
+        case CodeGen.CallingConv.SystemV -> callInArgSystemV(idx);
+        case CodeGen.CallingConv.Win64   -> callInArgWin64  (idx);
+        };
+    }
+
+    // WIN64(param passing)
+    static RegMask[] CALLINMASK_WIN64 = new RegMask[] {
+        RegMask.EMPTY,
+        RegMask.EMPTY,
+        RCX_MASK,
+        RDX_MASK,
+        R08_MASK,
+        R09_MASK,
+        RegMask.EMPTY,
+        RegMask.EMPTY
+    };
+    static int[] CALLINARG_WIN64 = new int[] {
+        0,   // Control, no register
+        0,   // Memory, no register
+        RCX, //
+        RDX,
+        R08,
+        R09,
+        0,
+        0,
+    };
+    static int callInArgWin64( int idx ) { return CALLINARG_WIN64[idx]; }
+
+    // caller saved(win64)
+    public static final long WIN64_ABI_CALLER_SAVED =
+        (1L << RAX) | (1L << RCX) | (1L << RDX) | (1L << R08) | (1L << R09) | (1L << R10) | (1L << R11);
+
+    // callee saved(win64)
+    public static final long WIN64_ABI_CALLEE_SAVED = ~WIN64_ABI_CALLER_SAVED;
+
+    // SystemV(param passing)
+    static RegMask[] CALLINMASK_SYSTEMV = new RegMask[] {
+        RegMask.EMPTY,
+        RegMask.EMPTY,
+        RDI_MASK,
+        RSI_MASK,
+        RDX_MASK,
+        RCX_MASK,
+        R08_MASK,
+        R09_MASK
+    };
+    static int[] CALLINARG_SYSTEMV = new int[] {
+        0,   // Control, no register
+        0,   // Memory, no register
+        RDI,
+        RSI,
+        RDX,
+        RCX,
+        R08,
+        R09,
+    };
+    static int callInArgSystemV( int idx ) { return CALLINARG_SYSTEMV[idx]; }
+
+    // caller saved(systemv)
+    // caller saved(win64)
+    public static final long SYSTEMV_ABI_CALLER_SAVED =
+        (1L << RAX) | (1L << RDI) | (1L << RSI) | (1L << RCX) | (1L << RDX) | (1L << R08) | (1L << R09) << (1L << R10) << (1L << R11);
+    // callee saved(systemv)
+    public static final long SYSTEMV_ABI_CALLE_SAVED = ~SYSTEMV_ABI_CALLER_SAVED;
+
+
+    static RegMask callInMask( int idx ) {
+        return switch( CodeGen.CODE._callingConv ) {
+        case CodeGen.CallingConv.SystemV -> CALLINMASK_SYSTEMV[idx];
+        case CodeGen.CallingConv.Win64   -> CALLINMASK_WIN64  [idx];
+        };
+    }
+
+    // Create a split op; any register to any register, including stack slots
+    @Override public Node split() {
+        throw Utils.TODO();
+    }
+
+    // Return a MachNode unconditional branch
+    @Override public CFGNode jump() {
+        throw Utils.TODO();
+    }
+
+    // Break an infinite loop
+    @Override public IfNode never( CFGNode ctrl ) {
+        throw Utils.TODO();
+    }
+
+    // Instruction selection
+    @Override public Node instSelect( Node n ) {
+        return switch( n ) {
+        case AddFNode     addf  -> addf(addf);
+        case AddNode      add   -> add(add);
+        case AndNode      and   -> and(and);
+        case BoolNode     bool  -> cmp(bool);
+        case CallEndNode  cend  -> new CallEndNode((CallNode)cend.in(0));
+        case CallNode     call  -> call(call);
+        case CProjNode    c     -> new CProjNode(c);
+        case ConstantNode con   -> con(con);
+        case DivFNode     divf  -> new DivFX86(divf);
+        case DivNode      div   -> new DivX86(div);
+        case FunNode      fun   -> new FunX86(fun);
+        case IfNode       iff   -> jmp(iff);
+        case LoadNode     ld    -> ld(ld);
+        case MemMergeNode mem   -> new MemMergeNode(mem);
+        case MulFNode     mulf  -> new MulFX86(mulf);
+        case MulNode      mul   -> mul(mul);
+        case NewNode      nnn   -> new NewX86(nnn);
+        case OrNode       or   ->  or(or);
+        case ParmNode     parm  -> new ParmX86(parm);
+        case PhiNode      phi   -> new PhiNode(phi);
+        case ProjNode     prj   -> prj(prj);
+        case ReadOnlyNode read  -> new ReadOnlyNode(read);
+        case ReturnNode   ret   -> new RetX86(ret,ret.fun());
+        case SarNode      sar   -> sar(sar);
+        case ShlNode      shl   -> shl(shl);
+        case ShrNode      shr   -> shr(shr);
+        case StartNode    start -> new StartNode(start);
+        case StopNode     stop  -> new StopNode(stop);
+        case StoreNode    st    -> st(st);
+        case SubFNode     subf  -> new SubFX86(subf);
+        case SubNode      sub   -> sub(sub);
+        case ToFloatNode  tfn   -> i2f8(tfn);
+        case XorNode      xor   -> xor(xor);
+
+        case LoopNode     loop  -> new LoopNode(loop);
+        case RegionNode   region-> new RegionNode(region);
+        default -> throw Utils.TODO();
+        };
+    }
+
+
+    // Attempt a full LEA-style break down.
+    private Node add( AddNode add ) {
+        Node lhs = add.in(1);
+        Node rhs = add.in(2);
+        if( lhs instanceof LoadNode ld && ld.nOuts()==1 )
+            return new AddMemX86(add,address(ld),ld.ptr(),idx,off,scale, imm(rhs),val);
+
+        if( rhs instanceof LoadNode ld && ld.nOuts()==1 )
+            throw Utils.TODO(); // Swap load sides
+
+        // Attempt a full LEA-style break down.
+        // Returns one of AddX86, AddIX86, LeaX86, or LHS
+        if( rhs instanceof ConstantNode off && off._con instanceof TypeInteger toff ) {
+            if( lhs instanceof AddNode ladd )
+                // ((base + (idx << scale)) + off)
+                return _lea(add,ladd.in(1),ladd.in(2),toff.value());
+            if( lhs instanceof ShlNode shift )
+                // (idx << scale) + off; no base
+                return _lea(add,null,shift,toff.value());
+
+            // lhs + rhs1
+            if( toff.value()==0 ) return add;
+            return new AddIX86(add, toff);
+        }
+        return _lea(add,lhs,rhs,0);
+    }
+
+
+    private Node addf( AddFNode addf ) {
+        if( addf.in(1) instanceof LoadNode ld && ld.nOuts()==1 )
+            return new AddFMemX86(addf,address(ld),ld.ptr(),idx,off,scale, addf.in(2));
+
+        if( addf.in(2) instanceof LoadNode ld && ld.nOuts()==1 )
+            throw Utils.TODO(); // Swap load sides
+
+        return new AddFX86(addf);
+    }
+
+
+    private Node _lea( Node add, Node base, Node idx, long off ) {
+        int scale = 1;
+        if( base instanceof ShlNode && !(idx instanceof ShlNode) ) throw Utils.TODO(); // Bug in canonicalization, should on RHS
+        if( idx instanceof ShlNode shift && shift.in(2) instanceof ConstantNode shfcon &&
+            shfcon._con instanceof TypeInteger tscale && 0 <= tscale.value() && tscale.value() <= 3 ) {
+            idx = shift.in(1);
+            scale = 1 << ((int)tscale.value());
+        }
+        // (base + idx) + off
+        return off==0 && scale==1
+            ? new AddX86(add)
+            : new LeaX86(add,base,idx,scale,off);
+    }
+
+
+    private Node and(AndNode and) {
+        if( and.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti )
+            return new AndIX86(and, ti);
+        throw Utils.TODO();
+    }
+
+    private Node call(CallNode call) {
+        if( call.fptr() instanceof ConstantNode con && con._con instanceof TypeFunPtr tfp )
+            return new CallX86(call, tfp);
+        return new CallRX86( call );
+    }
+
+    // Because X86 flags, a normal ideal Bool is 2 X86 ops: a "cmp" and at "setz".
+    // Ideal If reading from a setz will skip it and use the "cmp" instead.
+    private Node cmp( BoolNode bool ) {
+        Node cmp = _cmp(bool);
+        return new SetX86(cmp,bool.op());
+    }
+    private Node _cmp( BoolNode bool ) {
+        Node lhs = bool.in(1);
+        Node rhs = bool.in(2);
+        if( lhs instanceof LoadNode ld && ld.nOuts()==1 )
+            return new CmpMemX86(bool,address(ld),ld.ptr(),idx,off,scale, imm(rhs),val,false);
+
+        if( rhs instanceof LoadNode ld && ld.nOuts()==1 )
+            return new CmpMemX86(bool,address(ld),ld.ptr(),idx,off,scale, imm(lhs),val,true);
+
+        return rhs instanceof ConstantNode con && con._con instanceof TypeInteger ti
+            ? new CmpIX86(bool, ti)
+            : new  CmpX86(bool);
+    }
+
+    private Node con( ConstantNode con ) {
+        return switch( con._con ) {
+        case TypeInteger ti  -> new IntX86(con);
+        case TypeFloat   tf  -> new FltX86(con);
+        case TypeFunPtr  tfp -> new TFPX86(con);
+        case TypeMemPtr  tmp -> new ConstantNode(con);
+        case TypeNil     tn  -> throw Utils.TODO();
+        // TOP, BOTTOM, XCtrl, Ctrl, etc.  Never any executable code.
+        case Type t -> new ConstantNode(con);
+        };
+    }
+
+    private Node i2f8(ToFloatNode tfn) {
+        assert tfn.in(1)._type instanceof TypeInteger ti;
+        return new I2f8X86(tfn);
+    }
+
+    private Node jmp( IfNode iff ) {
+        // If/Bool combos will match to a Cmp/Set which sets flags.
+        // Most general arith ops will also set flags, which the Jmp needs directly.
+        // Loads do not set the flags, and will need an explicit TEST
+        if( !(iff.in(1) instanceof BoolNode) )
+            iff.setDef(1,new BoolNode.EQ(iff.in(1),new ConstantNode(TypeInteger.ZERO)));
+        return new JmpX86(iff, ((BoolNode)iff.in(1)).op());
+    }
+
+    private Node ld( LoadNode ld ) {
+        return new LoadX86(address(ld),ld.ptr(),idx,off,scale);
+    }
+
+    private Node mul(MulNode mul) {
+        return mul.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti
+            ? new MulIX86(mul, ti)
+            : new MulX86(mul);
+    }
+
+    private Node or(OrNode or) {
+        if( or.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti)
+            return new OrIX86(or, ti);
+        throw Utils.TODO();
+    }
+
+    private Node prj( ProjNode prj ) {
+        return new ProjX86(prj);
+    }
+
+    private Node sar( SarNode sar ) {
+        if( sar.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti)
+            return new SarX86(sar, ti);
+        throw Utils.TODO();
+    }
+
+    private Node shl( ShlNode shl ) {
+        if( shl.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti )
+            return new ShlIX86(shl, ti);
+        throw Utils.TODO();
+    }
+
+    private Node shr(ShrNode shr) {
+        if( shr.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti )
+            return new ShrIX86(shr, ti);
+        throw Utils.TODO();
+    }
+
+    private Node st( StoreNode st ) {
+        // Look for "*ptr op= val"
+        Node op = st.val();
+        if( op instanceof AddNode ) {
+            if( op.in(1) instanceof LoadNode ld &&
+                ld.in(0)==st.in(0) &&
+                ld.mem()==st.mem() &&
+                ld.ptr()==st.ptr() &&
+                ld.off()==st.off() ) {
+                if( op instanceof AddNode ) {
+                    return new MemAddX86(address(st),st.ptr(),idx,off,scale,imm(op.in(2)),val);
+                }
+                throw Utils.TODO();
+            }
+        }
+
+        return new StoreX86(address(st),st.ptr(),idx,off,scale,imm(st.val()),val);
+    }
+
+    private Node sub( SubNode sub ) {
+        return sub.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti
+            ? new AddIX86(sub, TypeInteger.constant(-ti.value()))
+            : new SubX86(sub);
+    }
+
+    private Node xor(XorNode xor) {
+        if(xor.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti)
+            return new XorIX86(xor, ti);
+        throw Utils.TODO();
+    }
+
+
+    // Gather X86 addressing mode bits prior to constructing.  This is a
+    // builder pattern, but saving the bits in a *local* *global* here to keep
+    // mess contained.
+    private static int off, scale, imm;
+    private static Node idx, val;
+    private <N extends MemOpNode> N address( N mop ) {
+        off = scale = imm = 0;  // Reset
+        idx = val = null;
+        Node base = mop.ptr();
+        // Skip/throw-away a ReadOnly, only used to typecheck
+        if( base instanceof ReadOnlyNode read ) base = read.in(1);
+        assert !(base instanceof AddNode) && base._type instanceof TypeMemPtr; // Base ptr always, not some derived
+        if( mop.off() instanceof AddNode add && add.in(2) instanceof ConstantNode con && con._con instanceof TypeInteger ti ) {
+            off = (int)ti.value();
+            assert off == ti.value(); // In 32-bit range
+            idx = add.in(1);
+            if( idx instanceof ShlNode shift && shift.in(2) instanceof ConstantNode shfcon &&
+                shfcon._con instanceof TypeInteger tscale && 0 <= tscale.value() && tscale.value() <= 3 ) {
+                idx = shift.in(1);
+                scale = (int)tscale.value();
+            }
+        } else {
+            if( mop.off() instanceof ConstantNode con && con._con instanceof TypeInteger ti ) {
+                off = (int)ti.value();
+                assert off == ti.value(); // In 32-bit range
+            } else {
+                idx = mop.off();
+            }
+        }
+        return mop;
+    }
+    private int imm( Node xval ) {
+        assert val==null && imm==0;
+        if( xval instanceof ConstantNode con && con._con instanceof TypeInteger ti ) {
+            val = null;
+            imm = (int)ti.value();
+            assert imm == ti.value(); // In 32-bit range
+        } else {
+            val = xval;
+        }
+        return imm;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/Field.java b/chapter20/src/main/java/com/seaofnodes/simple/type/Field.java
new file mode 100644
index 00000000..ffa9d2a6
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/Field.java
@@ -0,0 +1,74 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Represents a field in a struct. This is not a Type in the type system.
+ */
+public class Field extends Type {
+
+    // The pair {fieldName,type} uniquely identifies a field.
+
+    // Field name
+    public final String _fname;
+    // Type of the field
+    public final Type _type;
+    // Unique memory alias, not sensibly part of a "type" but very convenient here.
+    public final int _alias;
+    // Field must be written to exactly once, no more, no less
+    public final boolean _final;
+
+    private Field(String fname, Type type, int alias, boolean xfinal ) {
+        super(TFLD);
+        _fname = fname;
+        _type  = type;
+        _alias = alias;
+        _final = xfinal;
+    }
+    // Make with existing alias
+    public static Field make( String fname, Type type, int alias, boolean xfinal ) {
+        return new Field(fname,type,alias,xfinal).intern();
+    }
+    public Field makeFrom( Type type ) {
+        return type == _type ? this : new Field(_fname,type,_alias,_final).intern();
+    }
+    @Override public Field makeRO() { return _final ? this : make(_fname,_type.makeRO(),_alias,true);  }
+    @Override public boolean isFinal() { return _final && _type.isFinal(); }
+
+    public static final Field TEST = make("test",Type.NIL,-2,false);
+    public static final Field TEST2= make("test",Type.NIL,-2,true);
+    public static void gather(ArrayList<Type> ts) { ts.add(TEST); ts.add(TEST2); }
+
+    @Override Field xmeet( Type that ) {
+        Field fld = (Field)that; // Invariant
+        assert _fname.equals(fld._fname);
+        assert _alias==fld._alias;
+        return make(_fname,_type.meet(fld._type),_alias,_final | fld._final);
+    }
+
+    @Override
+    public Field dual() { return make(_fname,_type.dual(),_alias,!_final); }
+
+    @Override public Field glb() {
+        Type glb = _type.glb();
+        return (glb==_type && _final) ? this : make(_fname,glb,_alias,true);
+    }
+
+    // Override in subclasses
+    int hash() { return _fname.hashCode() ^ _type.hashCode() ^ _alias ^ (_final ? 1024 : 0); }
+
+    boolean eq(Type t) {
+        Field f = (Field)t;
+        return _fname.equals(f._fname) && _type==f._type && _alias==f._alias && _final==f._final;
+    }
+
+
+    @Override
+    public SB print( SB sb ) {
+        return _type.print(sb.p(_final?"":"!").p(_fname).p(":").p(_alias).p(" : "));
+    }
+
+    @Override public String str() { return _fname; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/Type.java b/chapter20/src/main/java/com/seaofnodes/simple/type/Type.java
new file mode 100644
index 00000000..847235dd
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/Type.java
@@ -0,0 +1,235 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+/**
+ * These types are part of a Monotone Analysis Framework,
+ * @see <a href="https://www.cse.psu.edu/~gxt29/teaching/cse597s21/slides/08monotoneFramework.pdf">see for example this set of slides</a>.
+ * <p>
+ * The types form a lattice; @see <a href="https://en.wikipedia.org/wiki/Lattice_(order)">a symmetric complete bounded (ranked) lattice.</a>
+ * <p>
+ * This wild lattice theory will be needed later to allow us to easily beef up
+ * the analysis and optimization of the Simple compiler... but we don't need it
+ * now, just know that it is coming along in a later Chapter.
+ * <p>g
+ * One of the fun things here is that while the theory is deep and subtle, the
+ * actual implementation is darn near trivial and is generally really obvious
+ * what we're doing with it.  Right now, it's just simple integer math to do
+ * simple constant folding e.g. 1+2 == 3 stuff.
+ */
+
+public class Type {
+    static final HashMap<Type,Type> INTERN = new HashMap<>();
+
+    // ----------------------------------------------------------
+    // Simple types are implemented fully here.  "Simple" means: the code and
+    // type hierarchy are simple, not that the Type is conceptually simple.
+    static final byte TBOT    = 0; // Bottom (ALL)
+    static final byte TTOP    = 1; // Top    (ANY)
+    static final byte TCTRL   = 2; // Ctrl flow bottom
+    static final byte TXCTRL  = 3; // Ctrl flow top (mini-lattice: any-xctrl-ctrl-all)
+    static final byte TNIL    = 4; // low null of all flavors
+    static final byte TXNIL   = 5; // high or choice null
+    static final byte TSIMPLE = 6; // End of the Simple Types
+
+    static final byte TPTR    = 7; // All nil-able scalar values
+    static final byte TINT    = 8; // All Integers; see TypeInteger
+    static final byte TFLT    = 9; // All Floats  ; see TypeFloat
+    static final byte TMEMPTR =10; // Memory pointer to a struct type
+    static final byte TFUNPTR =11; // Function pointer; unique signature and code address (just a bit)
+    static final byte TTUPLE  =12; // Tuples; finite collections of unrelated Types, kept in parallel
+    static final byte TMEM    =13; // All memory (alias 0) or A slice of memory - with specific alias
+    static final byte TSTRUCT =14; // Structs; tuples with named fields
+    static final byte TFLD    =15; // Named fields in structs
+    static final byte TRPC    =16; // Return Program Control (Return PC or RPC)
+
+    public final byte _type;
+
+    public boolean is_simple() { return _type < TSIMPLE; }
+    private static final String[] STRS = new String[]{"Bot","Top","Ctrl","~Ctrl","null","~nil"};
+    protected Type(byte type) { _type = type; }
+
+    public static final Type BOTTOM   = new Type( TBOT   ).intern(); // ALL
+    public static final Type TOP      = new Type( TTOP   ).intern(); // ANY
+    public static final Type CONTROL  = new Type( TCTRL  ).intern(); // Ctrl
+    public static final Type XCONTROL = new Type( TXCTRL ).intern(); // ~Ctrl
+    public static final Type NIL      = new Type( TNIL   ).intern(); // low null of all flavors
+    public static final Type XNIL     = new Type( TXNIL  ).intern(); // high or choice null
+    public static Type[] gather() {
+        ArrayList<Type> ts = new ArrayList<>();
+        ts.add(BOTTOM);
+        ts.add(CONTROL);
+        ts.add(NIL);
+        ts.add(XNIL);
+        TypeNil.gather(ts);
+        TypePtr.gather(ts);
+        TypeInteger.gather(ts);
+        TypeFloat.gather(ts);
+        TypeMemPtr.gather(ts);
+        TypeFunPtr.gather(ts);
+        TypeMem.gather(ts);
+        Field.gather(ts);
+        TypeStruct.gather(ts);
+        TypeTuple.gather(ts);
+        TypeRPC.gather(ts);
+        int sz = ts.size();
+        for( int i = 0; i < sz; i++ )
+            ts.add(ts.get(i).dual());
+        return ts.toArray(new Type[ts.size()]);
+    }
+
+    // Is high or on the lattice centerline.
+    public boolean isHigh       () { return _type==TTOP || _type==TXCTRL || _type==TXNIL; }
+    public boolean isHighOrConst() { return isHigh() || isConstant(); }
+
+    // Strict constant values, things on the lattice centerline.
+    // Excludes both high and low values
+    public boolean isConstant() { return _type==TNIL; }
+
+    // ----------------------------------------------------------
+
+    // Notes on Type interning: At the moment it is not easy to reset the
+    // interned types because we hold static references to several types and
+    // these are scattered around.  This means the INTERN cache will retain all
+    // types from every run of the Parser.  For this to work correctly types
+    // must be rigorous about defining when they are the same.  Also types need
+    // to be immutable once defined.  The rationale for interning is
+    // *correctness* with cyclic type definitions.  Simple structural recursive
+    // checks go exponential with merely sharing, but with cycles they will
+    // stack overflow and crash.  Interning means we do not need to have sharing
+    // checks with every type compare, only during interning.
+
+    // Factory method which interns "this"
+    public  <T extends Type> T intern() {
+        T nnn = (T)INTERN.get(this);
+        if( nnn==null )
+            INTERN.put(nnn=(T)this,this);
+        return nnn;
+    }
+
+    private int _hash;          // Hash cache; not-zero when set.
+    @Override
+    public final int hashCode() {
+        if( _hash!=0 ) return _hash;
+        _hash = hash();
+        if( _hash==0 ) _hash = 0xDEADBEEF; // Bad hash from subclass; use some junk thing
+        return _hash;
+    }
+    // Override in subclasses
+    int hash() { return _type; }
+
+    @Override
+    public final boolean equals( Object o ) {
+        if( o==this ) return true;
+        if( !(o instanceof Type t)) return false;
+        if( _type != t._type ) return false;
+        return eq(t);
+    }
+    // Overridden in subclasses; subclass can assume "this!=t" and java classes are same
+    boolean eq(Type t) { return true; }
+
+
+    // ----------------------------------------------------------
+    public final Type meet(Type t) {
+        // Shortcut for the self case
+        if( t == this ) return this;
+        // Same-type is always safe in the subclasses
+        if( _type==t._type ) return xmeet(t);
+        // TypeNil vs TypeNil meet
+        if( this instanceof TypeNil ptr0 && t instanceof TypeNil ptr1 )
+            return ptr0.nmeet(ptr1);
+        // Reverse; xmeet 2nd arg is never "is_simple" and never equal to "this".
+        if(   is_simple() ) return this.xmeet(t   );
+        if( t.is_simple() ) return t   .xmeet(this);
+        return Type.BOTTOM;     // Mixing 2 unrelated types
+    }
+
+    // Compute meet right now.  Overridden in subclasses.
+    // Handle cases where 'this.is_simple()' and unequal to 't'.
+    // Subclassed xmeet calls can assert that '!t.is_simple()'.
+    Type xmeet(Type t) {
+        assert is_simple(); // Should be overridden in subclass
+        // ANY meet anything is thing; thing meet ALL is ALL
+        if( _type==TBOT || t._type==TTOP ) return this;
+        if( _type==TTOP || t._type==TBOT ) return    t;
+
+        // RHS TypeNil vs NIL/XNIL
+        if( _type==  TNIL ) return t instanceof TypeNil ptr ? ptr.meet0() : (t._type==TXNIL ? TypePtr.PTR : BOTTOM);
+        if( _type== TXNIL ) return t instanceof TypeNil ptr ? ptr.meetX() : (t._type== TNIL ? TypePtr.PTR : BOTTOM);
+        // 'this' is only {TCTRL,TXCTRL}
+        // Other non-simple RHS things bottom out
+        if( !t.is_simple() ) return BOTTOM;
+        // If RHS is NIL/XNIL
+        if( t._type==TNIL || t._type==TXNIL ) return BOTTOM;
+        // Both are {TCTRL,TXCTRL} and unequal to each other
+        return _type==TCTRL || t._type==TCTRL ? CONTROL : XCONTROL;
+    }
+
+    public Type dual() {
+        return switch( _type ) {
+        case TBOT  -> TOP;
+        case TTOP  -> BOTTOM;
+        case TCTRL ->XCONTROL;
+        case TXCTRL-> CONTROL;
+        case TNIL  ->XNIL;
+        case TXNIL -> NIL;
+        default -> throw Utils.TODO(); // Should not reach here
+        };
+    }
+
+    // ----------------------------------------------------------
+    // Our lattice is defined with a MEET and a DUAL.
+    // JOIN is dual of meet of both duals.
+    public final Type join(Type t) {
+        if( this==t ) return this;
+        return dual().meet(t.dual()).dual();
+    }
+
+    // True if this "isa" t; e.g. 17 isa TypeInteger.BOT
+    public boolean isa( Type t ) { return meet(t)==t; }
+
+    // True if this "isa" t up to named structures
+    public boolean shallowISA( Type t ) { return isa(t); }
+
+    public Type nonZero() { return TypePtr.NPTR; }
+
+    // Make a zero version of this type, 0 for integers and null for pointers.
+    public Type makeZero() { return Type.NIL; }
+
+    /** Compute greatest lower bound in the lattice */
+    public Type glb() { return Type.BOTTOM; }
+
+    // Is forward-reference
+    public boolean isFRef() { return false; }
+
+    // All reachable struct Fields are final
+    public boolean isFinal() { return true; }
+
+    // Make all reachable struct Fields final
+    public Type makeRO() { return this; }
+
+    // ----------------------------------------------------------
+
+    // Size in bits to hold an instance of this type.
+    // Sizes are expected to be between 1 and 64 bits.
+    // Size 0 means this either takes no space (such as a known-zero field)
+    // or isn't a scalar to be stored in memory.
+    public int log_size() { throw Utils.TODO(); }
+
+    // ----------------------------------------------------------
+    // Useful in the debugger, which calls toString everywhere.
+    // This is a more verbose dev-friendly print.
+    @Override
+    public final String toString() {
+        return print(new SB()).toString();
+    }
+
+    public SB  print(SB sb) { return sb.p(str()); }
+    public SB gprint(SB sb) { return print(sb); }
+
+    // This is used by error messages, and is a shorted print.
+    public String str() { return STRS[_type]; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFloat.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFloat.java
new file mode 100644
index 00000000..aa205149
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFloat.java
@@ -0,0 +1,95 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Float Type
+ */
+public class TypeFloat extends Type {
+
+    public final static TypeFloat ONE = constant(1.0);
+    public final static TypeFloat FZERO = constant(0.0);
+    public final static TypeFloat F32 = make(32, 0);
+    public final static TypeFloat F64 = make(64, 0);
+
+    // - high -64, high -32, con 0, low +32, low +64
+    public final byte _sz;
+
+    /**
+     * The constant value or 0
+     */
+    public final double _con;
+
+    private TypeFloat(byte sz, double con) {
+        super(TFLT);
+        _sz = sz;
+        _con = con;
+    }
+    private static TypeFloat make(int sz, double con) {
+        return new TypeFloat((byte)sz,con).intern();
+    }
+
+    public static TypeFloat constant(double con) { return make(0, con); }
+
+    public static void gather(ArrayList<Type> ts) { ts.add(F64); ts.add(F32); ts.add(constant(3.141592653589793)); }
+
+    @Override public String str() {
+        return switch( _sz ) {
+        case -64 -> "~flt";
+        case -32 -> "~f32";
+        case   0 -> ""+_con+((float)_con==_con ? "f" : "");
+        case  32 ->  "f32";
+        case  64 ->  "flt";
+        default  -> throw Utils.TODO();
+        };
+    }
+    private boolean isF32() { return ((float)_con)==_con; }
+
+    @Override public boolean isHigh    () { return _sz< 0; }
+    @Override public boolean isConstant() { return _sz==0; }
+    @Override public int log_size() { return _sz==32 || _sz==-32 ? 2 : 3; }
+
+    public double value() { return _con; }
+
+    @Override
+    public TypeFloat xmeet(Type other) {
+        TypeFloat f = (TypeFloat)other;
+        // Invariant from caller: 'this' != 'other' and same class (TypeFloat).
+        TypeFloat i = (TypeFloat)other; // Contract
+        // Larger size in i1, smaller in i0
+        TypeFloat i0 = _sz < i._sz ? this : i;
+        TypeFloat i1 = _sz < i._sz ? i : this;
+
+        if( i1._sz== 64 ) return F64;
+        if( i0._sz==-64 ) return i1;
+        if( i1._sz== 32 )
+            return i0._sz==0 && !i0.isF32() ? F64 : F32;
+        if( i1._sz!=  0 ) return i1;
+        // i1 is a constant
+        if( i0._sz==-32 )
+            return i1.isF32() ? i1 : F64;
+        // Since both are constants, and are never equals (contract) unequals
+        // constants fall to bottom
+        return i0.isF32() && i1.isF32() ? F32 : F64;
+    }
+
+    @Override
+    public Type dual() {
+        return isConstant() ? this : make(-_sz,0); // Constants are a self-dual
+    }
+
+    @Override public Type makeZero() { return FZERO; }
+    @Override public Type glb() { return F64; }
+
+    @Override
+    int hash() { return (int)(Double.hashCode(_con) ^ _sz ^ (1<<17)); }
+    @Override
+    public boolean eq( Type t ) {
+        TypeFloat i = (TypeFloat)t; // Contract
+        // Allow NaN to check for equality
+        return _sz==i._sz && Double.doubleToLongBits(_con)==Double.doubleToLongBits(i._con);
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFunPtr.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFunPtr.java
new file mode 100644
index 00000000..be801c85
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeFunPtr.java
@@ -0,0 +1,104 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+/**
+ * Represents a Pointer to a function.
+ * <p></p>
+ * Functions have argument types and a return type, making a function
+ * signature.  Within a signature there can be many instances of functions, and
+ * each function is labeled with a small integer constant.  A TFP can represent
+ * a single signature and a set of functions; the set might contain only 1
+ * function or the zeroth function (the null ptr).
+ * <p></p>
+ * Functions with different signatures cannot be mixed, and will result in a
+ * bottom function type, which can only be null-checked.
+ */
+public class TypeFunPtr extends TypeNil {
+    // A TypeFunPtr is Signature and a set of functions.
+    public final TypeTuple _sig;
+    public final Type _ret;
+    // Cheesy easy implementation for a small set; 1 bit per unique function
+    // within the TypeTuple.  Can be upgraded to a BitSet for larger classes of
+    // functions.  Negative means "these 63 concrete bits plus infinite unknown more"
+    public final long _fidxs; // 63 unique functions per signature
+
+    private TypeFunPtr(byte nil, TypeTuple sig, Type ret, long fidxs) {
+        super(TFUNPTR,nil);
+        assert sig != null;
+        _sig = sig;
+        _ret = ret;
+        _fidxs = fidxs;
+    }
+
+    public static TypeFunPtr make( byte nil, TypeTuple sig, Type ret, long fidxs ) { return new TypeFunPtr(nil,sig,ret,fidxs).intern(); }
+    public static TypeFunPtr make( boolean nil, TypeTuple sig, Type ret ) { return make((byte)(nil ? 3 : 2),sig,ret,-1); }
+    @Override TypeFunPtr makeFrom( byte nil ) { return  nil ==_nil   ? this : make(  nil,_sig,_ret,   _fidxs); }
+    public TypeFunPtr makeFrom( Type ret ) { return     ret ==_ret   ? this : make( _nil,_sig, ret,   _fidxs); }
+    public TypeFunPtr makeFrom( int fidx ) { return make((byte)2, _sig,_ret,1L<<fidx ); }
+
+    public static TypeFunPtr BOT   = make((byte)3,TypeTuple.BOT,Type.BOTTOM,-1);
+    public static TypeFunPtr TEST  = make((byte)2,TypeTuple.TEST,TypeInteger.BOT,1);
+    public static TypeFunPtr TEST0 = make((byte)3,TypeTuple.TEST,TypeInteger.BOT,3);
+    public static void gather(ArrayList<Type> ts) { ts.add(TEST); ts.add(TEST0); ts.add(BOT); }
+
+    @Override
+    Type xmeet(Type t) {
+        TypeFunPtr that = (TypeFunPtr) t;
+        return TypeFunPtr.make(xmeet0(that),(TypeTuple)_sig.meet(that._sig), _ret.meet(that._ret), _fidxs | that._fidxs);
+    }
+
+    @Override
+    public TypeFunPtr dual() { return TypeFunPtr.make(dual0(), _sig.dual(), _ret.dual(), ~_fidxs); }
+
+    // RHS is NIL; do not deep-dual when crossing the centerline
+    @Override public Type meet0() { return _nil==3 ? this : make((byte)3,_sig,_ret,_fidxs); }
+
+    @Override public TypeFunPtr glb() { return make((byte)3,_sig,_ret,-1L); }
+
+    @Override public boolean isHigh    () { return _nil <= 1 || (_nil==2 && _fidxs==0); }
+    @Override public boolean isConstant() { return (_nil==2 && Long.bitCount(_fidxs)==1) || (_nil==3 && _fidxs==0); }
+
+    @Override public int log_size() { return 2; } // (1<<2)==4-byte pointers
+
+    public Type arg(int i) { return _sig._types[i]; }
+    public long fidxs() { return _fidxs; }
+    public Type ret() { return _ret; }
+    public int nargs() { return _sig._types.length; }
+
+    @Override
+    int hash() { return Utils.fold(_sig.hashCode() ^ _ret.hashCode() ^ _fidxs ^ super.hash()); }
+
+    @Override
+    boolean eq(Type t) {
+        TypeFunPtr ptr = (TypeFunPtr)t; // Invariant
+        return _sig == ptr._sig  && _ret == ptr._ret && _fidxs == ptr._fidxs && super.eq(ptr);
+    }
+
+    @Override public String str() { return print(new SB()).toString(); }
+    @Override public SB  print(SB sb) { return _print(sb,false,true); }
+    public SB print(SB sb, boolean n) { return _print(sb,false,n); }
+    @Override public SB gprint(SB sb) { return _print(sb,true ,true); }
+    private static SB _print(SB sb, boolean g, Type t) { return g ? t.gprint(sb) : t.print(sb); }
+    private SB _print(SB sb, boolean g, boolean n) {
+        sb.p(x()).p("{ ");
+        if( _sig._types!=null )
+            for( Type t : _sig._types )
+                _print(sb,g,t).p(" ");
+        _print(sb.p(g ? "&rarr; " : "-> "),g,_ret).p(" #");
+        if( isHigh() ) sb.p("~");
+        long fidxs = isHigh() ? ~_fidxs : _fidxs;
+        String fidx = fidxs==0 ? ""
+            : Long.bitCount(fidxs) == 1 ? ""+Long.numberOfTrailingZeros(fidxs)
+            : fidxs == -1 ? "ALL"
+            : "b"+Long.toBinaryString(fidxs); // Just some function bits
+        return sb.p(fidx).p("}").p(q());
+    }
+
+    // Usage: for( long fidxs=fidxs(); fidxs!=0; fidxs=nextFIDX(fidxs) { int fidxs = Long.numberOfTrailingZeros(fidxs); ... }
+    public static long nextFIDX(long fidxs) { return fidxs & (fidxs-1); }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeInteger.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
new file mode 100644
index 00000000..cccb85a5
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
@@ -0,0 +1,128 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Integer Type
+ */
+public class TypeInteger extends Type {
+
+    public final static TypeInteger ZERO= make(0,0);
+    public final static TypeInteger FALSE=ZERO;
+    public final static TypeInteger TRUE= make(1,1);
+
+    public final static TypeInteger I1  = make(-1,0);
+    public final static TypeInteger I8  = make(-128,127);
+    public final static TypeInteger I16 = make(-32768,32767);
+    public final static TypeInteger I32 = make(-1L<<31,(1L<<31)-1);
+    public final static TypeInteger BOT = make(Long.MIN_VALUE,Long.MAX_VALUE);
+    public final static TypeInteger TOP = BOT.dual();
+
+    public final static TypeInteger U1  = make(0,1);
+    public final static TypeInteger BOOL= U1;
+    public final static TypeInteger U8  = make(0,255);
+    public final static TypeInteger U16 = make(0,65535);
+    public final static TypeInteger U32 = make(0,(1L<<32)-1);
+
+    /**
+     * Describes an integer *range* - everything from min to max; both min and
+     * max are inclusive.  If min==max, this is a constant.
+     * <br>
+     * If min <= max, this is a  below center (towards bottom).
+     * If min >  max, this is an above center (towards top).
+     */
+    public final long _min, _max;
+
+    private TypeInteger(long min, long max) {
+        super(TINT);
+        _min = min;
+        _max = max;
+    }
+
+    // Strict non-zero contract
+    public static TypeInteger make(long lo, long hi) { return new TypeInteger(lo,hi).intern(); }
+
+    public static TypeInteger constant(long con) { return make(con, con); }
+
+    public static void gather(ArrayList<Type> ts) { ts.add(I32); ts.add(BOT); ts.add(U1); ts.add(I1); ts.add(U8); }
+
+    @Override public String str() {
+        if( isConstant() ) return ""+_min;
+        long lo = _min, hi = _max;
+        String x = "";
+        if( hi < lo ) {
+            lo = _max;  hi = _min;
+            x = "~";
+        }
+        return x+_str(lo,hi);
+    }
+    private static String _str(long lo, long hi) {
+        if( lo==Long.MIN_VALUE && hi==Long.MAX_VALUE ) return "int";
+        if( lo==       0 && hi==         1 ) return "bool";
+        if( lo==      -1 && hi==         0 ) return "i1";
+        if( lo==    -128 && hi==       127 ) return "i8";
+        if( lo==  -32768 && hi==     32767 ) return "i16";
+        if( lo== -1L<<31 && hi==(1L<<31)-1 ) return "i32";
+        if( lo==       0 && hi==      255  ) return "u8";
+        if( lo==       0 && hi==     65535 ) return "u16";
+        if( lo==       0 && hi==(1L<<32)-1 ) return "u32";
+        return "["+lo+"-"+hi+"]";
+    }
+
+    @Override public boolean isHigh    () { return _min >  _max; }
+    @Override public boolean isConstant() { return _min == _max; }
+
+    @Override public int log_size() {
+        if( this==I8  || this==U8 || this==BOOL ) return 0; // 1<<0 == 1 bytes
+        if( this==I16 || this==U16              ) return 1; // 1<<1 == 2 bytes
+        if( this==I32 || this==U32              ) return 2; // 1<<2 == 4 bytes
+        if( this==BOT                           ) return 3; // 1<<3 == 8 bytes
+        if( isHighOrConst() ) return 0;
+        throw Utils.TODO();
+    }
+
+    public long value() { assert isConstant(); return _min; }
+
+    // AND-mask of forced zeros.  e.g. unsigned types will return their mask;
+    // u8 will return 0xFF.  But also a range of 16-18 (0x10-0x12) will return
+    // 0x13 - no value in the range {16,17,18} will allow bit 0x04 to be set.
+    public long mask() {
+        if( isHigh() ) return 0;
+        if( isConstant() ) return _min;
+        // Those bit positions which differ min to max
+        long x = _min ^ _max;
+        // Highest '1' bit in the differ set.  Since the range is from min to
+        // max, all values below here are possible.
+        long ff1 = Long.highestOneBit(x);
+        // Make a all-1's mask from ff1, and set over the same bits (either min
+        // or max is ok).
+        long mask = _min | (ff1-1) | ff1;
+        return mask;
+    }
+
+    @Override
+    public Type xmeet(Type other) {
+        // Invariant from caller: 'this' != 'other' and same class (TypeInteger)
+        TypeInteger i = (TypeInteger)other; // Contract
+        return make(Math.min(_min,i._min), Math.max(_max,i._max));
+    }
+
+    @Override public TypeInteger dual() { return make(_max,_min); }
+
+    @Override public TypeInteger nonZero() {
+        if( isHigh() ) return this;
+        if( this==ZERO ) return null;                  // No sane answer
+        if( _min==0 ) return make(1,Math.max(_max,1)); // specifically good on BOOL
+        if( _max==0 ) return make(_min,-1);
+        return this;
+    }
+    @Override public Type makeZero() { return ZERO; }
+    @Override public TypeInteger glb() { return BOT; }
+    @Override int hash() { return Utils.fold(_min) * Utils.fold(_max); }
+    @Override public boolean eq( Type t ) {
+        TypeInteger i = (TypeInteger)t; // Contract
+        return _min==i._min && _max==i._max;
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMem.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMem.java
new file mode 100644
index 00000000..9ed4c7a8
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMem.java
@@ -0,0 +1,74 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.lang.Long;
+import java.util.BitSet;
+import java.util.ArrayList;
+
+
+/**
+ * Represents a slice of memory corresponding to a set of aliases
+ */
+public class TypeMem extends Type {
+
+    // Which slice of memory?
+    //  0 means TOP, no slice.
+    //  0 means BOT, all memory.
+    //  N means slice#N.
+    public final int _alias;
+    public final Type _t;       // Memory contents, some scalar type
+
+    private TypeMem(int alias, Type t) {
+        super(TMEM);
+        assert alias!=0 || (t==Type.TOP || t==Type.BOTTOM);
+        _alias = alias;
+        _t = t;
+    }
+
+    public static TypeMem make(int alias, Type t) { return new TypeMem(alias,t).intern(); }
+    public static final TypeMem TOP = make(0, Type.TOP   );
+    public static final TypeMem BOT = make(0, Type.BOTTOM);
+
+    public static void gather(ArrayList<Type> ts) { ts.add(make(1,Type.NIL)); ts.add(make(1,TypeInteger.ZERO)); ts.add(BOT); }
+
+    @Override
+    TypeMem xmeet(Type t) {
+        TypeMem that = (TypeMem) t; // Invariant: TypeMem and unequal
+        if( this==TOP ) return that;
+        if( that==TOP ) return this;
+        if( this==BOT ) return BOT;
+        if( that==BOT ) return BOT;
+        int alias = _alias==that._alias ? _alias : 0;
+        Type mt = _t.meet(that._t);
+        return make(alias,mt);
+    }
+
+    @Override
+    public Type dual() {
+        return make(_alias,_t.dual());
+    }
+
+    @Override public boolean isHigh() { return _t.isHigh(); }
+    @Override public Type glb() { return make(_alias,_t.glb()); }
+
+    @Override int hash() { return 9876543 + _alias + _t.hashCode(); }
+
+    @Override boolean eq(Type t) {
+        TypeMem that = (TypeMem) t; // Invariant
+        return _alias == that._alias && _t == that._t;
+    }
+
+    @Override public SB print(SB sb) {
+        sb.p("#");
+        if( _alias==0 ) return sb.p(_t._type==TTOP ? "TOP" : "BOT");
+        return _t.print(sb.p(_alias).p(":"));
+    }
+    @Override public SB gprint(SB sb) {
+        sb.p("#");
+        if( _alias==0 ) return sb.p(_t._type==TTOP ? "TOP" : "BOT");
+        return _t.gprint(sb.p(_alias).p(":"));
+    }
+
+    @Override public String str() { return toString(); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java
new file mode 100644
index 00000000..d7a8b17d
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java
@@ -0,0 +1,105 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Represents a Pointer to memory.
+ *
+ * Null is generic pointer to non-existent memory.
+ * *void is a non-Null pointer to all possible refs, both structs and arrays.
+ * Pointers can be to specific struct and array types, or a union with Null.
+ * The distinguished *$BOT ptr represents union of *void and Null.
+ * The distinguished *$TOP ptr represents the dual of *$BOT.
+ */
+public class TypeMemPtr extends TypeNil {
+    // A TypeMemPtr is pair (obj,nil)
+    // where obj is a TypeStruct, possibly TypeStruct.BOT/TOP
+    // where nil is an explicit null is allowed or not
+
+    // Examples:
+    // (Person,false) - a not-nil Person
+    // (Person,true ) - a Person or a nil
+    // (BOT   ,false) - a not-nil void* (unspecified struct)
+    // (TOP   ,true ) - a nil
+
+    public final TypeStruct _obj;
+
+    private TypeMemPtr(byte nil, TypeStruct obj) {
+        super(TMEMPTR,nil);
+        assert obj!=null;
+        _obj = obj;
+    }
+    static TypeMemPtr make(byte nil, TypeStruct obj) { return new TypeMemPtr(nil, obj).intern(); }
+    public static TypeMemPtr makeNullable(TypeStruct obj) { return make((byte)3, obj); }
+    public static TypeMemPtr make(TypeStruct obj) { return new TypeMemPtr((byte)2, obj).intern(); }
+    public TypeMemPtr makeFrom(TypeStruct obj) { return obj==_obj ? this : make(_nil, obj); }
+    public TypeMemPtr makeNullable() { return makeFrom((byte)3); }
+    @Override TypeMemPtr makeFrom(byte nil) { return nil==_nil ? this : make(nil,_obj); }
+    @Override public TypeMemPtr makeRO() { return makeFrom(_obj.makeRO()); }
+    @Override public boolean isFinal() { return _obj.isFinal(); }
+
+    // An abstract pointer, pointing to either a Struct or an Array.
+    // Can also be null or not, so 4 choices {TOP,BOT} x {nil,not}
+    public static TypeMemPtr BOT = make((byte)3, TypeStruct.BOT);
+    public static TypeMemPtr TOP = BOT.dual();
+    public static TypeMemPtr NOTBOT = make((byte)2,TypeStruct.BOT);
+
+    public static TypeMemPtr TEST= make((byte)2, TypeStruct.TEST);
+    public static void gather(ArrayList<Type> ts) { ts.add(NOTBOT); ts.add(BOT); ts.add(TEST); }
+
+    @Override
+    public TypeNil xmeet(Type t) {
+        TypeMemPtr that = (TypeMemPtr) t;
+        return TypeMemPtr.make(xmeet0(that), (TypeStruct)_obj.meet(that._obj));
+    }
+
+    @Override
+    public TypeMemPtr dual() { return TypeMemPtr.make( dual0(), _obj.dual()); }
+
+    // RHS is NIL; do not deep-dual when crossing the centerline
+    @Override Type meet0() { return _nil==3 ? this : make((byte)3,_obj); }
+
+
+    // True if this "isa" t up to named structures
+    @Override public boolean shallowISA( Type t ) {
+        if( !(t instanceof TypeMemPtr that) ) return false;
+        if( this==that ) return true;
+        if( xmeet0(that)!=that._nil ) return false;
+        if( _obj==that._obj ) return true;
+        if( _obj._name.equals(that._obj._name) )
+            return true;        // Shallow, do not follow matching names, just assume ok
+        throw Utils.TODO(); // return _obj.shallowISA(that._obj);
+    }
+
+    @Override public TypeMemPtr glb() { return make((byte)3,_obj.glb()); }
+    // Is forward-reference
+    @Override public boolean isFRef() { return _obj.isFRef(); }
+
+    @Override public int log_size() { return 2; } // (1<<2)==4-byte pointers
+
+    @Override int hash() { return _obj.hashCode() ^ super.hash(); }
+
+    @Override boolean eq(Type t) {
+        TypeMemPtr ptr = (TypeMemPtr)t; // Invariant
+        return _obj == ptr._obj  && super.eq(ptr);
+    }
+
+    @Override public String str() {
+        if( this== NOTBOT) return "*void";
+        if( this==    BOT) return "*void?";
+        return x()+"*"+_obj.str()+q();
+    }
+
+    @Override public SB print(SB sb) {
+        if( this== NOTBOT) return sb.p("*void");
+        if( this==    BOT) return sb.p("*void?");
+        return _obj.print(sb.p(x()).p("*")).p(q());
+    }
+    @Override public SB gprint(SB sb) {
+        if( this== NOTBOT) return sb.p("*void");
+        if( this==    BOT) return sb.p("*void?");
+        return _obj.gprint(sb.p(x()).p("*")).p(q());
+    }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeNil.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeNil.java
new file mode 100644
index 00000000..aee623ba
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeNil.java
@@ -0,0 +1,62 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Nil-able Scalar types
+ */
+public abstract class TypeNil extends Type {
+    // 0 = high-subclass choice nil
+    // 1 = high-subclass no nil
+    // 2 = low -subclass no nil
+    // 3 = low -subclass also nil
+    final byte _nil;
+
+    TypeNil(byte t, byte nil ) { super(t); _nil = nil; }
+
+    public static void gather(ArrayList<Type> ts) { }
+
+    abstract TypeNil makeFrom(byte nil);
+
+    byte xmeet0(TypeNil that) { return (byte)Math.max(_nil,that._nil); }
+
+    byte dual0() { return (byte)(3-_nil); }
+
+    // RHS is NIL
+    abstract Type meet0();
+
+    // RHS is XNIL
+    Type meetX() {
+        return _nil==0 ? XNIL : (_nil<=2 ? TypePtr.NPTR : TypePtr.PTR);
+    }
+
+    Type nmeet(TypeNil tn) {
+        // Invariants: both are TypeNil subclasses and unequal classes.
+        // If this is TypePtr, we went to TypePtr.nmeet and not here.
+        // If that is TypePtr, this is not (invariant); reverse and go again.
+        if( tn instanceof TypePtr ts ) return ts.nmeet(this);
+
+        // Two mismatched TypeNil, no Scalar.
+        if( _nil==0 && tn._nil==0 ) return XNIL;
+        if( _nil<=2 && tn._nil<=2 ) return TypePtr.NPTR;
+        return TypePtr.PTR;
+    }
+
+    @Override public boolean isHigh       () { return _nil <= 1; }
+    @Override public boolean isConstant   () { return false; }
+    @Override public boolean isHighOrConst() { return isHigh() || isConstant(); }
+
+    @Override public Type glb() { return Type.NIL; }
+
+    public boolean notNull() { return _nil==1 || _nil==2; }
+    public boolean nullable() { return _nil==3; }
+
+    final String q() { return _nil == 1 || _nil == 2 ? "" : "?"; }
+    final String x() { return isHigh() ? "~" : ""; }
+
+    int hash() { return _nil<<17; }
+
+    boolean eq(TypeNil ptr) { return _nil == ptr._nil; }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypePtr.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypePtr.java
new file mode 100644
index 00000000..e9091c25
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypePtr.java
@@ -0,0 +1,53 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Represents a Scalar; a single register-sized value.
+ */
+public class TypePtr extends TypeNil {
+
+    private TypePtr(byte nil) { super(TPTR,nil);  }
+
+    // An abstract pointer, pointing to either a Struct or an Array.
+    // Can also be null or not, so 4 choices {TOP,BOT} x {nil,not}
+    public static TypePtr XPTR = new TypePtr((byte)0).intern();
+    public static TypePtr XNPTR= new TypePtr((byte)1).intern();
+    public static TypePtr NPTR = new TypePtr((byte)2).intern();
+    public static TypePtr PTR  = new TypePtr((byte)3).intern();
+    private static final TypePtr[] PTRS = new TypePtr[]{XPTR,XNPTR,NPTR,PTR};
+
+    public static void gather(ArrayList<Type> ts) { ts.add(PTR); ts.add(NPTR); }
+
+    TypeNil makeFrom(byte nil) { throw Utils.TODO(); }
+
+    @Override public TypeNil xmeet(Type t) {
+        TypePtr that = (TypePtr) t;
+        return PTRS[xmeet0(that)];
+    }
+
+    @Override public TypePtr dual() { return PTRS[dual0()]; }
+
+    // High scalar loses, low scalar wins
+    @Override TypeNil nmeet(TypeNil tn) {
+        if( _nil==0 ) return tn; // High scalar loses
+        if( _nil==1 ) return tn.makeFrom(xmeet0(tn)); // High scalar loses
+        if( _nil==2 ) return tn._nil==3 ? PTR : NPTR; // Low scalar wins
+        return PTR; // this
+    }
+
+
+    // RHS is  NIL
+    @Override Type meet0() { return isHigh() ? NIL : PTR; }
+    // RHS is XNIL
+    // 0->xscalar, 1->nscalar, 2->nscalar, 3->scalar
+    @Override Type meetX() { return _nil==0 ? XNIL : (_nil==3 ? PTR : NPTR); }
+
+    @Override public TypePtr glb() { return PTR; }
+
+    private static final String[] STRS = new String[]{"~ptr","~nptr","nptr","ptr"};
+    @Override public String str() { return STRS[_nil]; }
+    @Override public SB print(SB sb) { return sb.p(str()); }
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeRPC.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeRPC.java
new file mode 100644
index 00000000..ec2f5f0a
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeRPC.java
@@ -0,0 +1,100 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashSet;
+
+/**
+ *  Return Program Control or Return PC or RPC
+ */
+public class TypeRPC extends Type {
+
+    // A set of CallEndNode IDs (or StopNode); commonly just one.
+    // Basically a sparse bit set
+    final HashSet<Integer> _rpcs;
+
+    // If true, invert the meaning of the bits
+    final boolean _any;
+
+    private TypeRPC(boolean any, HashSet<Integer> rpcs) {
+        super(TRPC);
+        _any = any;
+        _rpcs = rpcs;
+    }
+    private static TypeRPC make(boolean any, HashSet<Integer> rpcs) {
+        return new TypeRPC(any,rpcs).intern();
+    }
+
+    public static TypeRPC constant(int cend) {
+        HashSet<Integer> rpcs = new HashSet<>();
+        rpcs.add(cend);
+        return make(false,rpcs);
+    }
+
+    public  static final TypeRPC BOT = make(true,new HashSet<>());
+    private static final TypeRPC TEST2 = constant(2);
+    private static final TypeRPC TEST3 = constant(2);
+
+    public static void gather(ArrayList<Type> ts) { ts.add(BOT); ts.add(TEST2); ts.add(TEST3); }
+
+    @Override public String str() {
+        if( _rpcs.isEmpty() )
+            return _any ? "$[ALL]" : "$[]";
+        if( _rpcs.size()==1 )
+            for( Integer rpc : _rpcs )
+                return _any ? "$[-"+rpc+"]" : "$["+rpc+"]";
+        return "$["+(_any ? "-" : "")+_rpcs+"]";
+    }
+
+    @Override public boolean isConstant() {
+        return !_any && _rpcs.size()==1;
+    }
+
+    @Override
+    public TypeRPC xmeet(Type other) {
+        TypeRPC rpc = (TypeRPC)other;
+        // If the two sets are equal, the _any must be unequal (invariant),
+        // so they cancel and all bits are set.
+        if( _rpcs.equals(rpc._rpcs) )
+            return BOT;
+        // Classic union of bit sets (which might be infinite).
+        HashSet<Integer> lhs = _rpcs, rhs = rpc._rpcs;
+        // Smaller on left
+        if( lhs.size() > rhs.size() ) { lhs = rpc._rpcs; rhs = _rpcs; }
+
+        HashSet<Integer> rpcs = new HashSet<>();
+        boolean any = true;
+        // If both sets are infinite, intersect.
+        if( _any && rpc._any ) {
+            for( Integer i : lhs )  if( rhs.contains(i) )  rpcs.add(i);
+
+        } else if( !_any && !rpc._any ) {
+            // if neither set is infinite, union.
+            rpcs.addAll( lhs );
+            rpcs.addAll( rhs );
+            any = false;
+        } else {
+            // If one is infinite, subtract the other from it.
+            HashSet<Integer> sub = _any ? rpc._rpcs : _rpcs;
+            HashSet<Integer> inf = _any ? _rpcs : rpc._rpcs;
+            for( Integer i : inf )
+                if( inf.contains(i) && !sub.contains(i) )
+                    rpcs.add(i);
+        }
+        return make(any,rpcs);
+    }
+
+    @Override
+    public Type dual() { return make(!_any,_rpcs); }
+
+    @Override
+    int hash() { return _rpcs.hashCode() ^ (_any ? -1 : 0) ; }
+    @Override
+    public boolean eq( Type t ) {
+        TypeRPC rpc = (TypeRPC)t; // Contract
+        return _any==rpc._any && _rpcs.equals(rpc._rpcs);
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeStruct.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeStruct.java
new file mode 100644
index 00000000..6c5cb8d4
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeStruct.java
@@ -0,0 +1,248 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import java.util.ArrayList;
+
+/**
+ * Represents a struct type.
+ */
+public class TypeStruct extends Type {
+
+    // A Struct has a name and a set of fields; the fields themselves have
+    // names, types and aliases.  The name has no semantic meaning, but is
+    // useful for debugging.  Briefly during parsing a Struct can be a
+    // forward-ref; in this case the _fields array is null.
+
+    // Its illegal to attempt to load a field from a forward-ref struct.
+
+    // Example: "int rez = new S.x; struct S { int x; } return rez;" // Error, S not defined
+    // Rewrite: "struct S { int x; } int rez = new S.x; return rez;" // Ok, no forward ref
+    //
+    // During the normal optimization run, struct types "bottom out" at further
+    // struct references, so we don't have to handle e.g. cyclic types.  The
+    // "bottom out" is again the forward-ref struct.
+    public final String _name;
+    public final Field[] _fields;
+
+    TypeStruct(String name, Field[] fields) {
+        super(TSTRUCT);
+        _name = name;
+        _fields = fields;
+    }
+
+    // All fields directly listed
+    public static TypeStruct make(String name, Field... fields) { return new TypeStruct(name, fields).intern(); }
+    public static final TypeStruct TOP = make("$TOP",new Field[0]);
+    public static final TypeStruct BOT = make("$BOT",new Field[0]);
+    public static final TypeStruct TEST = make("test",new Field[]{Field.TEST});
+    // Forward-ref version
+    public static TypeStruct makeFRef(String name) { return make(name, (Field[])null); }
+    // Make a read-only version
+    @Override public TypeStruct makeRO() {
+        if( isFinal() ) return this;
+        Field[] flds = new Field[_fields.length];
+        for( int i=0; i<flds.length; i++ )
+            flds[i] = _fields[i].makeRO();
+        return make(_name,flds);
+    }
+
+    // Array
+    public static TypeStruct makeAry(TypeInteger len, int lenAlias, Type body, int bodyAlias) {
+        assert body instanceof TypeInteger || body instanceof TypeFloat || (body instanceof TypeNil tn && tn.nullable());
+        assert len.isa(TypeInteger.U32);
+        return make("[" + body.str() + "]",
+                    Field.make("#" ,len , lenAlias,true ),
+                    Field.make("[]",body,bodyAlias,false));
+    }
+
+    // A pair of self-cyclic types
+    private static final TypeStruct S1F = makeFRef("S1");
+    private static final TypeStruct S2F = makeFRef("S2");
+    public  static final TypeStruct S1  = make("S1", Field.make("a", TypeInteger.BOT, -1, false), Field.make("s2",TypeMemPtr.make((byte)2,S2F),-2, false) );
+    private static final TypeStruct S2  = make("S2", Field.make("b", TypeFloat  .F64, -3, false), Field.make("s1",TypeMemPtr.make((byte)2,S1F),-4, false) );
+
+    private static final TypeStruct ARY = makeAry(TypeInteger.U32,-1,TypeInteger.BOT,-2);
+
+    public static void gather(ArrayList<Type> ts) { ts.add(TEST); ts.add(BOT); ts.add(S1); ts.add(S2); ts.add(ARY); }
+
+    // Find field index by name
+    public int find(String fname) {
+        for( int i=0; i<_fields.length; i++ )
+            if( _fields[i]._fname.equals(fname) )
+                return i;
+        return -1;
+    }
+    public Field field(String fname) {
+        int idx = find(fname);
+        return idx== -1 ? null : _fields[idx];
+    }
+
+    // Find field index by alias
+    public int findAlias( int alias ) {
+        for( int i=0; i<_fields.length; i++ )
+            if( _fields[i]._alias==alias )
+                return i;
+        return -1;
+    }
+
+
+    @Override
+    Type xmeet(Type t) {
+        TypeStruct that = (TypeStruct) t;
+        if( this==TOP ) return that;
+        if( that==TOP ) return this;
+        if( this==BOT ) return BOT;
+        if( that==BOT ) return BOT;
+
+        // Within the same compilation unit, struct names are unique.  If the
+        // names differ, its different structs.  Across many compilation units,
+        // structs with the same name but different field layouts can be
+        // interned... which begs the question:
+        // "What is the meet of structs from two different compilation units?"
+        // And the answer is: "don't ask".
+        if( !_name.equals(that._name) )
+            return BOT;         // It's a struct; that's about all we know
+        if( this._fields==null ) return that;
+        if( that._fields==null ) return this;
+        if( _fields.length != that._fields.length ) return BOT;
+        // Just do field meets
+        Field[] flds = new Field[_fields.length];
+        for( int i=0; i<_fields.length; i++ ) {
+            Field f0 = _fields[i], f1 = that._fields[i];
+            if( !f0._fname.equals(f1._fname) || f0._alias != f1._alias )
+                return BOT;
+            flds[i] = (Field)f0.meet(f1);
+        }
+        return make(_name,flds);
+    }
+
+    @Override
+    public TypeStruct dual() {
+        if( this==TOP ) return BOT;
+        if( this==BOT ) return TOP;
+        if( _fields == null ) return this;
+        Field[] flds = new Field[_fields.length];
+        for( int i=0; i<_fields.length; i++ )
+            flds[i] = _fields[i].dual();
+        return make(_name,flds);
+    }
+
+    // Keeps the same struct, but lower-bounds all fields.
+    @Override public TypeStruct glb() {
+        if( _glb() ) return this;
+        // Need to glb each field
+        Field[] flds = new Field[_fields.length];
+        for( int i=0; i<_fields.length; i++ )
+            flds[i] = _fields[i].glb();
+        return make(_name,flds);
+    }
+    private boolean _glb() {
+        if( _fields!=null )
+          for( Field f : _fields )
+              if( f.glb() != f )
+                 return false;
+        return true;
+    }
+
+    // Is forward-reference
+    @Override public boolean isFRef() { return _fields==null; }
+    // All fields are final
+    @Override public boolean isFinal() {
+        if( _fields==null ) return true;
+        for( Field fld : _fields )
+            if( !fld.isFinal() )
+                return false;
+        return true;
+    }
+
+    @Override
+    boolean eq(Type t) {
+        TypeStruct ts = (TypeStruct)t; // Invariant
+        if( !_name.equals(ts._name) )
+            return false;
+        if( _fields == ts._fields ) return true;
+        if( _fields==null || ts._fields==null ) return false;
+        if( _fields.length!=ts._fields.length )
+            return false;
+        for( int i = 0; i < _fields.length; i++ )
+            if( _fields[i] != ts._fields[i] )
+                return false;
+        return true;
+    }
+
+    @Override
+    int hash() {
+        long hash = _name.hashCode();
+        if( _fields != null )
+            for( Field f : _fields )
+                hash = Utils.rot(hash,13) ^ f.hashCode();
+        return Utils.fold(hash);
+    }
+
+    @Override
+    public SB print(SB sb) {
+        sb.p(_name);
+        if( _fields == null ) return sb; // Forward reference struct, just print the name
+        sb.p(" {");
+        for( Field f : _fields )
+            f._type.print(sb).p(f._final ? " " : " !").p(f._fname).p("; ");
+        return sb.p("}");
+    }
+    @Override public SB gprint( SB sb ) { return sb.p(_name); }
+
+    @Override public String str() { return _name; }
+
+
+    public boolean isAry() { return _fields.length==2 && _fields[1]._fname.equals("[]"); }
+
+    public int aryBase() {
+        assert isAry();
+        if( _offs==null ) _offs = offsets();
+        return _offs[1];
+    }
+    public int aryScale() {
+        assert isAry();
+        return _fields[1]._type.log_size();
+    }
+
+
+    // Field offsets as packed byte offsets
+    private int[] _offs;  // Lazily computed and not part of the type semantics
+    public int offset(int idx) {
+        if( _offs==null ) _offs = offsets();
+        return _offs[idx];
+    }
+    private int[] offsets() {    // Field byte offsets
+        // Compute a layout for a collection of fields
+        assert _fields != null; // No forward refs
+
+        // Array layout is different: len,[pad],body...
+        if( isAry() )
+            return _offs = new int[]{ 0, _fields[1]._type.log_size() < 3 ? 4 : 8 };
+
+        // Compute a layout
+        int[] cnts = new int[4]; // Count of fields at log field size
+        for( Field f : _fields )
+            cnts[f._type.log_size()]++; // Log size is 0(byte), 1(i16/u16), 2(i32/f32), 3(i64/dbl)
+        int off = 0, idx = 0; // Base common struct fields go here, e.g. Mark/Klass
+        // Compute offsets to the start of each power-of-2 aligned fields.
+        int[] offs = new int[4];
+        for( int i=3; i>=0; i-- ) {
+            offs[i] = off;
+            off += cnts[i]<<i;
+        }
+        // Assign offsets to all fields.
+        // Really a hidden radix sort.
+        _offs = new int[_fields.length+1];
+        for( Field f : _fields ) {
+            int log = f._type.log_size();
+            _offs[idx++] = offs[log]; // Field offset
+            offs[log] += 1<<log;      // Next field offset at same alignment
+            cnts[log]--;              // Count down, should be all zero at end
+        }
+        _offs[_fields.length] = (off+7)& ~7; // Round out to max alignment
+        return _offs;
+    }
+
+}
diff --git a/chapter20/src/main/java/com/seaofnodes/simple/type/TypeTuple.java b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeTuple.java
new file mode 100644
index 00000000..6d3a2b69
--- /dev/null
+++ b/chapter20/src/main/java/com/seaofnodes/simple/type/TypeTuple.java
@@ -0,0 +1,97 @@
+package com.seaofnodes.simple.type;
+
+import com.seaofnodes.simple.SB;
+import java.util.ArrayList;
+
+public class TypeTuple extends Type {
+
+    public final Type[] _types;
+
+    private TypeTuple(Type[] types) { super(TTUPLE); _types = types; }
+    public  static TypeTuple make(Type... types) { return new TypeTuple(types).intern(); }
+
+    public static final TypeTuple BOT = new TypeTuple(new Type[0]).intern();
+    public static final TypeTuple TOP = new TypeTuple(null).intern();
+
+    public static final TypeTuple TEST = make(TypeInteger.BOT,TypeMemPtr.TEST);
+    public static final TypeTuple START= make(Type.CONTROL,TypeMem.TOP,TypeInteger.BOT);
+    public static final TypeTuple MAIN = make(TypeInteger.BOT);
+    public static final TypeTuple RET  = make(Type.CONTROL,TypeMem.BOT,Type.BOTTOM);
+
+    public static final TypeTuple IF_BOTH    = make(new Type[]{Type. CONTROL,Type. CONTROL});
+    public static final TypeTuple IF_NEITHER = make(new Type[]{Type.XCONTROL,Type.XCONTROL});
+    public static final TypeTuple IF_TRUE    = make(new Type[]{Type. CONTROL,Type.XCONTROL});
+    public static final TypeTuple IF_FALSE   = make(new Type[]{Type.XCONTROL,Type. CONTROL});
+
+    public  static void gather(ArrayList<Type> ts) { ts.add(BOT); ts.add(TEST); ts.add(START); ts.add(MAIN); ts.add(IF_TRUE); }
+
+    @Override
+    Type xmeet(Type other) {
+        TypeTuple tt = (TypeTuple)other;     // contract from xmeet
+        if( this==TOP ) return other;
+        if( tt  ==TOP ) return this ;
+        if( _types.length != tt._types.length )
+            return BOT;
+        Type[] ts = new Type[_types.length];
+        for( int i=0; i<_types.length; i++ )
+            ts[i] = _types[i].meet(tt._types[i]);
+        return make(ts);
+    }
+
+    @Override public TypeTuple dual() {
+        if( this==TOP ) return BOT;
+        if( this==BOT ) return TOP;
+        Type[] ts = new Type[_types.length];
+        for( int i=0; i<_types.length; i++ )
+            ts[i] = _types[i].dual();
+        return make(ts);
+    }
+
+    @Override
+    public Type glb() {
+        Type[] ts = new Type[_types.length];
+        for( int i=0; i<_types.length; i++ )
+            ts[i] = _types[i].glb();
+        return make(ts);
+    }
+
+    @Override public String str() { return print(new SB()).toString(); }
+
+    @Override public SB print(SB sb) {
+        if( this==TOP ) return sb.p("[TOP]");
+        if( this==BOT ) return sb.p("[BOT]");
+        sb.p("[  ");
+        for( Type t : _types )
+            t.print(sb).p(", ");
+        return sb.unchar(2).p("]");
+    }
+    @Override public SB gprint(SB sb) {
+        if( this==TOP ) return sb.p("[TOP]");
+        if( this==BOT ) return sb.p("[BOT]");
+        sb.p("[  ");
+        for( Type t : _types )
+            t.gprint(sb).p(", ");
+        return sb.unchar(2).p("]");
+    }
+
+    @Override
+    int hash() {
+        int sum = 0;
+        if( _types!=null ) for( Type type : _types ) sum ^= type.hashCode();
+        return sum;
+    }
+
+    @Override
+    boolean eq( Type t ) {
+        TypeTuple tt = (TypeTuple)t; // Contract
+        if( _types==null && tt._types==null ) return true;
+        if( _types==null || tt._types==null ) return false;
+        if( _types.length != tt._types.length ) return false;
+        for( int i=0; i<_types.length; i++ )
+            if( _types[i]!=tt._types[i] )
+                return false;
+        return true;
+    }
+
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java b/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
new file mode 100644
index 00000000..8f09cb3d
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
@@ -0,0 +1,69 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import java.nio.charset.StandardCharsets;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class BrainFuckTest {
+
+    @Test
+    public void testBrainfuck() {
+        var program = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.".getBytes(StandardCharsets.UTF_8);
+        var encoded = new StringBuilder("u8[] !program = new u8[").append(program.length).append("];");
+        for (int i = 0; i < program.length; i++) {
+            int value = program[i] & 0xFF;
+            encoded.append("program[").append(i).append("] = ").append(value).append(";");
+        }
+
+        CodeGen code = new CodeGen(
+                encoded + """
+
+int d = 0;
+u8[] !output = new u8[0];
+u8[] !data = new u8[100];
+
+for( int pc = 0; pc < program#; pc++ ) {
+    var command = program[pc];
+    if (command == 62) {
+        d++;
+    } else if (command == 60) {
+        d--;
+    } else if (command == 43) {
+        data[d]++;
+    } else if (command == 45) {
+        data[d]--;
+    } else if (command == 46) {
+        // Output a byte; increase the output array size
+        var old = output;
+        output = new u8[output# + 1];
+        for( int i = 0; i < old#; i++ )
+            output[i] = old[i];
+        output[old#] = data[d]; // Add the extra byte on the end
+    } else if (command == 44) {
+        data[d] = 42;
+    } else if (command == 91) {
+        if (data[d] == 0) {
+            for( int d = 1; d > 0; ) {
+                command = program[++pc];
+                if (command == 91) d++;
+                if (command == 93) d--;
+            }
+        }
+    } else if (command == 93) {
+        if (data[d]) {
+            for( int d = 1; d > 0; ) {
+                command = program[--pc];
+                if (command == 93) d++;
+                if (command == 91) d--;
+            }
+        }
+    }
+}
+return output;
+                """);
+        code.parse().opto().typeCheck()/*.instSelect("x86_64_v2", "SystemV")*/.GCM().localSched();
+        assertEquals("Hello World!\n", Eval2.eval(code, 0, 10000));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java
new file mode 100644
index 00000000..934eda76
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java
@@ -0,0 +1,94 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter01Test {
+
+    @Test
+    public void testSimpleProgram() {
+        CodeGen code = new CodeGen("return 1;").parse();
+        Node expr = code.expr();
+        if( expr instanceof ConstantNode con ) {
+            assertEquals(code._start,con.in(0));
+            assertEquals(TypeInteger.constant(1), con._type);
+        } else {
+            fail();
+        }
+    }
+
+    @Test
+    public void testZero() {
+        CodeGen code = new CodeGen("return 0;");
+        code.parse();
+        for( Node use : code._start._outputs )
+            if( use instanceof ConstantNode con && con._type instanceof TypeInteger )
+                assertEquals(TypeInteger.constant(0),con._type);
+    }
+
+    @Test
+    public void testBad1() {
+        try {
+            new CodeGen("ret;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'ret'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad2() {
+        try {
+            new CodeGen("return 0123;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error: integer values cannot start with '0'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad3() {
+        // this test used to fail in chapter 1
+        assertEquals("return 12;", new CodeGen("return - -12;").parse()._stop.print());
+    }
+
+    @Test
+    public void testBad4() {
+        try {
+            new CodeGen("return 100").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected ;: ",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad5() {
+        // this test used to fail in chapter 1
+        assertEquals("return -100;", new CodeGen("return -100;").parse()._stop.print());
+    }
+
+    @Test
+    public void testBad6() {
+        try {
+            new CodeGen("return100;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'return100'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad7() {
+        try {
+            new CodeGen("return 1;}").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, unexpected: }",e.getMessage());
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java
new file mode 100644
index 00000000..d8607c32
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java
@@ -0,0 +1,60 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter02Test {
+
+    @Test
+    public void testParseGrammar() {
+        CodeGen code = new CodeGen("return 1+2*3+-5;");
+        code.parse(); // No more disable peepholes
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testAddPeephole() {
+        CodeGen code = new CodeGen("return 1+2;");
+        code.parse();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testSubPeephole() {
+        CodeGen code = new CodeGen("return 1-2;");
+        code.parse();
+        assertEquals("return -1;", code.print());
+    }
+
+    @Test
+    public void testMulPeephole() {
+        CodeGen code = new CodeGen("return 2*3;");
+        code.parse();
+        assertEquals("return 6;", code.print());
+    }
+
+    @Test
+    public void testDivPeephole() {
+        CodeGen code = new CodeGen("return 6/3;");
+        code.parse();
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testMinusPeephole() {
+        CodeGen code = new CodeGen("return 6/-3;");
+        code.parse();
+        assertEquals("return -2;", code.print());
+    }
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen("return 1+2*3+-5;");
+        code.parse();
+        assertEquals("return 2;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java
new file mode 100644
index 00000000..4f9b2490
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java
@@ -0,0 +1,73 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter03Test {
+
+    @Test
+    public void testVarDecl() {
+        CodeGen code = new CodeGen("int a=1; return a;");
+        code.parse(); assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testVarAdd() {
+        CodeGen code = new CodeGen("int a=1; int b=2; return a+b;");
+        code.parse();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testVarScope() {
+        CodeGen code = new CodeGen("int a=1; int b=2; int c=0; { int b=3; c=a+b; } return c;");
+        code.parse();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testVarScopeNoPeephole() {
+        CodeGen code = new CodeGen("int a=1; int b=2; int !c=0; { int b=3; c=a+b;  } return c; ");
+        code.parse();           // Peepholes always run now
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testVarDist() {
+        CodeGen code = new CodeGen("int x0=1; int y0=2; int x1=3; int y1=4; return (x0-x1)*(x0-x1) + (y0-y1)*(y0-y1); ");
+        code.parse();
+        assertEquals("return 8;", code.print());
+    }
+
+    @Test
+    public void testSelfAssign() {
+        try {
+            new CodeGen("int a=a; return a;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'a'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testRedeclareVar() {
+        try {
+            new CodeGen("int a=1; int b=2; int c=0; int b=3; c=a+b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Redefining name 'b'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad1() {
+        try {
+            new CodeGen("int a=1; int b=2; int !c=0; { int b=3; c=a+b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected }: ",e.getMessage());
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java
new file mode 100644
index 00000000..d09b1748
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -0,0 +1,130 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+import org.junit.Ignore;
+
+import static org.junit.Assert.*;
+
+public class Chapter04Test {
+
+    @Test
+    public void testPeephole() {
+        CodeGen code = new CodeGen("return 1+arg+2; ");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testPeephole2() {
+        CodeGen code = new CodeGen("return (1+arg)+2;");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testAdd0() {
+        CodeGen code = new CodeGen("return 0+arg;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testAddAddMul() {
+        CodeGen code = new CodeGen("return arg+0+arg;");
+        code.parse();
+        assertEquals("return (arg<<1);", code.print());
+    }
+
+    @Test
+    public void testPeephole3() {
+        CodeGen code = new CodeGen("return 1+arg+2+arg+3; ");
+        code.parse();
+        assertEquals("return ((arg<<1)+6);", code.print());
+    }
+
+    @Test
+    public void testMul1() {
+        CodeGen code = new CodeGen("return 1*arg;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testVarArg() {
+        CodeGen code = new CodeGen("return arg; ");
+        code.parse();
+        assertTrue(code.ctrl() instanceof  FunNode);
+        assertTrue(code.expr() instanceof ParmNode);
+    }
+
+    // Adding functions means `main` does not constant fold the incoming arg value
+    @Ignore @Test
+    public void testConstantArg() {
+        CodeGen code = new CodeGen("return arg; ", TypeInteger.constant(2), 123L).parse();
+        assertEquals("return 2;", code.expr().in(1).toString());
+    }
+
+    @Test
+    public void testCompEq() {
+        CodeGen code = new CodeGen("return 3==3; ");
+        code.parse();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testCompEq2() {
+        CodeGen code = new CodeGen("return 3==4; ");
+        code.parse();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testCompNEq() {
+        CodeGen code = new CodeGen("return 3!=3; ");
+        code.parse();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testCompNEq2() {
+        CodeGen code = new CodeGen("return 3!=4; ");
+        code.parse();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testBug1() {
+        CodeGen code = new CodeGen("int a=arg+1; int !b=a; b=1; return a+2; ");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testBug2() {
+        CodeGen code = new CodeGen("int !a=arg+1; a=a; return a; ");
+        code.parse();
+        assertEquals("return (arg+1);", code.print());
+    }
+
+    @Test
+    public void testBug3() {
+        try { new CodeGen("inta=1; return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'inta'",e.getMessage()); }
+    }
+
+    @Test
+    public void testBug4() {
+        CodeGen code = new CodeGen("return -arg;");
+        code.parse();
+        assertEquals("return (-arg);", code.print());
+    }
+
+    @Test
+    public void testBug5() {
+        CodeGen code = new CodeGen("return arg--2;");
+        code.parse();
+        assertEquals("return (arg--2);", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java
new file mode 100644
index 00000000..86ec4136
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -0,0 +1,185 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter05Test {
+
+    @Test
+    public void testIfStmt() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg == 1)
+    a = arg+2;
+else {
+    a = arg-3;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,(arg+2),(arg-3));", code.print());
+    }
+
+    @Test
+    public void testTest() {
+        CodeGen code = new CodeGen(
+"""
+int c = 3;
+int b = 2;
+if (arg == 1) {
+    b = 3;
+    c = 4;
+}
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,3);", code.print());
+    }
+
+    @Test
+    public void testReturn2() {
+        CodeGen code = new CodeGen(
+"""
+if( arg==1 )
+    return 3;
+else
+    return 4;
+""");
+        code.parse();
+        assertEquals("return Phi(Region,3,4);", code.print());
+    }
+
+    @Test
+    public void testIfMergeB() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=0;
+if( arg==1 )
+    b=a;
+else
+    b=a+1;
+return a+b;""");
+        code.parse().opto();
+        assertEquals("return ((arg<<1)+Phi(Region,2,3));", code.print());
+    }
+
+    @Test
+    public void testIfMerge2() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=arg+2;
+if( arg==1 )
+    b=b+a;
+else
+    a=b+1;
+return a+b;""");
+        code.parse().opto();
+        assertEquals("return ((Phi(Region,(arg<<1),arg)+arg)+Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge3() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,2,3),Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge4() {
+        CodeGen code = new CodeGen(
+"""
+int a=0;
+int b=0;
+if( arg )
+    a=1;
+if( arg==0 )
+    b=2;
+return arg+a+b;
+""");
+        code.parse().opto();
+        assertEquals("return ((arg+Phi(Region,1,0))+Phi(Region,2,0));", code.print());
+    }
+
+    @Test
+    public void testMerge5() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg==2;
+if( arg==1 )
+{
+    a=arg==3;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return (arg==Phi(Region,3,2));", code.print());
+    }
+
+    @Test
+    public void testTrue() {
+      CodeGen code = new CodeGen("return true;").parse();
+      assertEquals("return 1;",code.print());
+    }
+
+    @Test
+    public void testHalfDef() {
+        try { new CodeGen("if( arg==1 ) int b=2; return b;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Cannot define a 'b' on one arm of an if",e.getMessage()); }
+    }
+
+    @Test
+    public void testHalfDef2() {
+        try { new CodeGen("if( arg==1 ) { int b=2; } else { int b=3; } return b;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'b'",e.getMessage()); }
+    }
+
+    @Test
+    public void testRegress1() {
+        try { new CodeGen("if(arg==2) int a=1; else int b=2; return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Cannot define a 'a' on one arm of an if",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testBadNum() {
+        try { new CodeGen("return 1-;").parse();  fail(); }
+        catch( RuntimeException e ) { assertEquals("Syntax error, expected an identifier or expression: ;",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword1() {
+        try { new CodeGen("int true=0; return true;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Expected an identifier, found 'true'",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword2() {
+        try { new CodeGen("int else=arg; if(else) else=2; else else=1; return else;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Expected an identifier, found 'else'",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword3() {
+        try { new CodeGen("int a=1; ififif(arg);a=2;return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'ififif'",e.getMessage()); }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java
new file mode 100644
index 00000000..117531f0
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -0,0 +1,304 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter06Test {
+
+    @Test
+    public void testPeepholeReturn() {
+        CodeGen code = new CodeGen("""
+if( true ) return 2;
+return 1;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertTrue(code.ctrl() instanceof FunNode);
+    }
+
+    @Test
+    public void testPeepholeRotate() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg)
+    a = 2;
+return (arg < a) < 3; // Because (arg < a) is a bool/uint1/[0-1], its always less than 3
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testPeepholeCFG() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( true )
+  a=2;
+else
+  a=3;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertTrue(code.ctrl() instanceof FunNode);
+    }
+
+    @Test
+    public void testIfIf() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg!=1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( a==2 )
+    b=42;
+else
+    b=5;
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,42,5);", code.print());
+    }
+
+    @Test
+    public void testIfArgIf() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( 1==1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( arg==2 )
+    b=a;
+else
+    b=5;
+return b;""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,2,5);", code.print());
+    }
+
+    @Test
+    public void testMerge3With2() {
+        CodeGen code = new CodeGen(
+"""
+arg=2;
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(2), 123L).parse().opto();
+        assertEquals("return 5;", code.print());
+    }
+
+    @Test
+    public void testMerge3With1() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1), 123L).parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,3,Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole1() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole3() {
+        CodeGen code = new CodeGen(
+"""
+arg=3;
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(3), 123L);
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testDemo1NonConst() {
+        CodeGen code = new CodeGen("""
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,1);", code.print());
+    }
+
+
+    @Test
+    public void testDemo1True() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testDemo1False() {
+        CodeGen code = new CodeGen(
+"""
+arg=0;
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(0), 123L);
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testDemo2NonConst() {
+        CodeGen code = new CodeGen("""
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""");
+        code.parse().opto();
+        assertEquals("return (Phi(Region,Phi(Region,2,3),0)+Phi(Region,3,1));", code.print());
+    }
+
+
+    @Test
+    public void testDemo2True() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 6;", code.print());
+    }
+
+    @Test
+    public void testDemo2arg2() {
+        CodeGen code = new CodeGen(
+"""
+arg=2;
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(2), 123L);
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java
new file mode 100644
index 00000000..6d6a3ce7
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java
@@ -0,0 +1,221 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter07Test {
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen(
+"""
+while(arg < 10) {
+    arg = arg + 1;
+}
+return arg;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testRegression() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if(arg){}else{
+    while(a < 10) {
+        a = a + 1;
+    }
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1,Phi(Loop,1,(Phi_a+1)));", code.print());
+    }
+
+    @Test
+    public void testWhileNested() {
+        CodeGen code = new CodeGen(
+"""
+int sum = 0;
+int i = 0;
+while(i < arg) {
+    i = i + 1;
+    int j = 0;
+    while( j < arg ) {
+        sum = sum + j;
+        j = j + 1;
+    }
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,Phi(Loop,Phi_sum,(Phi_sum+Phi(Loop,0,(Phi_j+1)))));", code.print());
+    }
+
+    @Test
+    public void testWhileScope() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    if (a == 2) a = 3;
+    else b = 4;
+}
+return b;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,2,Phi(Region,Phi_b,4));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhileNestedIfAndInc() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    if (a == 2) a = 3;
+    else b = 4;
+    b = b + 1;
+    a = a + 1;
+}
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,2,(Phi(Region,Phi_b,4)+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testWhile() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    a = a + 1;
+    a = a + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhilePeep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    a = a + 1;
+    a = a + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile2() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(arg) a = 2;
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,2);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile2Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(arg) a = 2;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,2);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile3() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile3Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile4() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile4Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java
new file mode 100644
index 00000000..350df18b
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java
@@ -0,0 +1,207 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter08Test {
+
+    @Test
+    public void testEx6() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        break;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+        Assert.assertEquals( "5", Eval2.eval(code, 1));
+        Assert.assertEquals("10", Eval2.eval(code, 6));
+    }
+
+
+    @Test
+    public void testEx5() {
+        CodeGen code = new CodeGen(
+                """
+int a = 1;
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 7)
+        continue;
+    a = a + 1;
+}
+return a;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,Phi(Region,Phi_a,(Phi_a+1)));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testEx4() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+    @Test
+    public void testEx3() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+
+    @Test
+    public void testEx2() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 6)
+        continue;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testEx1() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testRegress1() {
+        CodeGen code = new CodeGen(
+                """
+while( arg < 10 ) {
+    int a = arg+2;
+    if( a > 4 )
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testRegress2() {
+        CodeGen code = new CodeGen("if(1) return 0;  else while(arg>- -arg) arg=arg+1; return 0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBreakOutsideLoop() {
+        try {
+            new CodeGen("""
+if(arg <= 10) {
+    break;
+    arg = arg + 1;
+}
+return arg;
+""").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("No active loop for a break or continue",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testRegress3() {
+        CodeGen code = new CodeGen("""
+while(arg < 10) {
+    break;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testRegress4() {
+        CodeGen code = new CodeGen("""
+int a = 1;
+while(arg < 10) {
+    a = a + 1;
+    if (arg > 2) {
+        int a = 17;
+        break;
+    }
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,1,(Phi_a+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+    @Test
+    public void testRegress5() {
+        CodeGen code = new CodeGen("""
+int a = 1;
+while(1) {
+    a = a + 1;
+    if (a<10) continue;
+    break;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return (Phi(Loop,1,Add)+1);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode prj && prj._idx==1 );
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java
new file mode 100644
index 00000000..10f4a78b
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java
@@ -0,0 +1,296 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.Ignore;
+
+import static org.junit.Assert.*;
+
+public class Chapter09Test {
+
+    @Test
+    @Ignore
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+arg=0;
+while(v0) {
+        while(1) if(arg*arg*0==0) {}
+                while(0) {}
+    arg=1;
+}
+return 0;
+                """);
+        code.parse().opto();
+    }
+
+    @Test
+    public void testGVN1() {
+        CodeGen code = new CodeGen(
+                """
+int x = arg + arg;
+if(arg < 10) {
+    return arg + arg;
+}
+else {
+    x = x + 1;
+}
+return x;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,(arg<<1),(Shl+1));", code.print());
+        Assert.assertEquals( "2", Eval2.eval(code,  1));
+        Assert.assertEquals("23", Eval2.eval(code, 11));
+    }
+
+    @Test
+    public void testGVN2() {
+        CodeGen code = new CodeGen("return arg*arg-arg*arg;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        Assert.assertEquals("0", Eval2.eval(code,  1, 1));
+    }
+
+    @Test
+    public void testWorklist1() {
+        CodeGen code = new CodeGen("""
+int step = 1;
+while (arg < 10) {
+    arg = arg + step + 1;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+2));", code.print());
+        Assert.assertEquals("11", Eval2.eval(code,  1));
+    }
+
+    @Test
+    public void testWorklist2() {
+        CodeGen code = new CodeGen(
+                """
+int cond = 0;
+int one = 1;
+while (arg < 10) {
+    if (cond) one = 2;
+    arg = arg + one*3 + 1;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+4));", code.print());
+        Assert.assertEquals("13", Eval2.eval(code,  1));
+    }
+
+    @Test
+    public void testWorklist3() {
+        CodeGen code = new CodeGen(
+                """
+int v1 = 0;
+int v2 = 0;
+int v3 = 0;
+int v4 = 0;
+int v5 = 0;
+int v6 = 0;
+int v7 = 0;
+int v8 = 0;
+while (arg) {
+    if (v1) v2 = 1;
+    if (v2) v3 = 1;
+    if (v3) v4 = 1;
+    if (v4) v5 = 1;
+    if (v5) v6 = 1;
+    if (v6) v7 = 1;
+    if (v7) v8 = 1;
+    arg = arg + v8 + 1;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testRegionPeepBug() {
+        CodeGen code = new CodeGen(
+                """
+int v0=0;
+int v1=0;
+while(v1+arg) {
+    arg=0;
+    int v2=v0;
+    while(arg+1) {}
+    v0=1;
+    v1=v2;
+}
+                """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testWhile0() {
+        CodeGen code = new CodeGen("while(0) continue; if(0) arg=0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testWhile1() {
+        CodeGen code = new CodeGen("""
+if(0) while(0) {
+    int arg=arg;
+    while(0) {}
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+
+    @Test
+    public void testPrecedence() {
+        CodeGen code = new CodeGen("return 3-1+2;");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testSwap2() {
+        CodeGen code = new CodeGen("return 1+(1+1);");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+
+    @Test
+    public void testFuzz0() {
+        CodeGen code = new CodeGen("""
+int one = 1;
+int a = 0;
+int zero = 0;
+while(arg) {
+    a = -(one + a + 2);
+    arg = arg + 1;
+    one = one + zero;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(-(Phi_a+3)));", code.print());
+    }
+
+    @Test
+    public void testFuzz1() {
+        CodeGen code = new CodeGen("""
+while(1) {}
+while(arg) break;
+while(arg) arg=0;
+arg=0;
+int v0=0!=0<-0;
+return -0+0+0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+
+    @Test
+    public void testFuzz2() {
+        CodeGen code = new CodeGen("return 0+-0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz3() {
+        CodeGen code = new CodeGen("int v0=0; while(0==69) while(v0) return 0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz4() {
+        CodeGen code = new CodeGen("""
+while(1) {
+    arg=0<=0;
+    if(1<0) while(arg==-0) arg=arg-arg;
+}
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz5() {
+        CodeGen code = new CodeGen("""
+{
+    int v0=0;
+    while(1)
+            int v1=0--0;
+    while(v0)
+        break;
+    while(-v0) {
+        while(0+0+v0) continue;
+        break;
+    }
+    if(-0!=-0+0+v0) while(0+0+0+0)
+                break;
+}
+return 0!=0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz6() {
+        CodeGen code = new CodeGen(
+"""
+int v0=0;
+while(0==1) while(v0)
+        v0=1+v0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz7() {
+        CodeGen code = new CodeGen("""
+while(1) {}
+int v0=0;
+while(v0)
+    {}
+int v1=0;
+while(1)
+        v1=1;
+return v1+v0;
+                                   """);
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz8() {
+        CodeGen code = new CodeGen("while(arg) arg = arg - 1;  return arg;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testMeet() {
+        Type t1 = Type.TOP;
+        Type t2 = TypeInteger.TOP;
+        Assert.assertEquals(TypeInteger.TOP, t1.meet(t2));
+        Assert.assertEquals(TypeInteger.TOP, t2.meet(t1));
+        t1 = Type.BOTTOM;
+        t2 = TypeInteger.BOT;
+        Assert.assertEquals(Type.BOTTOM, t1.meet(t2));
+        Assert.assertEquals(Type.BOTTOM, t2.meet(t1));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
new file mode 100644
index 00000000..02029b3f
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -0,0 +1,396 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter10Test {
+
+    @Test
+    public void testFuzzer() {
+        CodeGen code = new CodeGen(
+"""
+int a = arg/3;
+int b = arg*5;
+int x = arg*7;
+int y = arg/11;
+int p; int g; int h;
+if( (arg/13)==0 ) {
+    p = x + y;
+    g = x;
+    h = y;
+} else {
+    p = a + b;
+    g = a;
+    h = b;
+}
+int r = g+h;
+return p-r;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testStruct() {
+        CodeGen code = new CodeGen("""
+struct Bar {
+    int a;
+    int b;
+};
+struct Foo {
+    int x;
+};
+Foo? foo = null;
+Bar !bar = new Bar;
+bar.a = 1;
+bar.a = 2;
+return bar.a;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen("""
+struct Vector2D { int x; int y; };
+Vector2D !v = new Vector2D;
+v.x = 1;
+if (arg)
+    v.y = 2;
+else
+    v.y = 3;
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return Vector2D;", code.print());
+    }
+
+    @Test
+    public void testBug() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int v0;
+};
+s0? v1=null;
+int v3=v1.zAicm;
+""");
+        try { code.parse();  fail(); }
+        catch( Exception e ) {  assertEquals("Accessing unknown field 'zAicm' from 'null'",e.getMessage());  }
+    }
+
+    @Test
+    public void testBug2() {
+        CodeGen code = new CodeGen("""
+struct s0 { int v0; };
+arg=0+new s0.0;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Expected an identifier, found 'null'",e.getMessage()); }
+    }
+
+    @Test
+    public void testLoop() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar !bar = new Bar;
+while (arg) {
+    bar.a = bar.a + 2;
+    arg = arg + 1;
+}
+return bar.a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_a+2));", code.print());
+    }
+
+    @Test
+    public void testIf() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar !bar = new Bar;
+if (arg) bar = null;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *Bar",e.getMessage()); }
+    }
+
+    @Test
+    public void testIf2() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar? !bar = null;
+if (arg) bar = new Bar;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing 'a'",e.getMessage()); }
+    }
+
+    @Test
+    public void testIf3() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar bar = null;
+if (arg) bar = null;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *Bar", e.getMessage()); }
+    }
+
+    @Test
+    public void testIfOrNull() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar? !bar = new Bar;
+if (arg) bar = null;
+if( bar ) bar.a = 1;
+return bar;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,null,Bar);", code.print());
+    }
+
+    @Test
+    public void testIfOrNull2() {
+        CodeGen code = new CodeGen(
+"""
+struct Bar { int a; };
+Bar? !bar = new Bar;
+if (arg) bar = null;
+int rez = 3;
+if( !bar ) rez=4;
+else bar.a = 1;
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,3);", code.print());
+    }
+
+    @Test
+    public void testWhileWithNullInside() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0? !v0 = new s0;
+int ret = 0;
+while(arg) {
+    ret = v0.v0;
+    v0 = null;
+    arg = arg - 1;
+}
+return ret;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) {
+            assertEquals("Might be null accessing 'v0'", e.getMessage()); }
+    }
+
+    @Test
+    public void testRedeclareStruct() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int v0;
+};
+s0? v1=new s0;
+s0? v1;
+v1=new s0;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Redefining name 'v1'", e.getMessage()); }
+    }
+
+    @Test
+    public void testIter() {
+        // Build and use an iterator
+        CodeGen code = new CodeGen(
+"""
+struct Iter {
+    int x;
+    int len;
+};
+Iter !i = new Iter;
+i.len = arg;
+int sum=0;
+while( i.x < i.len ) {
+    sum = sum + i.x;
+    i.x = i.x + 1;
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi(Loop,0,(Phi_x+1))+Phi_sum));", code.print());
+    }
+
+
+    @Test
+    public void test1() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+while(arg) {
+    s0 !v0 = new s0;
+    v0.v0 = arg;
+    arg = arg-1;
+    if (arg==5) ret=v0;
+
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+    @Test
+    public void test2() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+s0 !v0 = new s0;
+while(arg) {
+    v0.v0 = arg;
+    arg = arg-1;
+    if (arg==5) ret=v0;
+
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+
+    @Test
+    public void test3() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+while(arg < 10) {
+    s0 !v0 = new s0;
+    if (arg == 5) ret=v0;
+    arg = arg + 1;
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+    @Test
+    public void testBug3() {
+        CodeGen code = new CodeGen("""
+struct s0 { int f0; };
+return new s0;
+int v0=null.f0;
+""");
+        try { code.parse();  fail(); }
+        catch( Exception e ) {  assertEquals("Accessing unknown field 'f0' from 'null'",e.getMessage());  }
+    }
+
+    @Test
+    public void testBug4() {
+        CodeGen code = new CodeGen("""
+if(0) {
+    while(0) if(arg) continue;
+    int v0=0;
+    while(1) {
+        int v2=-arg;
+        v0=v2;
+    }
+}
+   """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBug5() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int f0;
+};
+if(0) return 0;
+else return new s0;
+if(new s0.f0) return 0;
+    """);
+        code.parse().opto();
+        assertEquals("return s0;", code.print());
+    }
+
+    @Test
+    public void testBug6MissedWorklist() {
+        CodeGen code = new CodeGen("""
+while(0) {}
+int v4=0;
+while(0<arg) {
+    v4=v4+1;
+    while(1) v4=-v4;
+    while(0) arg=-1;
+}
+return 0;
+    """);
+        code.parse().opto();
+    }
+
+    @Test
+    public void testBug7() {
+        CodeGen code = new CodeGen("""
+struct s0 {  int f0; };
+s0 v0 = new s0;
+while(v0.f0) {}
+s0 v1 = v0;
+return v1;
+    """);
+        code.parse().opto();
+        assertEquals("return (const)s0;", code.print());
+    }
+
+
+    @Test
+    public void testBug8() {
+        CodeGen code = new CodeGen("""
+int v2=0;
+while(0)
+while(0) {}
+{
+    {
+        {
+            int v36=0;
+            {
+                while(0) {
+                    {
+                        while(-v2) {
+                            {
+                                while(v36) {
+                                                while(v2) return 0;
+                                                break;
+                                }                            }
+                            if(-v2) break;
+                        }
+                    }
+                }
+            }
+        }    }
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBug9() {
+        CodeGen code = new CodeGen("""
+int v0=arg==0;
+while(v0) continue;
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
new file mode 100644
index 00000000..0b24bd5d
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -0,0 +1,552 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+
+
+import static org.junit.Assert.assertEquals;
+
+public class Chapter11Test {
+
+    // A placeholder test used to rapidly rotate through fuzzer produced issues
+    @Test
+    public void testFuzzer() {
+        CodeGen code = new CodeGen(
+"""
+while(---- -arg) {
+    while(-arg) {
+        while(-----arg*---0) {
+                int N=--false==false<--arg;
+                while(N<-4==N) {
+                    N=N+N;
+                }
+            }
+        {
+            int kzEl_r7EYz=3*----0!=-arg<(37*--97!=0/arg==arg)<=-(--arg!=0);
+            while(kzEl_r7EYz<---1) {
+                kzEl_r7EYz=kzEl_r7EYz+kzEl_r7EYz*arg>=24;
+                if(7) continue;
+                kzEl_r7EYz=false;
+                if(-kzEl_r7EYz+arg<-3) continue;
+                else {
+                    while(kzEl_r7EYz) continue;
+                    arg=----3;
+                    kzEl_r7EYz=-(-----arg*1>-kzEl_r7EYz);
+                    int v2uF_4ba=9;
+                }
+            }
+        }
+        int pjcp7rv=arg;
+        {
+            int m2ya3=--arg-pjcp7rv;
+            while(m2ya3<-----pjcp7rv>=pjcp7rv+--pjcp7rv!=---pjcp7rv!=-arg<---(-m2ya3)>m2ya3<=-----true>14!=--m2ya3) {
+                m2ya3=m2ya3+-(--0<=false<pjcp7rv/arg<=-true);
+                while((--m2ya3)<--arg<-----arg*false!=arg<pjcp7rv*arg) {
+                    pjcp7rv=-3+-arg;
+                    break;
+                }
+                while(-3) {
+                    while(67+0-61) m2ya3=m2ya3;
+                    if(----pjcp7rv==---(---arg)) pjcp7rv=0!=-23;
+                    else pjcp7rv=----89;
+                    while(m2ya3!=m2ya3<pjcp7rv) m2ya3=1;
+                    while(--arg<=pjcp7rv) pjcp7rv=-32<=-m2ya3+62;
+                }
+                break;
+            }
+        }
+        {
+            int arg=-1<-9!=(-arg>=-pjcp7rv>=arg<=arg);
+            while(arg<-arg) {
+                arg=arg+--arg;
+                {
+                    while((--93)--pjcp7rv*-pjcp7rv+arg) arg=0-(6>=(--(---41/(0))!=--pjcp7rv)>=---2*33);
+                    pjcp7rv=11;
+                    int c=pjcp7rv;
+                    if(--107) break;
+                    else break;
+                }
+            }
+        }
+        pjcp7rv=pjcp7rv;
+        int aR0Wkua=-pjcp7rv==pjcp7rv;
+        {
+            if(-0!=-0) while(-true) break;
+            else {
+                while(aR0Wkua) pjcp7rv=-0/pjcp7rv;
+                pjcp7rv=pjcp7rv;
+            }
+        }
+    }
+    if(-arg) {
+        {
+            int Isdlt0fr91=0!=arg;
+            while(Isdlt0fr91<-Isdlt0fr91==-Isdlt0fr91+true) {
+                Isdlt0fr91=Isdlt0fr91+-1!=true;
+                if(-arg) if(--arg<=Isdlt0fr91) Isdlt0fr91=-Isdlt0fr91;
+                int i=---arg<---arg!=--40;
+                {
+                    int jVX43Ln4Dm=-(6)==-Isdlt0fr91/----0;
+                    while(jVX43Ln4Dm<--(3-3)) {
+                        jVX43Ln4Dm=jVX43Ln4Dm+-0<25;
+                        i=24<--(jVX43Ln4Dm);
+                    }
+                }
+                i=(arg!=----false>=7);
+                int Te=5>-arg;
+                break;
+            }
+        }
+        arg=arg!=--true/arg;
+        {
+            int UX=arg;
+            while(UX<-3*arg) {
+                UX=UX+arg/-1;
+                arg=-3--(-UX- -47<arg==--arg==arg)/arg- -UX>=-arg;
+                if(---12) while(-UX) break;
+                break;
+            }
+        }
+        continue;
+    }
+    if(arg) arg=--0;
+    else if(1) continue;
+    int DtTlhjYq=19==arg;
+    {
+        arg=--DtTlhjYq<=(DtTlhjYq/---DtTlhjYq<=-DtTlhjYq);
+        if(---arg) continue;
+        else {
+                int Zsl=40;
+                while(Zsl<--Zsl--false>((Zsl))==Zsl!=--DtTlhjYq-DtTlhjYq-DtTlhjYq) {
+                    Zsl=Zsl+arg;
+                }
+            }
+        if((arg)) if(-DtTlhjYq) {
+            }
+            else while(((2)==3*arg/DtTlhjYq)<=0==---arg) return false;
+        else {
+                int lwbF=arg>=0;
+                while(lwbF<57) {
+                    lwbF=lwbF+--(-arg+lwbF)>=-2>=arg!=arg;
+                    arg=----0+0;
+                    while(49) break;
+                    if(true) DtTlhjYq=-----arg;
+                    DtTlhjYq=0!=-----(0);
+                }
+            }
+        arg=---arg!=DtTlhjYq/--0;
+        DtTlhjYq=-DtTlhjYq/(--arg<arg);
+        if(32) {
+                int q=-DtTlhjYq;
+                while(q<arg*(0*q)/0) {
+                    q=q+DtTlhjYq;
+                    DtTlhjYq=arg;
+                }
+            }
+        else if(--arg) if(15) break;
+                else arg=0==arg<=-55>DtTlhjYq;
+            else {
+            }
+        DtTlhjYq=-0;
+        {
+            while((0)<-arg) DtTlhjYq=-DtTlhjYq;
+        }
+        if(30/--(arg)>=0) DtTlhjYq=-0>=arg;
+        else {
+            int Y2wcIQJ=--DtTlhjYq*---11;
+            if(arg==arg) {
+                Y2wcIQJ=-----Y2wcIQJ;
+                Y2wcIQJ=Y2wcIQJ<7;
+                if(DtTlhjYq) arg=arg;
+                else break;
+                while(-arg!=-31==(false<=-15>=-DtTlhjYq+--6*-----Y2wcIQJ<=---arg!=-Y2wcIQJ<=---0<-arg*--Y2wcIQJ)) DtTlhjYq=arg!=3;
+            }
+            continue;
+        }
+        arg=DtTlhjYq;
+        arg=--3/(---arg)>=80>=-DtTlhjYq<=DtTlhjYq;
+        arg=51+---(-true)!=arg!=----1==-DtTlhjYq;
+        if(11<=arg) if((arg)+79<32+(-arg)) continue;
+            else if(true==DtTlhjYq) break;
+        break;
+    }
+}
+if(arg!=62==arg) {
+    while(---arg) {
+        {
+            int bhmDacPM=arg/arg;
+            while(bhmDacPM<arg) {
+                bhmDacPM=bhmDacPM+80*((-bhmDacPM)/---bhmDacPM>1)<bhmDacPM-2!=7;
+                arg=-0;
+                arg=bhmDacPM>=-arg+-arg;
+                break;
+            }
+        }
+        int arg=true;
+        arg=arg<=arg;
+        {
+            int KlC=30;
+            while(KlC<-2) {
+                KlC=KlC+-1!=25<=-KlC>KlC>----0;
+                int Ij=arg>=-arg<=---10;
+                {
+                    int LAbgurVa2R=-arg!=Ij;
+                    while(LAbgurVa2R<-true) {
+                        LAbgurVa2R=LAbgurVa2R+Ij;
+                        KlC=-LAbgurVa2R;
+                        Ij=42*(-Ij>true);
+                        while(Ij) arg=KlC;
+                        KlC=-----7>-(--KlC<--7)==-LAbgurVa2R;
+                    }
+                }
+                int a=Ij<=-KlC;
+                if(Ij) {
+                    int r1W=a!=-false;
+                }
+                else {
+                    arg=56>=Ij;
+                    while(54) break;
+                    arg=8>=-(a<--Ij)/a>=-a-KlC;
+                }
+                int Yt_T=KlC;
+                arg=KlC;
+            }
+        }
+        if(----false/--arg/12+-----0) if(-9+-arg) while(arg!=(arg)) arg=--1>=-71-arg!=---(--arg*11+102)/--arg;
+            else if(----arg) continue;
+        if(-arg-arg) {
+            arg=-(-arg)*--(-3)<(-7==-arg----arg);
+            {
+                int arg=arg;
+                while(arg<-0>arg==-arg-(-arg>1+11)) {
+                    arg=arg+6-arg!=--0>---30>=---arg<=arg/(3)+---arg;
+                }
+            }
+            arg=-arg+arg;
+            arg=--47+-arg<1>arg*(-arg==-arg- -0>3);
+            arg=(----arg)!=arg+--59;
+            arg=- -4+arg==-(arg)-arg;
+        }
+        else {
+            while(--true-----true*-25+-18>arg>=-----(-arg)---13) {
+                arg=-0+--true<false;
+                continue;
+            }
+            arg=true<=arg;
+            break;
+        }
+        arg=arg*22<--(0+-arg);
+        {
+            continue;
+        }
+    }
+    arg=1*---((3<=true)==---2);
+    arg=7+-(-1);
+    return arg+--true;
+}
+else {
+    int o3ypEsewxM=-(---arg);
+    int vzXB=(-(---11<=--o3ypEsewxM>=--0))<=-0/-arg;
+    int L=-arg;
+    int B4mHcrf=---vzXB;
+    int oZWGdzZl=-o3ypEsewxM;
+    int K6tQqa1=11;
+    while(0!=--L) {
+            int sdZfTM=vzXB*true+K6tQqa1;
+            while(sdZfTM<false) {
+                sdZfTM=sdZfTM+arg;
+                sdZfTM=oZWGdzZl;
+                K6tQqa1=-K6tQqa1;
+                arg=---K6tQqa1;
+                while((3+-K6tQqa1)<oZWGdzZl) {
+                    if(-----(-1)) sdZfTM=-false;
+                    {}
+                }
+                K6tQqa1=vzXB!=-(B4mHcrf+-7>false);
+                sdZfTM=vzXB;
+            }
+        }
+    L=false;
+    while(31) B4mHcrf=arg;
+    oZWGdzZl=-0<--oZWGdzZl<=--2;
+    if(K6tQqa1>=20<=46) {
+        if(-1+-L) if(oZWGdzZl) {
+                int wmhv=-----0;
+            }
+        int arg=0;
+        o3ypEsewxM=---(oZWGdzZl);
+        return -oZWGdzZl/0;
+    }
+    else if(arg) {
+            int yKk5=B4mHcrf>=4>K6tQqa1<-B4mHcrf/o3ypEsewxM;
+            return -K6tQqa1;
+        }
+        else {
+            if(---0) {
+                {}
+                {}
+            }
+            return o3ypEsewxM;
+        }
+}
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return Phi(Region,9,Top,Top,Top,Top);", code.print());
+    }
+
+
+    @Test
+    public void testPrimes() {
+        CodeGen code = new CodeGen(
+"""
+if( arg < 2 ) return 0;
+int primeCount = 1;
+int prime = 3;
+while( prime <= arg ) {
+    int isPrime = 1;
+    // Check for even case, so the next loop need only check odds
+    if( (prime/2)*2 == prime )
+        continue;
+    // Check odds up to sqrt of prime
+    int j = 3;
+    while( j*j <= prime ) {
+        if( (prime/j)*j == prime ) {
+            isPrime = 0;
+            break;
+        }
+        j = j + 2;
+    }
+    if( isPrime )
+        primeCount = primeCount + 1;
+    prime = prime + 2;
+}
+return primeCount;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi(Region,(Phi_primeCount+1),Phi_primeCount))));", code.print());
+        assertEquals("0", Eval2.eval(code,  1)); // No primes 1 or below
+        assertEquals("1", Eval2.eval(code,  2)); // 2
+        assertEquals("2", Eval2.eval(code,  3)); // 2, 3
+        assertEquals("2", Eval2.eval(code,  4)); // 2, 3
+        assertEquals("3", Eval2.eval(code,  5)); // 2, 3, 5
+        assertEquals("4", Eval2.eval(code, 10)); // 2, 3, 5, 7
+    }
+
+    @Test
+    public void testAntiDeps1() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v=new S;
+v.f = 2;
+int i=new S.f;
+i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertEquals("2", Eval2.eval(code, 0));
+        assertEquals("2", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testAntiDeps2() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+v.f = arg;
+S !t = new S;
+int i = 0;
+if (arg) {
+    if (arg+1) v = t;
+    i = v.f;
+} else {
+    v.f = 2;
+}
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,.f,0);", code.print());
+    }
+
+    @Test
+    public void testAntiDeps3() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v0 = new S;
+S? v1;
+if (arg) v1 = new S;
+if (v1) {
+    v0.f = v1.f;
+} else {
+    v0.f = 2;
+}
+return v0;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+
+    @Test
+    public void testAntiDeps4() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+v.f = arg;
+S t = new S;
+int i = v.f;
+if (arg+1) arg= 0;
+while (arg) v.f = 2;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps5() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+while(1) {
+    while(arg+1) { arg=arg-1; }
+    if (arg) break;
+    v.f = 2;
+}
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps6() {
+        CodeGen code = new CodeGen(
+"""
+struct s { int v; };
+s !ptr=new s;
+while( -arg )
+  ptr = new s;
+while(1)
+  arg = arg+ptr.v;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps7() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+int i = v.f;
+while (arg) {
+    v.f = arg;
+    arg = arg-1;
+}
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps8() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+while(arg) {
+    arg=arg-1;
+    int f = v.f;
+    v.f = 2;
+    if (arg) arg = f;
+    else v.f = 3;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps9() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+if (arg) {
+    v.f=2;
+    int i=t.f;
+    v.f=i;
+}
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testExample2() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+int i = arg;
+while (arg > 0) {
+    int j = i/3;
+    if (arg == 5)
+        v.f = j;
+    arg = arg - 1;
+}
+return v;
+                """);
+        code.parse().opto();
+        //assertEquals("return new S;", code.print());
+    }
+
+    @Test
+    public void testScheduleUse() {
+        CodeGen code = new CodeGen(
+"""
+int v0=0;
+while(0>=0) {
+    u1 v1=0;
+    v1=v0;
+    if(v1*0)
+        v0=-v1;
+}
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testLoopCarriedDep() {
+        CodeGen code = new CodeGen(
+"""
+u32 v0=0;
+{
+    int v1=0;
+    while(v1) {
+        v1=1>>>v0!=0;
+        v0=v1/0;
+    }
+    return v1;
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
new file mode 100644
index 00000000..21df8205
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -0,0 +1,62 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Ignore;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter12Test {
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFloat() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSquareRoot() {
+        CodeGen code = new CodeGen(
+"""
+flt guess = arg;
+while( 1 ) {
+    flt next = (arg/guess + guess)/2;
+    if( next == guess ) break;
+    guess = next;
+}
+return guess;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)/2.0f));", code.print());
+        assertEquals("3.0", Eval2.eval(code,  9));
+        assertEquals("1.414213562373095", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testFPOps() {
+        CodeGen code = new CodeGen(
+"""
+flt x = arg;
+return x+1==x;
+""");
+        code.parse().opto();
+        assertEquals("return ((flt)arg==(ToFloat+1.0f));", code.print());
+        assertEquals("0", Eval2.eval(code, 1));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
new file mode 100644
index 00000000..d05fd7d8
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -0,0 +1,247 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter13Test {
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testLinkedList0() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+return head.next.i;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing 'i'",e.getMessage()); }
+    }
+
+    @Test
+    public void testLinkedList1() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( next==null ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+    @Test
+    public void testCoRecur() {
+        CodeGen code = new CodeGen(
+"""
+struct int0 { int i; flt0? f; };
+struct flt0 { flt f; int0? i; };
+int0 !i0 = new int0;
+i0.i = 17;
+flt0 !f0 = new flt0;
+f0.f = 3.14;
+i0.f = f0;
+f0.i = i0;
+return f0.i.f.i.i;
+""");
+        code.parse().opto();
+        assertEquals("return 17;", code.print());
+    }
+
+    @Test
+    public void testNullRef0() {
+        CodeGen code = new CodeGen(
+"""
+struct N { N? next; int i; };
+N n = new N;
+return n.next;
+""");
+        code.parse().opto();
+        assertEquals("return null;", code.print());
+    }
+
+    @Test
+    public void testNullRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct M { int m; };
+struct N { M next; int i; };
+N n = new N { next = new M; };
+return n.next;
+""");
+        code.parse().opto();
+        assertEquals("return (const)M;", code.print());
+    }
+
+    @Test
+    public void testNullRef2() {
+        CodeGen code = new CodeGen(
+"""
+struct M { int m; };
+struct N { M next; int i; };
+N n = new N { next = null; }
+return n.next;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *M",e.getMessage()); }
+    }
+
+    @Test
+    public void testNullRef3() {
+        CodeGen code = new CodeGen(
+"""
+struct N { N? next; int i; };
+N !n = new N;
+n.i = 3.14;
+return n.i;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type 3.14 is not of declared type int",e.getMessage()); }
+    }
+
+    @Test
+    public void testEmpty() {
+        CodeGen code = new CodeGen(
+"""
+struct S{};
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testForwardRef0() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { S2? s; };
+return new S2;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Unknown struct type 'S2'",e.getMessage()); }
+    }
+
+    @Test
+    public void testForwardRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { S2? s; };
+struct S2 { int x; };
+return new S1.s=new S2;
+""");
+        code.parse().opto();
+        assertEquals("return S2;", code.print());
+    }
+
+    @Test
+    public void testcheckNull() {
+        CodeGen code = new CodeGen(
+"""
+struct I {int i;};
+struct P { I? pi; };
+P !p1 = new P;
+P !p2 = new P;
+p2.pi = new I;
+p2.pi.i = 2;
+if (arg) p1 = new P;
+return p1.pi.i + 1;
+""");
+        try { code.parse().opto().typeCheck();  fail(); }
+        catch( Exception e ) {  assertEquals("Might be null accessing 'i'",e.getMessage());  }
+    }
+
+    @Test
+    public void testCoRecur2() {
+        CodeGen code = new CodeGen(
+"""
+struct A { L? a; T? b; F? c; };  A? !a = new A;
+struct B { M? a; U? b; G? c; };  B? !b = new B;
+struct C { N? a; V? b; H? c; };  C? !c = new C;
+struct D { O? a; W? b; I? c; };  D? !d = new D;
+struct E { P? a; X? b; J? c; };  E? !e = new E;
+struct F { Q? a; Y? b; K? c; };  F? !f = new F;
+struct G { R? a; Z? b; L? c; };  G? !g = new G;
+struct H { S? a; A? b; M? c; };  H? !h = new H;
+struct I { T? a; B? b; N? c; };  I? !i = new I;
+struct J { U? a; C? b; O? c; };  J? !j = new J;
+struct K { V? a; D? b; P? c; };  K? !k = new K;
+struct L { W? a; E? b; Q? c; };  L? !l = new L;
+struct M { X? a; F? b; R? c; };  M? !m = new M;
+struct N { Y? a; G? b; S? c; };  N? !n = new N;
+struct O { Z? a; H? b; T? c; };  O? !o = new O;
+struct P { A? a; I? b; U? c; };  P? !p = new P;
+struct Q { B? a; J? b; V? c; };  Q? !q = new Q;
+struct R { C? a; K? b; W? c; };  R? !r = new R;
+struct S { D? a; L? b; X? c; };  S? !s = new S;
+struct T { E? a; M? b; Y? c; };  T? !t = new T;
+struct U { F? a; N? b; Z? c; };  U? !u = new U;
+struct V { G? a; O? b; A? c; };  V? !v = new V;
+struct W { H? a; P? b; B? c; };  W? !w = new W;
+struct X { I? a; Q? b; C? c; };  X? !x = new X;
+struct Y { J? a; R? b; D? c; };  Y? !y = new Y;
+struct Z { K? a; S? b; E? c; };  Z? !z = new Z;
+
+a.a=l;  a.b=t; a.c=f;
+b.a=m;  b.b=u; b.c=g;
+c.a=n;  c.b=v; c.c=h;
+d.a=o;  d.b=w; d.c=i;
+e.a=p;  e.b=x; e.c=j;
+f.a=q;  f.b=y; f.c=k;
+g.a=r;  g.b=z; g.c=l;
+h.a=s;  h.b=a; h.c=m;
+i.a=t;  i.b=b; i.c=n;
+j.a=u;  j.b=c; j.c=o;
+k.a=v;  k.b=d; k.c=p;
+l.a=w;  l.b=e; l.c=q;
+m.a=x;  m.b=f; m.c=r;
+n.a=y;  n.b=g; n.c=s;
+o.a=z;  o.b=h; o.c=t;
+p.a=a;  p.b=i; p.c=u;
+q.a=b;  q.b=j; q.c=v;
+r.a=c;  r.b=k; r.c=w;
+s.a=d;  s.b=l; s.c=x;
+t.a=e;  t.b=m; t.c=y;
+u.a=f;  u.b=n; u.c=z;
+v.a=g;  v.b=o; v.c=a;
+w.a=h;  w.b=p; w.c=b;
+x.a=i;  x.b=q; x.c=c;
+y.a=j;  y.b=r; y.c=d;
+z.a=k;  z.b=s; z.c=e;
+
+return a.b.c.a.b.c.a.b.c.a.b.c.a.b.c.a.b.c;
+
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return R;", code._stop.toString());
+        assertEquals("R{a=C{a=N{a=Y{a=J{a=U{a=F{a=Q{a=B{a=M{a=X{a=I{a=T{a=E{a=P{a=A{a=L{a=W{a=H{a=S{a=D{a=O{a=Z{a=K{a=V{a=G{a=$cyclic,b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic}", Eval2.eval(code,  0));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
new file mode 100644
index 00000000..17708c37
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
@@ -0,0 +1,226 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter14Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testRange() {
+        CodeGen code = new CodeGen(
+"""
+int b;
+if( arg ) b=1; else b=0;
+int c = 99;
+if( b < 0 ) c = -1;
+if( b > 2 ) c =  1;
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return 99;", code.print());
+        assertEquals("99", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testU8() {
+        CodeGen code = new CodeGen(
+"""
+u8 b = 123;
+b = b + 456;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 67;", code.print());
+        assertEquals("67", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testU8While() {
+        CodeGen code = new CodeGen(
+"""
+u8 b = 123;
+while( b ) b = b + 456;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testU1() {
+        CodeGen code = new CodeGen(
+"""
+bool b = 123;
+b = b + 456;// Truncate
+u1 c = b;   // No more truncate needed
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testAnd() {
+        CodeGen code = new CodeGen(
+"""
+int b = 123;
+b = b+456 & 31;                 // Precedence
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testRefLoad() {
+        CodeGen code = new CodeGen(
+"""
+struct Foo { u1 b; };
+Foo !f = new Foo;
+f.b = 123;
+return f.b;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSigned() {
+        CodeGen code = new CodeGen(
+"""
+i8 b = 255;                     // Chopped
+return b;                       // Sign extend
+""");
+        code.parse().opto();
+        assertEquals("return -1;", code.print());
+        assertEquals("-1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testI8() {
+        CodeGen code = new CodeGen(
+"""
+i8 b = arg;
+b = b + 1;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return (((((arg<<56)>>56)+1)<<56)>>56);", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+        assertEquals("-128", Eval2.eval(code, 127));
+    }
+
+    @Test
+    public void testMask() {
+        CodeGen code = new CodeGen(
+"""
+u16 mask = (1<<16)-1;           // AND mask
+int c = 123456789 & mask;
+return c;                       //
+""");
+        code.parse().opto();
+        assertEquals("return 52501;", code.print());
+        assertEquals("52501", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testOr() {
+        CodeGen code = new CodeGen(
+"""
+return (arg | 123 ^ 456) >>> 1;
+""");
+        code.parse().opto();
+        assertEquals("return (((arg|123)^456)>>>1);", code.print());
+        assertEquals("217", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testMaskFloat() {
+        CodeGen code = new CodeGen(
+"""
+flt f = arg;
+arg = f & 1;
+return arg;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot '&' flt",e.getMessage()); }
+    }
+
+    @Test
+    public void testCloneAnd() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+u32 v1 = 1&(1<<arg)&(1<<arg);
+while(arg) v1=-v0;
+while(v1) break;
+return v1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,(((1<<arg)&1)&Shl),0);", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testAndHigh() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+if(0&0>>>0) {
+    while(0) {
+        u8 v1=0;
+        v0=0>>>0;
+        v1=arg;
+        while(v1+0) {}
+    }
+}
+return v0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testTypes() {
+        CodeGen code = new CodeGen(
+"""
+i8  xi8  = 123456789;  if( xi8  !=        21 ) return -8;
+i16 xi16 = 123456789;  if( xi16 !=    -13035 ) return -16;
+i32 xi32 = 123456789;  if( xi32 != 123456789 ) return -32;
+i64 xi64 = 123456789;  if( xi64 != 123456789 ) return -64;
+int xint = 123456789;  if( xint != 123456789 ) return -64;
+
+u1  ui1  = 123456789;  if( ui1  !=         1 ) return 1;
+u8  ui8  = 123456789;  if( ui8  !=        21 ) return 8;
+u16 ui16 = 123456789;  if( ui16 !=     52501 ) return 16;
+u32 ui32 = 123456789;  if( ui32 != 123456789 ) return 32;
+
+flt fflt = 3.141592653589793;  if( fflt != 3.141592653589793 ) return 3;
+f64 ff64 = 3.141592653589793;  if( ff64 != 3.141592653589793 ) return 3;
+f32 ff32 = 3.141592653589793;  if( ff32 != 3.1415927410125732) return 5;
+
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
new file mode 100644
index 00000000..546eb0e9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -0,0 +1,380 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class Chapter15Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testCyclic() {
+        CodeGen code = new CodeGen(
+"""
+struct C { C? l; };
+C !c = new C;
+c.l = c;
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return C;", code.print());
+        assertEquals("C{l=$cyclic}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSafetyCheck() {
+        CodeGen code = new CodeGen(
+"""
+u8[] old = new u8[0];
+u8[] !output = new u8[1];
+int i = 0;
+while (i < old#) {
+    output[i] = old[i];
+    i = i + 1;
+}
+output[i] = 1;
+return output;
+""");
+        code.parse().opto();
+        assertEquals("return [u8];", code.print());
+        assertEquals("\u0001", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic1() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[2];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic2() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[2];
+int[] is2 = new int[2];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic3() {
+        CodeGen code = new CodeGen(
+"""
+int[] !a = new int[2];
+a[0] = 1;
+a[1] = 2;
+return a[0];
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic4() {
+        CodeGen code = new CodeGen(
+"""
+struct A { int i; };
+A?[] !a = new A?[2];
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return [*A?];", code.print());
+        assertEquals("*A {int !i; }?[ null,null]", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testBasic5() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int x; flt y; };
+// A new S
+S !s = new S; s.x=99; s.y = 3.14;
+
+// Double-d array of Ss.  Fill in one row.
+S?[]?[] !iss = new S?[]?[2];
+iss[0] = new S?[7];
+iss[0][2] = s;
+
+// Now pull out the filled-in value, with null checks
+flt rez;
+S?[]? is = iss[arg];
+if( !is ) rez = 1.2;
+else {
+    S? i = is[2];
+    if( !i ) rez = 2.3;
+    else rez = i.y;
+}
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1.2,Phi(Region,2.3,.y));", code.print());
+        assertEquals("3.14", Eval2.eval(code, 0));
+        assertEquals("1.2", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testBasic6() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int x; flt y; };
+// A new S
+S !s = new S; s.x=99; s.y = 3.14;
+
+// Double-d array of Ss.  Fill in one row.
+S?[]?[] !iss = new S?[]?[2];
+iss[0] = new S?[7];
+iss[0][2] = s;
+
+// Now pull out the filled-in value, with null checks
+flt rez = 1.2;
+if( iss[arg] )
+    if( iss[arg][2] )
+        rez = iss[arg][2].y;
+return rez;""");
+        code.parse().opto().typeCheck();
+        assertEquals("return Phi(Region,Phi(Region,.y,1.2),1.2);", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+        try { Eval2.eval(code, 10); fail(); } // Fails AIOOBE in Eval2, no range checks
+        catch( Exception e ) { assertEquals("Index 10 out of bounds for length 2",e.getMessage()); }
+    }
+
+    @Test
+    public void testTree() {
+        CodeGen code = new CodeGen(
+"""
+// Can we define a forward-reference array?
+struct Tree { Tree?[]? _kids; };
+Tree !root = new Tree;
+root._kids = new Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
+root._kids[0] = new Tree;
+return root;
+""");
+        code.parse().opto();
+        assertEquals("return Tree;", code.print());
+        assertEquals("Tree{_kids=*Tree?[ Tree{_kids=null},null]}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testNestedStructAddMemProj() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int a; int[] b; };
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testRollingSum() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg];
+// Fill [0,1,2,3,4,...]
+int i=0;
+while( i < ary# ) {
+    ary[i] = i;
+    i = i+1;
+}
+// Fill [0,1,3,6,10,...]
+i=0;
+while( i < ary# - 1 ) {
+    ary[i+1] = ary[i+1] + ary[i];
+    i = i+1;
+}
+return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
+""");
+        code.parse().opto();
+        assertEquals("return (.[]+(.[]*1000));", code.print());
+        assertEquals("1006", Eval2.eval(code,  4));
+    }
+
+    @Test
+    public void sieveOEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg], !primes = new int[arg];
+int nprimes = 0, p=2;
+// Find primes while p^2 < arg
+while( p*p < arg ) {
+    // skip marked non-primes
+    while( ary[p]==1 ) p = p + 1;
+    // p is now a prime
+    primes[nprimes] = p;  nprimes = nprimes + 1;
+    // Mark out the rest non-primes
+    int i = p + p;
+    while( i < ary# ) {
+        ary[i] = 1;
+        i = i + p;
+    }
+    p = p + 1;
+}
+// Now just collect the remaining primes, no more marking
+while( p < arg ) {
+    if( ary[p] == 0 ) {
+        primes[nprimes] = p;  nprimes = nprimes + 1;
+    }
+    p = p + 1;
+}
+// Copy/shrink the result array
+int[] !rez = new int[nprimes];
+int j = 0;
+while( j < nprimes ) {
+    rez[j] = primes[j];
+    j = j + 1;
+}
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return [int];", code.print());
+        assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+    @Test
+    public void testNewNodeInit() {
+        CodeGen code = new CodeGen(
+"""
+struct S {int i; flt f;};
+S !s1 = new S;
+S !s2 = new S;
+s2.i = 3;
+s2.f = 2.0;
+if (arg) s1 = new S;
+return s1.i + s1.f;
+""");
+        code.parse().opto();
+        assertEquals("return ((flt).i+.f);", code.print());
+        assertEquals("0.0", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testBad0() {
+        CodeGen code = new CodeGen(
+"""
+return new flt;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot allocate a flt",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad1() {
+        CodeGen code = new CodeGen(
+"""
+int is = new int[2];
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type *[int] is not of declared type int",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad2() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[3.14];
+return is[1];
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot allocate an array with length 3.14",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad3() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[arg];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  4));
+        try { Eval2.eval(code,0); }
+        catch( ArrayIndexOutOfBoundsException e ) { assertEquals("Array index 1 out of bounds for array length 0",e.getMessage()); }
+        try { Eval2.eval(code,-1); }
+        catch( NegativeArraySizeException e ) { assertEquals("-1",e.getMessage()); }
+    }
+
+    @Test
+    public void testProgress() {
+        CodeGen code = new CodeGen("""
+i8 v1=0&0;
+u8 v2=0;
+byte v4=0;
+if(0) {}
+while(v2<0) {
+    v4=0-v1;
+    break;
+}
+int v5=0&0;
+while(v5+(0&0)) {
+    int v7=0&0;
+    while(v7)
+        v4=0>>>v5;
+    while(v1)
+        return 0;
+}
+return v1;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSharpNot() {
+        CodeGen code = new CodeGen(
+"""
+if(0>>0) {}
+while(0) {}
+u32 v7=0;
+int v8=0;
+while(0<--1>>>---(v7*0==v8)) {}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+
+    @Test
+    public void testProgress2() {
+        CodeGen code = new CodeGen(
+"""
+if(1) {}
+else {
+        while(arg>>>0&0>>>0) {}
+    byte v3=0>>>0;
+                while(0) {}
+        int v7=0>>>0;
+        while(v7<0>>>0) {
+                    while(0+v7<=0) if(1) arg=-12;
+            if(arg) {
+                v3=arg+v3+0;
+                arg=0;
+            }
+        }
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
new file mode 100644
index 00000000..ad3dc690
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
@@ -0,0 +1,260 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter16Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testMulti0() {
+        CodeGen code = new CodeGen(
+"""
+int x, y;
+return x+y;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+    @Test
+    public void testMulti1() {
+        CodeGen code = new CodeGen(
+"""
+int x=2, y=x+1;
+return x+y;
+""");
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+        assertEquals("5", Eval2.eval(code,  0));
+    }
+
+//    @Test
+//    public void testFinal0() {
+//        CodeGen code = new CodeGen(
+//"""
+//int !x=2;
+//x=3;
+//return x;
+//""");
+//        try { code.parse().opto(); fail(); }
+//        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+//    }
+
+    @Test
+    public void testFinal1() {
+        CodeGen code = new CodeGen(
+"""
+int x=2, y=3;
+if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
+return y;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,9,3);", code.print());
+        assertEquals("3", Eval2.eval(code, 0));
+        assertEquals("9", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testConstruct0() {
+        CodeGen code = new CodeGen("""
+struct X { int x=3; };
+X z = new X;
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testConstruct1() {
+        CodeGen code = new CodeGen("""
+struct X { int !x; };
+X z = new X { x=3; };
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testConstruct2() {
+        CodeGen code = new CodeGen("""
+struct X { int x=3; };
+X z = new X { x = 4; };
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testStructFinal0() {
+        CodeGen code = new CodeGen("""
+struct Point { int !x, !y; };
+Point p = new Point { x=3; y=4; };
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return (const)Point;", code.print());
+        assertEquals("Point{x=3,y=4}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testStructFinal1() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point { x=5; y=6; };
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal2() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal3() {
+        CodeGen code = new CodeGen("""
+struct Point { var x; var y; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal4() {
+        CodeGen code = new CodeGen("""
+struct Point { val x=3; val y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal5() {
+        CodeGen code = new CodeGen("""
+struct Point { var x=3; var y=4; };
+Point !p = new Point;
+p.x++;
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return Point;", code.print());
+        assertEquals("Point{x=4,y=4}", Eval2.eval(code,  0));
+    }
+
+    // Same as the Chapter13 test with the same name, but using the new
+    // constructor syntax
+    @Test
+    public void testLinkedList1() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    head = new LLI { next=head; i=arg; };
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( !next ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+        assertEquals("1", Eval2.eval(code,  1));
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+    @Test
+    public void testLinkedList2() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    head = new LLI {
+        next=head;
+        // Any old code in the constructor
+        int !tmp=arg;
+        while( arg > 10 ) {
+            tmp = tmp + arg;
+            arg = arg - 1;
+        }
+        i=tmp;
+    };
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( !next ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+        assertEquals("1", Eval2.eval(code,  1));
+        assertEquals("2", Eval2.eval(code, 11));
+    }
+
+    @Test
+    public void testSquare() {
+        CodeGen code = new CodeGen(
+"""
+struct Square {
+    flt !side = arg;
+    // Newtons approximation to the square root, computed in a constructor.
+    // The actual allocation will copy in this result as the initial
+    // value for 'diag'.
+    flt !diag = arg*arg/2;
+    while( 1 ) {
+        flt next = (side/diag + diag)/2;
+        if( next == diag ) break;
+        diag = next;
+    }
+};
+return new Square;
+""");
+        code.parse().opto();
+        assertEquals("return Square;", code.print());
+        assertEquals("Square{side=3.0,diag=1.7320508075688772}", Eval2.eval(code,  3));
+        assertEquals("Square{side=4.0,diag=2.0}", Eval2.eval(code, 4));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java
new file mode 100644
index 00000000..a1d0f8b9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java
@@ -0,0 +1,556 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter17Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+int i = 0;
+i=i=1;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testInc0() {
+        CodeGen code = new CodeGen("""
+return arg++;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc1() {
+        CodeGen code = new CodeGen("""
+return arg+++arg++;
+""");
+        code.parse().opto();
+        assertEquals("return ((arg<<1)+1);", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc2() {
+        CodeGen code = new CodeGen("""
+//   -(arg--)-(arg--)
+return -arg---arg--;
+""");
+        code.parse().opto();
+        assertEquals("return (-((arg<<1)+-1));", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc3() {
+        CodeGen code = new CodeGen("""
+int[] !xs = new int[arg];
+xs[0]++;
+xs[1]++;
+return xs[0];
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc4() {
+        CodeGen code = new CodeGen("""
+u8[] !xs = new u8[1];
+xs[0]--;
+return xs[0];
+""");
+        code.parse().opto();
+        assertEquals("return 255;", code.print());
+        assertEquals("255", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc5() {
+        CodeGen code = new CodeGen("""
+struct S { u16 x; };
+S !s = new S;
+s.x--;
+return s.x;
+""");
+        code.parse().opto();
+        assertEquals("return 65535;", code.print());
+        assertEquals("65535", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc6() {
+        CodeGen code = new CodeGen("return --arg;");
+        code.parse().opto();
+        assertEquals("return (arg+-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc7() {
+        CodeGen code = new CodeGen("u8 x=0; return --x;");
+        code.parse().opto();
+        assertEquals("return 255;", code.print());
+        assertEquals("255", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc8() {
+        CodeGen code = new CodeGen("int x; x+=2; return x+=3;");
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+        assertEquals("5", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc9() {
+        CodeGen code = new CodeGen("flt x = 1.5; x++; return x;");
+        code.parse().opto();
+        assertEquals("return 2.5f;", code.print());
+        assertEquals("2.5", Eval2.eval(code, 0));
+    }
+
+    @Test public void testInt10() {
+        CodeGen code = new CodeGen("flt x = 1.5; x++; int i = x; return i;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type 2.5f is not of declared type int",e.getMessage()); }
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test public void testVar0() {
+        CodeGen code = new CodeGen("var d; return d;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar1() {
+        CodeGen code = new CodeGen("val d; return d;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar2() {
+        CodeGen code = new CodeGen("int x; x=3; x++; return x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar3() {
+        CodeGen code = new CodeGen("int x=3; x++; return x; // Ok, primitive so x is mutable despite initializer ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar4() {
+        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar5() {
+        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S{x=3;}; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar6() {
+        CodeGen code = new CodeGen("struct S{int x;}; S s=new S; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar7() {
+        CodeGen code = new CodeGen("struct S{int x;}; S s=new S{x=3;}; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar8() {
+        CodeGen code = new CodeGen("struct S{int x;}; S !s=new S; s.x++; return s.x; // Ok, has '!' so s.x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar9() {
+        CodeGen code = new CodeGen("struct S{int x;}; var s=new S; s.x++; return s.x; // Ok, has var so s.x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar10() {
+        CodeGen code = new CodeGen("struct S{int x;}; val s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar11() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { Bar? !bar; int y; };
+Foo !foo = new Foo { bar = bar; };
+foo.bar = bar; // Ok foo is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+val xfoo = foo; // Throw away mutability
+xfoo.bar.x++;   // Error, cannot mutate through xfoo
+ """);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar12() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { Bar? !bar; int y; };
+Foo !foo = new Foo;
+foo.bar = bar; // Ok bar is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+val xfoo = foo;        // Throw away mutability
+int x4 = xfoo.bar.x;   // Ok to read through xfoo, gets 4
+foo.bar.x++;           // Bumps to 5
+int x5 = xfoo.bar.x;   // Ok to read through xfoo, gets 5
+return x4*10+x5;
+""");
+        code.parse().opto();
+        assertEquals("return 45;", code.print());
+        assertEquals("45", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testVar13() {
+        CodeGen code = new CodeGen("""
+int i,i++;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Redefining name 'i'",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testVar14() {
+        CodeGen code = new CodeGen("""
+struct B {};
+struct A { B b; };
+A x = new A {
+    return b; // read before init
+    b = new B;
+};
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot read uninitialized field 'b'",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar15() {
+        CodeGen code = new CodeGen("""
+struct B {};
+struct A { B b; };
+return new A {
+    if (arg) b = new B; // Constructor ends with partial init of b
+}.b;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("'A' is not fully initialized, field 'b' needs to be set in a constructor",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar16() {
+        CodeGen code = new CodeGen(
+"""
+struct S{};
+val x = 1;
+val s = new S{x = 2;};
+return x;
+"""
+);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar17() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+    bool focused;
+};
+val focus = { Person p ->
+    p.focused = true;
+};
+Person me; // Person !me = new Person;
+focus(me);
+return me;
+"""
+);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testTrinary0() {
+        CodeGen code = new CodeGen("""
+return arg ? 1 : 2;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1,2);", code.print());
+        assertEquals("2", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary1() {
+        CodeGen code = new CodeGen("""
+return arg ? 0 : arg;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testTrinary2() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+var b = arg ? new Bar : null;
+return b ? b.x++ + b.x++ : -1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary3() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+var b = arg ? new Bar;
+return b ? b.x++ + b.x++ : -1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary4() {
+        // This test case will benefit from an unzipping transformation
+        CodeGen code = new CodeGen("""
+struct Bar { Bar? next; int x; };
+var b = arg ? new Bar { next = (arg==2) ? new Bar{x=2;}; x=1; };
+return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0"
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,.x,.x),0);", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+        assertEquals("2", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testTrinary5() {
+        CodeGen code = new CodeGen("""
+flt f=arg?1:1.2;
+return f;   // missing widening
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1.0f,1.2);", code.print());
+        assertEquals("1.2", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testTrinary6() {
+        CodeGen code = new CodeGen("""
+struct S{};
+return arg ? 7 : new S;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("No common type amongst int and reference",e.getMessage()); }
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testFor0() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor1() {
+        CodeGen code = new CodeGen("""
+int sum=0, i=0;
+for( ; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor2() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; ; i++ ) {
+    if( i>=arg ) break;
+    sum += i;
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor3() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; )
+    sum += i++;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor4() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return i;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Undefined name 'i'",e.getMessage()); }
+    }
+    @Test
+    public void testFor5() {
+        CodeGen code = new CodeGen("""
+for(;;arg++;) {}
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected Unexpected code after expression: ;",e.getMessage()); }
+    }
+
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testForward0() {
+        CodeGen code = new CodeGen("""
+struct A{
+    B? f1;
+    B? f2;
+};
+return new A;
+""");
+        code.parse().opto();
+        assertEquals("return A;", code.print());
+        assertEquals("A{f1=null,f2=null}", Eval2.eval(code,0));
+    }
+
+    @Test
+    public void testForward1() {
+        CodeGen code = new CodeGen("""
+struct A{
+    B?[]? nil_array_of_b;
+    B?[]  not_array_of_b = new B?[0];
+};
+return new A.not_array_of_b;
+""");
+        code.parse().opto();
+        assertEquals("return (const)[*B?];", code.print());
+        assertEquals("*B?[]", Eval2.eval(code,0));
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testLinkedList2() {
+        CodeGen code = new CodeGen("""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg-- )
+    head = new LLI { next=head; i=arg; };
+int sum=0;
+var ptr = head; // A read-only ptr, to be assigned from read-only next fields
+for( ; ptr; ptr = ptr.next )
+    sum += ptr.i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+.i));", code.print());
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+
+    @Test
+    public void sieveOfEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+var ary = new bool[arg], primes = new int[arg];
+var nprimes=0, p=0;
+// Find primes while p^2 < arg
+for( p=2; p*p < arg; p++ ) {
+    // skip marked non-primes
+    while( ary[p] ) p++;
+    // p is now a prime
+    primes[nprimes++] = p;
+    // Mark out the rest non-primes
+    for( int i = p + p; i < ary#; i += p )
+        ary[i] = true;
+}
+// Now just collect the remaining primes, no more marking
+for( ; p < arg; p++ )
+    if( !ary[p] )
+        primes[nprimes++] = p;
+// Copy/shrink the result array
+var !rez = new int[nprimes];
+for( int j=0; j<nprimes; j++ )
+    rez[j] = primes[j];
+return rez;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return [int];", code.print());
+        assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
new file mode 100644
index 00000000..db970f60
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -0,0 +1,369 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
+import org.junit.Ignore;
+
+public class Chapter18Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 0;
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testPhiParalleAssign() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(arg--) {
+  int t = a;
+  a = b;
+  b = t;
+}
+return a;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return Phi(Loop,1,Phi(Loop,2,Phi_a));", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+        assertEquals("2", Eval2.eval(code,  1));
+        assertEquals("1", Eval2.eval(code,  2));
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testType0() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? x2 = null; // null function ptr
+return x2;
+""");
+        code.parse().opto();
+        assertEquals("return null;", code._stop.toString());
+        assertEquals("null", Eval2.eval(code, 0 ) );
+    }
+
+    @Test
+    public void testFcn0() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? sq = { int x ->
+    x*x;
+};
+return sq;
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return { sq}; return (Parm_x(sq,int)*x); ]", code._stop.toString());
+        assertEquals("{ int -> int #1}", Eval2.eval(code, 3));
+    }
+
+    @Test
+    public void testFcn1() {
+        CodeGen code = new CodeGen(
+"""
+var sq = { int x ->
+    x*x;
+};
+return sq(arg)+sq(3);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return (sq( 3)+sq( arg)); return (Parm_x(sq,int,3,arg)*x); ]", code._stop.toString());
+        assertEquals("13", Eval2.eval(code, 2));
+    }
+
+    // Function scope test
+    @Test
+    public void testFcn2() {
+        CodeGen code = new CodeGen(
+"""
+int cnt=1;
+return { -> cnt; };
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Variable 'cnt' is out of function scope and must be a final constant",e.getMessage()); }
+    }
+
+    // Function scope test
+    @Test
+    public void testFcn3() {
+        CodeGen code = new CodeGen(
+"""
+val cnt=2;
+return { -> cnt; }();
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code._stop.toString());
+        assertEquals("2", Eval2.eval(code, 0));
+    }
+
+    // Function variables
+    @Test
+    public void testFcn4() {
+        CodeGen code = new CodeGen(
+"""
+var fcn = arg ? { int x -> x*x; } : { int x -> x+x; };
+return fcn(3);
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return Phi(Region,{ int -> int #1},{ int -> int #2})( 3); return (Parm_x($fun,int,3)*x); return (Parm_x($fun,int,3)<<1); ]", code._stop.toString());
+        assertEquals("6", Eval2.eval(code, 0));
+        assertEquals("9", Eval2.eval(code, 1));
+    }
+
+    // Recursive factorial test
+    @Test
+    public void testFcn5() {
+        CodeGen code = new CodeGen("val fact = { int x -> x <= 1 ? 1 : x*fact(x-1); }; return fact(arg);");
+        code.parse().opto().typeCheck();
+        assertEquals("Stop[ return fact( arg); return Phi(Region,1,(Parm_x(fact,int,arg,(x-1))*fact( Sub))); ]", code._stop.toString());
+        assertEquals( "1", Eval2.eval(code, 0));
+        assertEquals( "1", Eval2.eval(code, 1));
+        assertEquals( "2", Eval2.eval(code, 2));
+        assertEquals( "6", Eval2.eval(code, 3));
+        assertEquals("24", Eval2.eval(code, 4));
+    }
+
+    @Test
+    public void testFcn6() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int i; };
+val newS = { int x -> return new S { i=x; }; };
+return newS(1).i;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return 1;", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    // Double forward reference
+    @Test
+    public void testFcn7() {
+        CodeGen code = new CodeGen(
+"""
+if( arg ? f : g ) return 1;
+val f = {->1;};
+val g = {->2;};
+return 2;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("Stop[ return 1; return 1; return 2; ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFcn8() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? i2i = null;
+var id = {{int->int} f-> return f;};
+for(;;) {
+    if (i2i) return i2i(arg);
+    var x = {int i-> return i;};
+    arg = x(3);
+    i2i = id(x);
+}
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return x( Phi(Loop,arg,x( 3))); return Parm_i(x,int,3,Phi_arg); ]", code._stop.toString());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFcn9() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? i2i = null;
+for(;;) {
+    if (i2i) return i2i(arg);
+    var x = {int i-> return i;};
+    arg = x(3);
+}
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return Top;", code._stop.toString());
+        assertEquals(null, Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testFcn10() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+  int age;
+};
+
+val fcn = { Person?[] ps, int x ->
+  val tmp = ps[x];
+  if( ps[x] )
+    ps[x].age++;
+};
+
+var ps = new Person?[2];
+ps[0] = new Person;
+ps[1] = new Person;
+fcn(ps,1);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    // Function break
+    @Test
+    public void testErr1() {
+        CodeGen code = new CodeGen(
+"""
+for(;;) {
+    val f = { ->
+        break;
+    };
+    f();
+    return 2;
+}
+return 1;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("No active loop for a break or continue",e.getMessage()); }
+    }
+
+    // Calling and inlining a null function
+    @Test
+    public void testErr2() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? !i2i = { int i -> return i; };
+for(;;) {
+    if (i2i(2) == arg) break;
+    i2i = null;
+}
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null calling { int -> int #1}?",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testErr3() {
+        CodeGen code = new CodeGen(
+"""
+val f = { int i, int j -> return i+j; };
+return f();
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Expecting 2 arguments, but found 0",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testErr4() {
+        CodeGen code = new CodeGen(
+"""
+struct S {
+    {int} f = { -> x(); return 0; }; // Do not let fref x be a field
+};
+val x = { -> return 1; };
+S? s = null;
+for(;;) {
+    if (s) return s.x;
+}
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Accessing unknown field 'x' from '*S'",e.getMessage()); }
+    }
+
+    @Test
+    public void testErr5() {
+        CodeGen code = new CodeGen(
+"""
+val g = { ->
+    g();
+};
+return 0;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("No defined return type",e.getMessage()); }
+    }
+
+
+    // Mutual recursion.  Fails without SCCP to lift the recursive return types.
+    @Ignore @Test
+    public void testFcnMutRec() {
+        CodeGen code = new CodeGen(
+"""
+val is_even = { int x -> x ? is_odd (x-1) : true ; };
+val is_odd  = { int x -> x ? is_even(x-1) : false; };
+return is_even(arg);
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return is_even( arg); return Phi(Region,Phi(Region,is_even( ((Parm_x(is_even,int,arg,Sub)-1)-1)),0),1); ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code, 0));
+        assertEquals("0", Eval2.eval(code, 1));
+        assertEquals("1", Eval2.eval(code, 2));
+        assertEquals("0", Eval2.eval(code, 3));
+    }
+
+    // Forward ref to 'x' means that
+    @Ignore @Test
+    public void testForwardRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct S {
+    { int } f = { -> return x(); };
+};
+val x = { -> return 1; };
+S? s = null;
+for(;;) {
+    if (s) return s.f;
+}
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    // Inline hidden called more than once
+    @Test
+    public void testInline() {
+        CodeGen code = new CodeGen(
+"""
+{int->int}?! i2i = {int i->return i;};
+{{int->int}->{int->int}}! f2f = {{int->int} f->return f;};
+val o = i2i;
+if (arg) i2i = null;
+if (i2i) return i2i(arg);
+return f2f(o)(1);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return Phi(Region,o( arg),o( 1)); return Parm_i(o,int,arg,1); ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testOperField() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+    int coffee_count;
+};
+Person !p = new Person;
+p.coffee_count += 1;
+return p.coffee_count;
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 1;", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  2));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
new file mode 100644
index 00000000..a4857a01
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -0,0 +1,398 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
+import org.junit.Ignore;
+
+public class Chapter19Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+return 0;
+""");
+        code.parse().opto().typeCheck();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+
+
+    @Test
+    public void testString() {
+        CodeGen code = new CodeGen(
+"""
+struct String {
+    u8[] cs;
+    int _hashCode;
+};
+
+val equals = { String self, String s ->
+    if( self == s ) return true;
+    if( self.cs# != s.cs# ) return false;
+    for( int i=0; i< self.cs#; i++ )
+        if( self.cs[i] != s.cs[i] )
+            return false;
+    return true;
+};
+
+val hashCode = { String self ->
+    self._hashCode
+    ?  self._hashCode
+    : (self._hashCode = _hashCodeString(self));
+};
+
+val _hashCodeString = { String self ->
+    int hash=0;
+    if( self.cs ) {
+        for( int i=0; i< self.cs#; i++ )
+            hash = hash*31 + self.cs[i];
+    }
+    if( !hash ) hash = 123456789;
+    return hash;
+};
+
+String !s = new String { cs = new u8[17]; };
+s.cs[0] =  67; // C
+s.cs[1] = 108; // l
+hashCode(s);""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return Phi(Region,123456789,Phi(Loop,0,(.[]+((Phi_hash<<5)-Phi_hash)))); return Phi(Region,1,0,0,1); ]", code._stop.toString());
+        assertEquals("-2449306563677080489", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testBasic0() {
+        CodeGen code = new CodeGen("return 0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic1() {
+        CodeGen code = new CodeGen("return arg+1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (inc,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic2() {
+        CodeGen code = new CodeGen("return -17;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return -17;", code._stop.toString());
+    }
+
+
+    @Test
+    public void testBasic3() {
+        CodeGen code = new CodeGen("return arg==1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (set==,(cmp,arg));", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic4() {
+        CodeGen code = new CodeGen("return arg<<1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (shli,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic5() {
+        CodeGen code = new CodeGen("return arg >> 1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (sari,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic6() {
+        CodeGen code = new CodeGen("return arg >>> 1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (shri,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic7() {
+        CodeGen code = new CodeGen("return arg / 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (div,arg,2);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic8() {
+        CodeGen code = new CodeGen("return arg * 6;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (muli,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic9() {
+        CodeGen code = new CodeGen("return arg & 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (andi,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic10() {
+        CodeGen code = new CodeGen("return arg | 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (ori,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic11() {
+        CodeGen code = new CodeGen("return arg ^ 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (xori,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic12() {
+        CodeGen code = new CodeGen("return arg + 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (addf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic13() {
+        CodeGen code = new CodeGen("return arg - 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (subf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic14() {
+        CodeGen code = new CodeGen("return arg * 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (mulf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic15() {
+        CodeGen code = new CodeGen("return arg / 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (divf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic16() {
+        CodeGen code = new CodeGen(
+"""
+int arg1 =  arg + 1;
+return arg1 / arg;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (div,(inc,arg),arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic17() {
+        CodeGen code = new CodeGen(
+"""
+int arg1 =  arg + 1;
+return arg1 * arg;
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (mul,(inc,arg),arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testToFloat() {
+        CodeGen code = new CodeGen("""
+                int a = arg;
+                return a + 2.0;
+                """
+        ).parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (addf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testIfStmt() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg == 1)
+    a = arg+2;
+else {
+    a = arg-3;
+}
+return a;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Region,(addi,arg),(addi,arg));", code.print());
+    }
+
+    @Test
+    public void testIfMerge2() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=arg+2;
+if( arg==1 )
+    b=b+a;
+else
+    a=b+1;
+return a+b;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (add,(add,Phi(Region,(shli,arg),arg),arg),Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testLoop() {
+        CodeGen code = new CodeGen(
+"""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Loop,0,(add,Phi_sum,Phi(Loop,0,(inc,Phi_i))));", code.print());
+    }
+
+    @Test
+    public void testAlloc1() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int a; S? c; };
+return new S;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testLea1() {
+        CodeGen code = new CodeGen("int x = arg/3; return arg+x+7;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2",  "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testLea2() {
+        CodeGen code = new CodeGen("int x = arg/3; return arg+x*4+7;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testLea3() {
+        CodeGen code = new CodeGen("int x = arg/3; return x*4+arg;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2",  "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testAlloc2() {
+        CodeGen code = new CodeGen("int[] !xs = new int[3]; xs[arg]=1; return xs[arg&1];");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testAlloc3() {
+        CodeGen code = new CodeGen("int[] !xs = new int[3]; xs[arg]=1; return xs[arg&1]+3;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testArray1() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg];
+// Fill [0,1,2,3,4,...]
+for( int i=0; i<ary#; i++ )
+    ary[i] = i;
+// Fill [0,1,3,6,10,...]
+for( int i=0; i<ary#-1; i++ )
+    ary[i+1] += ary[i];
+return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testArray2() {
+        CodeGen code = new CodeGen(
+"""
+flt[] !A = new flt[arg], !B = new flt[arg];
+// Fill [0,1,2,3,4,...]
+for( int i=0; i<A#; i++ )
+    A[i] = i;
+for( int i=0; i<A#; i++ )
+    B[i] += A[i];
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testArray3() {
+        CodeGen code = new CodeGen(
+"""
+byte[] !A = new byte[arg];
+for( int i=0; i<A#; i++ )
+    A[i]++;
+return A[1];
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testNewton() {
+        CodeGen code = new CodeGen(
+"""
+// Newtons approximation to the square root
+val sqrt = { flt x ->
+    flt guess = x;
+    while( 1 ) {
+        flt next = (x/guess + guess)/2;
+        if( next == guess ) return guess;
+        guess = next;
+    }
+};
+flt farg = arg;
+return sqrt(farg);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Loop,(i2f8,arg),(divf,(addf,(divf,i2f8,Phi_guess),Phi_guess),2.0f));", code.print());
+    };
+
+
+    @Test
+    public void sieveOfEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+var ary = new bool[arg], primes = new int[arg];
+var nprimes=0, p=0;
+// Find primes while p^2 < arg
+for( p=2; p*p < arg; p++ ) {
+    // skip marked non-primes
+    while( ary[p] ) p++;
+    // p is now a prime
+    primes[nprimes++] = p;
+    // Mark out the rest non-primes
+    for( int i = p + p; i < ary#; i += p )
+        ary[i] = true;
+}
+// Now just collect the remaining primes, no more marking
+for( ; p < arg; p++ )
+    if( !ary[p] )
+        primes[nprimes++] = p;
+// Copy/shrink the result array
+var !rez = new int[nprimes];
+for( int j=0; j<nprimes; j++ )
+    rez[j] = primes[j];
+return rez;
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return [int];", code.print());
+        //assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+
+    @Test
+    public void testFcn1() {
+        CodeGen code = new CodeGen(
+"""
+val fcn = arg ? { int x -> x*x; } : { int x -> x+x; };
+return fcn(2)*10 + fcn(3);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("Stop[ return (add,Phi(Region,{ int -> int #1},{ int -> int #2})( 3),(muli,Phi_( 2))); return (mul,Parm_x($fun,int,3,2),x); return (shli,Parm_x($fun,int,3,2)); ]", code.print());
+    }
+
+    @Test
+    public void testFcn2() {
+        CodeGen code = new CodeGen(
+"""
+val sq = { int x -> x*x; };
+return sq(arg) + sq(3);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("Stop[ return (add,sq(),sq()); return (mul,Parm_x(sq,int,3,arg),x); ]", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
new file mode 100644
index 00000000..48458f95
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -0,0 +1,17 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class Chapter20Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+return 0;
+""");
+        code.parse().opto().typeCheck();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java b/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java
new file mode 100644
index 00000000..6ae8427c
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java
@@ -0,0 +1,448 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.type.*;
+import com.seaofnodes.simple.node.*;
+import java.util.*;
+
+public abstract class Eval2 {
+
+    // A mapping from Node ID to evaluation data Object.
+    // Data Objsts are a boxed Long or Double; or an Object[] of fields, which
+    // themselves are just more Objects.
+    private static class Frame {
+        private static int UID=1;
+
+        private final IdentityHashMap<Node,Object> _data;
+        private Frame _prior;   // Prior frame in this sequence, means when making a new frame we can find old stuff
+        private int _refcnt;    // TODO: Use this in a sentence (free/recycle unused stack frames)
+        final int _uid = UID++; // Debugging aid
+        Frame(Frame prior) {
+            _prior = prior;
+            if( prior!=null ) prior._refcnt++;
+            _data = new IdentityHashMap<>();
+            _refcnt = 1;
+        }
+
+        // Dec ref count
+        void dec() {
+            assert _refcnt>0;
+            if( --_refcnt == 0 ) {
+                Frame prior = _prior;
+                _prior = null;
+                _data.clear();
+                // TODO: FREE LIST?
+                if( prior!=null )
+                    prior.dec();
+            }
+        }
+
+        // Put a mapping from Node->Object
+        Node put(Node n, Object d) {
+            assert d!=null;
+            return put0(n,d);
+        }
+        // Put a mapping from Node->Object?
+        Node put0(Node n, Object d) {
+            assert _refcnt>0;
+            _data.put(n,d);
+            return n;
+        }
+        // Get a mapped Node, perhaps using the prior stack frame crawl
+        Object get(Node n) {
+            assert _refcnt>0;
+            Object d = _data.get(n);
+            return d != null ? d
+                : _prior == null ? null
+                : _prior.get(n);
+        }
+
+        // Short debugging print
+        public String p() {
+            return "#"+_uid + (_prior==null ? "" : " >> " + _prior.p());
+        }
+        // Long debugging print
+        @Override public String toString() {
+            String s = "";
+            if( _prior != null ) s+= _prior+" << ";
+            s += "#"+_uid+"[ ";
+            for( Node n : _data.keySet() )
+                s += n + ":" + _data.get(n) + ",";
+            s += "]";
+
+            return s;
+        }
+    }
+
+    // Classic Closure; an environment (stack of frames) and an execution point
+    private static class Closure {
+        // Where to return too; either a CallEnd or a Function
+        final CFGNode _cc;
+
+        // Stack frame at the execution point.  Includes Closures which
+        // recursively include other stack frames
+        private Frame _frame;
+
+        Closure(CFGNode cc, Frame frame) {
+            _cc = cc;           // One of Fun, CallEnd or Stop (null)
+            _frame = frame;
+            assert _frame._refcnt >=0;
+            _frame._refcnt++;
+        }
+
+        FunNode fun() { return (FunNode)_cc; }
+        CallEndNode cend() { return (CallEndNode)_cc; }
+        boolean isStop() { return _cc instanceof StopNode; } // or Stop
+
+        //
+        void pushFrame() {
+            _frame = new Frame(_frame);
+            _frame._refcnt++;
+        }
+
+        @Override public String toString() {
+            return _cc.toString();
+        }
+    }
+
+    // CodeGen has the linker tables
+    public static CodeGen CODE;
+
+    // Current active Frame, to avoid having to pass it everywhere
+    public static Frame F;
+
+    public static String eval( CodeGen code, long arg ) { return eval(code,arg,1000); }
+    public static String eval( CodeGen code, long arg, int timeout ) {
+        SB trace = null; // new SB(); // TRACE, set to null for off, new SB() for on
+        // Force local scheduling phase
+        if( code._phase.ordinal() < CodeGen.Phase.TypeCheck .ordinal() )  code.typeCheck();
+        if( code._phase.ordinal() < CodeGen.Phase.Schedule  .ordinal() )  code.GCM();
+        if( code._phase.ordinal() < CodeGen.Phase.LocalSched.ordinal() )  code.localSched();
+        // Set global, so don't have to pass everywhere
+        CODE = code;
+
+        // Timer for when we run too long.  Ticks once per backedge or function call
+        int loopCnt = 0;
+
+        // Current value for each Node; boxed Long or Double; or an Object[] of
+        // fields, which themselves are just more Objects.
+        F = new Frame(null);
+
+        // Start at the START
+        CFGNode BB = code._start, prior = null;
+        // Return from main hits Stop
+        F.put(BB,new Closure(code._stop,F));
+
+
+        // ------------
+        // Evaluate until exit or timeout.  Each outer loop step computes
+        // all data nodes under some new Control.
+        while( true ) {
+            assert BB!=null;
+            traceCtrl(BB,trace);
+            if( trace!=null ) System.out.println(F.p());
+
+            // Parallel assign Phis
+            int i = BB instanceof RegionNode r
+                    ? parallelAssignPhis(r,prior,arg,trace)
+                    : 0;
+
+            // Compute the data nodes until BB control
+            for( ; i < BB.nOuts(); i++ )
+                if( !(BB.out(i) instanceof CFGNode) )
+                    step(BB.out(i), trace);
+
+            // Find the next control target
+            prior = BB;
+            BB = BB.uctrl();      // Next unique control target
+            switch( prior ) {
+            case StartNode start:  F = new Frame(F); break; // Frame for the call to main, as-if Called
+            case CallNode  call :  BB = call(call); break;
+            case IfNode    iff  :  Object p = val(iff.pred()); BB = iff.cproj( p==null || (p instanceof Long x && x==0L)  ? 1 : 0);  break;
+            case ReturnNode ret :  if( clj(ret.rpc()).isStop() ) return exit(ret); else BB = ret(ret); break;
+            case FunNode   fun  :  if( loopCnt++ > timeout ) return null;  break; // Timeout
+            case LoopNode  loop :  if( loopCnt++ > timeout ) return null;  break; // Timeout
+            case CallEndNode cend: break;
+            case CProjNode cproj:  break;
+            case RegionNode r   :  break;
+            default:               throw Utils.TODO();
+            }
+            assert !BB.isDead();
+        }
+    }
+
+
+    // Phi cache; size is limited to number of Phis at a merge point
+    private static final Object[] PHICACHE = new Object[256];
+    static int parallelAssignPhis(RegionNode r, CFGNode prior, long arg, SB trace) {
+
+        // Compute input path on Phis for this Region
+        int path = r._inputs.find( prior );
+        // Parameters read from prior frame, Phis from local frame
+        Frame frame = (r instanceof FunNode ? F._prior : F);
+        boolean isMain = r instanceof FunNode fun && fun.sig().isa(CodeGen.CODE._main);
+
+        // Parallel assign Phis.  First parallel read and cache
+        int i;
+        for( i = 0; i < r.nOuts(); i++ ) {
+            if( !(r.out(i) instanceof PhiNode phi) ) break;
+            if( isMain && phi instanceof ParmNode parm && parm._idx==2 )
+                PHICACHE[i] = arg; // Reading the initial arguments to main()
+            else {
+                Node n = phi instanceof ParmNode parm
+                    // RPC reads the Call directly;
+                    // Parms may not be linked, so read call args directly
+                    ? (parm._idx==0 ? prior : prior.in(parm._idx))
+                    // Phis read from path input
+                    :  phi.in(path);
+                PHICACHE[i] = frame.get(n);
+            }
+        }
+        // Parallel assign; might assign before read, so read from cache
+        for( int j=0; j < i; j++ )
+            traceData(F.put0(r.out(j),PHICACHE[j]),trace);
+        // Return point in basic block past last Phi
+        return i;
+    }
+
+
+    // Make a call.
+    private static CFGNode call( CallNode call ) {
+        // Set up the Return PC and return frame (which is just the current frame).
+        // Really making a Continuation, but it's just a Closure
+        Closure cont = new Closure(call.cend(),F);
+        // Set the return continuation into the current frame RPC
+        F.put(call, cont );
+        // Next Frame to use
+        F = new Frame(F);
+        // Target function and environment
+        return CODE.link(tfp(call.fptr()));
+    }
+
+    private static CFGNode ret( ReturnNode ret ) {
+        // Fetch return expression value and continuation from current frame
+        Object rez = val(ret.expr());
+        Closure cont = clj(ret.rpc());
+        // Lower Frame reference count; might delete frame
+        F.dec();                // Lower ref count
+        // Install replacement Frame; set return result over the CallEnd
+        F = cont._frame;
+        F.put0(cont._cc,rez);   // Set return value into CallEnd
+        return cont._cc;        // Return CallEnd as the new control
+    }
+
+    private static String exit( ReturnNode ret ) {
+        return prettyPrint(ret.expr()._type,val(ret.expr()));
+    }
+
+    // Take a worklist step: one data op from the current Control is updated.
+    private static void step(Node n, SB trace) {
+        if( n instanceof PhiNode ) return;
+        // Compute new value
+        F.put0(n,compute(n));
+        traceData(n,trace);
+        // Also do any following projections, which are not in the local schedule otherwise
+        if( n instanceof MultiNode )
+            for( Node use : n._outputs )
+                step(use,trace);
+    }
+
+    // From here down shamelessly copied from Evaluator, written by @Xmilia
+    private static Object compute( Node n ) {
+        return switch( n ) {
+        case AddFNode     adf  -> d(adf.in(1)) +  d(adf.in(2));
+        case AddNode      add  -> x(add.in(1)) +  x(add.in(2));
+        case AndNode      and  -> x(and.in(1)) &  x(and.in(2));
+        case BoolNode.EQF eqf  -> d(eqf.in(1)) == d(eqf.in(2)) ? 1L : 0L;
+        case BoolNode.LEF lef  -> d(lef.in(1)) <= d(lef.in(2)) ? 1L : 0L;
+        case BoolNode.LTF ltf  -> d(ltf.in(1)) <  d(ltf.in(2)) ? 1L : 0L;
+        case BoolNode.EQ  eq   -> Objects.equals(val(eq.in(1)), val(eq.in(2))) ? 1L : 0L; // Bool EQ supports pointers, nil, and integers
+        case BoolNode.LE  le   -> x(le .in(1)) <= x(le .in(2)) ? 1L : 0L;
+        case BoolNode.LT  lt   -> x(lt .in(1)) <  x(lt .in(2)) ? 1L : 0L;
+        case CastNode    cast  -> val(cast.in(1));
+        case ConstantNode con  -> con(con._con);
+        case DivFNode     dvf  -> d(dvf.in(2))==0 ? 0D : d(dvf.in(1)) /  d(dvf.in(2));
+        case DivNode      div  -> x(div.in(2))==0 ? 0L : x(div.in(1)) /  x(div.in(2));
+        case LoadNode     ld   -> load(ld);
+        case MinusFNode   mnf  -> - d(mnf.in(1));
+        case MinusNode    sub  -> - x(sub.in(1));
+        case MulFNode     mlf  -> d(mlf.in(1)) *  d(mlf.in(2));
+        case MulNode      mul  -> x(mul.in(1)) *  x(mul.in(2));
+        case NewNode      alloc-> alloc(alloc);
+        case NotNode      not  -> x(not.in(1)) == 0 ? 1L : 0L;
+        case OrNode       or   -> x(or .in(1)) |  x(or .in(2));
+        case ProjNode     proj -> proj._type instanceof TypeMem ? "$mem" : val(proj.in(0));
+        case ReadOnlyNode read -> val(read.in(1));
+        case SarNode      sar  -> x(sar.in(1)) >> x(sar.in(2));
+        case MemMergeNode merge-> "$mem";
+        case ShlNode      shl  -> x(shl.in(1)) << x(shl.in(2));
+        case ShrNode      shr  -> x(shr.in(1)) >>>x(shr.in(2));
+        case StoreNode    st   -> store(st);
+        case SubNode      sub  -> x(sub.in(1)) -  x(sub.in(2));
+        case SubFNode     sbf  -> d(sbf.in(1)) -  d(sbf.in(2));
+        case ToFloatNode  toflt-> (double)x(toflt.in(1));
+        case XorNode      xor  -> x(xor.in(1)) ^  x(xor.in(2));
+        default -> throw Utils.TODO();
+        };
+    }
+
+    // Fetch without unboxing, searching up-Frame
+    static Object val( Node n ) { return F.get(n); }
+    // Fetch and unbox as primitive long
+    static long   x( Node n ) { Object d = F.get(n); return d==null ? 0 : (Long)  F.get(n);  }
+    // Fetch and unbox as primitive double
+    static double d( Node n ) { Object d = F.get(n); return d==null ? 0 : (Double)F.get(n);  }
+    // Fetch and unbox a function constant
+    static TypeFunPtr tfp(Node n) { return (TypeFunPtr)F.get(n); }
+    // Fetch and unbox a closure
+    static Closure clj(Node n) { return (Closure)F.get(n); }
+
+    // Java box ints and floats.  Other things can just be null or some informative string
+    private static Object con( Type t ) {
+        return switch ( t ) {
+        case TypeInteger i -> i.isConstant() ? (Long  )i.value() : "INT";
+        case TypeFloat   f -> f.isConstant() ? (Double)f.value() : "FLT";
+        case TypeMemPtr tmp -> tmp;
+        case TypeFunPtr tfp -> tfp;
+        case TypeMem mem -> "MEM";
+        default -> null;
+        };
+    }
+
+    // Convert array size to array element count
+    private static int offToIdx( long off, TypeStruct t) {
+        off -= t.aryBase();
+        int scale = t.aryScale();
+        long mask = (1L << scale)-1;
+        assert (off & mask) == 0;
+        return (int)(off>>scale);
+    }
+
+    // Builds and returns a pointer Object
+    private static Object alloc(NewNode alloc) {
+        TypeStruct type = alloc._ptr._obj;
+        if( type.isAry() ) {
+            long sz = (Long)val(alloc.in(1));
+            long x = offToIdx(sz, type);
+            int n = (int)x;
+            if( n!=x || n<0 )
+                throw new NegativeArraySizeException(""+n);
+            Object[] ary = new Object[n]; // Array body
+            var elem = type._fields[1]._type;
+            if (elem instanceof TypeInteger) {
+                Arrays.fill( ary, 0L );
+            } else if (elem instanceof TypeFloat) {
+                Arrays.fill( ary, 0D );
+            } else {
+                assert elem instanceof TypeMemPtr || elem instanceof TypeFunPtr;
+            }
+            return ary;
+        }
+
+        int num = type._fields.length;
+        Object[] ptr = new Object[num];
+        for( int i=0; i<num; i++ )
+            ptr[i] = con(type._fields[i]._type.makeZero());
+        return ptr;
+    }
+
+    private static Object load( LoadNode ld ) {
+        TypeMemPtr tmp = (TypeMemPtr)ld.ptr()._type;
+        Object[] fs = (Object[])val(ld.ptr());
+        if( ld._name.equals("#") )
+            return (long)fs.length;
+        int idx = tmp._obj.isAry()
+            ? offToIdx(x(ld.off()),tmp._obj)
+            : tmp._obj.find(ld._name);
+        return fs[idx];
+    }
+
+    private static Object store( StoreNode st ) {
+        if( st._name.equals("#") )
+            return "$mem";      // Eval stores the length in the java object[], no need to set it now
+        TypeMemPtr tmp = (TypeMemPtr)st.ptr()._type;
+        Object[] fs = (Object[])val(st.ptr());
+        int idx = tmp._obj.isAry()
+            ? offToIdx(x(st.off()),tmp._obj)
+            : tmp._obj.find(st._name);
+        Object val = val(st.val());
+        fs[idx] = val;
+        return "$mem";
+    }
+
+
+    // ------------------------------------------------------------------------
+    private static final IdentityHashMap<Object,Object> VISIT = new IdentityHashMap<>();
+
+
+    static void traceCtrl( CFGNode BB, SB sb ) {
+        if( sb==null ) return;
+        IRPrinter.printLine(BB,sb.p("--- "));
+        System.out.print(sb);
+        sb.clear();
+    }
+    static void traceData( Node n, SB sb ) {
+        if( sb==null ) return;
+        IRPrinter.printLine(n,sb).unchar();
+        _print( n._type, F.get(n), sb.p('\t'), VISIT );
+        System.out.println(sb);
+        sb.clear();
+        VISIT.clear();
+    }
+
+    // Use type to print x as a string.  Uses a new VISIT table so the debugger
+    // doesn't try to reuse VISIT if stopping mid-print.  The trace code reuses
+    // VISIT endlessly for some minor speed hope
+    static String prettyPrint( Type t, Object x ) { return _print(t,x,new SB(), new IdentityHashMap<>()).toString(); }
+    static SB _print( Type t, Object x, SB sb, IdentityHashMap<Object,Object> visit ) {
+        if( x instanceof String s ) return sb.p(s);
+        if( x == null ) return sb.p("null");
+        return switch( t ) {
+        case TypeInteger i -> sb.p(  (Long)x);
+        case TypeFloat   f -> sb.p((Double)x);
+        case TypeMemPtr tmp -> {
+            if( visit.containsKey(x) ) yield sb.p("$cyclic");
+            visit.put(x,x);
+            // Since never can close the type cycle, without cyclic types, have
+            // to handle FRefs even here
+            if( tmp.isFRef() )
+                tmp = tmp.makeFrom(((TypeMemPtr)Parser.TYPES.get(tmp._obj._name))._obj);
+
+            Object[] xs = (Object[])x; // Array of fields
+            if( tmp._obj.isAry() ) {
+                Type elem = tmp._obj._fields[1]._type;
+                if( elem == TypeInteger.U8 ) {
+                    // Shortcut u8[] as a String
+                    for( Object o : xs )
+                        sb.p((char)(long)(Long)o);
+                } else {
+                    // Array of elements
+                    elem.print(sb).p("[ ");
+                    for( Object o : xs )
+                        _print( elem, o, sb, visit ).p( "," );
+                    sb.unchar().p("]");
+                }
+            } else {
+                sb.p(tmp._obj._name).p("{");
+                Field[] flds = tmp._obj._fields;
+                for( int i=0; i<flds.length; i++ )
+                    _print( flds[i]._type,xs[i], sb.p(flds[i]._fname).p("="), visit ).p(",");
+                sb.unchar().p("}");
+            }
+            yield sb;
+        }
+        case TypeFunPtr tfp -> sb.p(x.toString());
+        case TypeRPC rpc -> sb.p(x.toString());
+        case TypeMem mem -> sb.p("$mem");
+        case TypeTuple tt -> {
+            if( tt._types.length>1 && tt._types[1] instanceof TypeMemPtr )
+                // Assume a NewNode
+                yield _print( tt._types[1], x, sb, visit );
+            throw Utils.TODO();
+        }
+        case Type tt -> {
+            if( tt == Type.NIL ) yield sb.p("null");
+            throw Utils.TODO();
+        }
+        };
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java b/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
new file mode 100644
index 00000000..d67b2065
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
@@ -0,0 +1,43 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.fuzzer.Fuzzer;
+import java.util.Random;
+import org.junit.Ignore;
+import org.junit.Test;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * To use the fuzzer run the <code>fuzzPeeps</code> methods.
+ * This can be done from IntelliJ Gui or remove the `@Ignore` annotation and start the test case from the command line
+ * via <code>mvn clean test -Dtest=com.seaofnodes.simple.Fuzzer08Test#fuzzPeeps</code>
+ */
+public class FuzzerWrap {
+
+    @Ignore
+    @Test
+    public void fuzzPeeps() {
+        var fuzzer = new Fuzzer();
+        for (int i=0; i<1000000; i++)
+            fuzzer.fuzzPeeps(i);
+        assertTrue(fuzzer.noExceptions());
+    }
+
+
+    @Test
+    public void fuzzPeepsSmall() {
+        Random R = new Random(System.currentTimeMillis());
+        var fuzzer = new Fuzzer();
+        for (int i=0; i<100; i++)
+            fuzzer.fuzzPeeps( R.nextLong());
+        assertTrue(fuzzer.noExceptions());
+    }
+
+    @Test
+    @Ignore
+    public void fuzzPeepTiming() {
+        var fuzzer = new Fuzzer();
+        int max_nid=0;
+        for (int i=0; i<1000000; i++)
+            max_nid = fuzzer.fuzzPeepTiming(i, max_nid);
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Main.java b/chapter20/src/test/java/com/seaofnodes/simple/Main.java
new file mode 100644
index 00000000..523bd306
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Main.java
@@ -0,0 +1,17 @@
+package com.seaofnodes.simple;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public class Main {
+    // Compile and run a simple program
+    public static void main( String[] args ) throws Exception {
+        // First arg is file, 2nd+ args are program args
+        String src = Files.readString(Path.of(args[0]));
+        int arg = Integer.valueOf(args[1]);
+        CodeGen code = new CodeGen(src);
+        code.parse().opto().typeCheck().GCM().localSched();
+        System.out.println(code._stop);
+        System.out.println(Eval2.eval(code,arg,100000));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
new file mode 100644
index 00000000..d48449d5
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
@@ -0,0 +1,65 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class MergeSortTest {
+
+    @Test
+    public void testMergeSort() {
+        CodeGen code = new CodeGen(
+"""
+// based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
+
+val merge_sort = { int[] a, int[] b, int n ->
+    copy_array(a, 0, n, b);
+    split_merge(a, 0, n, b);
+};
+
+val split_merge = { int[] b, int begin, int end, int[] a ->
+    if (end - begin <= 1)
+        return 0;
+    int middle = (end + begin) / 2;
+    split_merge(a, begin, middle, b);
+    split_merge(a, middle, end, b);
+    merge(b, begin, middle, end, a);
+    return 0;
+};
+
+val merge = { int[] b, int begin, int middle, int end, int[] a ->
+    int i = begin, j = middle;
+
+    for (int k = begin; k < end; k++) {
+        // && and ||
+        bool cond = false;
+        if (i < middle) {
+            if (j >= end)          cond = true;
+            else if (a[i] <= a[j]) cond = true;
+        }
+        if (cond) b[k] = a[i++];
+        else      b[k] = a[j++];
+    }
+};
+
+val copy_array = { int[] a, int begin, int end, int[] b ->
+    for (int k = begin; k < end; k++)
+        b[k] = a[k];
+};
+
+int[] !a = new int[arg];
+int[] !b = new int[a#];
+
+for (int i = 0; i < a#; i++)
+    a[i] = a# - i;
+
+merge_sort(a, b, a#);
+
+return a;
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return [int]; return 0; ]", code._stop.toString());
+        assertEquals("int[ 1,2,3,4,5,6,7,8,9,10,11]", Eval2.eval(code, 11));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java b/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
new file mode 100644
index 00000000..d50c302a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
@@ -0,0 +1,73 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class SchedulerTest {
+
+    private static void assertObj(Object obj, String name, Object... fields) {
+        assertEquals(Evaluator.Obj.class, obj.getClass());
+        var o = (Evaluator.Obj)obj;
+        assertEquals(name, o.struct()._name);
+        Assert.assertArrayEquals(fields, o.fields());
+    }
+
+    @Test
+    @Ignore
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+}
+S !v=new S;
+v.f = 2;
+int i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse();//.opto();
+        var eval = new Evaluator(code._stop);
+        assertEquals(2L, eval.evaluate(1, 10));
+    }
+
+    @Test
+    public void testStoreInIf() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+};
+S !v0=new S;
+if(arg) v0.f=1;
+return v0;
+""");
+        code.parse().opto();
+        var eval = new Evaluator(code._stop);
+        assertObj(eval.evaluate(0, 10), "S", 0L);
+        assertObj(eval.evaluate(1, 10), "S", 1L);
+    }
+
+    @Test
+    public void testStoreInIf2() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+};
+S !v=new S;
+v.f = 2;
+int i=new S.f;
+i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse().opto();
+        var eval = new Evaluator(code._stop);
+        assertEquals(2L, eval.evaluate(0, 10));
+        assertEquals(2L, eval.evaluate(1, 10));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java b/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
new file mode 100644
index 00000000..d94f5b5a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
@@ -0,0 +1,158 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.type.*;
+import org.junit.Assert;
+import org.junit.Test;
+import static org.junit.Assert.assertSame;
+
+public class TypeTest {
+
+    // Test basic properties and GLB
+    @Test
+    public void testTypeAdHoc() {
+        Assert.assertEquals( Type.BOTTOM, TypeInteger.TRUE.meet(TypeNil.NIL) );
+        Assert.assertEquals( Type.BOTTOM, TypeInteger.TOP.meet(TypeNil.NIL) );
+
+
+        TypeStruct s1 = TypeStruct.make("s1", new Field[]{
+                Field.make("a", TypeInteger.BOT,-1, false),
+                Field.make("b", TypeInteger.BOT,-2, false) });
+        TypeStruct s2 = TypeStruct.make("s2", new Field[]{
+                Field.make("a", TypeInteger.BOT,-3, false),
+                Field.make("b", TypeInteger.BOT,-4, false) });
+        Assert.assertEquals(s1.makeRO(), s1.glb());
+        Assert.assertNotEquals(s1, s1.dual());
+        Assert.assertEquals(s1.makeRO(), s1.dual().glb());
+
+        TypeMem m1 = TypeMem.make(1,TypeNil.NIL);
+        TypeMem m2 = TypeMem.make(2,TypeInteger.U16);
+        TypeMem m3 = TypeMem.make(3,TypeFloat.F64);
+        TypeMem m4 = TypeMem.make(4,TypeInteger.BOT);
+
+        Assert.assertNotEquals(m1, m2);
+        Assert.assertNotEquals(m2, m3);
+        Assert.assertNotEquals(m3, m4);
+
+        Assert.assertEquals(TypeStruct.BOT, s1.meet(s2));
+        Assert.assertEquals(TypeMem   .BOT, m1.meet(m2));
+        Assert.assertEquals(TypeMem.make(0,Type.BOTTOM), m1.meet(m3));
+        Assert.assertEquals(TypeMem   .BOT, m3.meet(m4));
+
+        Assert.assertEquals(TypeMem.make(1,Type.BOTTOM), m1.glb());
+        Assert.assertEquals(TypeMem.make(1,Type.XNIL), m1.dual());
+        Assert.assertEquals(m4.dual(), m4.glb().dual());
+
+        TypeMemPtr ptr1 = TypeMemPtr.make(s1);
+        Assert.assertEquals(s1, ptr1._obj);
+        TypeMemPtr ptr2 = TypeMemPtr.make(s2);
+        Assert.assertEquals(s2, ptr2._obj);
+
+        TypeMemPtr ptr1nil = TypeMemPtr.makeNullable(s1);
+        Assert.assertEquals(s1, ptr1nil._obj);
+        Assert.assertTrue( ptr1nil.nullable() );
+        Assert.assertNotNull( ptr1nil._obj );
+        TypeMemPtr ptr2nil = TypeMemPtr.makeNullable( s2);
+        Assert.assertEquals(s2, ptr2nil._obj);
+
+        Assert.assertNotEquals(ptr1, ptr2);
+        Assert.assertNotEquals(ptr1, ptr1.glb());
+        Assert.assertEquals(ptr1nil.makeRO(), ptr1.glb());
+
+        Assert.assertEquals(ptr1, ptr1.dual().dual());
+        Assert.assertEquals(ptr1.glb().makeRO(), ptr1.dual().glb());
+        Assert.assertEquals(TypeMemPtr.makeNullable(TypeStruct.BOT), ptr1.meet(ptr2nil));
+        Assert.assertEquals(ptr1.glb(), ptr1.meet(TypeNil.NIL).makeRO());
+
+        TypeMemPtr TOP = TypeMemPtr.TOP;
+        TypeMemPtr BOT = TypeMemPtr.makeNullable(TypeStruct.BOT);
+        TypeMemPtr PTR = TypeMemPtr.make(TypeStruct.BOT);
+        Type NULL = TypeNil.NIL;
+        Type PTR_meet_NULL = NULL.meet(PTR);
+        Assert.assertEquals(BOT, PTR_meet_NULL);
+        Type ptr1_meet_ptr2 = ptr1.meet(ptr2);
+        Assert.assertEquals(PTR, ptr1_meet_ptr2);
+        Type NULL_join_ptr1 = NULL.join(ptr1);
+        Assert.assertEquals(TypePtr.XNPTR, NULL_join_ptr1);
+        Type NULL_join_PTR = PTR.join(NULL);
+        Assert.assertEquals(TypePtr.XNPTR, NULL_join_PTR);
+        Type ptr1_dual = ptr1.dual();
+        Type nullableptr1_dual = ptr1nil.dual();
+    }
+
+    // Test theoretical properties.
+    // This is a symmetric complete bounded (ranked) lattice.
+    // Also, the meet is commutative and associative.
+    // The lattice has a dual (symmetric), and join is ~(~x meet ~y).
+    // See https://en.wikipedia.org/wiki/Lattice_(order).
+    @Test
+    public void testLatticeTheory() {
+        Type[] ts = Type.gather();
+
+        // Confirm commutative & complete
+        for( Type t0 : ts )
+            for( Type t1 : ts ) {
+                check_commute  (t0,t1);
+                check_symmetric(t0,t1);
+            }
+
+        // Confirm associative
+        for( Type t0 : ts )
+            for( Type t1 : ts )
+                for( Type t2 : ts )
+                    assoc(t0,t1,t2);
+
+        // Confirm symmetry.  If A isa B, then A.join(C) isa B.join(C)
+        for( Type t0 : ts )
+            for( Type t1 : ts )
+                if( t0.isa(t1) )
+                    for( Type t2 : ts ) {
+                        Type t02 = t0.join(t2);
+                        Type t12 = t1.join(t2);
+                        Type mt  = t02.meet(t12);
+                        assertSame(mt,t12);
+                    }
+    }
+
+    // By design in meet, args are already flipped to order _type, which forces
+    // symmetry for things with badly ordered _type fields.  The question is
+    // still interesting for other orders.
+    private static void check_commute( Type t0, Type t1 ) {
+        if( t0==t1 ) return;
+        if( t0.is_simple() && !t1.is_simple() ) return; // By design, flipped the only allowed order
+        Type mta = t0.meet(t1);
+        Type mtb = t1.meet(t0); // Reverse args and try again
+        assertSame(mta,mtb);
+    }
+
+    // A & B = MT
+    // Expect: ~A & ~MT == ~A
+    // Expect: ~B & ~MT == ~B
+    private static void check_symmetric( Type t0, Type t1 ) {
+        if( t1==t0 ) return;
+        Type mt = t0.meet(t1);
+        Type dm = mt.dual();
+        Type d0 = t0.dual();
+        Type d1 = t1.dual();
+        Type ta = dm.meet(d1);
+        Type tb = dm.meet(d0);
+        assertSame(ta,d1);
+        assertSame(tb,d0);
+    }
+
+    private static void assoc( Type t0, Type t1, Type t2 ) {
+        Type t01   = t0 .meet(t1 );
+        Type t12   = t1 .meet(t2 );
+        Type t01_2 = t01.meet(t2 );
+        Type t0_12 = t0 .meet(t12);
+        assertSame(t01_2,t0_12);
+    }
+
+    // Test cyclic types and meets
+    @Test
+    public void testCyclic0() {
+        Type d0 = TypeStruct.S1.dual();
+        Type d1 = d0.dual();
+        assertSame(TypeStruct.S1,d1);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
new file mode 100644
index 00000000..a3b87e90
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
@@ -0,0 +1,383 @@
+package com.seaofnodes.simple.evaluator;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+
+import java.util.*;
+
+public class Evaluator {
+
+    private static final Object MEMORY = new Object();
+
+    public record Obj(TypeStruct struct, Object[] fields) {
+        private void init(IdentityHashMap<Obj, Integer> objs) {
+            var oid = objs.get(this);
+            if (oid != null) {
+                if (oid != 0) objs.put(this, 0);
+                return;
+            }
+            objs.put(this, -1);
+            for (var obj : fields) {
+                if (obj instanceof Obj o) o.init(objs);
+            }
+        }
+        private static int p(StringBuilder sb, IdentityHashMap<Obj, Integer> objs, int id, String indentation, String step, String sep, Object obj) {
+            if (obj instanceof Obj o) return o.p(sb, objs, id, indentation, step, sep);
+            sb.append(obj);
+            return id;
+        }
+        private int p(StringBuilder sb, IdentityHashMap<Obj, Integer> objs, int id, String indentation, String step, String sep) {
+            var cid = objs.get(this);
+            assert cid != null;
+            if (cid > 0) {
+                sb.append("obj@").append(cid);
+                return id;
+            }
+            if (struct._name.equals("[u8]")) {
+                sb.append('"');
+                for (int i=struct._fields.length-1; i<fields.length; i++) {
+                    var v = fields[i];
+                    if (v == null) v = 0;
+                    assert v instanceof Number;
+                    var n = ((Number)v).byteValue() & 0xFF;
+                    if (n >= 0x20 && n < 0x80) {
+                        if (n == 0x22 || n == 0x5C) sb.append("\\");
+                        sb.append((char)n);
+                    } else {
+                        sb.append("\\x").append("0123456789abcdef".charAt(n >> 4)).append("0123456789abcdef".charAt(n & 0xF));
+                    }
+                }
+                sb.append('"');
+                return id;
+            }
+            sb.append("Obj<").append(struct._name).append(">");
+            if (cid == 0) {
+                cid = id++;
+                objs.put(this, cid);
+                sb.append("@").append(cid);
+            }
+            sb.append("{");
+            if (struct._fields.length == 0) {
+                assert !struct.isAry();
+                sb.append("}");
+                return id;
+            }
+            String nextIndent = indentation + step;
+            int e = struct._fields.length - 1;
+            for(int i=0; i<e; i++) {
+                sb.append(nextIndent).append(struct._fields[i]._fname).append("=");
+                id = p(sb, objs, id, nextIndent, step, sep, fields[i]);
+                sb.append(sep);
+            }
+            sb.append(nextIndent).append(struct._fields[e]._fname).append("=");
+            if (struct.isAry()) {
+                sb.append("[");
+                if (fields.length > e) {
+                    String innerIndent = nextIndent + step;
+                    sb.append(innerIndent);
+                    id = p(sb, objs, id, nextIndent, step, sep, fields[e]);
+                    for (int i = e+1; i < fields.length; i++) {
+                        sb.append(sep).append(innerIndent);
+                        id = p(sb, objs, id, nextIndent, step, sep, fields[i]);
+                    }
+                    sb.append(nextIndent);
+                }
+                sb.append("]");
+            } else {
+                id = p(sb, objs, id, nextIndent, step, sep, fields[e]);
+            }
+            sb.append(indentation).append("}");
+            return id;
+        }
+        private StringBuilder p(StringBuilder sb, String indentation, String step, String sep) {
+            var objs = new IdentityHashMap<Obj, Integer>();
+            init(objs);
+            p(sb, objs, 1, indentation, step, sep);
+            return sb;
+        }
+        @Override
+        public String toString() {
+            if (struct._name.equals("[u8]")) {
+                var sb = new StringBuilder();
+                for (int i=struct._fields.length-1; i<fields.length; i++) {
+                    var v = fields[i];
+                    if (v == null) v = 0;
+                    assert v instanceof Number;
+                    var n = ((Number)v).byteValue() & 0xFF;
+                    sb.append((char)n);
+                }
+                return sb.toString();
+            }
+            return p(new StringBuilder(), "", "", ",").toString();
+        }
+        public String pretty() {
+            return p(new StringBuilder(), "\n", "  ", "").toString();
+        }
+    }
+
+    private static int getFieldIndex(TypeStruct struct, MemOpNode memop, long off) {
+        int idx = struct.find(memop._name);
+        if( idx >= 0 ) return idx;
+        throw new AssertionError("Field "+memop._name+" not found in struct " + struct._name);
+    }
+
+    public enum Status {
+        TIMEOUT,
+        FALLTHROUGH
+    }
+
+    /**
+     * Find the start node from some node in the graph or null if there is no start node
+     */
+    private static StartNode findStart(BitSet visit, Node node) {
+        if (node == null) return null;
+        if( visit.get(node._nid) ) return null;
+        visit.set(node._nid);
+        StartNode start = node instanceof StartNode ? (StartNode) node : null;
+        for( Node def : node._inputs ) {
+            var res = findStart(visit,def);
+            if( res != null ) start = res;
+        }
+        for( Node use : node._outputs ) {
+            var res = findStart(visit,use);
+            if( res != null ) start = res;
+        }
+        return start;
+    }
+
+    private final Object[] values;
+    private final ArrayList<Object> phiCache = new ArrayList<>();
+    private final StartNode start;
+    private final Scheduler.Block startBlock;
+
+    public Evaluator(Node graph) {
+        var visited = new BitSet();
+        this.start = findStart(visited, graph);
+        if (this.start == null) {
+            this.values = null;
+            this.startBlock = null;
+            return;
+        }
+        this.startBlock = Scheduler.schedule(this.start);
+        this.values = new Object[visited.length()];
+    }
+
+    private long div(DivNode div) {
+        long in2 = vall(div.in(2));
+        return in2 == 0 ? 0 : vall(div.in(1)) / in2;
+    }
+    private double div(DivFNode div) {
+        double in2 = vald(div.in(2));
+        return in2 == 0 ? 0 : vald(div.in(1)) / in2;
+    }
+
+    private static long offToIdx(long off, TypeStruct t) {
+        off -= t.aryBase();
+        int scale = t.aryScale();
+        long mask = (1L << scale)-1;
+        assert (off & mask) == 0;
+        return off>>scale;
+    }
+
+    private Object alloc(NewNode alloc) {
+        TypeStruct type = alloc._ptr._obj;
+        Object[] body=null;
+        int num;
+        if( type.isAry() ) {
+            long sz = (Long)val(alloc.in(1));
+            long n = offToIdx(sz, type);
+            if( n < 0 )
+                throw new NegativeArraySizeException(""+n);
+            body = new Object[(int)n+1]; // Array body
+            var elem = type._fields[1]._type;
+            if (elem instanceof TypeInteger) {
+                for (int i=0; i<n; i++) body[i+1] = 0L;
+            } else if (elem instanceof TypeFloat) {
+                for (int i = 0; i < n; i++) body[i+1] = 0D;
+            } else {
+                assert elem instanceof TypeMemPtr;
+            }
+            // Length value
+            body[0] = vall(alloc.in(2+2));
+        } else {
+            body = new Object[num = type._fields.length];
+            for( int i=0; i<num; i++ )
+                body[i] = switch( alloc._ptr._obj._fields[i]._type ) {
+                case TypeInteger ti -> 0L;
+                case TypeFloat tf -> 0;
+                default -> null;
+                };
+        }
+        Object[] mems = new Object[type._fields.length+2];
+        // mems[0] is control
+        mems[1] = new Obj(type,body); // the ref
+        // mems[2+...] are memory aliases
+        return mems;
+    }
+
+    private Object load(LoadNode load) {
+        var from = (Obj)val(load.ptr());
+        var off = vall(load.off());
+        var idx = getFieldIndex(from.struct, load, (Long)off);
+        if( idx==from.struct._fields.length-1 && from.struct.isAry() ) {
+            long len = from.fields.length - from.struct._fields.length + 1;
+            long i = offToIdx(off, from.struct);
+            if( i < 0 || i >= len )
+                throw new ArrayIndexOutOfBoundsException("Array index out of bounds " + i + " < " + len);
+            return from.fields[(int)i+from.struct._fields.length-1];
+
+        } else
+            return from.fields[idx];
+    }
+
+    private Object store(StoreNode store) {
+        var to = (Obj)val(store.ptr());
+        var off = vall(store.off());
+        var val = val(store.val());
+        var idx = getFieldIndex(to.struct, store, (Long)off);
+        if( idx==to.struct._fields.length-1 && to.struct.isAry() ) {
+            long len = to.fields.length - to.struct._fields.length + 1;
+            long i = offToIdx(off, to.struct);
+            if( i < 0 || i >= len )
+                throw new RuntimeException("Array index out of bounds " + off + " <= " + len);
+            to.fields[(int)i+to.struct._fields.length-1] = val;
+        } else
+            to.fields[idx] = val;
+        return null;
+    }
+
+    private static boolean isTrue(Object obj) {
+        if (obj == null) return false;
+        if (obj instanceof Number n) return n.longValue() != 0;
+        return true;
+    }
+
+    private Object val(Node node) {
+        return values[node._nid];
+    }
+
+    private long vall(Node node) {
+        var v = val(node);
+        if (v instanceof Number n) return n.longValue();
+        throw new AssertionError("Not a long " + v);
+    }
+    private double vald(Node node) {
+        var v = val(node);
+        if (v instanceof Number n) return n.doubleValue();
+        if( v == null ) return 0;
+        throw new AssertionError("Not a double " + v);
+    }
+
+    private Object cons(ConstantNode cons) {
+        var type = cons.compute();
+        if (type instanceof TypeInteger i) return i.isConstant() ? i.value() : Integer.MAX_VALUE;
+        if (type instanceof TypeFloat i) return i.value();
+        return null;
+    }
+
+    private Object exec(Node node) {
+        return switch (node) {
+            case ConstantNode cons  -> cons(cons);
+            case AddNode      add   -> vall(add.in(1)) + vall(add.in(2));
+            case AddFNode     add   -> vald(add.in(1)) + vald(add.in(2));
+            case BoolNode.EQF eq    -> vald(eq.in(1)) == vald(eq.in(2)) ? 1L : 0L;
+            case BoolNode.LEF le    -> vald(le.in(1)) <= vald(le.in(2)) ? 1L : 0L;
+            case BoolNode.LTF lt    -> vald(lt.in(1)) <  vald(lt.in(2)) ? 1L : 0L;
+            case BoolNode.EQ  eq    -> Objects.equals(val(eq.in(1)), val(eq.in(2))) ? 1L : 0L;
+            case BoolNode.LE  le    -> vall(le.in(1)) <= vall(le.in(2)) ? 1L : 0L;
+            case BoolNode.LT  lt    -> vall(lt.in(1)) <  vall(lt.in(2)) ? 1L : 0L;
+            case DivNode      div   -> div(div);
+            case DivFNode     div   -> div(div);
+            case MinusNode    minus -> -vall(minus.in(1));
+            case MinusFNode   minus -> -vald(minus.in(1));
+            case MulNode      mul   -> vall(mul.in(1)) * vall(mul.in(2));
+            case MulFNode     mul   -> vald(mul.in(1)) * vald(mul.in(2));
+            case NotNode      not   -> isTrue(val(not.in(1))) ? 0L : 1L;
+            case SubNode      sub   -> vall(sub.in(1)) - vall(sub.in(2));
+            case SubFNode     sub   -> vald(sub.in(1)) - vald(sub.in(2));
+            case ShlNode      shl   -> vall(shl.in(1)) << vall(shl.in(2));
+            case ShrNode      shr   -> vall(shr.in(1)) >>> vall(shr.in(2));
+            case SarNode      sar   -> vall(sar.in(1)) >> vall(sar.in(2));
+            case AndNode      and   -> vall(and.in(1)) & vall(and.in(2));
+            case  OrNode      or    -> vall(or .in(1)) | vall(or .in(2));
+            case XorNode      xor   -> vall(xor.in(1)) ^ vall(xor.in(2));
+            case CastNode     cast  -> val(cast.in(1));
+            case ToFloatNode  cast  -> (double)vall(cast.in(1));
+            case LoadNode     load  -> load(load);
+            case StoreNode    store -> store(store);
+            case NewNode      alloc -> alloc(alloc);
+            case CProjNode    cproj -> ((Object[])val(cproj.ctrl()))[cproj._idx];
+            case ProjNode     proj  -> ((Object[])val( proj.in(0) ))[ proj._idx];
+            case MemMergeNode mem   -> null;
+            case ReadOnlyNode ro    -> val(ro.in(1));
+            case CallNode     call  -> Utils.TODO(); // should not reach here, go the IfNode route
+            default                 -> throw new AssertionError("Unexpected node " + node);
+        };
+    }
+
+    /**
+     * Run the graph until either a return is found or the number of loop iterations are done.
+     */
+    public Object evaluate(long parameter, int loops) {
+        if (start == null) return Status.TIMEOUT;
+        var s = new Object[start.compute()._types.length];
+        s[1] = MEMORY;
+        s[2] = parameter;
+        values[start._nid] = s;
+        int i=0;
+        Scheduler.Block block = this.startBlock;
+        for(;;) {
+            for(; i<block.nodes().length;i++) values[block.nodes()[i]._nid] = exec(block.nodes()[i]);
+            i=0;
+            switch (block.exit()) {
+            case null:
+                return Status.FALLTHROUGH;
+            case ReturnNode ret :  return val(ret .expr());
+            case IfNode ifn:
+                block = block.next()[isTrue(val(ifn.in(1))) ? 0 : 1];
+                if (block == null) return Status.FALLTHROUGH;
+                break;
+            case RegionNode region:
+                if (loops-- <= 0) return Status.TIMEOUT;
+                int exit = block.exitId();
+                assert exit > 0 && region.nIns() > exit;
+                block = block.next()[0];
+                assert block != null;
+                for (; i < block.nodes().length; i++) {
+                    if (!(block.nodes()[i] instanceof PhiNode phi)) break;
+                    var val = region instanceof FunNode fun && "main".equals(fun._name) && ((ParmNode)phi)._idx==2 && exit==1
+                            ? parameter
+                            : val(phi.in(exit));
+                    phiCache.add(val);
+                }
+                for (i=0; i<phiCache.size(); i++) {
+                    values[block.nodes()[i]._nid] = phiCache.get(i);
+                }
+                phiCache.clear();
+                break;
+            default:
+                throw Utils.TODO("Unexpected control node " + block.exit());
+            }
+        }
+    }
+
+    public static Object evaluate(StopNode graph) {
+        return evaluate(graph, 0);
+    }
+
+    public static Object evaluate(StopNode graph, long parameter) {
+        return evaluate(graph, parameter, 1000);
+    }
+
+    public static Object evaluate(StopNode graph, long parameter, int loops) {
+        var res = evaluateWithResult(graph, parameter, loops);
+        if (res == Status.TIMEOUT) throw new RuntimeException("Timeout");
+        return res;
+    }
+
+    public static Object evaluateWithResult(StopNode graph, long parameter, int loops) {
+        return new Evaluator(graph).evaluate(parameter, loops);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java
new file mode 100644
index 00000000..4bfa7628
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java
@@ -0,0 +1,606 @@
+package com.seaofnodes.simple.evaluator;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+
+import java.util.*;
+
+/**
+ * A late scheduler for test cases.
+ * <br>
+ * <br>
+ * This scheduler is used for tests and is not the final scheduler.
+ * <br>
+ * <br>
+ * The scheduler schedules not as late as possible. Since it is just for test cases this is fine.
+ * A better scheduler will try to place nodes outside of loops. Due to the schedule late strategy
+ * this scheduler might place initialization code in loops.
+ * <br>
+ * We schedule late here since memory edges have some implicit information. There can only be one
+ * memory edge (for a field) at a time. However, before <code>if</code> statements this might split.
+ * When scheduling early a store might be moved out of the loop but then there are two edges alive.
+ * The one through the store node and the adjacent one. This is an invalid schedule and instead of
+ * handling this case a late scheduler does not have this problem as memory edges are combined
+ * through phi nodes.
+ * <br>
+ * <br>
+ * A bit about this scheduler. It first discovers all alive nodes and allocates side data for them.
+ * Then the control flow graph is build. Then, all phis are placed and finally all the remaining nodes
+ * in an order where a node is placed when all alive uses are placed. Finally, the output is produced.
+ */
+public class Scheduler {
+
+    /**
+     * A basic block with a schedule of the containing nodes.
+     *
+     * @param nodes The nodes in the final schedule of this block
+     * @param exit The exit node of this block.
+     * @param exitId In case the next block is a region this gives the entry id into the region.
+     * @param next The next blocks.
+     */
+    public record Block(Node[] nodes, Node exit, int exitId, Block[] next) {}
+
+    /**
+     * Definition of a block in the building process.
+     */
+    private static class BasicBlock {
+
+        /**
+         * Dominator of this block
+         */
+        final BasicBlock dom;
+        /**
+         * Id of this block where <code>a.depth < b.depth</code> means that a is before b or
+         * both are in different branches.
+         */
+        final int depth;
+        /**
+         * Previous blocks
+         */
+        final BasicBlock[] prev;
+        /**
+         * Entry to this block
+         */
+        final Node entry;
+        /**
+         * Schedules node in reverse order.
+         */
+        final ArrayList<Node> reverseSchedule = new ArrayList<>();
+
+        /**
+         * Initialize the block.
+         * @param entry The node that started this block
+         * @param depth The depth of this node. All previous nodes need to have a lower value.
+         * @param prev The previous blocks.
+         */
+        BasicBlock(Node entry, int depth, BasicBlock... prev) {
+            BasicBlock dom = null;
+            int max = -1;
+            for(var bb: prev) {
+                max = Math.max(max, bb.depth);
+                dom = dom==null?bb:dom(dom, bb);
+            }
+            assert depth > max;
+            this.dom = dom;
+            this.depth = depth;
+            this.entry = entry;
+            this.prev = prev;
+        }
+        BasicBlock(Node entry, BasicBlock prev) {
+            this(entry,prev.depth+1,prev);
+        }
+
+    }
+
+    /**
+     * Ancillary data for nodes used during the scheduling process.
+     */
+    private static class NodeData {
+
+        /**
+         * The node this ancillary data is used for.
+         */
+        final Node node;
+
+        /**
+         * Number of alive users not yet scheduled.
+         */
+        int users = 1;
+
+        /**
+         * Block into which the node should be placed so far.
+         * This will be updated with every placed use.
+         */
+        BasicBlock block;
+
+        /**
+         * Initialize ancillary data for a node
+         * @param node The node this ancillary data is associated with.
+         */
+        NodeData(Node node) {
+            this.node = node;
+        }
+
+    }
+
+    /**
+     * Ancillary data for nodes.
+     */
+    private final IdentityHashMap<Node, NodeData> data = new IdentityHashMap<>();
+    /**
+     * List of nodes which can be placed since all users are placed.
+     */
+    private final Stack<NodeData> scheduleQueue = new Stack<>();
+
+    /**
+     * Get the ancillary data for an alive node.
+     * @param node The node for which the ancillary data is requested.
+     * @return The ancillary data for the node.
+     */
+    NodeData d(Node node) {
+        return od(node).orElseThrow(AssertionError::new);
+    }
+
+    /**
+     * Get the ancillary data for a potentially dead node.
+     * @param node The node for which the ancillary data is requested.
+     * @return The ancillary data for the node an alive node or
+     * <code>Optional.empty()</code> for <code>null</code> or dead nodes.
+     */
+    Optional<NodeData> od(Node node) {
+        return Optional.ofNullable(data.get(node));
+    }
+
+    /**
+     * Checks a node for validity
+     * @param data The node to check.
+     * @return true if all placed inputs are before this node.
+     */
+    private boolean isValid(NodeData data) {
+        return data.node._inputs.stream()
+                .map(i->i==null?null:d(i))
+                .map(d->d==null||d.users>0?null:d.block)
+                .allMatch(d->d==null||dom(d, data.block)==d);
+    }
+
+    /**
+     * Checks that node is not XCtrl.
+     * @param node The node to check.
+     * @return true if the node is not XCtrl.
+     */
+    private static boolean isNotXCtrl(Node node) {
+        return !(node instanceof ConstantNode c && c.compute() == Type.XCONTROL) && !(node instanceof XCtrlNode);
+    }
+
+    /**
+     * Return the dominator of <code>a</code> and <code>b</code>
+     * @param a Block a
+     * @param b Block b
+     * @return The dominator of <code>a</code> and <code>b</code>
+     */
+    private static BasicBlock dom(BasicBlock a, BasicBlock b) {
+        while (a!=b) {
+            if (a.depth >= b.depth) a=a.dom;
+            if (b.depth > a.depth) b=b.dom;
+        }
+        return a;
+    }
+
+    /**
+     * Return if a is before b.
+     * @param a Block a
+     * @param b Block b
+     * @return true is a is before b.
+     */
+    private static boolean isBefore(BasicBlock a, BasicBlock b) {
+        while (b.depth > a.depth) {
+            while (b.dom.depth > a.depth) b = b.dom;
+            for (int i=0; i<b.prev.length-1; i++) {
+                if (isBefore(a, b.prev[i])) return true;
+            }
+            b = b.prev[b.prev.length-1];
+        }
+        return a == b;
+    }
+
+    /**
+     * Is node placed during the control flow graph build.
+     * @param data Node to check.
+     * @return true if node is placed during the control flow graph build.
+     */
+    private static boolean isPinnedNode(NodeData data) {
+        return data.node instanceof CFGNode || data.node instanceof PhiNode;
+    }
+
+    /**
+     * Refine placement of a node.
+     * @param data The node to refine.
+     * @param block The block before the node should be scheduled.
+     */
+    private void refinePlacement(NodeData data, BasicBlock block) {
+        assert !isPinnedNode(data);
+        data.block = data.block == null ? block : dom(data.block, block);
+        assert isValid(data);
+    }
+
+    /**
+     * Refine placement if before is happening before data
+     * @param data The node for which the placement should be refined.
+     * @param before The node before which the data node should be placed.
+     */
+    private void optionalRefinePlacement(NodeData data, Node before) {
+        od(before).ifPresent(d->{
+            // before might be in a different branch. So check this case with isBefore
+            // and only refine the placement if it is not in a different branch.
+            if (isBefore(d.block, data.block)) refinePlacement(data, d.block);
+        });
+    }
+
+    /**
+     * Schedule all nodes not yet scheduled.
+     */
+    private void doSchedule() {
+        while (!scheduleQueue.isEmpty()) {
+            var data = scheduleQueue.pop();
+            assert !isPinnedNode(data);
+
+            assert data.block != null;
+            assert data.users == 0;
+
+            if (data.node instanceof LoadNode l) {
+                assert isValid(data);
+                // Handle anti-deps of load nodes.
+                // At this point all anti-dep nodes are scheduled,
+                // but they did not refine the placement
+                // so do that now.
+                var mem = l.in(1);
+                for(var out : mem._outputs) {
+                    if (out instanceof PhiNode p) {
+                        var r = p.in(0);
+                        for (int i = 1; i < p.nIns(); i++) {
+                            if (p.in(i) == mem) optionalRefinePlacement(data, r.in(i));
+                        }
+                    } else if (!(out instanceof LoadNode)) {
+                        optionalRefinePlacement(data, out);
+                    }
+                }
+            }
+
+            assert isValid(data);
+            data.block.reverseSchedule.add(data.node);
+
+            for(var in:data.node._inputs) {
+                if (in!=null) update(d(in), data.block);
+            }
+            if (data.node instanceof StoreNode s) {
+                // Store nodes have anti-deps to load nodes.
+                // So decrease the uses of these loads when the store is placed.
+                for (var out: s.in(1)._outputs) {
+                    if (out instanceof LoadNode) od(out).ifPresent(this::decUsers);
+                }
+            }
+        }
+
+        // Now all nodes should be placed and have a block assigned
+        assert this.data.values().stream().noneMatch(d->d.block==null);
+    }
+
+    /**
+     * Decrement the not-yet-placed users of a block.
+     * @param data The node for which the users should be decremented.
+     */
+    private void decUsers(NodeData data) {
+        assert data.users > 0;
+        if (--data.users == 0) {
+            assert data.block != null;
+            assert isValid(data);
+
+            // When all users are gone this node can be scheduled.
+            scheduleQueue.push(data);
+        }
+    }
+
+    /**
+     * Update the placement of a node
+     * @param data The node to update
+     * @param block The block before which the node should happen.
+     */
+    private void update(NodeData data, BasicBlock block) {
+        assert block != null;
+        if (data.users == 0) {
+            assert isPinnedNode(data);
+            return;
+        }
+        refinePlacement(data, block);
+        decUsers(data);
+    }
+
+    /**
+     * Checks if a CFG node is ready to be placed. This is used for regions joining branches.
+     * @param node The CFG node to check
+     * @return true if all parents of a CFG node are placed.
+     */
+    private boolean isCFGNodeReady(Node node) {
+        if (node instanceof LoopNode l) {
+            assert d(l.in(1)).block != null;
+        } else if (node instanceof RegionNode r) {
+            for(int i=1; i<r.nIns(); i++) {
+                if (od(r.in(i)).map(d->d.block==null).orElse(false)) return false;
+            }
+        } else if (node instanceof XCtrlNode) {
+            return false;
+        } else {
+            assert d(node.in(0)).block != null;
+        }
+        return true;
+    }
+
+    /**
+     * Schedule all phi nodes.
+     * @param phiQueue List of all the phi nodes to schedule.
+     */
+    private void schedulePhis(Stack<NodeData> phiQueue) {
+        while(!phiQueue.empty()) {
+            var data = phiQueue.pop();
+            var phi = (PhiNode) data.node;
+            var r = phi.in(0);
+            data.block = d(r).block;
+            for(int i=1; i<phi.nIns(); i++) {
+                var in = phi.in(i);
+                od(r.in(i)).ifPresent(d->update(d(in), d.block));
+            }
+        }
+    }
+
+    /**
+     * Build the control flow graph.
+     * @param start The start node.
+     */
+    private void doBuildCTF(StartNode start) {
+        var queue = new Stack<NodeData>();
+        var phiQueue = new Stack<NodeData>();
+        queue.push(d(start));
+        while (!queue.isEmpty()) {
+            var data = queue.pop();
+            var node = data.node;
+            assert node instanceof CFGNode;
+            BasicBlock block = switch (node) {
+            case StartNode s -> new BasicBlock(s, 0);
+            case LoopNode l -> new BasicBlock(l, d(l.in(1)).block);
+            case RegionNode r -> {
+                    var prev = new ArrayList<BasicBlock>();
+                    int depth = 0;
+                    for(int i=1; i<r.nIns(); i++) {
+                        if( !od(r.in(i)).isPresent() ) continue;
+                        BasicBlock bb = d(r.in(i)).block;
+                        prev.add(bb);
+                        depth = Math.max(depth,bb.depth);
+                    }
+                    yield new BasicBlock(r, depth+1, prev.toArray(BasicBlock[]::new));
+            }
+            case IfNode i -> d(i.in(0)).block;
+            case ReturnNode ret -> d(ret .in(0)).block;
+            case CallNode call -> throw Utils.TODO();
+            default -> new BasicBlock(node, d(node.in(0)).block);
+            };
+            data.block = block;
+            if (node instanceof RegionNode r) {
+                // Regions might have phis which need to be scheduled.
+                // Put them on a list for later scheduling.
+                for (var out:r._outputs) {
+                    if (out instanceof PhiNode p) {
+                        var d = this.data.get(p);
+                        if (d!=null) {
+                            d.users=0;
+                            phiQueue.push(d);
+                        }
+                    }
+                }
+            }
+            if( node instanceof FunNode fun ) {
+                // Cannot find CFG user from fun via a naive search, because always find
+                // Return but Return is not always the one CFG user.
+                CFGNode n = fun.uctrl();
+                assert isCFGNodeReady(n) && d(n).block==null;
+                queue.push(d(n));
+            } else if( !(node instanceof ReturnNode) ) {
+                for (Node n : node._outputs)
+                    if(n instanceof CFGNode && isCFGNodeReady(n) && d(n).block == null)
+                        queue.push(d(n));
+            }
+            var b = block;
+            for(var in:data.node._inputs) od(in).ifPresent(d->update(d, b));
+        }
+
+        // Schedule all phi nodes.
+        schedulePhis(phiQueue);
+    }
+
+    /**
+     * Mark a node alive and create ancillary data for it.
+     * @param queue List into which this node should be placed if it needs to be visited.
+     * @param node Node which should be marked alive.
+     * @param cfg If this node is a CFG node.
+     */
+    private void markAlive(Stack<NodeData> queue, Node node, boolean cfg) {
+        var nd = od(node).orElse(null);
+        if (nd != null) {
+            // Node was already visited, just increase the users.
+            if (nd.users>0) nd.users++;
+            return;
+        }
+        assert node instanceof CFGNode == cfg;
+        assert isNotXCtrl(node);
+        nd = new NodeData(node);
+        if (cfg) nd.users=0;
+        data.put(node, nd);
+        queue.push(nd);
+    }
+
+    /**
+     * Mark all alive nodes.
+     * First all CFG nodes are marked, then all other nodes.
+     * @param node THe start node.
+     */
+    private void doMarkAlive(Node node) {
+        var cfgQueue = new Stack<NodeData>();
+        var dataQueue = new Stack<NodeData>();
+        var mem = new Stack<NodeData>();
+        markAlive(cfgQueue, node, true);
+        // Mark all CFG nodes.
+        while (!cfgQueue.isEmpty()) {
+            var data = cfgQueue.pop();
+            node = data.node;
+            assert node instanceof CFGNode;
+            if (!(node instanceof ReturnNode) ) {
+                for (var out : node._outputs) if (out!=null && out instanceof CFGNode && isNotXCtrl(out)) markAlive(cfgQueue, out, true);
+            }
+            for (var in : node._inputs) if(in!=null && !(in instanceof CFGNode) && isNotXCtrl(in)) markAlive(dataQueue, in, false);
+        }
+        // Mark all other nodes.
+        while (!dataQueue.isEmpty()) {
+            var data = dataQueue.pop();
+            node = data.node;
+            assert !(node instanceof CFGNode);
+            if (node instanceof PhiNode phi) {
+                var r = phi.in(0);
+                for (int i=1; i<phi.nIns(); i++) {
+                    if (od(r.in(i)).isPresent()) markAlive(dataQueue, phi.in(i), false);
+                }
+            } else {
+                for (var in : node._inputs) if (in != null && !(in instanceof CFGNode)) markAlive(dataQueue, in, false);
+            }
+            if (node instanceof StoreNode) mem.push(data);
+        }
+        // Handle store nodes and increase load with an anti-dep to the store.
+        while (!mem.isEmpty()) {
+            var data = mem.pop();
+            node = data.node;
+            for(var out:node.in(1)._outputs) {
+                if (out instanceof LoadNode) od(out).ifPresent(d->d.users++);
+            }
+        }
+    }
+
+    /**
+     * Helper function to append the nodes of a block to an array of nodes
+     * @param arr The array the nodes of a block should be appended to.
+     * @param node A potentially separator node
+     * @param block The block from which the nodes should be appended.
+     * @return The combined new array.
+     */
+    private static Node[] appendNodes(Node[] arr, Node node, BasicBlock block) {
+        var idx = arr.length;
+        arr = Arrays.copyOf(arr, arr.length+block.reverseSchedule.size()+(node==null?0:1));
+        if (node != null) arr[idx++] = node;
+        for(int i=block.reverseSchedule.size()-1;i>=0;i--) {
+            arr[idx++] = block.reverseSchedule.get(i);
+        }
+        return arr;
+    }
+
+    /**
+     * Find the CFG output of a node
+     * @param node The node
+     * @return The CFG output of the node.
+     */
+    private static CFGNode findSingleCFGOut(Node node) {
+        if (node instanceof StartNode) {
+            for(var n:node._outputs)
+                if (n instanceof FunNode fun && "main".equals(fun._name) )
+                   return fun;
+            return null;
+        }
+        if( node instanceof FunNode fun ) return fun.uctrl();
+        assert node._outputs.stream().filter(x -> x instanceof CFGNode).limit(2).count()<=1;
+        for(var n:node._outputs) if(n instanceof CFGNode cfg) return cfg;
+        return null;
+    }
+
+    /**
+     * Build the final data structure after all the scheduling happened.
+     * @param start The start node
+     * @return The final schedule.
+     */
+    private Block build(Node start) {
+        var blocks = new IdentityHashMap<Node, Block>();
+        var queue = new Stack<NodeData>();
+        queue.push(d(start));
+
+        // Visit all CFG nodes and create blocks for them.
+        // This can combine blocks.
+        while(!queue.isEmpty()) {
+            var data = queue.pop();
+            var first = data.node;
+            Node prev;
+            var last = first;
+            Node[] arr = new Node[0];
+            if (first instanceof RegionNode) {
+                var nodes = new ArrayList<Node>();
+                for(var out: first._outputs) {
+                    if (out instanceof PhiNode) {
+                        if(od(out).isPresent()) nodes.add(out);
+                    }
+                }
+                arr = nodes.toArray(arr);
+            }
+            arr = appendNodes(arr, null, data.block);
+            assert !(first instanceof IfNode);
+            for(;;) {
+                prev = last;
+                last = findSingleCFGOut(last);
+                if (last == null) break;
+                if (last instanceof RegionNode) {
+                    if (blocks.get(last) == null && last != first)
+                        queue.push(d(last));
+                    break;
+                }
+                if (last instanceof ReturnNode) break;
+                if (last instanceof IfNode if_) {
+                    for(var out:if_._outputs) if (out instanceof CFGNode && blocks.get(out) == null) queue.push(d(out));
+                    break;
+                }
+                data = d(last);
+                arr = appendNodes(arr, data.node, data.block);
+            }
+            blocks.put(first, switch(last) {
+                case null -> new Block(arr, null, -1, new Block[0]);
+                case IfNode i -> new Block(arr, i, -1, new Block[2]);
+                case RegionNode r -> new Block(arr, r, r._inputs.find(prev), new Block[1]);
+                case ReturnNode r -> new Block(arr, r   , -1, new Block[0]);
+                default -> throw new AssertionError("Unexpected block exit node");
+            });
+        }
+        // Update the next pointer of all blocks.
+        for (var block: blocks.values()) {
+            switch(block.exit) {
+                case null: break;
+                case IfNode i:
+                    for(var out:i._outputs) if (out instanceof CProjNode p) block.next[p._idx] = blocks.get(p);
+                    break;
+                case RegionNode r:
+                    block.next[0] = blocks.get(r);
+                    break;
+                default:
+                    assert block.exit instanceof ReturnNode;
+            }
+        }
+        // And return the block for the start node.
+        return blocks.get(start);
+    }
+
+    /**
+     * Create a schedule for the program reachable from start.
+     * @param start The start node
+     * @return The final schedule.
+     */
+    public static Scheduler.Block schedule(StartNode start) {
+        var scheduler = new Scheduler();
+        scheduler.doMarkAlive(start);
+        scheduler.doBuildCTF(start);
+        scheduler.doSchedule();
+        return scheduler.build(start);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java
new file mode 100644
index 00000000..f7e0c4ad
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java
@@ -0,0 +1,174 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Eval2;
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.node.Node;
+import java.util.ArrayList;
+import java.util.Objects;
+import java.util.Random;
+import java.util.function.Consumer;
+
+/**
+ * Implementation of the fuzzer.
+ * Random testcases are generated using the ScriptGenerator.
+ * This will generate a script similar to how the parser parses it but instead of parsing it will
+ * randomly choose a variation the parser would parse and generate it.
+ * These scripts are the parsed by the parser and all exceptions are caught and filtered
+ * to only show one occurrence of one problem. This includes script which generate different
+ * results when the compiled graph with and without peeps is executed.
+ * To aid debugging scripts that cause errors are then reduced by applying rules and checking
+ * that the same issue persists.
+ */
+public class Fuzzer {
+
+    private static final int EVAL_TIMEOUT = 1000;
+
+    /**
+     * List of exceptions already encountered.
+     * This is used to filter new exceptions and discard them if they are already found.
+     */
+    private final ArrayList<Throwable> exceptions = new ArrayList<>();
+
+    /**
+     * Filter and record an exception in a script.
+     * @param e The exception caused by the script
+     * @param script The script causing the exception
+     * @param reproducer Reproducer which should be used to reproduce the test case.
+     */
+    private void recordException(Throwable e, String script, Consumer<String> reproducer, long seed) {
+        for (var ex : exceptions) {
+            if (FuzzerUtils.isExceptionFromSameCause(ex, e)) return;
+        }
+        exceptions.add(e);
+        System.out.println("========== Stack ==========");
+        e.printStackTrace(System.out);
+        System.out.println("========== Seed ==========");
+        System.out.println(seed);
+        //System.out.println("========== Code ===========");
+        //System.out.println(script);
+        System.out.println("========= Reduced =========");
+        System.out.println(Reducer.reduce(script, e, reproducer));
+        System.out.println("===========================");
+        System.out.flush();
+    }
+
+    private static boolean neq(Object a, Object b) {
+        if (Objects.equals(a, b)) return false;
+        return true;
+    }
+
+    /**
+     * Check that two graphs result in the same output when supplied with a value
+     * @param e1 Evaluator for the first graph
+     * @param e2 Evaluator for the second graph
+     * @param in The input value to both graphs to test for an equal output
+     */
+    private static void checkGraphs(CodeGen code1, CodeGen code2, long in) {
+        var r1 = Eval2.eval(code1, in, EVAL_TIMEOUT);
+        var r2 = Eval2.eval(code2, in, EVAL_TIMEOUT);
+        if( r1 == null || r2 == null ) return; // Timeout test invalid
+        if( neq(r1, r2) )
+            throw new RuntimeException("Different calculations values " + r1 + " vs " + r2);
+    }
+
+    /**
+     * Run checks for script. Compile the script with peeps enabled and disabled.
+     * Check that exceptions raised in the parser by both methods are the same and only happens if the script may be invalid.
+     * If the script was successfully parsed check that both version behave the same.
+     * @param script The script to test
+     * @param valid If the script is definitely valid. If not some exceptions may be suppressed.
+     */
+    private static void runCheck(String script, boolean valid) {
+        CodeGen code1;
+        try {
+            code1 = FuzzerUtils.parse(script, 123);
+        } catch (RuntimeException e1) {
+            try {
+                FuzzerUtils.parse(script, 456);
+            } catch (RuntimeException e2) {
+                if (FuzzerUtils.isExceptionFromSameCause(e1, e2)) {
+                    if (!valid || e1.getClass() == Parser.ParseException.class) return;
+                } else {
+                    e1.addSuppressed(e2);
+                }
+            }
+            throw e1;
+        }
+        CodeGen code2 = FuzzerUtils.parse(script, 456);
+        checkGraphs(code1, code2, 0);
+        checkGraphs(code1, code2, 1);
+        checkGraphs(code1, code2, 10);
+    }
+
+    /**
+     * Check that the script does not result in exceptions.
+     * @param script The script to test.
+     * @param valid If the script is valid or if it might contain syntax errors.
+     */
+    private void check(String script, boolean valid, long seed) {
+        try {
+            runCheck(script, valid);
+        } catch (Throwable e) {
+            recordException(e, script, s->runCheck(s, valid), seed);
+        }
+    }
+
+    /**
+     * Run one test with the given seed, and check for peephole counts.
+     * @param seed The seed to use for generating this test case
+     */
+    public int fuzzPeepTiming(long seed, int max_nids) {
+        var rand = new Random(seed);
+        var sb = new StringBuilder();
+        new ScriptGenerator(rand, sb, true).genProgram();
+        try {
+            var code = new CodeGen(sb.toString());
+
+            code.parse();
+            int nids = code.UID();
+            if( nids <= max_nids ) return max_nids; // Smaller, looking for trends as we grow
+            int parse_peeps= code._iter_cnt;
+            int parse_nops = code._iter_nop_cnt;
+            double parse_nop_ratio = (double)parse_nops/parse_peeps;
+            double parse_peeps_per_node = (double)parse_peeps/nids;
+
+            code.opto();
+            int iter_peeps= code._iter_cnt;
+            int iter_nops = code._iter_nop_cnt;
+            double iter_nop_ratio = (double)iter_nops/iter_peeps;
+            double iter_peeps_per_node = (double)iter_peeps/nids;
+
+            System.out.printf("%6d | Parsing: peeps: %5d, nops: %5d, ratio: %5.3f, last UID: %5d ps/node: %5.3f  | Iter: peeps: %6d, nops: %6d, ratio: %5.3f, ps/node: %5.3f\n",
+                              seed,
+                              parse_peeps,parse_nops,parse_nop_ratio,nids,parse_peeps_per_node,
+                              iter_peeps , iter_nops, iter_nop_ratio,      iter_peeps_per_node);
+            return nids;
+        } catch (Throwable e) {
+            // ignore exceptions, let the normal fullPeeps catch and reduce,
+            // we're interested in valid program optimizations
+        }
+        return max_nids;
+    }
+
+
+    /**
+     * Run one test with the given seed.
+     * @param seed The seed to use for generating this test case
+     */
+    public void fuzzPeeps(long seed) {
+        var rand = new Random(seed);
+        var sb = new StringBuilder();
+        var valid = new ScriptGenerator(rand, sb, true).genProgram();
+        check(sb.toString(), valid, seed);
+    }
+
+
+    /**
+     * Check that no exceptions happened.
+     * @return true if no exception happened
+     */
+    public boolean noExceptions() {
+        return exceptions.isEmpty();
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
new file mode 100644
index 00000000..0781ad67
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
@@ -0,0 +1,111 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.IterPeeps;
+import com.seaofnodes.simple.node.Node;
+import com.seaofnodes.simple.node.StopNode;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.OutputStream;
+import java.io.PrintStream;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Field;
+import java.util.BitSet;
+
+/**
+ * Some utilities for the fuzzer.
+ */
+class FuzzerUtils {
+
+    /**
+     * Get the val of a private field
+     */
+    @SuppressWarnings("unchecked")
+    public static <T> T getFieldValue(Object obj, String name) throws NoSuchFieldException, IllegalAccessException {
+        return (T) (obj instanceof Class<?> clz ? getField(clz, name).get(null) : getField(obj.getClass(), name).get(obj));
+    }
+
+    /**
+     * Get access to a private field
+     */
+    public static Field getField(Class<?> clz, String name) throws NoSuchFieldException {
+        var field = clz.getDeclaredField(name);
+        try {
+            field.setAccessible(true);
+        } catch (Throwable e) {
+            // Intentionally left empty
+        }
+        return field;
+    }
+
+    /**
+     * Try to rethrow an exception or create a runtime exception and throw it.
+     */
+    public static RuntimeException rethrow(Throwable e) {
+        if (e instanceof RuntimeException re) return re;
+        if (e instanceof Error er) throw er;
+        return new RuntimeException(e);
+    }
+
+    /**
+     * Some problems might trigger debug output. Suppress this output with a null print stream during fuzzing.
+     */
+    public static final PrintStream NULL_PRINT_STREAM = new PrintStream(OutputStream.nullOutputStream());
+
+    /**
+     * Check that the messages are similar.
+     */
+    private static boolean similarMessages(String a, String b) {
+        if (a == null || b == null) return true;
+        a = a.replaceAll("'\\w+'", "'normalized'").replaceAll("variable \\w+", "variable normalized");
+        b = b.replaceAll("'\\w+'", "'normalized'").replaceAll("variable \\w+", "variable normalized");
+        return a.equals(b);
+    }
+
+    /**
+     * Check if both stack traces have the same first entry. Empty stack traces can happen with NPE optimization
+     * and allow the other to be any stack trace.
+     */
+    private static boolean sameStackTraceOrigin(StackTraceElement[] a, StackTraceElement[] b) {
+        if (a == null || a.length == 0 || b == null || b.length == 0) return true; // One or both stack traces are missing.
+        return a[0].equals(b[0]);
+    }
+
+    /**
+     * Checks if two exceptions are caused by the same problem.
+     */
+    public static boolean isExceptionFromSameCause(Throwable a, Throwable b) {
+        if (a == null || b == null) return a == b; // Handle the null case
+        if (a.getClass() != b.getClass()) return false; // Different classes
+        if (!similarMessages(a.getMessage(), b.getMessage())) return false; // Different messages. Null is allowed as wildcard
+        var s1 = a.getStackTrace();
+        var s2 = b.getStackTrace();
+        if (!sameStackTraceOrigin(s1, s2)) return false; // Different stack trace origins
+        if (!isExceptionFromSameCause(a.getCause(), b.getCause())) return false; // Different causes
+        var o1 = a.getSuppressed();
+        var o2 = b.getSuppressed();
+        if (o1 == null || o2 == null || o1.length != o2.length) return o1 == o2; // Different suppression
+        for (int i=0; i<o1.length; i++) {
+            if (!isExceptionFromSameCause(o1[i], o2[i])) return false; // Different suppression
+        }
+        return true;
+    }
+
+    /**
+     * Parse script with peepholes enabled or disabled
+     */
+    public static CodeGen parse(String script, long workListSeed) {
+        var err = System.err;
+        var out = System.out;
+        try {
+            System.setErr(NULL_PRINT_STREAM);
+            System.setOut(NULL_PRINT_STREAM);
+            var code = new CodeGen(script, TypeInteger.BOT, workListSeed);
+            return code.parse().opto().typeCheck().GCM().localSched();
+        } finally {
+            System.setErr(err);
+            System.setOut(out);
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java
new file mode 100644
index 00000000..3731b40c
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java
@@ -0,0 +1,176 @@
+package com.seaofnodes.simple.fuzzer;
+
+import java.util.Arrays;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * This class is used to reduce test cases created by the fuzzer.
+ * It applies rewrite rules to the test case and checks that the
+ * test still produces the same exception.
+ * This is done in a fixpoint iteration until every rewrite produces
+ * no or a different exception.
+ */
+public class Reducer {
+
+    private interface Replacer extends BiConsumer<StringBuilder, Matcher> {}
+
+    /**
+     * Holder for the rewrite rules
+     */
+    private record Replace(Pattern pattern, boolean iterate, Replacer... replacements) {
+        Replace(Pattern p, Object... replacements) {
+            this(p, replacements[0] == Boolean.TRUE, Arrays.stream(replacements).filter(o->!(o instanceof Boolean)).map(Replace::from).toArray(Replacer[]::new));
+        }
+        private static Replacer from(Object o) {
+            if (o instanceof Replacer r) return r;
+            if (o instanceof Integer i) return (s, m)->s.append(m.group(i));
+            if (o instanceof String r) return (s, m)->s.append(r);
+            throw new IllegalArgumentException();
+        }
+    }
+
+    /**
+     * List of rewrite rules.
+     */
+    private static final Replace[] REPLACEMENTS = {
+            new Replace(Pattern.compile("\\b(?:[^\\W0]|\\w\\w+)\\b"), "0", "1"),
+            new Replace(Pattern.compile("(?<=\\n|^)[^\\n]+(?=\\n|$)"), true, ""),
+            new Replace(Pattern.compile("(?<=[+\\-*/<>=(])--"), ""),
+            new Replace(Pattern.compile("\\b--"), "+"),
+            new Replace(Pattern.compile("-"), ""),
+            new Replace(Pattern.compile("\\b\\+-"), "-"),
+            new Replace(Pattern.compile("(?<![+\\-*/<>=])(?:-|\\*|/|>=|<=|>|<|!=|==)(?![+\\-*/<>=])"), "+"),
+            new Replace(Pattern.compile("\\{((?:[^{}]|\\{})+)(?:\\n[ \\t]*)?}"), "", "{}", 1),
+            new Replace(Pattern.compile("(?<=\\n|^)([ \\t]*)\\{\\n(.*?)\\n\\1}", Pattern.DOTALL), 2),
+            new Replace(Pattern.compile("\\(([^()]+)\\)"), 1),
+            new Replace(Pattern.compile("\\d+\\+"), ""),
+            new Replace(Pattern.compile("\\+\\d+"), ""),
+            new Replace(Pattern.compile("\\n\\n+"), "\n"),
+            new Replace(Pattern.compile("^\\n+|\\n+$"), ""),
+            new Replace(Pattern.compile("else *"), ""),
+            new Replace(Pattern.compile("\\bif\\([^()]+\\) *"), ""),
+            new Replace(Pattern.compile("\\bwhile\\([^()]+\\) *"), ""),
+            new Replace(Pattern.compile("\\bstruct \\w+ \\{[^{}]*}"), "")
+    };
+
+    /**
+     * Predicate to test if the reduced script generates the same error.
+     */
+    private final Predicate<String> tester;
+
+    /**
+     * Create a reducer with a test function.
+     * @param tester Test function which returns true when the same issue is found in the script.
+     */
+    private Reducer(Predicate<String> tester) {
+        this.tester = tester;
+    }
+
+    /**
+     * Rewrites the script with one rewrite rule.
+     */
+    private String doReplacement(String script, Pattern pattern, Replacer[] replacements) {
+        var matcher = pattern.matcher(script);
+        var sb = new StringBuilder();
+        var last = 0;
+        var skip = 0;
+        outer:
+        while (matcher.find(last + skip)) {
+            sb.append(script, last, matcher.start());
+            last = matcher.end();
+            skip = last == matcher.start() ? 1 : 0;
+            var pos = sb.length();
+            for (var replacement : replacements) {
+                replacement.accept(sb, matcher);
+                var tail = sb.length();
+                sb.append(script, last, script.length());
+                if (tester.test(sb.toString())) {
+                    sb.setLength(tail);
+                    continue outer;
+                }
+                sb.setLength(pos);
+            }
+            last = matcher.start();
+            skip = 1;
+        }
+        sb.append(script, last, script.length());
+        return sb.toString();
+    }
+
+    /**
+     * Clean up variable names from the random ones generated by the fuzzer.
+     */
+    private String cleanVariables(String script) {
+        var matcher = Pattern.compile("\\b([0-9a-zA-Z_]+) ([0-9a-zA-Z_]+)").matcher(script);
+        int[] num = {0, 0};
+        while (matcher.find()) {
+            var type = matcher.group(1);
+            var var = matcher.group(2);
+            if (type.equals("new")) continue;
+            String prefix = "v";
+            int t = 0;
+            if (type.equals("struct")) {
+                t = 1;
+                prefix = "s";
+            }
+            if (var.matches(prefix+"\\d+")) continue;
+            while (script.contains(prefix+num[t])) num[t]++;
+            var n = script.replaceAll("\\b"+var+"\\b", prefix + num[t]);
+            if (tester.test(n)) {
+                script = n;
+            }
+        }
+        return script;
+    }
+
+    /**
+     * Run all rewrite rules once.
+     */
+    private String doAllReplacements(String script) {
+        for (var replace: REPLACEMENTS) {
+            String old;
+            do {
+                old = script;
+                script = doReplacement(script, replace.pattern, replace.replacements);
+            } while (replace.iterate && !old.equals(script));
+        }
+        return script;
+    }
+
+    /**
+     * Reduce the script to a minimal version which produces the same problem with a test function.
+     * @param tester Test function which returns true when the same issue is found in the script.
+     */
+    public static String reduce(String script, Predicate<String> tester) {
+        var reducer = new Reducer(tester);
+        String old;
+        do {
+            old = script;
+            script = reducer.doAllReplacements(script);
+            script = reducer.cleanVariables(script);
+        } while (!script.equals(old));
+        return script;
+    }
+
+    /**
+     * Reduce the script to a minimal version which produces the same problem with a reproducer.
+     * @param ex The exception originally caused by the script
+     * @param reproducer Test function which throws an exception which will be checked against ex.
+     */
+    public static String reduce(String script, Throwable ex, Consumer<String> reproducer) {
+        return reduce(script, s->{
+            Throwable nex = null;
+            try {
+                reproducer.accept(s);
+            } catch (Throwable e) {
+                nex = e;
+            }
+            return FuzzerUtils.isExceptionFromSameCause(nex, ex);
+        });
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
new file mode 100644
index 00000000..f119fa1a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
@@ -0,0 +1,869 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.node.ScopeNode;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Random;
+import java.util.function.Predicate;
+import static com.seaofnodes.simple.Parser.KEYWORDS;
+
+
+/**
+ * Generate a pseudo random script.
+ * This generator will generate the same script for two random number generators initialized with the same seed.
+ * To generate valid code it implements the parser but instead of parsing it emits the statements and expressions.
+ * It is guaranteed to terminate.
+ */
+public class ScriptGenerator {
+
+    private static final int MAX_STATEMENTS_PER_BLOCK = 5;
+    private static final int MAX_BINARY_EXPRESSIONS_PER_EXPRESSION = 10;
+    private static final int MAX_UNARY_EXPRESSIONS_PER_EXPRESSION = 6;
+    private static final int MAX_NAME_LENGTH = 10;
+    private static final int MAX_BLOCK_DEPTH = 4;
+    private static final int MAX_EXPRESSION_DEPTH = 10;
+    private static final int MAX_SUFFIX_RECURSIVE_DEPTH = 10;
+
+    /**
+     * Number of spaces per indentation
+     */
+    private static final int INDENTATION = 4;
+    /**
+     * Valid characters for identifiers. The last 10 are not valid for the first character.
+     */
+    private static final String VAR_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789";
+
+    /**
+     * Flag for a statement that it does not pass on control flow to the next statement.
+     */
+    private static final int FLAG_STOP = 0x01;
+    /**
+     * Flag for a statement that it contains a final if statement without an else branch.
+     */
+    private static final int FLAG_IF_WITHOUT_ELSE = 0x02;
+    /**
+     * Binary operators.
+     */
+    private static final String[] BINARY_OP = {"==", "!=", "<", "<=", ">", ">=", "+", "-", "*", "/", "&", ">>", ">>>", "<<"};
+    /**
+     * Unary operators.
+     */
+    private static final String[] UNARY_OP = {"-"};
+
+    private static class Type {
+        final String name;
+        Type(String name) {this.name=name;}
+        boolean isa(Type other) { return this == other; }
+    }
+
+    private static class TypeStruct extends Type {
+        record Field (String name, Type type, TypeStruct struct) {}
+        Field[] fields;
+        final TypeNullable nullable = new TypeNullable(this);
+        TypeStruct(String name) {
+            super(name);
+        }
+        boolean isa(Type other) { return this == other || other == nullable; }
+    }
+
+    private static class TypeNullable extends Type {
+
+        final Type base;
+
+        TypeNullable(Type base) {
+            super(base.name+"?");
+            this.base = base;
+        }
+
+    }
+
+    private static final Type TYPE_FLT = new Type("flt");
+
+    private static class TypeInt extends Type {
+
+        TypeInt(String name) {
+            super(name);
+        }
+
+        @Override
+        boolean isa(Type other) {
+            return super.isa(other) || other == TYPE_FLT || other instanceof TypeInt;
+        }
+    }
+
+    private static final List<TypeInt> INTTYPES = new ArrayList<>();
+
+    static {
+        for( var e : Parser.defaultTypes().entrySet() ) {
+            if( e.getValue() instanceof TypeInteger ) {
+                INTTYPES.add(new TypeInt(e.getKey()));
+            }
+        }
+    }
+
+    private static final Type TYPE_INT = INTTYPES.stream().filter(t->t.name.equals("int")).findAny().get();
+    private static final Type TYPE_BOOL = INTTYPES.stream().filter(t->t.name.equals("bool")).findAny().get();
+
+    private static class Variable {
+        final String name;
+        final Type declared;
+        final Variable shadowing;
+        Type type;
+        boolean shadowed = false;
+
+        Variable(String name, Type type, Variable var) {
+            this.name = name;
+            this.declared = type;
+            this.type = type;
+            this.shadowing = var;
+        }
+    }
+
+    /**
+     * The random number generator used for random decisions.
+     */
+    private final Random random;
+    /**
+     * Indentation depth.
+     */
+    private int indentation = 0;
+    /**
+     * Output string builder
+     */
+    private final StringBuilder sb;
+    /**
+     * Number of nested loops
+     */
+    private int loopDepth = 0;
+    /**
+     * Current scope start in the variables list.
+     */
+    private int currScopeStart = 0;
+    /**
+     * The depth of blocks allowed.
+     */
+    private int depth = MAX_BLOCK_DEPTH;
+    /**
+     * The depth of expressions allowed.
+     */
+    private int exprDepth = MAX_EXPRESSION_DEPTH;
+    /**
+     * Current variables in scope.
+     */
+    private final ArrayList<Variable> variables = new ArrayList<>();
+    /**
+     * All defined structs.
+     */
+    private final ArrayList<TypeStruct> structs = new ArrayList<>();
+    /**
+     * All forward declared structs
+     */
+    private final ArrayList<TypeStruct> forwardStructs = new ArrayList<>();
+    /**
+     * Allow to declare structs.
+     */
+    private boolean allowStructs = true;
+    /**
+     * If this needs to generate valid scripts or is also allowed to generate invalid ones.
+     */
+    private boolean generateValid;
+    /**
+     * If this script might be invalid.
+     */
+    private boolean maybeInvalid = false;
+
+
+    /**
+     *
+     * @param random the random number generator.
+     * @param sb the script will be written to this string builder.
+     * @param generateValid if the script should be guaranteed valid or if it is allowed to contain bugs.
+     */
+    public ScriptGenerator(Random random, StringBuilder sb, boolean generateValid) {
+        this.random = random;
+        this.sb = sb;
+        this.generateValid = generateValid;
+    }
+
+    /**
+     * Random number with log distribution
+     * @param max The maximum value
+     * @return A random number in the range [0, max) with higher numbers being more uncommon.
+     */
+    private int randLog(int max) {
+        max--;
+        int n = 1<<max;
+        var num = random.nextInt(n);
+        for (int i=max-1; i>=0; i--) {
+            if ((num & (1<<i))!=0) return max-i-1;
+        }
+        return max;
+    }
+
+    /**
+     * Helper function to print indentation.
+     * @return sb for chaining
+     */
+    private StringBuilder printIndentation() {
+        return sb.repeat(' ', indentation);
+    }
+
+    /**
+     * Generate a random name for variables. This might be invalid when it is a keyword.
+     * @return The random name generated
+     */
+    private StringBuilder getRandomName() {
+        int len = random.nextInt(MAX_NAME_LENGTH) + 1;
+        StringBuilder sb = new StringBuilder(len);
+        sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length()-10)));
+        for (int i=1; i<len; i++)
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+        return sb;
+    }
+
+    /**
+     * Should invalid code be generated?
+     * @return True if invalid code should be generated
+     */
+    private boolean generateInvalid() {
+        if (generateValid || random.nextInt(1000)>2) return false;
+        maybeInvalid = true;
+        return true;
+    }
+
+    /**
+     * Lookup a variable by name
+     * @param name name of the variable
+     * @return The index of the variable in variables or -1
+     */
+    private int lookup(String name) {
+        for (int i=variables.size()-1; i>=0; i--) {
+            if (variables.get(i).name.equals(name)) return i;
+        }
+        return -1;
+    }
+
+    /**
+     * Lookup a variable by name
+     * @param name name of the variable
+     * @return THe variable of null if not found
+     */
+    private Variable lookupVar(String name) {
+        int idx = lookup(name);
+        return idx == -1 ? null : variables.get(idx);
+    }
+
+    /**
+     * Add a variable to the current scope
+     * @param name The name of the variable
+     * @param type The declared type of the variable
+     */
+    private void addVariable(String name, Type type) {
+        var old = lookupVar(name);
+        variables.add(new Variable(name, type, old));
+        if (old != null) old.shadowed = true;
+    }
+
+    /**
+     * Pop variables to level to
+     * @param to Level until which variables should be popped
+     */
+    private void popVariables(int to) {
+        while (variables.size() > to) {
+            var v = variables.removeLast();
+            if (v.shadowing != null) v.shadowing.shadowed = false;
+        }
+    }
+
+    /**
+     * Get a random visible variable patching pred
+     * @param pred The predicate the variable needs to match
+     * @return A random visible variable matching pred or null if no variable mached pred.
+     */
+    private Variable findVisibleVariablesMatching(Predicate<Variable> pred) {
+        int num=0;
+        for (var v:variables) {
+            if (!v.shadowed && pred.test(v)) num++;
+        }
+        if (num == 0) return null;
+        num = random.nextInt(num);
+        for (var v:variables) {
+            if (!v.shadowed && pred.test(v) && num-- == 0) return v;
+        }
+        throw new AssertionError();
+    }
+
+    /**
+     * Get a structure by name
+     * @param name Name of the structure
+     * @return The structure of null
+     */
+    private TypeStruct getStruct(String name) {
+        for (var s:structs) {
+            if (s.name.equals(name)) return s;
+        }
+        for (var s:forwardStructs) if (s.name.equals(name)) return s;
+        return null;
+    }
+
+    /**
+     * Generate a variable name. This might be new random name or a name from an outer scope.
+     * If the program is allowed to be invalid this can return keywords and already used variable names in the current scope.
+     * @return The variable name.
+     */
+    private String getVarName() {
+        if (currScopeStart > 0 && random.nextInt(10) > 7) {
+            // Use a variable outside the current scope.
+            var v = variables.get(random.nextInt(currScopeStart));
+            if (lookup(v.name) < currScopeStart) return v.name;
+            if (!generateValid) {
+                maybeInvalid = true;
+                return v.name;
+            }
+        }
+        // Generate a new random variable name
+        StringBuilder sb = getRandomName();
+        var v = sb.toString();
+        if (!generateValid && (KEYWORDS.contains(v) || lookup(v) >= currScopeStart)) {
+            maybeInvalid = true;
+            return v;
+        }
+        while (KEYWORDS.contains(v) || lookup(v) >= currScopeStart) {
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+            v = sb.toString();
+        }
+        return v;
+    }
+
+    private <T> T randFromList(List<T> list) {
+        return list.get(random.nextInt(list.size()));
+    }
+
+    /**
+     * Get a random structure name
+     * @return A random structure name
+     */
+    private String getStructName() {
+        if (!structs.isEmpty() && generateInvalid()) return randFromList(structs).name;
+        if (!forwardStructs.isEmpty() && generateInvalid()) return randFromList(forwardStructs).name;
+
+        // Generate a new random struct name
+        StringBuilder sb = getRandomName();
+        var v = sb.toString();
+        if (!generateValid && (KEYWORDS.contains(v) || getStruct(v) != null)) {
+            maybeInvalid = true;
+            return v;
+        }
+        while (KEYWORDS.contains(v) || getStruct(v) != null) {
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+            v = sb.toString();
+        }
+        return v;
+    }
+
+    public TypeInt getIntType() {
+        return randFromList(INTTYPES);
+    }
+
+    /**
+     * Get a random type
+     * @return A random type
+     */
+    private Type getType(boolean allowForward) {
+        int t = random.nextInt(10);
+        if( t<5 || structs.isEmpty() ) return getIntType();
+        if( t<7 ) return TYPE_FLT;
+        if (allowForward && random.nextInt(10)==0) {
+            int i=random.nextInt(forwardStructs.size()+1);
+            if (i>0) return forwardStructs.get(i-1).nullable;
+            var name = getStructName();
+            var struct = new TypeStruct(name);
+            forwardStructs.add(struct);
+            return struct.nullable;
+        }
+        TypeStruct struct = randFromList(structs);
+        if (random.nextBoolean()) return struct.nullable;
+        return struct;
+    }
+
+    private Type getType() {
+        return getType(false);
+    }
+
+    /**
+     * Generates a program and writes it into the string builder supplied in the constructor.
+     * @return If the program is allowed to be invalid returns if something potentially invalid was generated.
+     */
+    public boolean genProgram() {
+        var oldGenerateValid = generateValid;
+        if (!generateValid && random.nextBoolean()) generateValid = true;
+        this.maybeInvalid = false;
+        addVariable(ScopeNode.ARG0, TYPE_INT);
+        currScopeStart = variables.size();
+        if ((genStatements() & FLAG_STOP) == 0) {
+            if (generateValid || random.nextInt(10)<7) {
+                genReturn();
+            } else {
+                this.maybeInvalid = true;
+            }
+        }
+        generateValid = oldGenerateValid;
+        return !this.maybeInvalid;
+    }
+
+    /**
+     * Generate a list of statements.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the last statement generated
+     */
+    public int genStatements() {
+        var num = random.nextInt(MAX_STATEMENTS_PER_BLOCK * (depth+1));
+        for (int i=0; i<num; i++) {
+            printIndentation();
+            var stop = genStatement();
+            sb.append("\n");
+            if ((stop & FLAG_STOP) != 0) return stop;
+        }
+        return 0;
+    }
+
+    /**
+     * Generate a single statement
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genStatement() {
+        return switch (random.nextInt(12)) {
+            case 0 -> allowStructs || generateInvalid() ? genStruct() : genAssignment();
+            case 1 -> genBlock();
+            case 2 -> genIf();
+            case 3 -> genCountedLoop();
+            case 4 -> genWhile();
+            case 5, 6 -> genDecl();
+            case 7, 8, 9 -> genAssignment();
+            case 10 -> genNullCheck();
+            default -> genExit();
+        };
+    }
+
+    /**
+     * Generate a new structure
+     * @return 0
+     */
+    public int genStruct() {
+        int idx = random.nextInt(forwardStructs.size()+10);
+        TypeStruct struct;
+        if (idx < 10) {
+        var name = getStructName();
+            struct = new TypeStruct(name);
+            forwardStructs.add(struct);
+        } else {
+            struct = forwardStructs.get(idx-10);
+        }
+        var fields = new TypeStruct.Field[generateInvalid() ? 0 : random.nextInt(10)];
+        sb.append("struct ").append(struct.name).append(" {\n");
+        indentation += INDENTATION;
+        for (int i=0; i<fields.length; i++) {
+            var fieldName = getRandomName();
+            var type = getType(true);
+            printIndentation().append(type.name).append(" ").append(fieldName).append(";\n");
+            fields[i] = new TypeStruct.Field(fieldName.toString(), type, struct);
+        }
+        indentation -= INDENTATION;
+        printIndentation().append("};");
+        struct.fields = fields;
+        forwardStructs.remove(struct);
+        structs.add(struct);
+        return 0;
+    }
+
+    /**
+     * Generate a statement for if, else and while blocks.
+     * This is special since it disallows declarations and prefers to generate blocks.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genStatementBlock() {
+        var oldAllowStructs = allowStructs;
+        allowStructs = false;
+        indentation += INDENTATION;
+        int res;
+        if (depth == 0) {
+            res = random.nextBoolean() ? genAssignment() : genExit();
+        } else {
+            depth--;
+            res = switch (random.nextInt(12)) {
+                case 1, 2, 3, 4, 5 -> {
+                    depth++;
+                    indentation -= INDENTATION;
+                    var ret = genBlock();
+                    indentation += INDENTATION;
+                    depth--;
+                    yield ret;
+                }
+                case 6 -> genIf();
+                case 7 -> genCountedLoop();
+                case 8 -> genWhile();
+                case 9 -> genAssignment();
+                case 10 -> genNullCheck();
+                default -> genExit();
+            };
+            depth++;
+        }
+        indentation -= INDENTATION;
+        allowStructs = oldAllowStructs;
+        return res;
+    }
+
+    /**
+     * Generate an exit. This can be return or break and continue when in a loop.
+     * @return FLAG_STOP
+     */
+    public int genExit() {
+        if (loopDepth == 0 && generateValid) return genReturn();
+        return switch (random.nextInt(7)) {
+            case 0,1,2 -> {
+                if (loopDepth == 0) maybeInvalid = true;
+                sb.append("continue;");
+                yield FLAG_STOP;
+            }
+            case 3,4,5 -> {
+                if (loopDepth == 0) maybeInvalid = true;
+                sb.append("break;");
+                yield FLAG_STOP;
+            }
+            default -> genReturn();
+        };
+    }
+
+    /**
+     * Generate a block statement. After a certain depth only empty blocks are generated to ensure termination of the generator.
+     * @return flag FLAG_STOP for the generated statement
+     */
+    public int genBlock() {
+        if (depth == 0) {
+            sb.append("{}");
+            return 0;
+        }
+        var oldAllowStructs = allowStructs;
+        var oldCSS = currScopeStart;
+        allowStructs = false;
+        currScopeStart = variables.size();
+        depth--;
+        sb.append("{\n");
+        indentation += INDENTATION;
+        var stop = genStatements();
+        indentation -= INDENTATION;
+        printIndentation().append("}");
+        popVariables(currScopeStart);
+        depth++;
+        currScopeStart = oldCSS;
+        allowStructs = oldAllowStructs;
+        return stop & ~FLAG_IF_WITHOUT_ELSE;
+    }
+
+    /**
+     * Generate an if statement with an optional else block.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genIf() {
+        sb.append("if(");
+        genExpression(TYPE_BOOL, true);
+        sb.append(") ");
+        var stop = genStatementBlock();
+        if ((stop & FLAG_IF_WITHOUT_ELSE) == 0 && random.nextInt(10) > 3) {
+            sb.append("\n");
+            printIndentation().append("else ");
+            stop &= genStatementBlock();
+        } else {
+            stop = FLAG_IF_WITHOUT_ELSE;
+        }
+        return stop;
+    }
+
+    /**
+     * Generate a block with a null check
+     * if (nullable) { handle_nullable_as_non_nullable; }
+     */
+    public int genNullCheck() {
+        var v = findVisibleVariablesMatching(va->va.declared instanceof TypeNullable);
+        if (v == null) return genIf();
+        var n = (TypeNullable)v.declared;
+        boolean negate = random.nextBoolean();
+        sb.append("if(");
+        if (negate) sb.append("!");
+        sb.append(v.name).append(")");
+        if (!negate) v.type = n.base;
+        var stop = genStatementBlock();
+        v.type = n;
+        if ((stop & FLAG_IF_WITHOUT_ELSE) == 0 && random.nextInt(10) > 3) {
+            sb.append("\n");
+            printIndentation().append("else ");
+            if (negate) v.type = n.base;
+            stop &= genStatementBlock();
+            v.type = n;
+        } else {
+            stop = FLAG_IF_WITHOUT_ELSE;
+        }
+        return stop;
+    }
+
+    /**
+     * Generate a while loop.
+     * @return 0
+     */
+    public int genWhile() {
+        sb.append("while(");
+        genExpression(TYPE_BOOL, true);
+        sb.append(") ");
+        loopDepth++;
+        genStatementBlock();
+        loopDepth--;
+        return 0;
+    }
+
+    /**
+     * Generate a counted loop of the form
+     * <code>
+     *     {
+     *         int varname = start_expr;
+     *         while (varname < end_expr) loop_body;
+     *     }
+     * </code>
+     * @return 0
+     */
+    public int genCountedLoop() {
+        if (depth == 0) return genWhile();
+        var oldCSS = currScopeStart;
+        currScopeStart = variables.size();
+        sb.append("{\n");
+        indentation += INDENTATION;
+        String name = getVarName();
+        printIndentation().append("int ").append(name).append("=");
+        genExpression(TYPE_INT, true);
+        sb.append(";\n");
+        addVariable(name, TYPE_INT);
+        printIndentation().append("while(").append(name).append("<");
+        genExpression(TYPE_INT, true);
+        sb.append(") {\n");
+        indentation += INDENTATION;
+        depth--;
+        loopDepth++;
+        printIndentation().append(name).append("=").append(name).append("+");
+        genExpression(TYPE_INT, true);
+        sb.append(";\n");
+        genStatements();
+        loopDepth--;
+        depth++;
+        indentation -= INDENTATION;
+        printIndentation().append("}\n");
+        indentation -= INDENTATION;
+        printIndentation().append("}");
+        popVariables(currScopeStart);
+        currScopeStart = oldCSS;
+        return 0;
+    }
+
+    /**
+     * Generate a declaration statement.
+     * @return 0
+     */
+    public int genDecl() {
+        var type = getType();
+        var name = getVarName();
+        // Always make them mutable
+        sb.append(generateInvalid() ? getRandomName() : type.name).append(" !").append(name);
+        if (!(type instanceof TypeNullable) || random.nextBoolean()) {
+            sb.append("=");
+            genExpression(type, true);
+        }
+        sb.append(";");
+        addVariable(name, type);
+        return 0;
+    }
+
+    /**
+     * Generate an assignment statement.
+     * @return 0
+     */
+    public int genAssignment() {
+        Type type;
+        Type declared;
+        if (generateInvalid()) {
+            sb.append(getRandomName());
+            type = getType();
+            declared = type;
+        } else {
+            var v = findVisibleVariablesMatching(va->true);
+            if (v == null) return genDecl();
+            sb.append(v.name);
+            type = v.type;
+            declared = v.declared;
+        }
+        if (generateInvalid()) {
+            var name = getRandomName();
+            sb.append(".").append(name);
+            declared = getType();
+        } else if (type instanceof TypeStruct s && s.fields.length > 0 && random.nextBoolean()) {
+            var field = s.fields[random.nextInt(s.fields.length)];
+            sb.append(".").append(field.name);
+            declared = field.type;
+        }
+        sb.append("=");
+        genExpression(declared, true);
+        sb.append(";");
+        return 0;
+    }
+
+    /**
+     * Generate a return statement.
+     * @return FLAG_STOP
+     */
+    public int genReturn() {
+        var type = getType();
+        sb.append("return ");
+        genExpression(type, true);
+        sb.append(";");
+        return FLAG_STOP;
+    }
+
+    /**
+     * Generate a binary expression.
+     * This method does not care about operator precedence.
+     */
+    public void genExpression(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        if (!(type instanceof TypeInt) && type != TYPE_FLT) {
+            genUnary(type, false);
+            return;
+        }
+        var num = randLog(MAX_BINARY_EXPRESSIONS_PER_EXPRESSION);
+        while(num-->0) {
+            genUnary(type, false);
+            sb.append(BINARY_OP[random.nextInt(BINARY_OP.length)]);
+        }
+        genUnary(type, false);
+    }
+
+    /**
+     * Generate a unary expression.
+     */
+    public void genUnary(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        if (!(type instanceof TypeInt) && type != TYPE_FLT) {
+            genSuffix(type, false);
+            return;
+        }
+        var num = randLog(MAX_UNARY_EXPRESSIONS_PER_EXPRESSION);
+        while(num-->0) {
+            sb.append(UNARY_OP[random.nextInt(UNARY_OP.length)]);
+        }
+        genSuffix(type, false);
+    }
+
+    public TypeStruct.Field getField(Type type) {
+        int n=0;
+        for (var s: structs) {
+            for (var f: s.fields) {
+                if (f.type.isa(type)) n++;
+            }
+        }
+        if (n==0) return null;
+        n = random.nextInt(n);
+        for (var s: structs) {
+            for (var f: s.fields) {
+                if (f.type.isa(type)) if (n--==0) return f;
+            }
+        }
+        throw new AssertionError();
+    }
+
+    /**
+     * Generate
+     */
+    public void genSuffix(Type type, boolean change) {
+        genSuffixRecursive(type, change, MAX_SUFFIX_RECURSIVE_DEPTH);
+    }
+
+    public void genSuffixRecursive(Type type, boolean change, int depth) {
+        if (change && generateInvalid()) type = getType();
+        if (depth > 0 && random.nextBoolean()) {
+            if (generateInvalid()) {
+                var field = getRandomName();
+                var t = getType();
+                genSuffixRecursive(t, true, depth-1);
+                sb.append(".").append(field);
+                return;
+            } else {
+                var field = getField(type);
+                if (field != null) {
+                    genSuffixRecursive(field.struct, true, depth-1);
+                    sb.append(".").append(field.name);
+                    return;
+                }
+            }
+        }
+        genPrimary(type, false);
+    }
+
+    /**
+     * Generate a primary expression.
+     */
+    public void genPrimary(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        var rand = random.nextInt(10);
+        if (rand == 0 && exprDepth != 0) {
+            sb.append("(");
+            exprDepth--;
+            genExpression(type, false);
+            exprDepth++;
+            sb.append(")");
+        } else if (rand < 6) {
+            genVariable(type);
+        } else {
+            genConst(type);
+        }
+    }
+
+    /**
+     * Generate a constant.
+     */
+    public void genConst(Type type) {
+        if (generateInvalid()) type = getType();
+        if (type instanceof TypeInt || (type == TYPE_FLT && random.nextBoolean())) {
+            var rand = random.nextInt(10);
+            switch (rand) {
+                case 0 -> sb.append("true");
+                case 1 -> sb.append("false");
+                default -> sb.append(random.nextInt(1<<(rand-2)));
+            }
+        } else if (type == TYPE_FLT) {
+            sb.append(random.nextFloat());
+        } else if (type instanceof TypeNullable n) {
+            if ((n.base instanceof TypeStruct s && s.fields == null) || random.nextBoolean()) {
+                sb.append("null");
+            } else {
+                sb.append("new ").append(generateInvalid() ? getRandomName() : n.base.name);
+            }
+        } else {
+            sb.append("new ").append(generateInvalid() ? getRandomName() : type.name);
+        }
+    }
+
+    /**
+     * Generate a variable. If there are none generate a number instead.
+     * If the program is allowed to be invalid a random name can be generated in some cases.
+     */
+    public void genVariable(Type type) {
+        if (generateInvalid()) {
+            sb.append(getRandomName());
+            return;
+        }
+        if (generateInvalid()) type = getType();
+        var t = type;
+        var v = findVisibleVariablesMatching(va->va.type.isa(t));
+        if (v == null) genConst(type);
+        else sb.append(v.name);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
new file mode 100644
index 00000000..188e0a9f
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
@@ -0,0 +1,15 @@
+
+struct Person {
+  int age;
+};
+
+val fcn = { Person?[] ps, int x ->
+  val tmp = ps[x];
+  if( ps[x] )
+    ps[x].age++;
+};
+
+Person?[] !ps = new Person?[2];
+ps[0] = new Person;
+ps[1] = new Person;
+fcn(ps,1);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp
new file mode 100644
index 00000000..049132d9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp
@@ -0,0 +1,5 @@
+
+val fcn = (arg&1)
+    ? { int x -> x*x; }
+    : { int x -> x+x; };
+fcn(arg);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
new file mode 100644
index 00000000..a64564f0
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
@@ -0,0 +1,42 @@
+
+//val fact = { int n -> n <= 1 ? 1 : fact(n-1)*n; }
+struct LL { LL? next; int payload; };
+
+
+struct String {
+
+    val _hashCodeString = { ->
+        int hash=0;
+        for( int i=0; i< cs#; i++ )
+            hash = hash*31 + cs[i];
+        if( !hash ) hash = 123456789;
+        return hash;
+    };
+
+    val equals = { String s ->
+        if( self == s ) return true;
+        if( cs# != s.cs# ) return false;
+        for( int i=0; i< #; i++ )
+            if( [i] != s.cs[i] )
+                return false;
+        return true;
+    };
+
+    int _hashCode = hash();
+    u8[] cs;
+};
+
+
+
+val hashCode= { String self ->
+    int hash = self._hashCode
+    ? self._hashCode
+    : self._hashCode = _hashCodeString(self);
+    return hash;
+};
+
+
+String s = new String { cs = new u8[17]; };
+s.cs[0] =  67; // C
+s.cs[1] = 108; // l
+hashCode(s);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp
new file mode 100644
index 00000000..0788e6c5
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp
@@ -0,0 +1,32 @@
+
+int[] !ary = new int[arg], !primes = new int[arg];
+int nprimes = 0, p=2;
+// Find primes while p^2 < arg
+while( p*p < arg ) {
+    // skip marked non-primes
+    while( ary[p]==1 ) p = p + 1;
+    // p is now a prime
+    primes[nprimes] = p;  nprimes = nprimes + 1;
+    // Mark out the rest non-primes
+    int i = p + p;
+    while( i < ary# ) {
+        ary[i] = 1;
+        i = i + p;
+    }
+    p = p + 1;
+}
+// Now just collect the remaining primes, no more marking
+while( p < arg ) {
+    if( ary[p] == 0 ) {
+        primes[nprimes] = p;  nprimes = nprimes + 1;
+    }
+    p = p + 1;
+}
+// Copy/shrink the result array
+int[] !rez = new int[nprimes];
+int j = 0;
+while( j < nprimes ) {
+    rez[j] = primes[j];
+    j = j + 1;
+}
+return rez;