Cleanup & backportclinit

The phase rework, made new phases explicit and add them to the CodeGen driver.  Fix the flag-spilling on X86 and ARM.  Fix the GCM conservative anti-deps and backport.

69 files changed, 1439 insertions, 913 deletions

diff --git a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
index eca2b9ce..5ceda6a9 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
@@ -291,8 +291,7 @@ public class Parser {
         }
 
         // The initializer owns its run-once flag store. Parent initialization
-        // is a structural requirement, to be executed before this body when
-        // CLInit runtime lowering is added.
+        // is a structural requirement, executed before this body by CLInit lowering.
         if( fun.isClz() ) {
             Node self = fun.parm(2);
             Field flag = ((TypeMemPtr)self._type)._obj.field("$init");
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
index 3909f881..47ec0112 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
@@ -8,9 +8,6 @@ import com.seaofnodes.simple.print.*;
 import com.seaofnodes.simple.type.*;
 import com.seaofnodes.simple.util.*;
 import java.io.File;
-import java.io.IOException;
-import java.nio.file.Files;
-import java.nio.file.Path;
 import java.util.*;
 
 
@@ -32,8 +29,9 @@ public class CodeGen {
         IterPostOpto,           // Peepholes and inlining using SCCP results
         FinalizeIR,             // Field layout, offset cleanup, function/CU roots
         TypeCheck,              // Last check for bad programs
+        Serialize,              // Save ideal IR, including opaque class initialization
+        Lower,                  // Expand checked class initialization to ordinary IR
         LoopTree,               // Build a loop tree; break infinite loops
-        Serialize,              // Serialize public IR for future compiles to link
         Unlink,                 // Unlink call sites before machine code generation
         Select,                 // Convert to target hardware nodes
         Schedule,               // Global schedule (code motion) nodes
@@ -185,7 +183,7 @@ public class CodeGen {
     public final XCtrlNode XCTRL;
 
     public Node constant( Type t ) {
-        assert _phase==null || _phase.ordinal() <= Phase.FinalizeIR.ordinal();
+        assert _phase==null || _phase.ordinal() <= Phase.Lower.ordinal();
         return ConstantNode.make(t).peephole();
     }
     public ConstantNode con( Type t ) { return (ConstantNode)constant(t); }
@@ -239,7 +237,9 @@ public class CodeGen {
     }
 
 
-    // Run requested phases.
+    // Run requested phases. File export must request Serialize before Lower;
+    // requesting Export up front does that automatically. Encoding alone does
+    // not retain reloadable ideal IR.
 
     // No code emission, just IR generation
     public CodeGen driver( Phase phase ) { return driver(phase,null,null,false,false,0); }
@@ -256,25 +256,64 @@ public class CodeGen {
     // Write an object file for a specific cpu/os pair
 
     public CodeGen driver( String cpu, String callingConv, boolean inMemory, boolean emitEntrySymbol ) { return driver(Phase.Export,cpu,callingConv,inMemory,emitEntrySymbol,0); }
-    // Generic driver
-    public CodeGen driver( Phase phase, String cpu, String callingConv, boolean inMemory, boolean emitEntrySymbol, int dump ) {
-        int p1 = phase.ordinal(), p2 = _phase==null ? -1 : _phase.ordinal();
-        if( p2 < p1 && p2 <  Phase.Parse     .ordinal() ) { parse();     p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Iter      .ordinal() ) { iter();      p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Opto      .ordinal() ) { opto();      p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.IterPostOpto.ordinal() ) { iterPostOpto(); p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.FinalizeIR.ordinal() ) { finalizeIR(); p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.TypeCheck .ordinal() ) { typeCheck(); p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.LoopTree  .ordinal() ) { loopTree();  p2 = dump(dump); }
-        if( p2 < p1 && p1 >= Phase.Encoding  .ordinal() ) { unlinkImports(); p2 = dump(dump); }
-        if( p2 < p1 && p1 >= Phase.Encoding  .ordinal() ) { serialize(); p2 = dump(dump); } // Include ideal graph in object file
-        if( p2 < p1 && p2 <  Phase.Unlink    .ordinal() ) { unlink();    p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Select    .ordinal() && cpu != null ) { instSelect(cpu,callingConv); p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Schedule  .ordinal() ) { GCM();       p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.LocalSched.ordinal() ) { localSched();p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.RegAlloc  .ordinal() ) { regAlloc();  p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Encoding  .ordinal() ) { encode();    p2 = dump(dump); }
-        if( p2 < p1 && p2 <  Phase.Export    .ordinal() ) { exportELF(inMemory,emitEntrySymbol); p2 = dump(dump); }
+
+    // The Generic driver
+    public CodeGen driver( Phase target, String cpu, String callingConv, boolean inMemory, boolean emitEntrySymbol, int dump ) {
+        // Parse a Simple file, and for mentioned external symbols either load
+        // from .o or recursively parse
+        step(target, Phase.Parse,        this::parse,        dump);
+        // Run peepholes to a fixed point
+        step(target, Phase.Iter,         this::iter,         dump);
+        // Run SCCP (and resolve int/flt expressions)
+        step(target, Phase.Opto,         this::opto,         dump);
+        // Run peepholes to a fixed point again, on the better types.
+        step(target, Phase.IterPostOpto, this::iterPostOpto, dump);
+        // Field layouts; field symbols become constant offsets
+        step(target, Phase.FinalizeIR,   this::finalizeIR,   dump);
+        // Final error check - bad programs fail here
+        step(target, Phase.TypeCheck,    this::typeCheck,    dump);
+        // Save reloadable ideal IR for a later seperate compilation
+        step(target, Phase.Serialize, () -> Serialize.forTarget(this,target,inMemory), dump);
+        // Replace "fat" nodes with their exploded explicit IR; this can
+        // introduce CFG diamonds
+        step(target, Phase.Lower,        this::lower,        dump);
+        // Compute the loop-tree, used for approximating exec frequencies for
+        // scheduling and register allocation
+        step(target, Phase.LoopTree,     this::loopTree,     dump);
+        // Drop imports for machine selection, retain them for ideal evaluation.
+        step(target, Phase.Unlink, () -> unlink(cpu!=null), dump);
+        // Instruction selection
+        step(target, Phase.Select, () -> instSelect(cpu,callingConv), dump);
+        // Global Code Motion
+        step(target, Phase.Schedule,     this::GCM,          dump);
+        // Local (basic block only) scheduling
+        step(target, Phase.LocalSched,   this::localSched,   dump);
+        // Register allocation
+        step(target, Phase.RegAlloc,     this::regAlloc,     dump);
+        // Encode machine instructions into bits
+        step(target, Phase.Encoding,     this::encode,       dump);
+        // Export bits (and serialized IR) into ELF files
+        step(target, Phase.Export, () -> exportELF(inMemory,emitEntrySymbol), dump);
+        return this;
+    }
+
+    // The driver names the order; optional phases decide locally whether to run.
+    private void step(Phase target, Phase next, Runnable work, int dump) {
+        if( next.ordinal() > target.ordinal() || (_phase!=null && _phase.ordinal()>=next.ordinal()) ) return;
+        Phase prior = _phase;
+        work.run();
+        if( _phase!=prior ) dump(dump);
+    }
+
+    // All phase entry points share ordering checks, timing, and viewer notification.
+    // Record elapsed time even on failure, but report completion only on success.
+    CodeGen phase(Phase next, boolean ordered, Runnable work) {
+        assert ordered : "Cannot run "+next+" after "+_phase;
+        _phase = next;
+        long t0 = System.currentTimeMillis();
+        work.run();             // Do The Phase
+        _times[next.ordinal()] = System.currentTimeMillis() - t0;
+        if( _obs!=null ) _obs.phase(next.name()); // Record for viewer
         return this;
     }
 
@@ -283,17 +322,14 @@ public class CodeGen {
     }
 
     // Verbose printing during compilation
-    private int dump(int dump) {
+    private void dump(int dump) {
         int p2 = _phase.ordinal();
-        if( (dump & (1<<p2)) == 0 ) return p2;
-
-
+        if( (dump & (1<<p2)) == 0 ) return;
         if( (dump & (1<<30)) != 0 )
             System.err.println("After "+_phase+":");
         System.err.println(_phase.ordinal() >= Phase.LocalSched.ordinal()
                            ? asm(new SB()).toString()
                            : IRPrinter.prettyPrint(this));
-        return p2;
     }
 
 
@@ -430,25 +466,7 @@ public class CodeGen {
     public final Parser P;
 
     // Parse ASCII text into Sea-of-Nodes IR
-    public CodeGen parse() {
-        assert _phase == null;
-        _phase = Phase.Parse;
-        long t0 = System.currentTimeMillis();
-
-        Parser.TYPES.clear();
-        Parser.TYPES.putAll(Parser.INIT_TYPES);
-        if( _src != null ) {
-            // No source file, just the source itself.
-            ParseAll.parseSource(this,_srcName==null ? "Test" : _srcName,_src);
-        } else {
-            // Path from module root to source file
-            ParseAll.parsePath(this,_srcName);
-        }
-
-        _times[Phase.Parse.ordinal()] = System.currentTimeMillis() - t0;
-        if( _obs != null ) _obs.phase(_phase.name());
-        return this;
-    }
+    public CodeGen parse() { return phase(Phase.Parse, _phase==null, () -> ParseAll.parse(this,_src)); }
 
 
     // ---------------------------
@@ -464,126 +482,14 @@ public class CodeGen {
 
     // Pessimistic peepholes after parsing.  This lifts loaded and parsed
     // types before the optimistic Opto pass resets types and lets them fall.
-    public CodeGen iter() {
-        assert _phase == Phase.Parse;
-        _phase = Phase.Iter;
-        long t0 = System.currentTimeMillis();
-
-        // The phase shift closes all parser-in-progress states and freezes
-        // unknown external inputs.  Imported nodes carry post-Opto escape
-        // precision, but Iter is a fresh pessimistic solve: memory escape
-        // summaries must restart at FULL so newly discovered private escapes
-        // can only be removed, never added.  Seed the complete graph once.
-        boolean hasImports = _externPaths != null;
-        _start.walk(n -> {
-            if( !(n instanceof ConstantNode) )
-                n._type = hasImports ? iterImportReset(n._type) : iterEscapeReset(n._type);
-            add(n);
-            return null;
-        });
-        _iter.iterate(this);
-        // Expensive assert.
-        assert !expensiveAssert() || Opto.fixedPointCheck(this);
-
-        _times[Phase.Iter.ordinal()] = System.currentTimeMillis() - t0;
-        if( _obs != null ) _obs.phase(_phase.name());
-        return this;
-    }
-
-    private static Type iterEscapeReset(Type t) {
-        if( t instanceof TypeMem mem )
-            return mem._one ? mem : mem.makeFrom(XInt.FULL,XInt.FULL);
-        if( t instanceof TypeTuple tt ) {
-            TypeTuple rez = tt;
-            for( int i=0; i<tt._types.length; i++ ) {
-                Type tx = iterEscapeReset(tt._types[i]);
-                if( tx != tt._types[i] ) rez = rez.makeFrom(i,tx);
-            }
-            return rez;
-        }
-        return t;
-    }
-
-    private static Type iterImportReset(Type t) {
-        if( t.isHigh() )
-            return t.dual();
-        if( t instanceof TypeMem mem )
-            return TypeMem.make(mem._alias,iterImportReset(mem._t),mem._one,mem._clz,mem._final,XInt.FULL,XInt.FULL);
-        if( t instanceof TypeMemPtr )
-            return t.makeStorage();
-        if( t instanceof TypeStruct )
-            return t.makeStorage();
-        if( t instanceof TypeTuple tt ) {
-            TypeTuple rez = tt;
-            for( int i=0; i<tt._types.length; i++ ) {
-                Type tx = iterImportReset(tt._types[i]);
-                if( tx != tt._types[i] ) rez = rez.makeFrom(i,tx);
-            }
-            return rez;
-        }
-        return t;
-    }
-
+    public CodeGen iter() { return phase(Phase.Iter, _phase==Phase.Parse, () -> Iter.run(this)); }
 
     // SCCP and numeric-mode resolution; leave cleanup work queued for Iter.
-    public CodeGen opto() {
-        assert _phase == Phase.Iter;
-        _phase = Phase.Opto;
-        long t0 = System.currentTimeMillis();
+    public CodeGen opto() { return phase(Phase.Opto, _phase==Phase.Iter, () -> Opto.opto(this)); }
 
-        Opto.opto(this);
-
-        _times[Phase.Opto.ordinal()] = System.currentTimeMillis() - t0;
-        if( _obs != null ) _obs.phase(_phase.name());
-        return this;
-    }
+    public CodeGen iterPostOpto() { return phase(Phase.IterPostOpto, _phase==Phase.Opto, () -> _iter.iterate(this)); }
 
-    public CodeGen iterPostOpto() {
-        assert _phase == Phase.Opto;
-        _phase = Phase.IterPostOpto;
-        long t0 = System.currentTimeMillis();
-        // Use SCCP types and the sharp call graph for peepholes and inlining.
-        _iter.iterate(this);
-        _times[Phase.IterPostOpto.ordinal()] = System.currentTimeMillis() - t0;
-        if( _obs != null ) _obs.phase(_phase.name());
-        return this;
-    }
-
-    public CodeGen finalizeIR() {
-        assert _phase == Phase.IterPostOpto;
-        _phase = Phase.FinalizeIR;
-        long t0 = System.currentTimeMillis();
-
-        // Freeze field sizes and replace symbolic field offsets by constants.
-        for( int i=0; i<_start.nOuts(); i++ ) {
-            Node use = _start.out(i);
-            if( use instanceof ConFldOffNode off ) {
-                Node con = off.asOffset();
-                assert con != null : off._ts._name+"."+off._fname;
-                off.subsume(con);
-                i--;
-            }
-        }
-        _iter.iterate(this); // Propagate field offsets and clean up.
-
-        // Retain surviving functions for emission without adding unknown callers.
-        for( FunNode fun : _linker )
-            if( fun != null && !fun.isDead() && !fun._type.isHigh() )
-                keepInCompUnit(fun);
-        for( CompUnit cu : _compunits.values() ) {
-            ProjNode mem = cu._start.proj(1);
-            if( mem != null ) mem.unkeep();
-        }
-        // Stable print order: initializers first, then other Returns by NID.
-        for( Node stop : _stop._inputs )
-            Arrays.sort(stop._inputs._es,0,stop.nIns(),
-                        (x,y) -> ((((ReturnNode)x).fun().isClz() ? -1 : x._nid) -
-                                  (((ReturnNode)y).fun().isClz() ? -1 : y._nid) ));
-
-        _times[Phase.FinalizeIR.ordinal()] = System.currentTimeMillis() - t0;
-        if( _obs != null ) _obs.phase(_phase.name());
-        return this;
-    }
+    public CodeGen finalizeIR() { return phase(Phase.FinalizeIR, _phase==Phase.IterPostOpto, () -> FinalizeIR.run(this)); }
 
     // Root a surviving function without claiming that it has unknown callers.
     void keepInCompUnit(FunNode fun) {
@@ -597,58 +503,7 @@ public class CodeGen {
 
     // ---------------------------
     // Last check for bad programs
-    public CodeGen typeCheck() {
-        assert _phase == Phase.FinalizeIR;
-        _phase = Phase.TypeCheck;
-        long t0 = System.currentTimeMillis();
-
-        // Check for class-init cycles first; such a cycle can prevent other
-        // things from resolving types. The dependency graph is temporary.
-        String clzInitCycle = new ClassInitDependencies(this).check();
-        if( clzInitCycle != null )
-            throw Parser.error(clzInitCycle,null);
-
-        Ary<Node> errs = new Ary<>(Node.class);
-        _stop.walk( n -> {
-                if( n.err() != null )
-                    errs.add(n);
-                return null;
-            });
-        _times[Phase.TypeCheck.ordinal()] = System.currentTimeMillis() - t0;
-
-        if( !errs.isEmpty() ) {
-            // Prefer an originating error over a secondary error caused by a
-            // BOTTOM input.  If all errors are downstream-poisoned, retain
-            // the old first-error behavior.
-            Node min = null;
-            for( Node n : errs )
-                if( noBottomInputs(n) )
-                    {  min = n;  break; }
-            if( min==null )
-                min = errs.at(0);
-            for( Node n : errs )
-                if( n!=min &&
-                    noBottomInputs(n) &&
-                    ((n   instanceof MemOpNode nmop &&
-                      min instanceof MemOpNode mmop &&
-                      nmop._loc.before(mmop._loc)) ||
-                     (n   instanceof CFGNode ncfg &&
-                      min instanceof CFGNode mincfg &&
-                      ncfg.idepth() < mincfg.idepth())) )
-                    min = n;
-            if( _obs != null ) _obs.error(min, min.err().getMessage());
-            throw min.err();
-        }
-        if( _obs != null ) _obs.phase("TypeCheck");
-        return this;
-    }
-
-    private static boolean noBottomInputs(Node n) {
-        for( Node def : n._inputs )
-            if( def!=null && !(def instanceof FldOffNode) && def._type==Type.BOTTOM )
-                return false;
-        return true;
-    }
+    public CodeGen typeCheck() { return phase(Phase.TypeCheck, _phase==Phase.FinalizeIR, () -> TypeCheck.run(this)); }
 
     public static TypeStruct requiredStruct(Node n) {
         // CNC: remove? cleanup?
@@ -659,62 +514,21 @@ public class CodeGen {
     }
 
     // ---------------------------
+    // TypeCheck queued surviving CLInits during its existing error walk.
+    public CodeGen lower() {
+        return phase(Phase.Lower, (_phase==Phase.TypeCheck || _phase==Phase.Serialize), () -> _iter.iterate(this));
+    }
+
+    // ---------------------------
     // Build the loop tree; break never-exit loops
     public CodeGen loopTree() {
-        assert _phase.ordinal() <= Phase.Serialize.ordinal();
-        _phase = Phase.LoopTree;
-        long t0 = System.currentTimeMillis();
-        // Build the loop tree, fix never-exit loops
-        _start.buildLoopTree( _linker, _stop);
-        // Invariant theory: No more type or code changes after Opto.  The
-        // LoopTree stuff is used to do layouts now, but not core opts.  TODO:
-        // at some future date we'll do loop opts (e.g. peeling, unrolling)
-        // that will totally impact code shape, types and core opts - but this
-        // will be done in tandem with Opto changes.
-        //_iter.iterate(this);
-        _times[Phase.LoopTree.ordinal()] = System.currentTimeMillis() - t0;
-        return this;
+        return phase(Phase.LoopTree, _phase==Phase.Lower, () -> _start.buildLoopTree(_linker,_stop));
     }
 
     // ---------------------------
     public BAOS _serial;
     public void serialize() {
-        assert _phase.ordinal() <= Phase.Serialize.ordinal();
-        _phase = Phase.Serialize;
-        long t0 = System.currentTimeMillis();
-        // Does not change compiler phase; just records IR
-        Serialize.serialize(this);
-        _times[Phase.Serialize.ordinal()] = System.currentTimeMillis() - t0;
-    }
-
-    // Unlink imported function bodies before serialization.  Calls to them
-    // remain as normal calls through their function pointer, and codegen later
-    // turns them into external relocations.
-    private void unlinkImports() {
-        assert _phase.ordinal() <= Phase.Serialize.ordinal();
-        // Imported function constants keep their symbolic identity, not an
-        // embedded copy of the other object's Return and body.
-        for( Node n : _start._outputs.asAry() )
-            if( n instanceof FunPtrNode ptr && ptr.ret()!=null && !owns(ptr.fun()) ) {
-                ptr.liftType(ptr._type);
-                ptr.setDef(1,null);
-            }
-        for( FunNode fun : _linker ) {
-            if( fun==null || fun.isDead() || owns(fun) )
-                continue;
-            for( int i=1; i<fun.nIns(); i++ )
-                if( fun.in(i) instanceof CallNode call )
-                    call.unlink(fun,i--);
-        }
-        for( int i=0; i<_stop.nIns(); i++ ) {
-            StopCUNode stop=(StopCUNode)_stop.in(i);
-            CompUnit cu=_compunits.get(stop.start()._fname);
-            if( cu._src==null ) _stop.delDef(i--);
-        }
-        // The whole-object wrappers now summarize only the emitted units.
-        _stop._type=_stop.compute();
-        _start._type=_start.compute();
-        //_iter.iterate(this);
+        phase(Phase.Serialize, _phase==Phase.TypeCheck, () -> Serialize.serialize(this));
     }
 
     // ---------------------------
@@ -740,208 +554,15 @@ public class CodeGen {
     // Convert to target hardware nodes
     public CodeGen instSelect( String cpu, String callingConv ) { return instSelect(cpu,callingConv,PORTS); }
     public CodeGen instSelect( String cpu, String callingConv, String base ) {
-        assert _phase.ordinal() <= Phase.Unlink.ordinal();
-        _phase = Phase.Select;
-
-        _callingConv = callingConv;
-
-        // Not timing the class load...
-        // Look for CPU in fixed named place:
-        //   com.seaofnodes.simple.node.cpus."cpu"."cpu.class"
-        String clzFile = base+"."+cpu+"."+cpu;
-        try { _mach = ((Class<Machine>) Class.forName( clzFile )).getDeclaredConstructor(new Class[]{CodeGen.class}).newInstance(this); }
-        catch( Exception e ) { throw new RuntimeException(e); }
-
-        _cCallingConv = _mach.cCallingConv(callingConv);
-
-        // Build global copies of common register masks.
-        long callerSave = _mach.callerSave();
-        long cCallerSave= _mach.callerSave(_cCallingConv);
-        long  neverSave = _mach. neverSave();
-        int maxReg = Math.min(64,_mach.regs().length);
-        assert maxReg>=64 || (-1L << maxReg & callerSave)==0; // No stack slots in callerSave
-        assert maxReg>=64 || (-1L << maxReg & cCallerSave)==0; // No stack slots in cCallerSave
-        _callerSave = new RegMask(callerSave);
-        _cCallerSave= new RegMask(cCallerSave);
-
-        // Build a Return RegMask array.  All returns have the following inputs:
-        // 0 - ctrl
-        // 1 - memory
-        // 2 - varies with returning GPR,FPR
-        // 3 - RPC
-        // 4+- Caller save registers
-        _retMasks = new RegMask[(maxReg-_callerSave.size()-Long.bitCount( neverSave ))+4];
-        for( int reg=0, i=4; reg<maxReg; reg++ )
-            if( !_callerSave.test(reg) && ((1L<<reg)&neverSave)==0 )
-                _retMasks[i++] = new RegMask(reg);
-        _rpcMask = new RegMask(_mach.rpc());
-        _retMasks[3] = _rpcMask;
-
-        // Convert to machine ops
-        long t0 = System.currentTimeMillis();
-        _uid = 1;               // All new machine nodes reset numbering
-        var map = new IdentityHashMap<Node,Node>();
-        _instSelect( _stop, map );
-        _stop  = (StopNode)map.get(_stop );
-        StartNode start = (StartNode)map.get(_start);
-        _start = start==null ? new StartNode(_start) : start;
-        _instOuts(_stop,visit());
-        _visit.clear();
-
-        // Replace the CompUnit stop (and list of functions)
-        // with hardware-specific ones
-        for( CompUnit cu : _compunits.values() ) {
-            cu._start= (StartCUNode)map.get(cu._start);
-            cu._stop = (StopCUNode )map.get(cu._stop );
-        }
-
-        _times[Phase.Select.ordinal()] = System.currentTimeMillis() - t0;
-        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;
-        if( n instanceof StoreNode st && StaticData.preinitialized(this,st) )
-            return _instSelect(st.mem(),map);
-        Node x = map.get(n);
-        if( x !=null ) return x; // Been there, done that
-
-        // If n is a MachNode already, 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 MachNode ) {
-            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.
-        if( n instanceof MemOpNode mem && mem.off() instanceof ExternOffsetNode off ) {
-            // External fields replace base+offset with symbol+0. Keep the ideal
-            // declaring type on the address for machine load/store width selection.
-            TypeMemPtr ptr = (TypeMemPtr)mem.ptr()._type;
-            n._inputs.set(2,new ExternNode(TypeMemPtr.make((byte)2,ptr._obj,true),off._extern));
-            n._inputs.set(3,ConstantNode.raw(TypeInteger.ZERO));
-        }
-        map.put(n, x=_mach.instSelect(n) );
-        // Carry loop-tree and pre-order info across the ideal->mach transition
-        if( n instanceof CFGNode ncfg && x instanceof CFGNode xcfg ) {
-            xcfg._ltree = ncfg._ltree;
-            xcfg._pre = ncfg._pre;
-        }
-        // 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) );
-        // Post selection action
-        if( x instanceof MachNode mach ) {
-            if( n instanceof ReturnNode ret )
-                ((ReturnNode)mach)._fun = (FunNode)map.get(ret._fun);
-            mach.postSelect(this);  // Post selection action
-        }
-
-        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);
-                // CallNode special: outputs are partially ordered; CallEnd in slot 0
-                if( in instanceof CallNode call && n instanceof CallEndNode cend && call.out(0) != cend )
-                    call._outputs.swap(0,call.nOuts()-1);
-                _instOuts(in,visit);
-            }
+        return InstSelect.select(this,cpu,callingConv,base);
     }
 
     // ---------------------------
     public void unlink() {
-        assert _phase.ordinal() <= Phase.Select.ordinal();
-        _phase = Phase.Unlink;
-        long t0 = System.currentTimeMillis();
-
-    	// The remaining passes assume all calls are unlinked; i.e. we are throwing
-    	// away the Call Graph here.  Functions only reachable from internal calls
-    	// need to be re-hooked to stop/start less they go dead.
-        for( FunNode fun : _linker ) {
-            // Already linked to start, not going dead
-            if( fun==null || fun.isDead() )
-                continue;
-
-            // Imported functions are not emitted by this object.  Unlink any
-            // concrete calls so they become normal external relocations.
-            if( !owns(fun) ) {
-                while( fun.nIns() > 1 ) {
-                    if( fun.in(1) instanceof CallNode call )
-                        call.unlink(fun,1);
-                    else
-                        fun.removeDeadPath(1);
-                }
-                StartCUNode start = fun._compunit._start;
-                StopCUNode  stop  = fun._compunit._stop;
-                // Unhook the Stop->Return edge also
-                ReturnNode ret = fun.ret();
-                int idx = stop._inputs.find(ret);
-                if( idx != -1 ) {
-                    stop._inputs.del(idx);
-                    ret.delUse(stop);
-                }
-                //
-                if( stop.nIns()==0 ) {
-                    idx = _stop._inputs.find(stop);
-                    if( idx != -1 )
-                        _stop.delDef(idx);
-                    if( start.nIns() > 0 && start.in(0) != null )
-                        start.setDef(0,null);
-                    if( start.nIns() > 1 && start.in(1) != null )
-                        start.setDef(1,null);
-                }
-                continue;
-            }
-
-            // Insert the post-Opto code-generation hook.  Unlike an Opto-time
-            // Start input, this no longer carries unknown-caller semantics.
-            ReturnNode ret = fun.ret();
-            StartNode start = fun._compunit._start;
-            assert start!=null;
-            if( fun.nIns() <= 1 || fun.in(1) != start ) {
-                fun.insertDef(1,start);
-                for( Node use : fun._outputs )
-                    if( use instanceof ParmNode parm )
-                        parm.insertDef(1,ConstantNode.raw(parm._type));
-                if( fun._compunit._stop._inputs.find(ret) == -1 )
-                    fun._compunit._stop.addDef(ret);
-            }
-            // Unlink from Call
-            for( int i=2; i<fun.nIns(); i++ )
-                ((CallNode)fun.in(i)).unlink(fun,i--);
-            if( fun.rpc()==null ) { // Ensure valid RPC
-                // First make sure a valid RPC; single-call into multi-fun will have each
-                // function having a single call site, so the RPC becomes a constant and
-                // folds - but since multiple targets, the Call never inlines.  Recreate a
-                // valid RPC so codegen (and Eval2) understands the calling convention.
-                ParmNode rpc = new ParmNode( "$rpc", 0, ret.rpc()._type, fun );
-                rpc.addDef(ret.rpc());
-                ret.setDef( 3, rpc.init() );
-            }
-        }
-
-        _stop.walk(n -> {
-            if( n instanceof CallEndNode cend )
-                for( int i=1; i<cend.nIns(); i++ )
-                    if( cend.in(i) instanceof ReturnNode )
-                        cend.delDef(i--);
-            if( n instanceof CallNode call )
-                call.unlink_all();
-            return null;
-        });
-
-        _times[Phase.Unlink.ordinal()] = System.currentTimeMillis() - t0;
+        unlink(true);
+    }
+    private void unlink(boolean removeImports) {
+        phase(Phase.Unlink, _phase==Phase.LoopTree, () -> Unlink.run(this,removeImports));
     }
 
     // ---------------------------
@@ -950,39 +571,22 @@ public class CodeGen {
 
     // Global schedule (code motion) nodes
     public CodeGen GCM() {
-        assert _phase.ordinal() <= Phase.Select.ordinal();
-        _phase = Phase.Schedule;
-        long t0 = System.currentTimeMillis();
-
-        GlobalCodeMotion.buildCFG(this);
-        _times[Phase.Schedule.ordinal()] = System.currentTimeMillis() - t0;
-
-        return this;
+        return phase(Phase.Schedule, (_phase==Phase.Unlink || _phase==Phase.Select), () -> GlobalCodeMotion.buildCFG(this));
     }
 
     // ---------------------------
     // Local (basic block) scheduler phase, a classic list scheduler
-    public CodeGen localSched() {
-        assert _phase == Phase.Schedule;
-        _phase = Phase.LocalSched;
-        long t0 = System.currentTimeMillis();
-        ListScheduler.sched(this);
-        _times[Phase.LocalSched.ordinal()] = System.currentTimeMillis() - t0;
-        return this;
-     }
+    public CodeGen localSched() { return phase(Phase.LocalSched, _phase==Phase.Schedule, () -> ListScheduler.sched(this)); }
 
 
     // ---------------------------
     // Register Allocation
     public RegAlloc _regAlloc;
     public CodeGen regAlloc() {
-        assert _phase == Phase.LocalSched;
-        _phase = Phase.RegAlloc;
-        long t0 = System.currentTimeMillis();
-        _regAlloc = new RegAlloc(this);
-        _regAlloc.regAlloc();
-        _times[Phase.RegAlloc.ordinal()] = System.currentTimeMillis() - t0;
-        return this;
+        return phase(Phase.RegAlloc, _phase==Phase.LocalSched, () -> {
+            _regAlloc = new RegAlloc(this);
+            _regAlloc.regAlloc();
+        });
     }
 
     // Human-readable register name
@@ -998,32 +602,16 @@ public class CodeGen {
     // ---------------------------
     // Encoding
     public Encoding _encoding;
-    public CodeGen encode() {
-        assert _phase == Phase.RegAlloc;
-        _phase = Phase.Encoding;
-        long t0 = System.currentTimeMillis();
-
-        _encoding = new Encoding(this).encode();
-
-        _times[Phase.Encoding.ordinal()] = System.currentTimeMillis() - t0;
-        return this;
-    }
+    public CodeGen encode() { return phase(Phase.Encoding, _phase==Phase.RegAlloc, () -> _encoding = new Encoding(this).encode()); }
 
     // ---------------------------
     // Exporting to external formats
     ElfWriter _elf;
     public CodeGen exportELF( boolean inMemory, boolean emitEntrySymbol ) {
-        assert _phase == Phase.Encoding;
-        _phase = Phase.Export;
-        long t0 = System.currentTimeMillis();
-        if( _encoding!=null ) {
-            if( inMemory )
-                new LinkMem(this).link(_encoding); // In memory patching
-            else
-                _elf = new ElfWriter(this).export(emitEntrySymbol);
-        }
-        _times[Phase.Export.ordinal()] = System.currentTimeMillis() - t0;
-        return this;
+        return phase(Phase.Export, _phase==Phase.Encoding, () -> {
+            if( inMemory ) new LinkMem(this).link(_encoding);
+            else           _elf = new ElfWriter(this).export(emitEntrySymbol);
+        });
     }
 
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfWriter.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfWriter.java
index 1b6281b8..b3eac583 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfWriter.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfWriter.java
@@ -282,6 +282,8 @@ public class ElfWriter {
     // ------------------------------------------------------------------------
 
     public ElfWriter export(boolean emitEntrySymbol) {
+        if( _code._serial==null )
+            throw new IllegalStateException("ELF export needs ideal IR: request Export from the driver, or Serialize before Lower");
         // Sections are created in the order they are emitted.
         _sections = new Ary<>(Section.class);
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/FinalizeIR.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/FinalizeIR.java
new file mode 100644
index 00000000..923486c6
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/FinalizeIR.java
@@ -0,0 +1,44 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.node.*;
+import java.util.Arrays;
+
+// Comnpute field layouts only after SCCP and its peepholes converge.
+// Keep surviving functions rooted without introducing unknown callers.
+abstract class FinalizeIR {
+    static void run(CodeGen code) {
+        // Compute field layouts and replace symbolic field offsets by constants.
+        for( int i=0; i<code._start.nOuts(); i++ ) {
+            Node use = code._start.out(i);
+            if( use instanceof ConFldOffNode off ) {
+                Node con = off.asOffset();
+                assert con != null : off._ts._name+"."+off._fname;
+                off.subsume(con);
+                i--;
+            }
+        }
+        code._iter.iterate(code); // Propagate field offsets and clean up.
+
+        // Retain surviving functions for emission without adding unknown callers.
+        for( FunNode fun : code._linker )
+            if( fun != null ) {
+                // A folded static function field can leave a detached body
+                // with internal cycles. It has no callers; later phases must
+                // not revive it merely because its nodes are still allocated.
+                if( fun.isDead() || fun._type.isHigh() ) {
+                    code._linker.set(fun.sig().fidx(),null);
+                    continue;
+                }
+                code.keepInCompUnit(fun);
+            }
+        for( CompUnit cu : code._compunits.values() ) {
+            ProjNode mem = cu._start.proj(1);
+            if( mem != null ) code.add(mem.unkeep());
+        }
+        // Stable print order: initializers first, then other Returns by NID.
+        for( Node stop : code._stop._inputs )
+            Arrays.sort(stop._inputs._es,0,stop.nIns(),
+                        (x,y) -> ((((ReturnNode)x).fun().isClz() ? -1 : x._nid) -
+                                  (((ReturnNode)y).fun().isClz() ? -1 : y._nid) ));
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/GlobalCodeMotion.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/GlobalCodeMotion.java
index 33d971e9..09eb8d33 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/GlobalCodeMotion.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/GlobalCodeMotion.java
@@ -60,7 +60,7 @@ public abstract class GlobalCodeMotion {
                 if( use==null || globals.containsKey(use) ) continue;
                 FunNode fun = useFun(use);
                 if( fun==null ) continue; // Global metadata has no function owner.
-                assert CodeGen.CODE.owns(fun);
+                assert CodeGen.CODE._mach==null || CodeGen.CODE.owns(fun); // Ideal evaluation includes imported bodies.
                 var local = copies.computeIfAbsent(fun,f -> new IdentityHashMap<>());
                 Node copy = cloneGlobal(con,fun,globals,local);
                 for( int i=0; i<use.nIns(); i++ )
@@ -142,8 +142,9 @@ public abstract class GlobalCodeMotion {
         // Record Load NIDs at all their CFG block choices, then check against
         // Store block choices to force a Load above an anti-dependent Store.
         int[] anti = new int[code.UID()];
+        Ary<Node> antideps = new Ary<>(Node.class);
         // Breadth-first scheduling
-        breadth(code._stop,ns,late,anti);
+        breadth(code._stop,ns,late,anti, antideps);
 
         // Copy the best placement choice into the control slot
         for( int i=0; i<late.length; i++ )
@@ -151,7 +152,7 @@ public abstract class GlobalCodeMotion {
                 ns[i].setDef(0,late[i]);
     }
 
-    private static void breadth(Node stop, Node[] ns, CFGNode[] late, int[] anti) {
+    private static void breadth(Node stop, Node[] ns, CFGNode[] late, int[] anti, Ary<Node> antideps) {
         // Things on the worklist have some (but perhaps not all) uses done.
         WorkList<Node> work = new WorkList<>();
         work.push(stop);
@@ -172,12 +173,12 @@ public abstract class GlobalCodeMotion {
 
                 // Loads need their memory inputs' uses also done
                 if( n instanceof MemOpNode ld && ld._isLoad )
-                    for( Node memuse : ld.antiDeps() )
+                    for( Node memuse : ld.antiDeps(antideps) )
                         if( late[memuse._nid]==null )
                             continue outer;
 
                 // All uses done, schedule
-                _doSchedLate(n,ns,late,anti);
+                _doSchedLate(n,ns,late,anti,antideps);
             }
 
             // A use just finished; reconsider its inputs and waiting loads,
@@ -194,7 +195,7 @@ public abstract class GlobalCodeMotion {
         }
     }
 
-    private static void _doSchedLate(Node n, Node[] ns, CFGNode[] late, int[] anti) {
+    private static void _doSchedLate(Node n, Node[] ns, CFGNode[] late, int[] anti, Ary<Node> antideps) {
         // 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;
@@ -205,7 +206,7 @@ public abstract class GlobalCodeMotion {
 
         // Loads may need anti-dependencies, raising their LCA
         if( n instanceof MemOpNode load && load._isLoad )
-            lca = find_anti_dep(lca,load,early,late,anti);
+            lca = find_anti_dep(lca,load,early,late,anti, antideps);
 
         // Walk up from the LCA to the early, looking for best place.  This is
         // the lowest execution frequency, approximated by least loop depth and
@@ -256,38 +257,26 @@ public abstract class GlobalCodeMotion {
                 if( def.in(i)!=null ) wakeLoads(def.in(i),late,work,visit);
     }
 
-    private static CFGNode find_anti_dep(CFGNode lca, MemOpNode load, CFGNode early, CFGNode[] late, int[] anti) {
+    private static CFGNode find_anti_dep(CFGNode lca, MemOpNode load, CFGNode early, CFGNode[] late, int[] anti, Ary<Node> antideps) {
         // We could skip final-field loads here.
         // Walk LCA->early, flagging Load's block location choices
         for( CFGNode cfg=lca; cfg!=early.idom(); cfg = cfg.idom() )
             anti[cfg._nid] = load._nid;
         // Walk load->mem uses, looking for Stores causing an anti-dep
-        for( Node mem : load.antiDeps() ) {
-            switch( mem ) {
-            case MemOpNode st:
-                assert late[st._nid]!=null;
-                lca = anti_dep(load,late[st._nid],st.cfg0(),lca,st,anti);
-                break;
-            case EscapeNode st:
-                assert late[st._nid]!=null;
-                lca = anti_dep(load,late[st._nid],st.cfg0(),lca,st,anti);
-                break;
-            case CallNode call:
-                assert late[call._nid]!=null;
-                lca = anti_dep(load,late[call._nid],call.cfg0(),lca,call,anti);
-                break;
-            case CLInitNode init:
-                assert late[init._nid]!=null;
-                lca = anti_dep(load,late[init._nid],init.cfg0(),lca,init,anti);
-                break;
-            case PhiNode phi:
-                // Repeat anti-dep for matching Phi inputs.
-                // No anti-dep edges but may raise the LCA.
+        for( Node mem : load.antiDeps(antideps) ) {
+            if( mem instanceof PhiNode phi ) {
+                // Inputs carrying different memory might overwrite this alias.
+                // Raise the LCA for those paths; the unchanged-memory paths
+                // do not clobber the load.  No scheduling edge to the Phi.
                 for( int i=1; i<phi.nIns(); i++ )
-                    if( phi.in(i)==load.mem() )
+                    if( phi.in(i)!=load.mem() )
                         lca = anti_dep(load,phi.region().cfg(i),load.mem().cfg0(),lca,null,anti);
-                break;
-            default: throw Utils.TODO("Should not reach here");
+            } else {
+                // Hunt for clobbering stores
+                assert mem instanceof MemOpNode || mem instanceof EscapeNode ||
+                    mem instanceof CallNode || mem instanceof CLInitNode;
+                assert late[mem._nid]!=null;
+                lca = anti_dep(load,late[mem._nid],mem.cfg0(),lca,mem,anti);
             }
         }
         return lca;
@@ -297,12 +286,15 @@ public abstract class GlobalCodeMotion {
     private static CFGNode anti_dep( MemOpNode load, CFGNode stblk, CFGNode defblk, CFGNode lca, Node st, int[] anti ) {
         // A conditional writer can precede the load without dominating its late block.
         // Walk back to the first overlap with the load's placement range.
-        for( ; stblk != defblk.idom(); stblk = stblk.idom() ) {
+        // A different Phi input need not be dominated by this memory's
+        // definition. Stop at its depth rather than looking for that ancestor.
+        // Retain the sentinel too: a function entry has a null idom.
+        for( ; stblk != defblk.idom() && stblk.idepth() >= defblk.idepth(); stblk = stblk.idom() ) {
             // Store and Load overlap, need anti-dependence
             if( anti[stblk._nid]==load._nid ) {
                 lca = stblk.domLCA(lca,null); // Raise Loads LCA
                 if( lca == stblk && st != null && !(st instanceof CallNode) && st._inputs.find(load) == -1 ) // And if something moved,
-                    st.addDef(load);   // Add anti-dep as well; Calls already end their block.
+                    st.addDef(load);   // Add anti-dep as well (calls already end their block)
                 return lca;            // Cap this stores' anti-dep to here
             }
         }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java
new file mode 100644
index 00000000..5fc002a1
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/InstSelect.java
@@ -0,0 +1,126 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+import java.util.BitSet;
+import java.util.IdentityHashMap;
+
+// Replace ideal nodes with machine nodes while preserving CFG/loop metadata.
+// Selection also owns target ABI masks and rebuilding the copied graph's uses.
+class InstSelect {
+    private final CodeGen _code;
+    private InstSelect(CodeGen code) { _code=code; }
+
+    static CodeGen select(CodeGen code, String cpu, String callingConv, String base) {
+        // Ideal evaluation schedules the ideal graph without a CPU port.
+        if( cpu==null ) return code;
+        return code.phase(CodeGen.Phase.Select, code._phase==CodeGen.Phase.Unlink,
+                          () -> new InstSelect(code).run(cpu,callingConv,base));
+    }
+
+    private void run(String cpu, String callingConv, String base) {
+        _code._callingConv = callingConv;
+
+        // Look for CPU in fixed named place:
+        //   com.seaofnodes.simple.node.cpus."cpu"."cpu.class"
+        String clzFile = base+"."+cpu+"."+cpu;
+        try { _code._mach = Class.forName(clzFile).asSubclass(Machine.class).getDeclaredConstructor(CodeGen.class).newInstance(_code); }
+        catch( Exception e ) { throw new RuntimeException(e); }
+
+        _code._cCallingConv = _code._mach.cCallingConv(callingConv);
+
+        // Build global copies of common register masks.
+        long callerSave = _code._mach.callerSave();
+        long cCallerSave= _code._mach.callerSave(_code._cCallingConv);
+        long  neverSave = _code._mach. neverSave();
+        int maxReg = Math.min(64,_code._mach.regs().length);
+        assert maxReg>=64 || (-1L << maxReg & callerSave)==0; // No stack slots in callerSave
+        assert maxReg>=64 || (-1L << maxReg & cCallerSave)==0; // No stack slots in cCallerSave
+        _code._callerSave = new RegMask(callerSave);
+        _code._cCallerSave= new RegMask(cCallerSave);
+
+        // Build a Return RegMask array.  All returns have the following inputs:
+        // 0 - ctrl
+        // 1 - memory
+        // 2 - varies with returning GPR,FPR
+        // 3 - RPC
+        // 4+- Caller save registers
+        _code._retMasks = new RegMask[(maxReg-_code._callerSave.size()-Long.bitCount( neverSave ))+4];
+        for( int reg=0, i=4; reg<maxReg; reg++ )
+            if( !_code._callerSave.test(reg) && ((1L<<reg)&neverSave)==0 )
+                _code._retMasks[i++] = new RegMask(reg);
+        _code._rpcMask = new RegMask(_code._mach.rpc());
+        _code._retMasks[3] = _code._rpcMask;
+
+        // Convert to machine ops
+        _code._uid = 1;               // All new machine nodes reset numbering
+        var map = new IdentityHashMap<Node,Node>();
+        _instSelect( _code._stop, map );
+        _code._stop  = (StopNode)map.get(_code._stop );
+        StartNode start = (StartNode)map.get(_code._start);
+        _code._start = start==null ? new StartNode(_code._start) : start;
+        _instOuts(_code._stop,_code.visit());
+        _code._visit.clear();
+
+        // Replace the CompUnit stop (and list of functions)
+        // with hardware-specific ones
+        for( CompUnit cu : _code._compunits.values() ) {
+            cu._start= (StartCUNode)map.get(cu._start);
+            cu._stop = (StopCUNode )map.get(cu._stop );
+        }
+    }
+
+    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 MachNode already, 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 MachNode ) {
+            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.
+        if( n instanceof MemOpNode mem && mem.off() instanceof ExternOffsetNode off ) {
+            // External fields replace base+offset with symbol+0. Keep the ideal
+            // declaring type on the address for machine load/store width selection.
+            TypeMemPtr ptr = (TypeMemPtr)mem.ptr()._type;
+            n._inputs.set(2,new ExternNode(TypeMemPtr.make((byte)2,ptr._obj,true),off._extern));
+            n._inputs.set(3,ConstantNode.raw(TypeInteger.ZERO));
+        }
+        map.put(n, x=_code._mach.instSelect(n) );
+        // Carry loop-tree and pre-order info across the ideal->mach transition
+        if( n instanceof CFGNode ncfg && x instanceof CFGNode xcfg ) {
+            xcfg._ltree = ncfg._ltree;
+            xcfg._pre = ncfg._pre;
+        }
+        // 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) );
+        // Post selection action
+        if( x instanceof MachNode mach ) {
+            if( n instanceof ReturnNode ret )
+                ((ReturnNode)mach)._fun = (FunNode)map.get(ret._fun);
+            mach.postSelect(_code);  // Post selection action
+        }
+
+        return x;
+    }
+
+    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);
+                // CallNode special: outputs are partially ordered; CallEnd in slot 0
+                if( in instanceof CallNode call && n instanceof CallEndNode cend && call.out(0) != cend )
+                    call._outputs.swap(0,call.nOuts()-1);
+                _instOuts(in,visit);
+            }
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Iter.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Iter.java
new file mode 100644
index 00000000..c5120370
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Iter.java
@@ -0,0 +1,60 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+
+// Establish a pessimistic fixed point after parsing/loading. Later Iter runs
+// reuse the worklist and types produced by the preceding phase.
+abstract class Iter {
+    static void run(CodeGen code) {
+        // The phase shift closes all parser-in-progress states and freezes
+        // unknown external inputs.  Imported nodes carry post-Opto escape
+        // precision, but Iter is a fresh pessimistic solve: memory escape
+        // summaries must restart at FULL so newly discovered private escapes
+        // can only be removed, never added.  Seed the complete graph once.
+        boolean hasImports = code._externPaths != null;
+        code._start.walk(n -> {
+            if( !(n instanceof ConstantNode) )
+                n._type = hasImports ? iterImportReset(n._type) : iterEscapeReset(n._type);
+            code.add(n);
+            return null;
+        });
+        code._iter.iterate(code);
+        // Expensive assert.
+        assert !CodeGen.expensiveAssert() || Opto.fixedPointCheck(code);
+    }
+
+    private static Type iterEscapeReset(Type t) {
+        if( t instanceof TypeMem mem )
+            return mem._one ? mem : mem.makeFrom(XInt.FULL,XInt.FULL);
+        if( t instanceof TypeTuple tt ) {
+            TypeTuple rez = tt;
+            for( int i=0; i<tt._types.length; i++ ) {
+                Type tx = iterEscapeReset(tt._types[i]);
+                if( tx != tt._types[i] ) rez = rez.makeFrom(i,tx);
+            }
+            return rez;
+        }
+        return t;
+    }
+
+    private static Type iterImportReset(Type t) {
+        if( t.isHigh() )
+            return t.dual();
+        if( t instanceof TypeMem mem )
+            return TypeMem.make(mem._alias,iterImportReset(mem._t),mem._one,mem._clz,mem._final,XInt.FULL,XInt.FULL);
+        if( t instanceof TypeMemPtr )
+            return t.makeStorage();
+        if( t instanceof TypeStruct )
+            return t.makeStorage();
+        if( t instanceof TypeTuple tt ) {
+            TypeTuple rez = tt;
+            for( int i=0; i<tt._types.length; i++ ) {
+                Type tx = iterImportReset(tt._types[i]);
+                if( tx != tt._types[i] ) rez = rez.makeFrom(i,tx);
+            }
+            return rez;
+        }
+        return t;
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/LRG.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/LRG.java
index 3a4596fe..fdde8838 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/LRG.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/LRG.java
@@ -62,6 +62,8 @@ public class LRG {
 
     public int nadj() { return _adj==null ? 0 : _adj._len; }
 
+    public RegMask useMask() { return _machUse==null ? null : _machUse.regmap(_uidx); }
+
     void addNeighbor(LRG lrg) {
         if( _adj==null ) _adj = new Ary<>(LRG.class);
         _adj.push(lrg);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Opto.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Opto.java
index c41a29ac..ef222f60 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Opto.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Opto.java
@@ -73,8 +73,10 @@ abstract public class Opto {
                 FunNode fun = ret.fun();
                 // Start is a semantic unknown-caller edge.  Public functions
                 // keep it; closed-world functions must be reached by a
-                // concrete Call edge discovered during SCCP.
-                if( !(code.owns(fun) && fun.isClz()) &&
+                // concrete Call edge discovered during SCCP. Initializers,
+                // including private/imported ones, are called by opaque CLInit
+                // obligations whose Call edges are introduced only in Lower.
+                if( !fun.isClz() &&
                     !code.publicFIDX(fun.sig().fidx()) &&
                     fun.in(1) instanceof StartNode ) {
                     fun.removeDeadPath(1);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
index bb123634..7ce727fd 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/ParseAll.java
@@ -13,6 +13,18 @@ import java.util.*;
 // Parse a given file, and all its dependencies
 public abstract class ParseAll {
 
+    static void parse(CodeGen code, String src) {
+        Parser.TYPES.clear();
+        Parser.TYPES.putAll(Parser.INIT_TYPES);
+        if( src != null ) {
+            // No source file, just the source itself.
+            parseSource(code,code._srcName==null ? "Test" : code._srcName,src);
+        } else {
+            // Path from module root to source file
+            parsePath(code,code._srcName);
+        }
+    }
+
     // Worklist of symbols to search and files to parse
     private static final Ary<CompUnit> WORK = new Ary<>(CompUnit.class);
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
index 1ce68080..ac792988 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
@@ -518,7 +518,7 @@ public class RegAlloc {
         // fixed register uses.  Ordinary pressure splits keep the old shallow
         // boundary behavior.
         for( Node n : _ns ) {
-            if( n instanceof SplitNode && min!=max ) continue; // Ignoring splits; since spilling need to split in a deeper loop
+            if( n instanceof SplitNode split && !split.isNonStackSplit() && min!=max ) continue; // Ordinary splits already reach stack storage.
             if( n.isDead() ) continue; // Some Cloneable went dead by other spill changes
             // If this is a 2-address commutable op (e.g. AddX86, MulX86) and the rhs has only a single user,
             // commute the inputs... which chops the LHS live ranges' upper bound to just the RHS.
@@ -572,8 +572,8 @@ public class RegAlloc {
     }
 
     private static long ldepth( long ld, Node n, CFGNode cfg ) {
-        // Do not count splits
-        if( n instanceof SplitNode ) return ld;
+        // Ordinary splits already reach stack storage; register-only transfers do not.
+        if( n instanceof SplitNode split && !split.isNonStackSplit() ) return ld;
         // Collect min/max loop depth
         int min = (int)ld;
         int max = (int)(ld>>32);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
index 1806be24..6a23252d 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
@@ -8,6 +8,13 @@ import java.util.*;
 
 abstract public class Serialize {
 
+    // Encoding/emulation need only machine code. File export also needs ideal
+    // IR for a later compiler to import; an explicit Serialize request stops here.
+    static void forTarget(CodeGen code, CodeGen.Phase target, boolean inMemory) {
+        if( target==CodeGen.Phase.Serialize || (target.ordinal()>=CodeGen.Phase.Export.ordinal() && !inMemory) )
+            code.serialize();
+    }
+
     static void serialize( CodeGen code ) {
 
         // Get all Nodes in a sane order
@@ -68,6 +75,15 @@ abstract public class Serialize {
         // Initialize the mapping from bits/tags to types
         Type.TAGOFFS();
 
+        IdentityHashMap<Node,Integer> anodes = new IdentityHashMap<>();
+        for( Node n : nodes ) anodes.put(n,anodes.size()+1); // 0 is null.
+        // The saved wrappers summarize this object's units only. Keep the
+        // live whole-program graph intact for subsequent lowering.
+        TypeTuple stopType = TypeTuple.STOP_HIGH;
+        for( Node n : nodes.last()._inputs )
+            if( anodes.containsKey(n) ) stopType = (TypeTuple)stopType.meet(n._type);
+        Type startType = TypeTuple.make(Type.CONTROL,stopType.mem(),((StartNode)nodes.at(0)).arg());
+
         BAOS baos = new BAOS();
         // A - Print the C0DE header. The format is not versioned yet.
         baos.write('C').write('0').write('D').write('E');
@@ -91,6 +107,8 @@ abstract public class Serialize {
             if( n instanceof ParmNode parm ) parm._declaredType.gather(types);
             if( n instanceof TypeNode con ) con._con .gather(types);
         }
+        stopType.gather(types);
+        startType.gather(types);
         // A defined class remains importable even when its initializer body dies.
         for( TypeStruct ts : pubTypes )
             if( Parser.startsClzPrefix(ts._name) &&
@@ -190,21 +208,20 @@ abstract public class Serialize {
         // How many nodes?
         baos.packed4(nodes._len);
 
-        // Radix sort by Node ID#, new compressed NIDs
-        IdentityHashMap<Node,Integer> anodes = new IdentityHashMap<>();
-        for( Node n : nodes )
-            anodes.put(n,anodes.size()+1); // +1 bias, reserve 0 for null
         // First cut: 1 byte opcode, optional per-node info, includes variable nIns
         for( Node n : nodes ) {
             baos.packed1(n.serialTag().ordinal());
-            baos.packed2(types.get(n._type));
+            baos.packed2(types.get(n==nodes.at(0) ? startType : n==nodes.last() ? stopType : n._type));
             n.packed(baos,strs,types,anodes);
         }
         // Write out the input indices packed.
         for( Node n : nodes ) {
             for( int j=0; j<n.nIns(); j++ ) {
+                if( !writeInput(n,j,anodes) ) continue;
                 Node def = n.in(j);
                 Integer idx = def==null ? Integer.valueOf(0) : anodes.get(def);
+                // Imported function constants retain their symbol, not a body.
+                if( idx==null && n instanceof FunPtrNode && j==1 ) idx=0;
                 assert idx != null : "Missing serialized input for "+n+" input "+j+" def "+def;
                 baos.packed2(idx);
             }
@@ -214,6 +231,22 @@ abstract public class Serialize {
 
         return baos;
     }
+
+    // Omit cross-object call-graph links without unlinking the live IR.
+    // A parameter follows exactly the same retained callers as its function.
+    private static boolean writeInput(Node n, int i, IdentityHashMap<Node,Integer> nodes) {
+        if( n instanceof ParmNode parm ) n=parm.fun();
+        if( (n instanceof FunNode || n instanceof CallEndNode) && i>0 )
+            return nodes.containsKey(n.in(i));
+        if( n instanceof StopNode ) return nodes.containsKey(n.in(i));
+        return true;
+    }
+
+    public static int nIns(Node n, IdentityHashMap<Node,Integer> nodes) {
+        int len=0;
+        for( int i=0; i<n.nIns(); i++ ) if( writeInput(n,i,nodes) ) len++;
+        return len;
+    }
     public static <T> void gather( HashMap<T,Integer> strs, T s) {
         if( s!=null && !strs.containsKey(s) )
             strs.put(s,strs.size());
@@ -450,7 +483,6 @@ abstract public class Serialize {
 
     // --------------------------------------------------
     public static Ary<Node> nodeOrder( CodeGen code, CompUnit cu ) {
-        assert code._start._ltree != null; // Uses loop tree
         BitSet visit = code.visit();
         Ary<Node> nodes = new Ary<>(Node.class);
         visit.set(code._stop._nid);
@@ -501,7 +533,6 @@ abstract public class Serialize {
 
     // --------------------------------------------------
     public static Ary<Node> nodeOrder( CodeGen code ) {
-        assert code._start._ltree != null; // Uses loop tree
         Ary<Node> nodes = new Ary<>(Node.class);
         BitSet visit = code.visit();
         nodes.add(code._start);
@@ -555,6 +586,9 @@ abstract public class Serialize {
     private static void _funWalk( FunNode fun, Ary<Node> rpo, BitSet visit ) {
         int start = rpo._len;
         _funRPO(fun,rpo,visit);
+        // A nonreturning function still owns a Return, even before LoopTree
+        // inserts synthetic exits. No loop-depth ordering is needed on disk.
+        _funRPO(fun.ret(),rpo,visit);
         int len = rpo._len - start;
         for( int i=0; i< len>>1; i++ )
             rpo.swap(start+i,start+len-1-i);
@@ -566,13 +600,9 @@ abstract public class Serialize {
         visit.set(n._nid);              // Stop recursion
         // Walk outputs ordered
         if( n instanceof CFGNode ncfg ) {
-            // If nodes walk outer loops before inner, so they hit the
-            // Return first, so Return is at the bottom of the RPO.
             if( n instanceof IfNode iff ) {
                 CProjNode c0 = iff.cproj(0);
                 CProjNode c1 = iff.cproj(1);
-                if( c0._ltree.depth() > c1._ltree.depth() )
-                    { c0 = c1; c1 = iff.cproj(0); }
                 _funRPO(c0,rpo,visit);
                 _funRPO(c1,rpo,visit);
             } else if( n instanceof StopNode ) {
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/StaticData.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/StaticData.java
index f9f16008..616753d4 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/StaticData.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/StaticData.java
@@ -56,24 +56,6 @@ public final class StaticData {
         return owner;
     }
 
-    // A final field whose declaration already denotes this exact constant is
-    // available as that value to every ideal Load. Materialize it in the object
-    // image instead of emitting the redundant initializer Store. This lowering
-    // leaves serialized ideal IR intact, so imports retain their memory edges.
-    static boolean preinitialized(CodeGen code,StoreNode st) {
-        if( !(st.ptr()._type instanceof TypeMemPtr ptr) || !ptr._one || !isClass(ptr._obj) ) return false;
-        CompUnit owner=owner(code,ptr._obj);
-        if( owner==null || owner._src==null ) return false;
-        if( !(Parser.TYPES.get(ptr._obj._name) instanceof TypeStruct ts) ) return false;
-        Field fld=ts.field(st._name);
-        if( fld==null || !fld._final || !fld._t.isConstant() || !st.val()._type.isConstant() ) return false;
-        Type value=st.val()._type, declared=fld._t;
-        if( declared instanceof TypeFunPtr fp && value instanceof TypeFunPtr vp ) return fp.fidx()==vp.fidx();
-        if( declared instanceof TypeMemPtr ptr0 && value instanceof TypeMemPtr ptr1 )
-            return pointerConstant(ptr0) && ptr0._obj==ptr1._obj;
-        return declared==value;
-    }
-
     ObjectData object(Type t) {
         Object key=isClass(t) ? ((TypeStruct)t)._name
             : t instanceof TypeFunPtr fp ? functionSymbol(fp) : t;
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/TypeCheck.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/TypeCheck.java
new file mode 100644
index 00000000..9b4b0995
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/TypeCheck.java
@@ -0,0 +1,57 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.util.Ary;
+
+// Reject invalid optimized programs before lowering erases their source-level
+// obligations. Queue surviving CLInits during the same walk for Lower's Iter.
+abstract class TypeCheck {
+    static void run(CodeGen code) {
+        // Check for class-init cycles first; such a cycle can prevent other
+        // things from resolving types. The dependency graph is temporary.
+        String clzInitCycle = new ClassInitDependencies(code).check();
+        if( clzInitCycle != null )
+            throw Parser.error(clzInitCycle,null);
+
+        Ary<Node> errs = new Ary<>(Node.class);
+        code._stop.walk( n -> {
+                if( n.err() != null )
+                    errs.add(n);
+                if( n instanceof CLInitNode ) code.add(n);
+                return null;
+            });
+
+        if( !errs.isEmpty() ) {
+            // Prefer an originating error over a secondary error caused by a
+            // BOTTOM input.  If all errors are downstream-poisoned, retain
+            // the old first-error behavior.
+            Node min = null;
+            for( Node n : errs )
+                if( noBottomInputs(n) )
+                    {  min = n;  break; }
+            if( min==null )
+                min = errs.at(0);
+            for( Node n : errs )
+                if( n!=min &&
+                    noBottomInputs(n) &&
+                    ((n   instanceof MemOpNode nmop &&
+                      min instanceof MemOpNode mmop &&
+                      nmop._loc.before(mmop._loc)) ||
+                     (n   instanceof CFGNode ncfg &&
+                      min instanceof CFGNode mincfg &&
+                      ncfg.idepth() < mincfg.idepth())) )
+                    min = n;
+            if( code._obs != null ) code._obs.error(min, min.err().getMessage());
+            throw min.err();
+        }
+    }
+
+    private static boolean noBottomInputs(Node n) {
+        for( Node def : n._inputs )
+            if( def!=null && !(def instanceof FldOffNode) && def._type==Type.BOTTOM )
+                return false;
+        return true;
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Unlink.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Unlink.java
new file mode 100644
index 00000000..fb1c4a6f
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Unlink.java
@@ -0,0 +1,112 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.simple.node.*;
+
+// Discard call-graph edges after LoopTree. Machine selection keeps only this
+// object's bodies; ideal evaluation keeps imports so their calls can execute.
+abstract class Unlink {
+    private static void unlinkImports(CodeGen code) {
+        // Imported function constants keep their symbolic identity, not an
+        // embedded copy of the other object's Return and body.
+        for( Node n : code._start._outputs.asAry() )
+            if( n instanceof FunPtrNode ptr && ptr.ret()!=null && !code.owns(ptr.fun()) ) {
+                ptr.liftType(ptr._type);
+                ptr.setDef(1,null);
+            }
+        for( FunNode fun : code._linker ) {
+            if( fun==null || fun.isDead() || code.owns(fun) )
+                continue;
+            for( int i=1; i<fun.nIns(); i++ )
+                if( fun.in(i) instanceof CallNode call )
+                    call.unlink(fun,i--);
+        }
+        for( int i=0; i<code._stop.nIns(); i++ ) {
+            StopCUNode stop=(StopCUNode)code._stop.in(i);
+            CompUnit cu=code._compunits.get(stop.start()._fname);
+            if( cu._src==null ) code._stop.delDef(i--);
+        }
+        // The whole-object wrappers now summarize only the emitted units.
+        code._stop ._type=code._stop .compute();
+        code._start._type=code._start.compute();
+    }
+
+    static void run(CodeGen code, boolean removeImports) {
+        if( removeImports ) unlinkImports(code);
+
+        // The remaining passes assume all calls are unlinked; i.e. we are throwing
+        // away the Call Graph here.  Functions only reachable from internal calls
+        // need to be re-hooked to stop/start less they go dead.
+        for( FunNode fun : code._linker ) {
+            // Already linked to start, not going dead
+            if( fun==null || fun.isDead() )
+                continue;
+
+            // Imported functions are not emitted by this object. Ideal
+            // evaluation retains them so their calls can actually execute.
+            if( removeImports && !code.owns(fun) ) {
+                while( fun.nIns() > 1 ) {
+                    if( fun.in(1) instanceof CallNode call )
+                        call.unlink(fun,1);
+                    else
+                        fun.removeDeadPath(1);
+                }
+                StartCUNode start = fun._compunit._start;
+                StopCUNode  stop  = fun._compunit._stop;
+                // Unhook the Stop->Return edge also
+                ReturnNode ret = fun.ret();
+                int idx = stop._inputs.find(ret);
+                if( idx != -1 ) {
+                    stop._inputs.del(idx);
+                    ret.delUse(stop);
+                }
+                //
+                if( stop.nIns()==0 ) {
+                    idx = code._stop._inputs.find(stop);
+                    if( idx != -1 )
+                        code._stop.delDef(idx);
+                    if( start.nIns() > 0 && start.in(0) != null )
+                        start.setDef(0,null);
+                    if( start.nIns() > 1 && start.in(1) != null )
+                        start.setDef(1,null);
+                }
+                continue;
+            }
+
+            // Insert the post-Opto code-generation hook.  Unlike an Opto-time
+            // Start input, this no longer carries unknown-caller semantics.
+            ReturnNode ret = fun.ret();
+            StartNode start = fun._compunit._start;
+            assert start!=null;
+            if( fun.nIns() <= 1 || fun.in(1) != start ) {
+                fun.insertDef(1,start);
+                for( Node use : fun._outputs )
+                    if( use instanceof ParmNode parm )
+                        parm.insertDef(1,ConstantNode.raw(parm._type));
+                if( fun._compunit._stop._inputs.find(ret) == -1 )
+                    fun._compunit._stop.addDef(ret);
+            }
+            // Unlink from Call
+            for( int i=2; i<fun.nIns(); i++ )
+                ((CallNode)fun.in(i)).unlink(fun,i--);
+            if( fun.rpc()==null ) { // Ensure valid RPC
+                // First make sure a valid RPC; single-call into multi-fun will have each
+                // function having a single call site, so the RPC becomes a constant and
+                // folds - but since multiple targets, the Call never inlines.  Recreate a
+                // valid RPC so codegen (and Eval2) understands the calling convention.
+                ParmNode rpc = new ParmNode( "$rpc", 0, ret.rpc()._type, fun );
+                rpc.addDef(ret.rpc());
+                ret.setDef( 3, rpc.init() );
+            }
+        }
+
+        code._stop.walk(n -> {
+            if( n instanceof CallEndNode cend )
+                for( int i=1; i<cend.nIns(); i++ )
+                    if( cend.in(i) instanceof ReturnNode )
+                        cend.delDef(i--);
+            if( n instanceof CallNode call )
+                call.unlink_all();
+            return null;
+        });
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/BulkMemPhiNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/BulkMemPhiNode.java
index 850a5711..c6a6ff3b 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/BulkMemPhiNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/BulkMemPhiNode.java
@@ -125,7 +125,7 @@ public class BulkMemPhiNode extends PhiNode {
 
     // True if the MemMerge has no precise slice still covered by this Phi.
     private boolean canPeek(MemMergeNode mmm) {
-        return missingAlias(mmm,false)==0;
+        return missingAlias(mmm)==0;
     }
 
     // Return an alias required by an input but still covered by this Phi, or 0.
@@ -137,7 +137,7 @@ public class BulkMemPhiNode extends PhiNode {
             assert !(con._con instanceof TypeMem tmem && tmem._alias != 1);
             yield 0;
         }
-        case MemMergeNode mmm -> missingAlias(mmm,false);
+        case MemMergeNode mmm -> missingAlias(mmm);
         case MemOpNode mem -> unsplit(mem._alias);
         case BulkMemPhiNode bulk -> missingAlias(bulk);
         default -> throw Utils.TODO("Should not reach here");
@@ -154,7 +154,7 @@ public class BulkMemPhiNode extends PhiNode {
         return switch(use) {
         case ScopeNode scope -> 0;
         case ParmNode parm -> 0;
-        case MemMergeNode mmm -> missingAlias(mmm,true);
+        case MemMergeNode mmm -> missingAlias(mmm);
         case BulkMemPhiNode bulk -> missingAlias(bulk);
         case MemOpNode mem -> unsplit(mem._alias);
         case MemPhiNode phi -> unsplit(phi._alias);
@@ -183,14 +183,14 @@ public class BulkMemPhiNode extends PhiNode {
         return 0;
     }
 
-    // First precise MemMerge slice still covered by this Phi.  When inspecting
-    // a user, ignore slots which point back to this Phi.
-    private int missingAlias(MemMergeNode mmm, boolean user) {
+    // First explicit MemMerge slice still covered by this Phi. A user's slice
+    // may point to this Phi after a precise Phi folds; splitting is still valid.
+    private int missingAlias( MemMergeNode mmm ) {
         for( int alias=2; alias<mmm.nIns(); alias++ )
             if( mmm.in(alias)!=null &&
                 mmm.alias(alias)!=mmm.in(1) &&
                 !_aliases.get(alias) )
-                { assert (!user || mmm.in(alias)!=this); return alias; }
+                return alias;
         return 0;
     }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/CLInitNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/CLInitNode.java
index 9a41cc18..7bc17c75 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/CLInitNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/CLInitNode.java
@@ -99,7 +99,65 @@ public class CLInitNode extends CFGNode implements MultiNode {
         return CodeGen.CODE.con(((TypeTuple)_type)._types[2]);
     }
 
-    @Override public Node idealize() { return null; }
+    @Override public Node idealize() {
+        if( CodeGen.CODE._phase!=CodeGen.Phase.Lower || bypass() || in(0)._type.isHigh() ) return null;
+        if( CodeGen.CODE._midAssert ) return this;
+        // Until entry arguments become arrays, ordinary initializers receive zero.
+        return expand(CodeGen.CODE.con(TypeInteger.ZERO));
+    }
+
+    // Called only after cycle/type checking. The initialized arm skips the
+    // call; both arms rejoin with whole memory and a known-true flag slice.
+    private Node expand(Node arg) {
+        FunNode target = CodeGen.CODE.link(cu());
+        assert target!=null && !target.isDead();
+        keep();
+        Node ctrl = in(0);
+        Node memory = mem();
+
+        // A child body may assume its parent has finished. Establish that
+        // requirement first, then test the child's flag in the resulting memory.
+        CompUnit parent = cu()._par;
+        if( parent!=null ) {
+            Node ptr = CodeGen.CODE.con(TypeMemPtr.make((byte)2,parent._clz,true));
+            Field flag = parent._clz.field("$init");
+            Node off = CodeGen.CODE.con(parent._clz.offset(parent._clz.find("$init")));
+            Node parentReady = CodeGen.CODE.add(new LoadNode(_loc,"$init",flag._alias,ctrl,memory,ptr,off).init());
+            CLInitNode init = CodeGen.CODE.add(new CLInitNode(_loc,ctrl,memory,ptr,parentReady).init());
+            ctrl = CodeGen.CODE.add(new CProjNode(init,0,ScopeNode.CTRL).init());
+            memory = CodeGen.CODE.add(new ProjNode(init,1,ScopeNode.MEM0).init());
+        }
+
+        Node childOff = CodeGen.CODE.con(cu()._clz.offset(cu()._clz.find("$init")));
+        // Read the child's flag after establishing its parent's memory effects.
+        Node ready = CodeGen.CODE.add(new LoadNode(_loc,"$init",flag()._alias,ctrl,memory,ptr(),childOff).init());
+
+        IfNode iff = CodeGen.CODE.add(new IfNode(ctrl,ready).init());
+        Node done = CodeGen.CODE.add(new CProjNode(iff,0,"True").init());
+        Node cold = CodeGen.CODE.add(new CProjNode(iff,1,"False").init());
+
+        Node fptr = new FunPtrNode(target.sig(),CodeGen.CODE._start,target.ret()).peephole();
+        CallNode call = CodeGen.CODE.add(new CallNode(_loc,cold,memory,ptr(),arg,fptr).init());
+        CallEndNode end = new CallEndNode(call,TypeRPC.constant(CodeGen.CODE.rpc(_loc._cu._cname)));
+        // This is a lowered call, after interprocedural analysis. Do not add
+        // new parameter flows to a body already optimized by SCCP.
+        CodeGen.CODE.add(end.init());
+        Node called = CodeGen.CODE.add(new CProjNode(end,0,ScopeNode.CTRL).init());
+        Node after = CodeGen.CODE.add(new ProjNode(end,1,ScopeNode.MEM0).init());
+        RegionNode region = CodeGen.CODE.add(new RegionNode(_loc,null,done,called).init());
+        Node merged = CodeGen.CODE.add(new BulkMemPhiNode(ScopeNode.MEM0,region,memory,after).init());
+
+        // Replace the individual outputs; no tuple-pack node or second
+        // representation of CLInit is needed while the projections collapse.
+        for( Node use : _outputs.asAry() ) {
+            if( use==null ) continue; // Our temporary keep.
+            assert use instanceof Proj;
+            int idx = ((Proj)use).idx();
+            use.subsume(idx==0 ? region : idx==1 ? merged : CodeGen.CODE.con(((TypeTuple)_type)._types[2]));
+        }
+        CodeGen.CODE.invalidateIDepthCaches();
+        return unkeep(); // Iter removes this now-unused node.
+    }
 
     // Resolve a precise flag slice even when the parser did not yet know the
     // class/alias and could only install the whole-memory projection.
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/CallEndNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
index 555d0c65..cfc58ce9 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
@@ -40,7 +40,7 @@ public class CallEndNode extends CFGNode implements MultiNode {
     }
     @Override public Tag serialTag() { return Tag.CallEnd; }
     public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) {
-        baos.packed1(nIns());
+        baos.packed1(Serialize.nIns(this,anodes));
         // Linked CallEnds depend on Return types which depend on CallEnds;
         // break the cycle
         baos.packed2(types.get(_type));
@@ -108,7 +108,9 @@ public class CallEndNode extends CFGNode implements MultiNode {
         // effects.
         if( (nIns()-1)+externs < tfp.nfcns() ) {
             // If during Opto, assume call won't be called and thus won't return anything.
-            boolean opto = CodeGen.CODE._phase.ordinal() >= CodeGen.Phase.Opto.ordinal();
+            // Lowered calls deliberately have no links into optimized bodies.
+            boolean opto = CodeGen.CODE._phase.ordinal() >= CodeGen.Phase.Opto.ordinal() &&
+                           CodeGen.CODE._phase.ordinal() <  CodeGen.Phase.Lower.ordinal();
             Type tmem = opto ? TypeMem.TOP : TypeMem.BOT;
             Type ret  = opto ? Type.TOP    : tfp.ret();
             return TypeTuple.make(Type.CONTROL,tmem,ret);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/CallNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/CallNode.java
index b4bb5e72..71f6d146 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/CallNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/CallNode.java
@@ -101,6 +101,9 @@ public class CallNode extends CFGNode {
 
     @Override
     public Node idealize() {
+        // Lowering may introduce calls after the call graph has been analyzed.
+        // These use the callee interface without reopening its parameter flow.
+        if( CodeGen.CODE._phase.ordinal() >= CodeGen.Phase.Lower.ordinal() ) return null;
         CallEndNode cend = cend();
         if( cend==null ) return null; // Still building
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/ConstantNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
index 4357570e..0569f352 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
@@ -37,13 +37,13 @@ public class ConstantNode extends TypeNode {
     }
     static Node make( BAOS bais, Type[] types)  { return raw(types[bais.packed2()]); }
 
-    // Semantic constant construction through FinalizeIR.  A unique internal
+    // Semantic constant construction through Lower.  A unique internal
     // function identity carries a lifetime edge to the function's Return.
     public static Node make( Type type ) {
         if( type==Type. CONTROL ) return new CtrlNode();
         if( type==Type.XCONTROL ) return new XCtrlNode();
         if( CodeGen.CODE._phase != null &&
-            CodeGen.CODE._phase.ordinal() > CodeGen.Phase.FinalizeIR.ordinal() )
+            CodeGen.CODE._phase.ordinal() > CodeGen.Phase.Lower.ordinal() )
             return raw(type);
         if( type instanceof TypeFunPtr tfp && tfp.isConstant() ) {
             FunNode fun = CodeGen.CODE._link(tfp);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/FunNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/FunNode.java
index 7f9a2819..edde247a 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/FunNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/FunNode.java
@@ -45,7 +45,7 @@ public class FunNode extends RegionNode {
     @Override public Tag serialTag() { return Tag.Fun; }
     @Override public void packed(BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node,Integer> anodes ) {
         assert !_folding;
-        baos.packed1(nIns());          // Number of linked calls
+        baos.packed1(Serialize.nIns(this,anodes)); // Object-local linked calls
         baos.packed2(types.get(_sig)); // NPE if fails lookup
         baos.packed2(_name==null ? 0 : strs.get(_name));
         baos.packed2(_approxUIDs);
@@ -171,7 +171,8 @@ public class FunNode extends RegionNode {
         //   through class-field loads and other initially imprecise values.
         // - FIDX is not in the escape set
         // - Not called anywhere else; post Opto called-not-escaped functions need to still be hooked to start
-        if( in(1) instanceof StartCUNode start ) {
+        // Opaque CLInit obligations need their bodies even without Call edges.
+        if( !isClz() && in(1) instanceof StartCUNode start ) {
             boolean preOpto = CodeGen.CODE._phase == null ||
                 CodeGen.CODE._phase.ordinal() < CodeGen.Phase.Opto.ordinal();
             if( !preOpto && !start.escapedFIDX(_sig.fidx()) && nIns()<=2 && _ret!=null ) {
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/MemOpNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
index b31e14d5..bfbd46c3 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
@@ -6,13 +6,9 @@ import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.codegen.CodeGen;
 import com.seaofnodes.simple.codegen.GlobalBits;
 import com.seaofnodes.simple.type.*;
-import com.seaofnodes.simple.util.BAOS;
-import com.seaofnodes.simple.util.Utils;
+import com.seaofnodes.simple.util.*;
 import java.lang.StringBuilder;
-import java.util.BitSet;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.IdentityHashMap;
+import java.util.*;
 
 /**
  * Convenience common base for Load and Store.
@@ -140,27 +136,24 @@ public abstract class MemOpNode extends TypeNode {
 
     // Memory writers which must follow this read. A packaging node is not a
     // write; follow this alias through aggregates to its writers.
-    public ArrayList<Node> antiDeps() {
-        ArrayList<Node> deps = new ArrayList<>();
-        antiDeps(mem(),deps,new BitSet());
-        return deps;
+    public Ary<Node> antiDeps( Ary<Node> antideps ) {
+        antideps.clear();
+        return antiDeps(mem(),antideps);
     }
 
-    private void antiDeps(Node mem, ArrayList<Node> deps, BitSet visit) {
-        if( visit.get(mem._nid) ) return;
-        visit.set(mem._nid);
+    private Ary<Node> antiDeps( Node mem, Ary<Node> antideps )  {
         for( Node use : mem._outputs ) {
             if( use instanceof MemMergeNode merge ) {
-                Node slice = _alias<merge.nIns() ? merge.in(_alias) : null;
-                if( (slice==mem) || (slice==null && merge.in(1)==mem) )
-                    antiDeps(merge,deps,visit);
+                if( merge.alias(_alias)==mem )
+                    antiDeps(merge,antideps);
             } else if( use instanceof CallNode || use instanceof CLInitNode ||
                        (use instanceof MemOpNode st && !st._isLoad && st._alias==_alias) ||
                        (use instanceof EscapeNode esc && esc.fld()._alias==_alias) ||
                        (use instanceof MemPhiNode phi && phi._alias==_alias) ||
                        (use instanceof BulkMemPhiNode phi && !phi.isSplit(_alias)) ) {
-                if( !deps.contains(use) ) deps.add(use);
+                if( !antideps.contains(use) ) antideps.add(use);
             }
         }
+        return antideps;
     }
 }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/ParmNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/ParmNode.java
index 899d7639..278c5308 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/ParmNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/ParmNode.java
@@ -3,6 +3,7 @@ package com.seaofnodes.simple.node;
 import com.seaofnodes.print.ExprPrinter;
 
 import com.seaofnodes.simple.type.*;
+import com.seaofnodes.simple.codegen.Serialize;
 import com.seaofnodes.simple.util.BAOS;
 
 import java.util.HashMap;
@@ -23,7 +24,7 @@ public class ParmNode extends PhiNode {
     public ParmNode(ParmNode parm) { super(parm, parm._label ); _idx = parm._idx; _declaredType = parm._declaredType; }
     @Override public Tag serialTag() { return Tag.Parm; }
     @Override public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) {
-        baos.packed1(nIns());   // Number of linked calls
+        baos.packed1(Serialize.nIns(this,anodes)); // Object-local linked calls
         baos.packed2(_label==null ? 0 : strs.get(_label));
         baos.packed2(types.get(_declaredType)); // NPE if fails lookup
         baos.packed1(_idx);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/SplitNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/SplitNode.java
index 0e104c15..3042f857 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/SplitNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/SplitNode.java
@@ -13,6 +13,8 @@ public abstract class SplitNode extends MachConcreteNode {
     public final String _kind;  // Kind of split
     public final byte _round;   // Debugging info for which RegAlloc round
     public SplitNode(LRG lrg,String kind, byte round, Node[] nodes) { super(nodes); _lrg=lrg; _kind = kind; _round = round; }
+    // A register-only transfer may need another split to reach stack storage.
+    public boolean isNonStackSplit() { return false; }
     @Override public String op() { return "mov"; }
     @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
         p.p("mov(");
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StartNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StartNode.java
index 84c8a3a7..495be0a2 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StartNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/StartNode.java
@@ -45,11 +45,11 @@ public class StartNode extends LoopNode implements MultiNode {
         // Find module.<clinit>, it's the start.
         CFGNode C = null;
         for( Node use : _outputs )
-            if( use instanceof FunNode fun && fun.isModInit() )
+            if( use instanceof FunNode fun && CodeGen.CODE.entryClinitName().equals(fun._name) )
                 { assert C==null; C = fun; }
         if( C==null )
             for( FunNode fun : CodeGen.CODE._linker )
-                if( fun!=null && !fun.isDead() && fun.isModInit() )
+                if( fun!=null && !fun.isDead() && CodeGen.CODE.entryClinitName().equals(fun._name) )
                     { assert C==null; C = fun; }
         return C;
     }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StopCUNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StopCUNode.java
index f2bd5841..d3a356ed 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StopCUNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/StopCUNode.java
@@ -41,7 +41,7 @@ public class StopCUNode extends StopNode {
         // below must not forget private bits already discovered precisely from
         // that Return on an earlier SCCP step.
         if( CodeGen.CODE._phase.ordinal() >= CodeGen.Phase.Opto.ordinal() &&
-            CodeGen.CODE._phase.ordinal() <= CodeGen.Phase.FinalizeIR.ordinal() &&
+            CodeGen.CODE._phase.ordinal() <= CodeGen.Phase.Lower.ordinal() &&
             _type instanceof TypeTuple old && old.mem() instanceof TypeMem omem )
             xmem = xmem.makeFrom(XInt.meet(xmem._escFs,omem._escFs),
                                  XInt.meet(xmem._escAs,omem._escAs));
@@ -102,7 +102,7 @@ public class StopCUNode extends StopNode {
         // input refinement add bits, reversing Iter's monotonic direction.
         // This normalization is needed only for Opto's optimistic grand cycle.
         if( CodeGen.CODE._phase.ordinal() < CodeGen.Phase.Opto.ordinal() ||
-            CodeGen.CODE._phase.ordinal() > CodeGen.Phase.FinalizeIR.ordinal() ) return mem;
+            CodeGen.CODE._phase.ordinal() > CodeGen.Phase.Lower.ordinal() ) return mem;
         int[] escFs = XInt.isHigh(mem._escFs)
             ? XInt.meet(prior._escFs,CodeGen.CODE.publicFIDXs())
             : mem._escFs;
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StopNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StopNode.java
index e52a49a2..a7e52563 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StopNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/StopNode.java
@@ -3,6 +3,7 @@ package com.seaofnodes.simple.node;
 import com.seaofnodes.print.ExprPrinter;
 
 import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.codegen.Serialize;
 import com.seaofnodes.simple.type.*;
 import com.seaofnodes.simple.util.BAOS;
 
@@ -18,7 +19,7 @@ public class StopNode extends CFGNode {
     }
     public StopNode(StopNode stop) { super(stop); }
     @Override public Tag serialTag() { return Tag.Stop; }
-    @Override public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) { baos.packed1(nIns()); }
+    @Override public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) { baos.packed1(Serialize.nIns(this,anodes)); }
     static Node make( BAOS bais ) {
         StopNode stop = new StopNode();
         stop.setDefX(bais.packed1()-1,null);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index 418b1e92..8a0bf8d4 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -89,6 +89,16 @@ public class StoreNode extends MemOpNode {
         Type decl = declaredType();
         if( decl != Type.BOTTOM )
             { assert decl != Type.TOP; val = val.join(decl); }
+        // A singleton class's final constant field lives in the static image.
+        // Its precise memory slice is a constant too; ordinary peepholes can
+        // replace this Store before scheduling or instruction selection.
+        // A constant runtime value alone is not enough: mutable fields (notably
+        // $init) still need their writes, and instance fields need allocation.
+        Field fld = ptr._obj.field(_name);
+        if( _alias!=1 && ptr._one && Parser.startsClzPrefix(ptr._obj._name) &&
+            fld!=null && fld._final && decl.isConstant() )
+            return TypeMem.make(_alias,val,true,true,true,mem._escFs,mem._escAs).escapesFrom(val);
+
         // Allocation uses a private TypeMem and nothing else does.  This
         // memory is truly private; a temporary singleton until it escapes -
         // which is never does in a constructor.
@@ -108,7 +118,6 @@ public class StoreNode extends MemOpNode {
         Type t = val.meet(tfld);
         // Bulk memory's final bit describes its conservative remainder, not
         // this newly precise slice.  Slice finality comes from the field.
-        Field fld = ptr._obj.field(_name);
         boolean xfinal = fld != null && fld._final;
         return TypeMem.make(_alias,t,mem._one,mem._clz,xfinal,mem._escFs,mem._escAs).escapesFrom(val);
     }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitFlagsARM.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitFlagsARM.java
new file mode 100644
index 00000000..25e5d501
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitFlagsARM.java
@@ -0,0 +1,21 @@
+package com.seaofnodes.simple.node.cpus.arm;
+
+import com.seaofnodes.isa.Arm64;
+import com.seaofnodes.simple.codegen.*;
+
+// NZCV transfers require a GPR. Further splits can spill that GPR to the stack.
+public class SplitFlagsARM extends SplitARM {
+    private static final RegMask MASK = new RegMask(arm.WR_BITS,1L);
+    SplitFlagsARM(LRG lrg,String kind,byte round) { super(lrg,kind,round); }
+    @Override public boolean isNonStackSplit() { return true; }
+    @Override public RegMask regmap(int i) { return MASK; }
+    @Override public RegMask outregmap() { return MASK; }
+
+    @Override public void encoding(Encoding enc) {
+        short dst=enc.reg(this), src=enc.reg(in(1));
+        if( dst==src ) return;
+        if( src==arm.FLAGS ) enc.add4(Arm64.flags(dst,false));
+        else if( dst==arm.FLAGS ) enc.add4(Arm64.flags(src,true));
+        else super.encoding(enc);
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitGPRARM.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitGPRARM.java
new file mode 100644
index 00000000..c9b2127a
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitGPRARM.java
@@ -0,0 +1,11 @@
+package com.seaofnodes.simple.node.cpus.arm;
+
+import com.seaofnodes.simple.codegen.*;
+
+// Keep a saved NZCV value in GPRs and stack slots through subsequent spills.
+public class SplitGPRARM extends SplitARM {
+    private static final RegMask MASK = new RegMask(arm.WR_BITS,-2L);
+    SplitGPRARM(LRG lrg,String kind,byte round) { super(lrg,kind,round); }
+    @Override public RegMask regmap(int i) { return MASK; }
+    @Override public RegMask outregmap() { return MASK; }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
index 8c9bed95..3c965da5 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
@@ -288,7 +288,16 @@ public class arm extends Machine {
     @Override public int rpc() { return X30; }
 
     // Create a split op; any register to any register, including stack slots
-    @Override public SplitNode split(LRG lrg, String kind, byte round) {  return new SplitARM(lrg,kind,round);  }
+    @Override public SplitNode split(LRG lrg, String kind, byte round) {
+        RegMask def = lrg._machDef==null ? null : lrg._machDef.outregmap(), use = lrg.useMask();
+        if( (def!=null && def.size1() && def.test(FLAGS)) ||
+            (use!=null && use.size1() && use.test(FLAGS)) )
+            return new SplitFlagsARM(lrg,kind,round);
+        // Spilling the saved flags requires a GPR between NZCV and the stack.
+        if( lrg._machDef instanceof SplitFlagsARM || lrg._machDef instanceof SplitGPRARM )
+            return new SplitGPRARM(lrg,kind,round);
+        return new SplitARM(lrg,kind,round);
+    }
 
     // Return a MachNode unconditional branch
     @Override public CFGNode jump() {
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitFlagsX86.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitFlagsX86.java
new file mode 100644
index 00000000..cb7694f9
--- /dev/null
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitFlagsX86.java
@@ -0,0 +1,25 @@
+package com.seaofnodes.simple.node.cpus.x86_64_v2;
+
+import com.seaofnodes.isa.X86;
+import com.seaofnodes.simple.codegen.*;
+
+// Flag snapshots can use GPRs or stack slots, but never XMM registers.
+public class SplitFlagsX86 extends SplitX86 {
+    private static final RegMask MASK = new RegMask(x86_64_v2.WR_BITS | (1L<<x86_64_v2.FLAGS) | x86_64_v2.SPILLS,-1L);
+    SplitFlagsX86(LRG lrg,String kind,byte round) { super(lrg,kind,round); }
+    @Override public RegMask regmap(int i) { return MASK; }
+    @Override public RegMask outregmap() { return MASK; }
+
+    @Override public void encoding(Encoding enc) {
+        short dst=enc.reg(this), src=enc.reg(in(1));
+        if( dst==src ) return;
+        if( dst==x86_64_v2.FLAGS || src==x86_64_v2.FLAGS ) {
+            boolean toFlags = dst==x86_64_v2.FLAGS;
+            int reg = toFlags ? src : dst;
+            if( reg>=x86_64_v2.MAX_REG )
+                X86.flagsStack(enc,fun(enc).computeStackOffset(enc._code,reg),toFlags);
+            else
+                X86.flags(enc,reg,toFlags);
+        } else super.encoding(enc);
+    }
+}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitX86.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitX86.java
index b2b643d3..46f2cb16 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitX86.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/SplitX86.java
@@ -16,12 +16,10 @@ public class SplitX86 extends SplitNode {
     @Override public RegMask regmap(int i) { return x86_64_v2.SPLIT_MASK; }
     @Override public RegMask outregmap() { return x86_64_v2.SPLIT_MASK; }
 
-    // Need to handle 8 cases: . reg->reg, reg->xmm, reg->flags, xmm->reg, xmm->xmm, xmm->flags, flags->reg, flags->xmm,
-    // flags->flags.
+    // Moves among GPRs, XMM registers, and stack slots.
     @Override public void encoding( Encoding enc ) {
         short dst=enc.reg(this), src=enc.reg(in(1));
-        if( dst==x86_64_v2.FLAGS ) { X86.flags(enc,src,true); return; }
-        if( src==x86_64_v2.FLAGS ) { X86.flags(enc,dst,false); return; }
+        assert dst!=x86_64_v2.FLAGS && src!=x86_64_v2.FLAGS;
         boolean dstX=dst>=x86_64_v2.XMM_OFFSET, srcX=src>=x86_64_v2.XMM_OFFSET;
         // Stack spills
         if( dst >= x86_64_v2.MAX_REG ) {
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
index 7b351533..3dc93bf6 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
@@ -47,7 +47,7 @@ public class x86_64_v2 extends Machine {
     static RegMask DIV_MASK = new RegMask(RD_BITS & ~(1L<<RAX) & ~(1L<<RDX));
 
     static final long SPILLS = -(1L << MAX_REG);
-    static final RegMask SPLIT_MASK = new RegMask(WR_BITS | FP_BITS /* | (1L<<FLAGS)*/ | SPILLS, -1L );
+    static final RegMask SPLIT_MASK = new RegMask(WR_BITS | FP_BITS | SPILLS, -1L );
 
     // Load/store mask; both GPR and FPR
     static RegMask MEM_MASK = new RegMask(WR_BITS | FP_BITS);
@@ -267,7 +267,9 @@ public class x86_64_v2 extends Machine {
 
     // Create a split op; any register to any register, including stack slots
     @Override public SplitNode split(LRG lrg, String kind, byte round ) {
-        return new SplitX86(lrg,kind, round);
+        return lrg._machDef!=null && lrg._machDef.outregmap().test(FLAGS)
+            ? new SplitFlagsX86(lrg,kind,round)
+            : new SplitX86(lrg,kind,round);
     }
 
     // Return a MachNode unconditional branch
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java b/chapter25/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java
index e9231d9a..f2ed2f72 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java
@@ -17,7 +17,7 @@ public class SimpleGraphObserver extends GraphCapture<Node> {
     @Override protected void compile(String src) {
         _code = new CodeGen(src);
         _code._obs = this;
-        _code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        _code.driver(CodeGen.Phase.TypeCheck);
     }
     @Override protected String phase() { return _code._phase.name(); }
     @Override protected int pos() { return _code._phase == CodeGen.Phase.Parse ? _code.P.pos() : -1; }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/BulkMemPhiTest.java b/chapter25/src/test/java/com/seaofnodes/simple/BulkMemPhiTest.java
new file mode 100644
index 00000000..31c0302b
--- /dev/null
+++ b/chapter25/src/test/java/com/seaofnodes/simple/BulkMemPhiTest.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import com.seaofnodes.simple.type.TypeMem;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class BulkMemPhiTest {
+    // Reduced from Capitalize's Lower-phase failure. A precise MemMerge slot
+    // may still be supplied by bulk memory which covers the requested alias.
+    @Test public void testBulkInPreciseSlot() {
+        CodeGen code=new CodeGen("");
+        code._phase=CodeGen.Phase.Lower;
+        Node m0=code.con(TypeMem.START), m1=code.con(TypeMem.BOT);
+        Node ctrl=new CProjNode(code._start,0,"Ctrl").init();
+        Node iff=new IfNode(ctrl,code.con(TypeInteger.BOOL)).init();
+        RegionNode region=new RegionNode(null,null,
+            new CProjNode(iff,0,"True").init(),
+            new CProjNode(iff,1,"False").init()).init();
+        BulkMemPhiNode bulk=new BulkMemPhiNode("$mem",region,m0,m1).init();
+        // A later init check proves its call arm dead. Its precise Phi can
+        // collapse before the surrounding aggregate gets another peephole.
+        RegionNode done=new RegionNode(null,null,region,code.XCTRL).init();
+        MemPhiNode precise=new MemPhiNode("$4",4,done,bulk,m1).init();
+        MemMergeNode merge=new MemMergeNode(null,m0);
+        merge.alias(4,precise);
+        merge.init();
+        Node folded=precise.peepholeOpt();
+        assertSame(bulk,folded);
+        precise.subsume(folded);
+
+        assertFalse(bulk.isSplit(4));
+        assertSame(bulk,merge.alias(4));
+        // Splitting this still-covered alias must tolerate the direct bulk use.
+        Node mem = bulk.idealize();
+        bulk.subsume(mem);
+    }
+}
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter05Test.java
index 5b57e701..afdb1071 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter05Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -20,7 +20,7 @@ else {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,(arg+2),(arg-3));", code.print());
     }
 
@@ -36,7 +36,7 @@ if (arg == 1) {
 }
 return c;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,4,3);", code.print());
     }
 
@@ -64,7 +64,7 @@ if( arg==1 )
 else
     b=a+1;
 return a+b;""");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return ((arg<<1)+Phi(Region,2,3));", code.print());
     }
 
@@ -79,7 +79,7 @@ if( arg==1 )
 else
     a=b+1;
 return a+b;""");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return ((Phi(Region,(arg<<1),arg)+arg)+Phi(Region,4,5));", code.print());
     }
 
@@ -99,7 +99,7 @@ else
     a=5;
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,3,5,2,4);", code.print());
     }
 
@@ -115,7 +115,7 @@ if( arg==0 )
     b=2;
 return arg+a+b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         String ir = code.print();
         assertTrue(ir,
                    ir.equals("return ((arg+Phi(Region,1,0))+Phi(Region,2,0));") ||
@@ -133,7 +133,7 @@ if( arg==1 )
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (arg==Phi(Region,3,2));", code.print());
     }
 
@@ -148,7 +148,7 @@ else
     a=3;
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter06Test.java
index c503b56c..d1af5d14 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter06Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -15,7 +15,7 @@ public class Chapter06Test {
 if( true ) return 2;
 return 1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 2;", code.print());
         assertTrue(code.ctrl() instanceof FunNode);
     }
@@ -29,7 +29,7 @@ if (arg)
     a = 2;
 return (arg < a) < 3; // Because (arg < a) is a bool/uint1/[0-1], its always less than 3
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
     }
 
@@ -44,7 +44,7 @@ else
   a=3;
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 2;", code.print());
         assertTrue(code.ctrl() instanceof FunNode);
     }
@@ -65,7 +65,7 @@ else
     b=5;
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,42,5);", code.print());
     }
 
@@ -84,7 +84,7 @@ if( arg==2 )
 else
     b=5;
 return b;""");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,2,5);", code.print());
     }
 
@@ -104,7 +104,7 @@ else if( arg==3 )
 else
     a=5;
 return a;
-""", TypeInteger.constant(2)).parse().iter().opto().iterPostOpto().finalizeIR();
+""", TypeInteger.constant(2)).driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 5;", code.print());
     }
 
@@ -124,7 +124,7 @@ else if( arg==3 )
 else
     a=5;
 return a;
-""", TypeInteger.constant(1)).parse().iter().opto().iterPostOpto().finalizeIR();
+""", TypeInteger.constant(1)).driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
     }
 
@@ -144,7 +144,7 @@ else
     a=5;
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,3,5,4);", code.print());
     }
 
@@ -165,7 +165,7 @@ else
     a=5;
 return a;
 """, TypeInteger.constant(1));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
     }
 
@@ -186,7 +186,7 @@ else
     a=5;
 return a;
 """, TypeInteger.constant(3));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 4;", code.print());
     }
 
@@ -202,7 +202,7 @@ if( arg ) {
 }
 return a+b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,4,1);", code.print());
     }
 
@@ -221,7 +221,7 @@ if( arg ) {
 }
 return a+b;
 """, TypeInteger.constant(1));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 4;", code.print());
     }
 
@@ -239,7 +239,7 @@ if( arg ) {
 }
 return a+b;
 """, TypeInteger.constant(0));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
     }
 
@@ -257,7 +257,7 @@ if( arg ) {
 }
 return a+b+c;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,6,1,5);", code.print());
     }
 
@@ -278,7 +278,7 @@ if( arg ) {
 }
 return a+b+c;
 """, TypeInteger.constant(1));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 6;", code.print());
     }
 
@@ -298,7 +298,7 @@ if( arg ) {
 }
 return a+b+c;
 """, TypeInteger.constant(2));
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 5;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter07Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter07Test.java
index 498038c1..7094c0d5 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter07Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter07Test.java
@@ -17,7 +17,7 @@ while(arg < 10) {
 }
 return arg;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -34,7 +34,7 @@ if(arg){}else{
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1,Phi(Loop,1,(Phi_a+1)));", code.print());
     }
 
@@ -54,7 +54,7 @@ while(i < arg) {
 }
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,0,Phi(Loop,Phi_sum,(Phi_sum+Phi(Loop,0,(Phi_j+1)))));", code.print());
     }
 
@@ -89,7 +89,7 @@ while(a < 10) {
 }
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,2,(Phi(Region,Phi_b,4)+1));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -106,7 +106,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -122,7 +122,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -148,7 +148,7 @@ int a = 1;
 while(arg) a = 2;
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,2);", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -164,7 +164,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -180,7 +180,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -197,7 +197,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -214,7 +214,7 @@ while(a < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter08Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter08Test.java
index 61815840..376e472b 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter08Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter08Test.java
@@ -22,7 +22,7 @@ while(arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,(Phi(Loop,arg,Add)+1),Add,Phi_arg);", code.print());
         assertTrue(code.ctrl() instanceof RegionNode);
         Assert.assertEquals( "5", Eval2.eval(code, 1));
@@ -45,7 +45,7 @@ while(arg < 10) {
 }
 return a;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,1,Phi(Region,Phi_a,(Phi_a+1),Phi_a));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -64,7 +64,7 @@ while(arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
         assertTrue(code.ctrl() instanceof RegionNode);
     }
@@ -80,7 +80,7 @@ while(arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
         assertTrue(code.ctrl() instanceof RegionNode);
     }
@@ -99,7 +99,7 @@ while(arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -116,7 +116,7 @@ while(arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
         assertTrue(code.ctrl() instanceof CProjNode);
     }
@@ -132,14 +132,14 @@ while( arg < 10 ) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -167,7 +167,7 @@ while(arg < 10) {
 }
 return arg;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return arg;", code.print());
     }
 
@@ -184,7 +184,7 @@ while(arg < 10) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,Phi(Loop,1,(Phi_a+1)),Add);", code.print());
         assertTrue(code.ctrl() instanceof RegionNode);
     }
@@ -200,7 +200,7 @@ while(1) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (Phi(Loop,1,Add)+1);", code.print());
         assertTrue(code.ctrl() instanceof CProjNode prj && prj._idx==1 );
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter09Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter09Test.java
index 839b834d..7025b98a 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter09Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter09Test.java
@@ -24,7 +24,7 @@ while(v0) {
 }
 return 0;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
     }
 
     @Test
@@ -40,7 +40,7 @@ else {
 }
 return x;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,(arg<<1),(Shl+1));", code.print());
         Assert.assertEquals( "2", Eval2.eval(code,  1));
         Assert.assertEquals("23", Eval2.eval(code, 11));
@@ -49,7 +49,7 @@ return x;
     @Test
     public void testGVN2() {
         CodeGen code = new CodeGen("return arg*arg-arg*arg;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         Assert.assertEquals("0", Eval2.eval(code,  1, 1));
     }
@@ -63,7 +63,7 @@ while (arg < 10) {
 }
 return arg;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,arg,(Phi_arg+2));", code.print());
         Assert.assertEquals("11", Eval2.eval(code,  1));
     }
@@ -80,7 +80,7 @@ while (arg < 10) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,arg,(Phi_arg+4));", code.print());
         Assert.assertEquals("13", Eval2.eval(code,  1));
     }
@@ -109,7 +109,7 @@ while (arg) {
 }
 return arg;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -128,14 +128,14 @@ while(v1+arg) {
 }
 return 0;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
     @Test
     public void testWhile0() {
         CodeGen code = new CodeGen("while(0) continue; if(0) arg=0; return arg;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return arg;", code.print());
     }
 
@@ -148,7 +148,7 @@ if(0) while(0) {
 }
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -156,14 +156,14 @@ return 0;
     @Test
     public void testPrecedence() {
         CodeGen code = new CodeGen("return 3-1+2;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 4;", code.print());
     }
 
     @Test
     public void testSwap2() {
         CodeGen code = new CodeGen("return 1+(1+1);");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
     }
 
@@ -181,7 +181,7 @@ while(arg) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,0,(-(Phi_a+3)));", code.print());
     }
 
@@ -195,7 +195,7 @@ arg=0;
 int v0=0!=0<-0;
 return -0+0+0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
@@ -203,14 +203,14 @@ return -0+0+0;
     @Test
     public void testFuzz2() {
         CodeGen code = new CodeGen("return 0+-0;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
     @Test
     public void testFuzz3() {
         CodeGen code = new CodeGen("int v0=0; while(0==69) while(v0) return 0; return 1;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
     }
 
@@ -222,7 +222,7 @@ while(1) {
     if(1<0) while(arg==-0) arg=arg-arg;
 }
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
@@ -244,7 +244,7 @@ while(1) {
 }
 return 0!=0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
@@ -257,7 +257,7 @@ while(0==1) while(v0)
         v0=1+v0;
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -273,14 +273,14 @@ while(1)
         v1=1;
 return v1+v0;
                                    """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
     @Test
     public void testFuzz8() {
         CodeGen code = new CodeGen("while(arg) arg = arg - 1;  return arg;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter10Test.java
index 1b542d63..924884ac 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter10Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -12,7 +12,7 @@ public class Chapter10Test {
             "if(1) return new S; else return 0;"
         } ) {
             String src = "struct S { int x; }; " + body;
-            var code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            var code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
             // This chapter also has constructor/class-init Returns in the CompUnit.
             var entry = (com.seaofnodes.simple.node.FunNode)code._start.uctrl();
             org.junit.Assert.assertTrue(body,
@@ -102,7 +102,7 @@ if( (arg/13)==0 ) {
 int r = g+h;
 return p-r;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -122,7 +122,7 @@ bar.a = 1;
 bar.a = 2;
 return bar.a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 2;", code.print());
     }
 
@@ -138,7 +138,7 @@ else
     v.y = 3;
 return v;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return Test.Vector2D; return MEM[ 2:___ 3:.x=0; 4:.y=0;]; return Test.Vector2D; ]", code.print());
     }
 
@@ -151,7 +151,7 @@ struct s0 {
 s0? v1=null;
 int v3=v1.zAicm;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();  fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck);  fail(); }
         catch( Exception e ) {  assertEquals("Might be null accessing 'zAicm'",e.getMessage());  }
     }
 
@@ -176,7 +176,7 @@ while (arg) {
 }
 return bar.a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return Phi(Loop,0,(Phi_a+2)); return MEM[ 2:___ 3:.a=0;]; return Test.Bar; ]", code.print());
     }
 
@@ -189,7 +189,7 @@ if (arg) bar = null;
 bar.a = 1;
 return bar.a;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Type null is not of declared type *Test.Bar",e.getMessage()); }
     }
 
@@ -202,7 +202,7 @@ if (arg) bar = new Bar;
 bar.a = 1;
 return bar.a;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Might be null accessing 'a'",e.getMessage()); }
     }
 
@@ -215,7 +215,7 @@ if (arg) bar = null;
 bar.a = 1;
 return bar.a;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Type null is not of declared type *Test.Bar", e.getMessage()); }
     }
 
@@ -228,7 +228,7 @@ if (arg) bar = null;
 if( bar ) bar.a = 1;
 return bar.a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1,.a);", code.print());
     }
 
@@ -244,7 +244,7 @@ if( !bar ) rez=4;
 else bar.a = 1;
 return rez;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,4,3);", code.print());
     }
 
@@ -261,7 +261,7 @@ while(arg) {
 }
 return ret;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) {
             assertEquals("Might be null accessing 'v0'", e.getMessage()); }
     }
@@ -298,7 +298,7 @@ while( i.x < i.len ) {
 }
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return Phi(Loop,0,(Phi(Loop,0,(Phi_x+1))+Phi_sum)); return MEM[ 2:___ 3:.x=0; 4:.len=0;]; return Test.Iter; ]", code.print());
     }
 
@@ -317,7 +317,7 @@ while(arg) {
 }
 return ret;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return Phi(Loop,Test.s0,Phi(Region,Test.s0,Phi_ret)); return MEM[ 2:___ 3:.v0=0;]; return Test.s0; ]", code.print());
     }
 
@@ -334,7 +334,7 @@ while(arg) {
 }
 return ret.v0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return .v0;", code.print());
     }
 
@@ -351,7 +351,7 @@ while(arg < 10) {
 }
 return ret.v0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return .v0;", code.print());
     }
 
@@ -370,7 +370,7 @@ s0 b = new s0();
 // a.x==1, b.x==1, cnt==2
 return a.x * 100 + b.x * 10 + cnt;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return 112; return MEM[ 2:___ 3:___ 4:.x=1;]; return Test.s0; ]", code.print());
     }
 
@@ -399,7 +399,7 @@ if(0) {
 }
 return 0;
    """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -413,7 +413,7 @@ if(0) return 0;
 else return new s0;
 if(new s0.f0) return 0;
     """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("Stop[ return Test.s0; return MEM[ 2:___ 3:.f0=0;]; return Test.s0; ]", code.print());
     }
 
@@ -429,7 +429,7 @@ while(0<arg) {
 }
 return 0;
     """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
     }
 
     @Test
@@ -441,7 +441,7 @@ while(v0.f0) {}
 s0 v1 = v0;
 return v1;
     """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return (const)Test.s0; return MEM[ 2:___ 3:.f0=0;]; return Test.s0; ]", code.print());
     }
 
@@ -474,7 +474,7 @@ while(0) {}
 }
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -485,7 +485,7 @@ int v0=arg==0;
 while(v0) continue;
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index 19c531f8..fae7611d 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -14,7 +14,7 @@ public class Chapter12Test {
 """
 return 3;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
         assertEquals("3", Eval2.eval(code,  0));
     }
@@ -34,7 +34,7 @@ while( arg ) {
 }
 return head.next.i;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Might be null accessing 'next'",e.getMessage()); }
     }
 
@@ -56,7 +56,7 @@ _LLI? next = head.next;
 if( next==null ) return 1;
 return next.q;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Phi(Region,1,.q,0);", code.print());
         assertEquals("2", Eval2.eval(code,  3));
     }
@@ -75,7 +75,7 @@ i0.f = f0;
 f0.i = i0;
 return f0.i.f.i.i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 17;", code.print());
     }
 
@@ -87,7 +87,7 @@ struct _N { !_N? !next; int i; };
 _N n = new _N;
 return n.next;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return null;", code.print());
     }
 
@@ -100,7 +100,7 @@ struct N { !M !next; int i; new N = { !M m -> next = m; }; };
 N n = new N(new M);
 return n.next;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return (const)Test.M; return MEM[ 2:___ 3:.m=0;]; return Test.M; return MEM[ 2:___ 3:___ 4:___ 5:___ 6:___ 7:.next=Parm_m(Test.N.N,*Test.M {i64 !m; }); 8:.i=0;]; return MEM[ 2:___ 3:___ 4:___ 5:___ 6:___ 7:___ 8:.i=0;]; return Test.N; ]", code.print());
     }
 
@@ -113,7 +113,7 @@ struct N { !M !next; int i; new N = { !M m -> next = m; }; };
 N n = new N(null);
 return n.next;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Argument #0 isa null, but must be a *Test.M {i64 !m; }",e.getMessage()); }
     }
 
@@ -126,20 +126,20 @@ struct N { !N? !next; int i; };
 n.i = 3.14;
 return n.i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("3",Eval2.eval(code,0));
     }
 
     @Test
     public void testNullRef4() {
         CodeGen code = new CodeGen("return -null-5/null-5;");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot null + 5",e.getMessage()); }
     }
 
     @Test public void testNullRef5() {
         CodeGen code = new CodeGen("return null+42;");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot null + 42",e.getMessage()); }
     }
 
@@ -150,7 +150,7 @@ return n.i;
 struct _S{};
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -162,7 +162,7 @@ return 0;
 struct S1 { S2? s; };
 return new S2;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Unknown struct type 'S2'",e.getMessage()); }
     }
 
@@ -174,7 +174,7 @@ struct _S1 { !_S2? !s; };
 struct _S2 { int x; };
 return (new _S1).s=new _S2;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Test._S2;", code.print());
     }
 
@@ -191,7 +191,7 @@ p2.pi.i = 2;
 if (arg) p1 = new P;
 return p1.pi.i + 1;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();  fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck);  fail(); }
         catch( Exception e ) {  assertEquals("Might be null accessing 'i'",e.getMessage());  }
     }
 
@@ -210,7 +210,7 @@ c.f0=a;  c.f1=b;
 return a.f0.f1.f0.f1.f0;
 
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck().GCM().localSched();
+        code.driver(CodeGen.Phase.FinalizeIR).driver(CodeGen.Phase.Schedule).localSched();
         assertEquals("return Test._B;", code.print());
         assertEquals("Test._B{f0=Test._C{f0=Test._A{f0=$cyclic,f1=$cyclic},f1=$cyclic},f1=$cyclic}", Eval2.eval(code,  0));
     }
@@ -276,7 +276,7 @@ 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().iter().opto().iterPostOpto().finalizeIR().typeCheck().GCM().localSched();
+        code.driver(CodeGen.Phase.FinalizeIR).driver(CodeGen.Phase.Schedule).localSched();
         assertEquals("return Test._R;", code.print());
         assertEquals("Test._R{a=Test._C{a=Test._N{a=Test._Y{a=Test._J{a=Test._U{a=Test._F{a=Test._Q{a=Test._B{a=Test._M{a=Test._X{a=Test._I{a=Test._T{a=Test._E{a=Test._P{a=Test._A{a=Test._L{a=Test._W{a=Test._H{a=Test._S{a=Test._D{a=Test._O{a=Test._Z{a=Test._K{a=Test._V{a=Test._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/chapter25/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter13Test.java
index 9786006c..214bc69e 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter13Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -34,7 +34,7 @@ while( prime <= arg ) {
 }
 return primeCount;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi_primeCount,(Phi_primeCount+1))));", code.print());
         assertEquals("0", Eval2.eval(code,  1)); // No primes 1 or below
         assertEquals("1", Eval2.eval(code,  2)); // 2
@@ -73,7 +73,7 @@ i=v.f;
 if (arg) v.f=1;
 return i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 2;", code.print());
         assertEquals("2", Eval2.eval(code, 0));
         assertEquals("2", Eval2.eval(code, 1));
@@ -96,7 +96,7 @@ if (arg) {
 }
 return i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,.f,0);", code.print());
     }
 
@@ -115,7 +115,7 @@ if (v1) {
 }
 return v0.f;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,.f,2);", code.print());
     }
 
@@ -133,7 +133,7 @@ if (arg+1) arg= 0;
 while (arg) v.f = 2;
 return i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return arg;", code.print());
     }
 
@@ -150,7 +150,7 @@ while(1) {
 }
 return v.f;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,0,2);", code.print());
         for( int arg : new int[]{-1,0,1,3,100} )
             assertEquals("0",Eval2.eval(code,arg));
@@ -167,7 +167,7 @@ while( -arg )
 while(1)
   arg = arg+ptr.v;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
@@ -185,7 +185,7 @@ while (arg) {
 }
 return i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -205,7 +205,7 @@ while(arg) {
 }
 return arg;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -223,7 +223,7 @@ if (arg) {
 }
 return v.f;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -242,7 +242,7 @@ while (arg > 0) {
 }
 return v;
                 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         //assertEquals("return new _S;", code.print());
     }
 
@@ -259,7 +259,7 @@ while(0>=0) {
 }
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Top;", code.print());
     }
 
@@ -277,7 +277,7 @@ u32 v0=0;
     return v1;
 }
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
index ccca2e2b..e058a822 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
@@ -18,7 +18,7 @@ public class Chapter14FloatTest {
             {"f32 rounded=arg+16777216.0; return rounded;", "1.6777232E7", "1.6777199E7"}
         };
         for( String[] test : tests ) {
-            var code = new CodeGen(test[0]).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            var code = new CodeGen(test[0]).driver(CodeGen.Phase.TypeCheck);
             assertEquals(test[0],test[1],Eval2.eval(code,17));
             assertEquals(test[0],test[2],Eval2.eval(code,-17));
         }
@@ -26,7 +26,7 @@ public class Chapter14FloatTest {
 
 
     @Test public void testSubZeroFloat() {
-        var code = new CodeGen("flt x = arg; return 0-x;").parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        var code = new CodeGen("flt x = arg; return 0-x;").driver(CodeGen.Phase.TypeCheck);
         // Compare strings so +0.0 and -0.0 remain distinct.
         assertEquals("0.0", Eval2.eval(code,0));
         assertEquals("-1.0", Eval2.eval(code,1));
@@ -40,7 +40,7 @@ public class Chapter14FloatTest {
             {"return 2.5; return 7;", "2.5"}
         } ) {
             String src = test[0];
-            var code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            var code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
             assertEquals(src,test[1],Eval2.eval(code,0));
         }
     }
@@ -53,7 +53,7 @@ public class Chapter14FloatTest {
 """
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -65,7 +65,7 @@ return 0;
 flt x = 3.14;
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -84,7 +84,7 @@ return guess;
 """);
         // TODO: One of the problems with <clinit> returning an OS error code,
         // is it chops all results to int.
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,(flt)arg,((Phi_guess+(ToFloat/Phi_guess))*0.5f));", code.print());
         assertEquals("3.0", Eval2.eval(code,  9));
         assertEquals("1.414213562373095", Eval2.eval(code,  2));
@@ -97,7 +97,7 @@ return guess;
 flt x = arg;
 return x+1==x;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return ((flt)arg==(ToFloat+1.0f));", code.print());
         assertEquals("0", Eval2.eval(code, 1));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter14Test.java
index 3ba03b48..bc2ad8d3 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter14Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter14Test.java
@@ -16,7 +16,7 @@ public class Chapter14Test {
 """
 return 3.14;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3.14;", code.print());
         assertEquals("3.14", Eval2.eval(code,  0));
     }
@@ -32,7 +32,7 @@ if( b < 0 ) c = -1;
 if( b > 2 ) c =  1;
 return c;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 99;", code.print());
         assertEquals("99", Eval2.eval(code,  0));
     }
@@ -45,7 +45,7 @@ u8 b = 123;
 b = b + 456;// Truncate
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 67;", code.print());
         assertEquals("67", Eval2.eval(code,  0));
     }
@@ -59,7 +59,7 @@ u8 b = 123;
 while( b ) b = b + 456;// Truncate
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -72,7 +72,7 @@ b = b + 456;// Truncate
 u1 c = b;   // No more truncate needed
 return c;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -85,7 +85,7 @@ int b = 123;
 b = b+456 & 31;                 // Precedence
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
         assertEquals("3", Eval2.eval(code,  0));
     }
@@ -99,7 +99,7 @@ struct _Foo { u1 b; };
 f.b = 123;
 return f.b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -111,7 +111,7 @@ return f.b;
 i8 b = 255;                     // Chopped
 return b;                       // Sign extend
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return -1;", code.print());
         assertEquals("-1", Eval2.eval(code,  0));
     }
@@ -124,7 +124,7 @@ i8 b = arg;
 b = b + 1;// Truncate
 return b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (((((arg<<56)>>56)+1)<<56)>>56);", code.print());
         assertEquals("1", Eval2.eval(code, 0));
         assertEquals("-128", Eval2.eval(code, 127));
@@ -138,7 +138,7 @@ u16 mask = (1<<16)-1;           // AND mask
 int c = 123456789 & mask;
 return c;                       //
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 52501;", code.print());
         assertEquals("52501", Eval2.eval(code,  0));
     }
@@ -149,7 +149,7 @@ return c;                       //
 """
 return (arg | 123 ^ 456) >>> 1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (((arg|123)^456)>>>1);", code.print());
         assertEquals("217", Eval2.eval(code,  0));
     }
@@ -162,7 +162,7 @@ flt f = arg;
 arg = f & 1;
 return arg;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot '&' flt",e.getMessage()); }
     }
 
@@ -175,7 +175,7 @@ while(arg) v1=-v0;
 while(v1) break;
 return v1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,(((1<<arg)&1)&Shl),0);", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -194,7 +194,7 @@ if(0&0>>>0) {
 }
 return v0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -220,7 +220,7 @@ f32 ff32 = 3.141592653589793;  if( ff32 != 3.1415927410125732) return 5;
 
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter15Test.java
index 3c1254d2..25f00474 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter15Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -17,7 +17,7 @@ public class Chapter15Test {
 """
 return 3.14;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3.14;", code.print());
         assertEquals("3.14", Eval2.eval(code,  0));
     }
@@ -31,7 +31,7 @@ struct _C { !_C? !l; };
 c.l = c;
 return c;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Test._C;", code.print());
         assertEquals("Test._C{l=$cyclic}", Eval2.eval(code,  0));
     }
@@ -50,7 +50,7 @@ while (i < old#) {
 output[i] = 1;
 return output;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return []u8;", code.print());
         assertEquals("\u0001", Eval2.eval(code,  0));
     }
@@ -62,7 +62,7 @@ return output;
 int[] is = new int[2];
 return is[1];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -75,7 +75,7 @@ int[] is = new int[2];
 int[] is2 = new int[2];
 return is[1];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -89,7 +89,7 @@ a[0] = 1;
 a[1] = 2;
 return a[0];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -102,7 +102,7 @@ struct _A { int i; };
 !_A?[] !a = new !_A?[2];
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return []*Test._A?;", code.print());
         assertEquals("*Test._A {i64 !i; }?[ null,null]", Eval2.eval(code, 0));
     }
@@ -131,7 +131,7 @@ else {
 }
 return rez;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1.2,.y,2.3);", code.print());
         assertEquals("3.14", Eval2.eval(code, 0));
         assertEquals("1.2", Eval2.eval(code, 1));
@@ -156,7 +156,7 @@ if( iss[arg] )
     if( iss[arg][2] )
         rez = iss[arg][2].y;
 return rez;""");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Phi(Region,1.2,1.2,.y);", code.print());
         assertEquals("3.14", Eval2.eval(code,  0));
         try { Eval2.eval(code, 10); fail(); } // Fails AIOOBE in Eval2, no range checks
@@ -174,7 +174,7 @@ root._kids = new !_Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
 root._kids[0] = new _Tree;
 return root;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Test._Tree;", code.print());
         assertEquals("Test._Tree{_kids=*Test._Tree {*[]*Test._Tree?[mutable]? !_kids; }?[ Test._Tree{_kids=null},null]}", Eval2.eval(code,  0));
     }
@@ -186,7 +186,7 @@ return root;
 struct _S { int a; int[] !b; new _S = { int[] ary -> b=ary; }; };
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -209,7 +209,7 @@ while( i < ary# - 1 ) {
 }
 return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return (.[]+(.[]*1000));", code.print());
         assertEquals("1006", Eval2.eval(code,  4));
     }
@@ -218,7 +218,7 @@ return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
     public void sieveOEratosthenes() throws IOException {
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/sieve.smp"));
         CodeGen code = new CodeGen(src+"return sieve(arg);");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return []u32;", code.print());
         assertEquals("u32[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
     }
@@ -235,7 +235,7 @@ s2.f = 2.0;
 if (arg) s1 = new _S;
 return s1.i + s1.f;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return ((flt).i+.f);", code.print());
         assertEquals("0.0", Eval2.eval(code,  0));
     }
@@ -247,7 +247,7 @@ return s1.i + s1.f;
 """
 return new flt;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Cannot allocate a flt",e.getMessage()); }
     }
 
@@ -258,7 +258,7 @@ return new flt;
 flt is = new int[2];
 return is;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Type *[]i64 is not of declared type flt",e.getMessage()); }
     }
 
@@ -269,7 +269,7 @@ return is;
 int[] is = new int[3.14];
 return is[1];
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot '<<' 3.14",e.getMessage()); }
     }
 
@@ -279,7 +279,7 @@ return is[1];
 int[] is = new int[arg];
 return is[1];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  4));
         try { Eval2.eval(code,-1); fail(); }
@@ -312,7 +312,7 @@ while(v5+(0&0)) {
 }
 return v1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -328,7 +328,7 @@ int v8=0;
 while(0<--1>>>---(v7*0==v8)) {}
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 
@@ -353,7 +353,7 @@ else {
 }
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
     }
 }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter16Test.java
index ad9b99bc..2942cfee 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter16Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter16Test.java
@@ -15,7 +15,7 @@ public class Chapter16Test {
 """
 return 3.14;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3.14;", code.print());
         assertEquals("3.14", Eval2.eval(code,  0));
     }
@@ -28,7 +28,7 @@ return 3.14;
 int x, y;
 return x+y;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -39,7 +39,7 @@ return x+y;
 int x=2, y=x+1;
 return x+y;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 5;", code.print());
         assertEquals("5", Eval2.eval(code,  0));
     }
@@ -52,7 +52,7 @@ struct _X { int x=3; };
 _X z = new _X;
 return z.x;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
         assertEquals("3", Eval2.eval(code,  0));
     }
@@ -64,7 +64,7 @@ struct _X { int x=3; new _X = { int xx -> x=xx; }; };
 _X z = new _X(4);
 return z.x;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 4;", code.print());
         assertEquals("4", Eval2.eval(code,  0));
     }
@@ -85,7 +85,7 @@ _LLI? next = head.next;
 if( !next ) return 1;
 return next.i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1,.i,0);", code.print());
         assertEquals("0", Eval2.eval(code,  0));
         assertEquals("1", Eval2.eval(code,  1));
@@ -115,7 +115,7 @@ _LLI? next = head.next;
 if( !next ) return 1;
 return next.i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1,.i,0);", code.print());
         assertEquals("0", Eval2.eval(code,  0));
         assertEquals("1", Eval2.eval(code,  1));
@@ -140,7 +140,7 @@ struct _Square {
 };
 return new _Square;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Test._Square;", code.print());
         assertEquals("Test._Square{side=3.0,diag=1.7320508075688772}", Eval2.eval(code,  3));
         assertEquals("Test._Square{side=4.0,diag=2.0}", Eval2.eval(code, 4));
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter17aTest.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
index 95a0fc37..ea7afe56 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
@@ -15,7 +15,7 @@ int x=2, y=3;
 if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
 return y;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,9,3);", code.print());
         assertEquals("3", Eval2.eval(code, 0));
         assertEquals("9", Eval2.eval(code, 1));
@@ -28,7 +28,7 @@ struct _X { int ~x; new _X = { int xx -> x=xx; }; };
 _X z = new _X(3);
 return z.x;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 3;", code.print());
         assertEquals("3", Eval2.eval(code,  0));
     }
@@ -40,7 +40,7 @@ struct _Point { int ~x, ~y; new _Point = { int xx, int yy -> x=xx; y=yy; }; };
 _Point p = new _Point(3,4);
 return p;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (const)Test._Point;", code.print());
         assertEquals("Test._Point{x=3,y=4}", Eval2.eval(code,  0));
     }
@@ -53,7 +53,7 @@ struct _Point { int x=3, y=4; new _Point = { int xx, int yy -> x=xx; y=yy; }; };
 p.x++;
 return p;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
 
@@ -65,7 +65,7 @@ struct _Point { int x=3, y=4; };
 p.x++;
 return p;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
 
@@ -77,7 +77,7 @@ _Point p = new _Point;
 p.x++;
 return p;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("'Test._Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
     }
 
@@ -89,7 +89,7 @@ _Point p = new _Point;
 p.x++;
 return p;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
 
@@ -101,7 +101,7 @@ struct _Point { var x=3; var y=4; };
 p.x++;
 return p;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Test._Point;", code.print());
         assertEquals("Test._Point{x=4,y=4}", Eval2.eval(code,  0));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter17bTest.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
index 6137c166..e85ce31d 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
@@ -15,7 +15,7 @@ public class Chapter17bTest {
 """
 return 1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -27,7 +27,7 @@ return 1;
         CodeGen code = new CodeGen("""
 return arg++;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return arg;", code.print());
         assertEquals("0", Eval2.eval(code, 0));
     }
@@ -37,7 +37,7 @@ return arg++;
         CodeGen code = new CodeGen("""
 return arg+++arg++;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return ((arg<<1)+1);", code.print());
         assertEquals("1", Eval2.eval(code, 0));
     }
@@ -48,7 +48,7 @@ return arg+++arg++;
 //   -(arg--)-(arg--)
 return -arg---arg--;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (-((arg<<1)+-1));", code.print());
         assertEquals("1", Eval2.eval(code, 0));
     }
@@ -61,7 +61,7 @@ xs[0]++;
 xs[1]++;
 return xs[0];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code, 2));
     }
@@ -73,7 +73,7 @@ u8[] !xs = new u8[1];
 xs[0]--;
 return xs[0];
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 255;", code.print());
         assertEquals("255", Eval2.eval(code, 2));
     }
@@ -86,7 +86,7 @@ struct _S { u16 x; };
 s.x--;
 return s.x;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 65535;", code.print());
         assertEquals("65535", Eval2.eval(code, 2));
     }
@@ -94,7 +94,7 @@ return s.x;
     @Test
     public void testInc6() {
         CodeGen code = new CodeGen("return --arg;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return (arg+-1);", code.print());
         assertEquals("-1", Eval2.eval(code, 0));
     }
@@ -102,7 +102,7 @@ return s.x;
     @Test
     public void testInc7() {
         CodeGen code = new CodeGen("u8 x=0; return --x;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 255;", code.print());
         assertEquals("255", Eval2.eval(code, 0));
     }
@@ -110,7 +110,7 @@ return s.x;
     @Test
     public void testInc8() {
         CodeGen code = new CodeGen("int x; x+=2; return x+=3;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 5;", code.print());
         assertEquals("5", Eval2.eval(code, 0));
     }
@@ -118,14 +118,14 @@ return s.x;
     @Test
     public void testInc9() {
         CodeGen code = new CodeGen("flt x = 1.5; x++; return x;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("2",Eval2.eval(code,0));
     }
 
@@ -133,73 +133,73 @@ return s.x;
     // ---------------------------------------------------------------
     @Test public void testVar0() {
         CodeGen code = new CodeGen("var d; return d;");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Syntax error, expected `=expression` but found `;`",e.getMessage()); }
     }
 
     @Test public void testVar1() {
         CodeGen code = new CodeGen("val d; return d;");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Syntax error, expected `=expression` but found `;`",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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code, 0));
     }
 
     @Test public void testVar5() {
         CodeGen code = new CodeGen("struct _S{int x; new _S={ int xx -> x=xx; };}; !_S? !s; s=new _S(3); s.x++; return s.x; // Ok, no initializer so x is mutable ");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.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; new S={ int xx -> x=xx; };}; ~S s = new S(3); s.x++; return s.x; // Error initializer so x is immutable ");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code, 0));
     }
 
     @Test public void testVar10() {
         CodeGen code = new CodeGen("struct S{int x;}; ~S s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
 
@@ -218,7 +218,7 @@ foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
 xfoo.bar.x++;   // Error, cannot mutate through xfoo
 return xfoo.bar.x;
  """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
 
@@ -239,7 +239,7 @@ foo.bar.x++;           // Bumps to 5
 int x5 = xfoo.bar.x;   // Ok to read through xfoo, gets 5
 return x4*10+x5;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 45;", code.print());
         assertEquals("45", Eval2.eval(code, 0));
     }
@@ -249,7 +249,7 @@ return x4*10+x5;
         CodeGen code = new CodeGen("""
 int i,i++;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Redefining name 'i'",e.getMessage()); }
     }
 
@@ -264,7 +264,7 @@ struct A { !B !b; new A = { ->
 }; };
 A x = new A;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Field 'b' might not be initialized",e.getMessage()); }
     }
 
@@ -296,7 +296,7 @@ A x = new A;
             "!B !b; new A = { -> if (arg) { b = new B; return 0; } b = new B; };",
         } ) {
             CodeGen code = new CodeGen("struct B {}; struct A { "+fields+" }; return new A.b != null;");
-            code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            code.driver(CodeGen.Phase.TypeCheck);
             assertEquals("1",Eval2.eval(code,0));
             assertEquals("1",Eval2.eval(code,1));
         }
@@ -314,7 +314,7 @@ val x = 1;
 return x;
 """
 );
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Undefined name 'x'",e.getMessage()); }
     }
 
@@ -343,7 +343,7 @@ return me;
         CodeGen code = new CodeGen("""
 return arg ? 1 : 2;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1,2);", code.print());
         assertEquals("2", Eval2.eval(code, 0));
         assertEquals("1", Eval2.eval(code, 1));
@@ -354,7 +354,7 @@ return arg ? 1 : 2;
         CodeGen code = new CodeGen("""
 return arg ? 0 : arg;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code, 0));
     }
@@ -368,7 +368,7 @@ val get = { !S s -> s.x; };
 if( !s || !arg ) return 0;
 return get(s);
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
     }
 
     @Test
@@ -378,7 +378,7 @@ struct _Bar { int x; };
 var b = arg ? new _Bar : null;
 return b ? b.x++ + b.x++ : -1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
         assertEquals("-1", Eval2.eval(code, 0));
 
@@ -392,7 +392,7 @@ struct _Bar { int x; };
 var b = arg ? new _Bar;
 return b ? b.x++ + b.x++ : -1;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
         assertEquals("-1", Eval2.eval(code, 0));
         assertEquals("1", Eval2.eval(code, 1));
@@ -406,7 +406,7 @@ struct _Bar { !_Bar? !next; int x; new _Bar = { !_Bar? !n, int xx -> next=n; x=x
 var b = arg ? new _Bar((arg==2) ? new _Bar(null,2), 1);
 return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0"
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,.x,0,.x);", code.print());
         assertEquals("0", Eval2.eval(code, 0));
         assertEquals("1", Eval2.eval(code, 1));
@@ -419,7 +419,7 @@ return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0
 flt f=arg?1:1.2;
 return f;   // missing widening
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Region,1.0f,1.2);", code.print());
         assertEquals("1.2", Eval2.eval(code,  0));
     }
@@ -431,7 +431,7 @@ return f;   // missing widening
 struct S{};
 return arg ? 7 : new S;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Cannot return generic scalar",e.getMessage()); }
     }
 
@@ -444,7 +444,7 @@ for( int i=0; i<arg; i++ )
     sum += i;
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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));
@@ -457,7 +457,7 @@ for( ; i<arg; i++ )
     sum += i;
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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));
@@ -472,7 +472,7 @@ for( int i=0; ; i++ ) {
 }
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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));
@@ -485,7 +485,7 @@ for( int i=0; i<arg; )
     sum += i++;
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         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));
@@ -498,7 +498,7 @@ for( int i=0; i<arg; i++ )
     sum += i;
 return i;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Undefined name 'i'",e.getMessage()); }
     }
     @Test
@@ -506,7 +506,7 @@ return i;
         CodeGen code = new CodeGen("""
 for(;;arg++;) {}
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Syntax error, expected `Unexpected code after expression` but found `;`",e.getMessage()); }
     }
 
@@ -522,7 +522,7 @@ struct _A {
 };
 return new _A;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Test._A;", code.print());
         assertEquals("Test._A{f1=null,f2=null}", Eval2.eval(code,0));
     }
@@ -537,7 +537,7 @@ struct _A {
 };
 return new _A(new !B?[0]).array_of_b;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return []*B?;", code.print());
         assertEquals("*B {}?[]", Eval2.eval(code,0));
     }
@@ -556,7 +556,7 @@ for( ; ptr; ptr = ptr.next )
     sum += ptr.i;
 return sum;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return Phi(Loop,0,(Phi_sum+.i));", code.print());
         assertEquals("45", Eval2.eval(code, 10));
     }
@@ -587,7 +587,7 @@ for( int j=0; j<nprimes; j++ )
     rez[j] = primes[j];
 return rez;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck().GCM();
+        code.driver(CodeGen.Phase.FinalizeIR).driver(CodeGen.Phase.Schedule);
         assertEquals("return []i64;", code.print());
         assertEquals("i64[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter18Test.java
index d88d8e9d..ae1dca5f 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter18Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -91,7 +91,7 @@ public class Chapter18Test {
              "No common type amongst int and reference"}
         } ) {
             try {
-                new CodeGen(test[0]).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+                new CodeGen(test[0]).driver(CodeGen.Phase.TypeCheck);
                 fail("Expected incompatible return types: " + test[0]);
             } catch( Parser.ParseException e ) {
                 assertEquals("Cannot return generic scalar",e.getMessage());
@@ -140,7 +140,7 @@ while(arg--) {
 }
 return a;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Phi(Loop,1,Phi(Loop,2,Phi_a));", code.print());
         assertEquals("1", Eval2.eval(code,  0));
         assertEquals("2", Eval2.eval(code,  1));
@@ -157,7 +157,7 @@ return a;
 {int -> int}? x2 = null; // null function ptr
 return x2;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return null;", code.print());
         assertEquals("null", Eval2.eval(code, 0 ) );
     }
@@ -170,7 +170,7 @@ return x2;
     x*x;
 };
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return { sq}; return (Parm_x(sq,i64)*x); ]", code.print());
         assertEquals("{ ptr i64 -> i64 #[ 3]}", Eval2.eval(code, 3));
     }
@@ -197,7 +197,7 @@ return _sq(arg)+_sq(3);
 int cnt=1;                      // Global scope; exactly one of these
 return { -> cnt++; };           // Escape global-scope variable is OK
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return { ptr -> i64 #[ 3]}; return .cnt; ]", code.print());
         assertEquals("{ ptr -> i64 #[ 3]}", Eval2.eval(code, 0));
     }
@@ -216,7 +216,7 @@ val B = ctr();                  // Make a counter
 A();                            // Increment counter A
 return A()*10 + B();            // Incr A and B; result: 2*10+1 == 21
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("Variable 'cnt' is out of function scope and must be a final constant",e.getMessage()); }
     }
 
@@ -228,7 +228,7 @@ return A()*10 + B();            // Incr A and B; result: 2*10+1 == 21
 val cnt=2;
 return { -> cnt; }();
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return 2;", code.print());
         assertEquals("2", Eval2.eval(code, 0));
     }
@@ -241,7 +241,7 @@ return { -> cnt; }();
 var fcn = arg ? { int x -> x*x; } : { int x -> x+x; };
 return fcn(3);
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("Stop[ return #2; return (Parm_x($fun3,i64,3)*x); return (Parm_x($fun4,i64,3)<<1); ]", code.print());
         assertEquals("6", Eval2.eval(code, 0));
         assertEquals("9", Eval2.eval(code, 1));
@@ -251,7 +251,7 @@ return fcn(3);
     @Test
     public void testFcn5() {
         CodeGen code = new CodeGen("val _fact = { int x -> x <= 1 ? 1 : x*_fact(x-1); }; return _fact(arg);");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         String ir = code.print();
         assertTrue(ir.equals("Stop[ return #2; return Phi(Region,1,(Parm_x(_fact,arg,(x-1))*#2)); ]") ||
                    ir.equals("Stop[ return Phi(Region,1,(arg*#2)); return Phi(Region,1,(Parm_x(_fact,(arg-1),(x-1))*#2)); ]") ||
@@ -269,7 +269,7 @@ return fcn(3);
     @Test
     public void testFcn5Float() {
         CodeGen code = new CodeGen("val _fact = { int x -> x <= 1 ? 1.0 : x*_fact(x-1); }; return _fact(arg);");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("1.0",  Eval2.eval(code, 0));
         assertEquals("1.0",  Eval2.eval(code, 1));
         assertEquals("2.0",  Eval2.eval(code, 2));
@@ -280,7 +280,7 @@ return fcn(3);
     @Test
     public void testFcn5Minus() {
         CodeGen code = new CodeGen("val _neg = { int x -> x ? -_neg(x-1) : 1; }; return _neg(arg);");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals( "1", Eval2.eval(code, 0));
         assertEquals("-1", Eval2.eval(code, 1));
         assertEquals( "1", Eval2.eval(code, 2));
@@ -295,7 +295,7 @@ struct _S { int i; new _S = { int x -> i=x; }; };
 val _newS = { int x -> return new _S(x); };
 return _newS(1).i;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -310,7 +310,7 @@ val _g = {->2;};
 if( arg ? _f : _g ) return 1;
 return 2;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code,  0));
     }
@@ -388,7 +388,7 @@ for(;;) {
 }
 return 1;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR(); fail(); }
+        try { code.driver(CodeGen.Phase.FinalizeIR); fail(); }
         catch( Exception e ) { assertEquals("No active loop for a break or continue",e.getMessage()); }
     }
 
@@ -404,7 +404,7 @@ for(;;) {
 }
 return 0;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Might be null calling { ptr i64 -> i64 #[ 3]}?",e.getMessage()); }
     }
 
@@ -416,7 +416,7 @@ return 0;
 val f = { int i, int j -> return i+j; };
 return f();
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Expecting 3 arguments, but found 1",e.getMessage()); }
     }
 
@@ -432,7 +432,7 @@ val x = { -> return 1; };
 S? s = new S;
 return s.x;
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("Accessing unknown field 'x' from '*Test.S'",e.getMessage()); }
     }
 
@@ -445,7 +445,7 @@ val g = { ->
 };
 return g();
 """);
-        try { code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { code.driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) { assertEquals("No defined return type",e.getMessage()); }
     }
 
@@ -459,7 +459,7 @@ 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().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("Stop[ return #2; return Phi(Region,0,1,#2); ]", code.print());
         assertEquals("1", Eval2.eval(code, 0));
         assertEquals("0", Eval2.eval(code, 1));
@@ -481,7 +481,7 @@ for(;;) {
     if (s) return s.f;
 }
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck().GCM();
+        code.driver(CodeGen.Phase.FinalizeIR).driver(CodeGen.Phase.Schedule);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  0));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter19Test.java
index 2763e53d..6f290279 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter19Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -37,7 +37,7 @@ public class Chapter19Test {
         CodeGen code = new CodeGen("""
 return 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  2));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index 9f537fe7..0458941e 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -69,7 +69,7 @@ return f(s);
         // The entry of g can disappear before its Return is folded into f.
         // Exercise both worklist orders; deleting the entry does not kill 123.
         for( int seed=0; seed<64; seed++ ) {
-            CodeGen code = new CodeGen(src,seed,true).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            CodeGen code = new CodeGen(src,seed,true).driver(CodeGen.Phase.TypeCheck);
             assertEquals("seed "+seed, "123", Eval2.eval(code,0));
         }
     }
@@ -92,7 +92,7 @@ return f(s);
     @Test
     public void testJig() {
         CodeGen code = new CodeGen("return 0;");
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 0;", code.print());
         assertEquals("0", Eval2.eval(code,  2));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter21Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter21Test.java
index 83342ab8..07ae42eb 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter21Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter21Test.java
@@ -48,7 +48,7 @@ public class Chapter21Test {
                 else if(i==4) b.x=40;
             }
             return sum;
-            """).parse().iter().opto().iterPostOpto().finalizeIR();
+            """).driver(CodeGen.Phase.FinalizeIR);
         // The i==2 read still sees 10: three reads of 10, then three of 30.
         assertEquals("120",Eval2.eval(code,0));
         assertEquals("60",Eval2.eval(code,1));
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
index cbb08438..00d77f65 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter22Test.java
@@ -88,7 +88,7 @@ public class Chapter22Test {
 
     @Test public void testSubZeroTypeError() {
         try {
-            new CodeGen("return null-0;").parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            new CodeGen("return null-0;").driver(CodeGen.Phase.TypeCheck);
             fail("Subtraction must reject null even when the other operand is zero");
         } catch( Parser.ParseException e ) {
             assertEquals("Cannot null - 0",e.getMessage());
@@ -283,7 +283,7 @@ aa.c = cc;
 bb.c = cc;
 return cc.cz;
 """;
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 25;", code.print());
         assertEquals("25", Eval2.eval(code, 0));
     }
@@ -322,7 +322,7 @@ return 0;
     @Test
     public void testStrLoad() {
         CodeGen code = new CodeGen("return \"abc\"[1];");
-        code.parse().iter().opto().iterPostOpto().finalizeIR();
+        code.driver(CodeGen.Phase.FinalizeIR);
         assertEquals("return .[];", code.print());
     }
 
@@ -342,7 +342,7 @@ val _sum = { i32[~] is ->  // final array
 };
 return _sum(is);
 """;
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Phi(Loop,0,(Phi_sum+.[]));", code.print());
         assertEquals("14", Eval2.eval(code, 0));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter23Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter23Test.java
index b5da4d91..df02d3b4 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter23Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter23Test.java
@@ -120,10 +120,10 @@ return a && b ? 0 : 1;  // Expected answer 0
 
     @Test
     public void testLogicalValueSemantics() {
-        assertEquals("42", Eval2.eval(new CodeGen("return 7 && 42;").parse().iter().opto().iterPostOpto().finalizeIR(), 0));
-        assertEquals("0",  Eval2.eval(new CodeGen("return 0 && 42;").parse().iter().opto().iterPostOpto().finalizeIR(), 0));
-        assertEquals("7",  Eval2.eval(new CodeGen("return 7 || 42;").parse().iter().opto().iterPostOpto().finalizeIR(), 0));
-        assertEquals("42", Eval2.eval(new CodeGen("return 0 || 42;").parse().iter().opto().iterPostOpto().finalizeIR(), 0));
+        assertEquals("42", Eval2.eval(new CodeGen("return 7 && 42;").driver(CodeGen.Phase.FinalizeIR), 0));
+        assertEquals("0",  Eval2.eval(new CodeGen("return 0 && 42;").driver(CodeGen.Phase.FinalizeIR), 0));
+        assertEquals("7",  Eval2.eval(new CodeGen("return 7 || 42;").driver(CodeGen.Phase.FinalizeIR), 0));
+        assertEquals("42", Eval2.eval(new CodeGen("return 0 || 42;").driver(CodeGen.Phase.FinalizeIR), 0));
     }
 
     @Test
@@ -133,7 +133,7 @@ struct S {};
 S? s = arg ? new S;
 return !(!s || !arg) ? 1 : 0;
 """);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        code.driver(CodeGen.Phase.TypeCheck);
         assertEquals("0", Eval2.eval(code, 0));
         assertEquals("1", Eval2.eval(code, 1));
     }
@@ -146,7 +146,7 @@ struct S { !S? !fld; new S = { !S? f -> fld=f; }; };
 val ptr = arg == 1 ? null : new S(arg==1 ? null : new S(null));
 return ptr && ptr.fld ? "true" : "false";
 """;
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("true", Eval2.eval(code, 0));
 
         // Evaluate on RISC5 emulator
@@ -276,7 +276,7 @@ struct _Scan {
 return _s.peek('q');
 """;
 
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return Phi(Region,0,1);", code.print());
         assertEquals("1", Eval2.eval(code, 0));
         testCPU(src,"x86_64_v2", "win64",23,null);
@@ -301,7 +301,7 @@ struct _Scan {
 return s.skip().x;
 """;
 
-        try { new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck(); fail(); }
+        try { new CodeGen(src).driver(CodeGen.Phase.TypeCheck); fail(); }
         catch( Exception e ) {
             // Bad error message, but basically requires a mutable 'x' field.
             org.junit.Assert.assertTrue(e.getMessage().startsWith("Argument #0 isa"));
@@ -331,7 +331,7 @@ struct _Scan {
 return _s.require('[');
 """;
 
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return (.[]==91);", code.print());
         assertEquals("1", Eval2.eval(code, 0));
         testCPU(src,"x86_64_v2", "win64",4, null);
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
index 4bfb0d30..2f125ed0 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
@@ -257,7 +257,7 @@ while (cnt) {
 }
 return x;
 """;
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
     }
 
@@ -272,7 +272,7 @@ while( cnt-- )
     x = 2-x;
 return x;
 """;
-        CodeGen code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals("return 1;", code.print());
     }
 
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
index 4e8effbe..275be96a 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
@@ -28,6 +28,36 @@ import static org.junit.Assert.*;
 
 public class Chapter25Test {
 
+    @Test public void testFlagSpills() throws IOException {
+        com.seaofnodes.simple.codegen.FlagSpillTestSupport.run();
+    }
+
+    @Ignore
+    @Test
+    public void testJig() {
+        String src = "{ i32 -> i32 } close = \"C\"; val main = { u8[] a -> if (a# > 1) return close(0);  return a[0]; };";
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.Encoding,"riscv","SystemV");
+        assertEquals("return (arg+3);", code.print());
+        assertEquals("3",Eval2.eval(code,0));
+    }
+
+    @Test public void testConditionalClassInitX86() throws IOException {
+        Path build=Path.of("build/objs");
+        Files.createDirectories(build);
+        Path dir=Files.createTempDirectory(build,"init_flags_");
+        // Keep B separately compiled so its first-touch check survives.
+        new CodeGen(null,dir.toString(),null,"B","int value=17+arg;",123,true,TypeInteger.BOT)
+            .driver("x86_64_v2","win64",false,false);
+        // GCM can hoist the fused B.$init compare above the test of take.
+        // Its flags then cross another flag definition and need a legal split.
+        new CheckedCodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+            "Main","val run={int take -> return take ? B.value : 0; };",123,true,TypeInteger.BOT)
+            .driver(CodeGen.Phase.Encoding,"x86_64_v2","win64");
+        // Remove successful fixtures; preserve the object if compilation fails.
+        Files.delete(dir.resolve("B.o"));
+        Files.delete(dir);
+    }
+
     @Test public void testPublicInstanceMethod() {
         String src = """
             struct Scan {
@@ -63,15 +93,6 @@ public class Chapter25Test {
         }
     }
 
-    @Ignore
-    @Test
-    public void testJig() {
-        String src = "int x = arg/17; if( arg == 0 ) return arg + x; return arg + x;";
-        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
-        assertEquals("return (arg+3);", code.print());
-        assertEquals("3",Eval2.eval(code,0));
-    }
-
     @Test public void testNeverReturnPointerRiscV() {
         new CodeGen("""
             struct _S { int x; };
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/ClassInitDependenciesTest.java b/chapter25/src/test/java/com/seaofnodes/simple/ClassInitDependenciesTest.java
index cc010668..47e10f97 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/ClassInitDependenciesTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/ClassInitDependenciesTest.java
@@ -433,6 +433,88 @@ public class ClassInitDependenciesTest {
         assertEquals(1,stores[0]);
     }
 
+    @Test public void testInitializationExecution() throws Exception {
+        Path dir=tempDir("execution-");
+        object(dir,dir,"State","int count=0;");
+        object(dir,dir,"B","State.count++; int value=17+arg;");
+        String src="int value=arg ? B.value+B.value : 0; return value+100*State.count;";
+        for( long seed : new long[]{1,123,987654321} ) {
+            CodeGen code=new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+                "Main",src,seed,true,TypeInteger.BOT).driver(CodeGen.Phase.TypeCheck);
+            assertNotNull(code._stop.walk(n -> n instanceof CLInitNode ? n : null));
+            assertEquals("0",Eval2.eval(code,0));
+            assertNull(code._stop.walk(n -> n instanceof CLInitNode ? n : null));
+            assertEquals("134",Eval2.eval(code,1));
+        }
+
+        object(dir,dir,"Main","val run={int take -> "+src.replace("arg ?","take ?")+" };");
+        Path cfile=dir.resolve("check.c");
+        Files.writeString(cfile,"""
+            #include <stdint.h>
+            __attribute__((CALL_CONV)) extern int64_t run(int64_t take);
+            int main(void) {
+                return run(0)!=0 || run(1)!=134 || run(1)!=134 || run(0)!=100;
+            }
+            """);
+        String exe=dir.resolve(TestC.OS.startsWith("Windows") ? "check.exe" : "check").toString();
+        TestC.linkExe(dir.resolve("Main.o").toString(),TestC.CALL_CONVENTION.equals("win64") ? "ms_abi" : "sysv_abi",
+            cfile.toString(),new Ary<>(new String[]{dir.resolve("B.o").toString(),dir.resolve("State.o").toString()}),exe);
+        assertEquals("",TestC.exec(exe));
+        for( String cpu : new String[]{"arm","riscv"} )
+            new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+                "Main",src,123,true,TypeInteger.BOT).driver(CodeGen.Phase.Encoding,cpu,"SystemV");
+    }
+
+    @Test public void testParentInitializationExecution() throws Exception {
+        Path dir=tempDir("execution-");
+        object(dir,dir,"State","int count=0;");
+        module(dir,dir,"P",Map.of("P","val C=C; State.count=State.count*10+1;",
+            "P/C","State.count=State.count*10+2; int value=arg;"));
+        for( long seed : new long[]{1,123,987654321} ) {
+            CodeGen code=new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+                "Main","return P.C.value+State.count;",seed,true,TypeInteger.BOT).driver(CodeGen.Phase.TypeCheck);
+            assertEquals("12",Eval2.eval(code,99));
+        }
+        object(dir,dir,"Main","val run={ -> P.C.value+State.count; };");
+        Path cfile=dir.resolve("check.c");
+        Files.writeString(cfile,"""
+            #include <stdint.h>
+            __attribute__((CALL_CONV)) extern int64_t run(void);
+            int main(void) { return run()!=12 || run()!=12; }
+            """);
+        String exe=dir.resolve(TestC.OS.startsWith("Windows") ? "check.exe" : "check").toString();
+        TestC.linkExe(dir.resolve("Main.o").toString(),TestC.CALL_CONVENTION.equals("win64") ? "ms_abi" : "sysv_abi",
+            cfile.toString(),new Ary<>(new String[]{dir.resolve("P.o").toString(),dir.resolve("State.o").toString()}),exe);
+        assertEquals("",TestC.exec(exe));
+    }
+
+    @Test public void testNonreturningObject() throws Exception {
+        Path dir=tempDir("nonreturning-");
+        object(dir,dir,"Spin","val spin_noInline={ -> while(1) {} return 7; };");
+        CodeGen code=new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+            "Main","Spin.spin_noInline(); return 7;",123,true,TypeInteger.BOT).driver(CodeGen.Phase.TypeCheck);
+        assertNull(Eval2.eval(code,0,10));
+    }
+
+    @Test public void testImportedPrivateInitializer() throws Exception {
+        Path dir=tempDir("private-");
+        module(dir,dir,"Library",Map.of("Library","val read={ -> _Hidden.value; };",
+            "Library/_Hidden","int value=17+arg;"));
+        CodeGen code=new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+            "Main","return Library.read();",123,true,TypeInteger.BOT).driver(CodeGen.Phase.TypeCheck);
+        assertEquals("17",Eval2.eval(code,99));
+        // Even a request stopping at Select must drop imported bodies. They
+        // remain available only to the ideal evaluator above, not this object.
+        for( String cpu : new String[]{"x86_64_v2","arm","riscv"} ) {
+            CodeGen selected=new CodeGen(null,dir.toString(),new Ary<>(new String[]{dir.toString()}),
+                "Main","return Library.read();",123,true,TypeInteger.BOT).driver(CodeGen.Phase.Select,cpu,"SystemV");
+            assertNull(selected._serial);
+            for( CompUnit cu : selected._compunits.values() )
+                if( cu._src==null ) assertNull(cu._stop);
+            selected.driver(CodeGen.Phase.Encoding,cpu,"SystemV");
+        }
+    }
+
     @Test public void testOverlappingFunctionAndClassCycles() throws Exception {
         // Fixed function graph: Opto/inlining must not erase the overlap that
         // exercises SCC traversal. One clinit is legal, two in the SCC are not.
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java b/chapter25/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
index db41363a..e2d822d0 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
@@ -88,7 +88,7 @@ public class CompoundAssignmentTest {
     }
 
     private static void check(String src, long arg, long expected) {
-        var code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        var code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals(src, Long.toString(expected), Eval2.eval(code, arg));
     }
 }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Eval2.java b/chapter25/src/test/java/com/seaofnodes/simple/Eval2.java
index 21e677ce..366bd7f4 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Eval2.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Eval2.java
@@ -114,6 +114,9 @@ public abstract class Eval2 {
     // Current active Frame, to avoid having to pass it everywhere
     public static Frame F;
 
+    // Class pointers and initializer self parameters share one object per run.
+    private static final HashMap<String,Object[]> CLASSES = new HashMap<>();
+
     public static String eval( CodeGen code, long arg ) { return eval(code,arg,1000); }
     public static String eval( CodeGen code, long arg, int timeout ) {
         if( code._start.uctrl()==null ) return ""; // The empty program
@@ -122,6 +125,7 @@ public abstract class Eval2 {
         code.driver(CodeGen.Phase.LocalSched);
         // Set global, so don't have to pass everywhere
         CODE = code;
+        CLASSES.clear();
 
         // Timer for when we run too long.  Ticks once per backedge or function call
         int loopCnt = 0;
@@ -140,7 +144,7 @@ public abstract class Eval2 {
                 TypeStruct clz = ((TypeMemPtr)fun.sig().arg(0))._obj;
                 // Map from the <clinit> self parameter to the
                 // singleton class structure.
-                F.put(fun.parm(2),alloc(clz));
+                F.put(fun.parm(2),classObject(clz));
             }
 
 
@@ -203,9 +207,9 @@ public abstract class Eval2 {
 
             // Parms read from Call args -
             // - except RPC is the actual prior frame
-            // - except <clinit> takes the singleton class object and external args
+            // - except entry <clinit> takes the external program argument
             Object val;
-            if( isClz && phi instanceof ParmNode parm && parm._idx==3 )
+            if( isClz && prior instanceof StartNode && phi instanceof ParmNode parm && parm._idx==3 )
                 PHICACHE[i] = arg; // Reading the initial arguments to <clinit>
             else {
                 Node n = phi instanceof ParmNode parm
@@ -349,6 +353,8 @@ public abstract class Eval2 {
                     yield new Object[0];
                 }
 
+            } else if( Parser.startsClzPrefix(tmp._obj._name) ) {
+                yield classObject(tmp._obj);
             } else {
                 // Constant object with all zeros
                 yield alloc(tmp._obj);
@@ -417,6 +423,12 @@ public abstract class Eval2 {
         return ptr;
     }
 
+    private static Object[] classObject(TypeStruct type) {
+        Object[] ptr = CLASSES.get(type._name);
+        if( ptr==null ) CLASSES.put(type._name,ptr=alloc(type));
+        return ptr;
+    }
+
     private static Object not( NotNode not ) {
         Object n = val(not.in(1));
         return ( n==null || (n instanceof Double D && D==0.0) || n instanceof Long L && L==0 )
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Main.java b/chapter25/src/test/java/com/seaofnodes/simple/Main.java
index 97129f5b..1248a6cf 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Main.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Main.java
@@ -11,7 +11,7 @@ public class Main {
         String src = Files.readString(Path.of(args[0]));
         int arg = Integer.valueOf(args[1]);
         CodeGen code = new CodeGen(src);
-        code.parse().iter().opto().iterPostOpto().finalizeIR().typeCheck().GCM().localSched();
+        code.driver(CodeGen.Phase.FinalizeIR).driver(CodeGen.Phase.Schedule).localSched();
         System.out.println(code._stop);
         System.out.println(Eval2.eval(code,arg,100000));
     }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java b/chapter25/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
index 4934c91f..adeba136 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
@@ -58,7 +58,7 @@ public class MemoryEncodingTest {
         // Exercise both unresolved Store aliases and nested value-Phi cleanup.
         for( long seed : new long[]{0,9,126} )
             for( int p=0; p<sources.length; p++ ) {
-                CodeGen code=new CodeGen(sources[p],seed,true).parse().iter().opto().iterPostOpto().finalizeIR();
+                CodeGen code=new CodeGen(sources[p],seed,true).driver(CodeGen.Phase.FinalizeIR);
                 if( p==0 ) assertNull(code._stop.walk(n ->
                     n instanceof LoadNode ld && ld.ptr() instanceof ProjNode ptr &&
                     ptr.in(0) instanceof NewNode nn &&
@@ -86,7 +86,7 @@ public class MemoryEncodingTest {
             if (arg>1) { v=p.x; p.x=41; p.y=5; }
             else       { v=q.x; q.x=42; }
             return v;
-            """).parse().iter().opto().iterPostOpto().finalizeIR();
+            """).driver(CodeGen.Phase.FinalizeIR);
         StopNode stop = code._stop;
         assertEquals(2,countMemoryNodes(stop,LoadNode.class,new BitSet()));
         assertEquals("-1",Eval2.eval(code,-1));
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/MutabilityTest.java b/chapter25/src/test/java/com/seaofnodes/simple/MutabilityTest.java
index 9727857e..8bd77c06 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/MutabilityTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/MutabilityTest.java
@@ -6,12 +6,12 @@ import com.seaofnodes.simple.codegen.CodeGen;
 
 public class MutabilityTest {
     private static void ok(String src, String result) {
-        var code = new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+        var code = new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         assertEquals(result,Eval2.eval(code,0));
     }
     private static void bad(String src) {
         try {
-            new CodeGen(src).parse().iter().opto().iterPostOpto().finalizeIR().typeCheck();
+            new CodeGen(src).driver(CodeGen.Phase.TypeCheck);
         } catch( RuntimeException expected ) {
             String msg = expected.getMessage();
             assertTrue("Expected a permission error, got: "+expected,
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/PhaseTest.java b/chapter25/src/test/java/com/seaofnodes/simple/PhaseTest.java
new file mode 100644
index 00000000..7252378a
--- /dev/null
+++ b/chapter25/src/test/java/com/seaofnodes/simple/PhaseTest.java
@@ -0,0 +1,64 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.graph.GraphObserver;
+import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.codegen.CodeGen.Phase;
+import com.seaofnodes.simple.node.Node;
+import java.util.ArrayList;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class PhaseTest {
+    private static final String SRC = "int sum=0; for(int i=0; i<arg; i++) sum+=i; return sum;";
+
+    @Test public void testIdealPhasesAndResume() {
+        ArrayList<String> phases = new ArrayList<>();
+        CodeGen code = new CodeGen(SRC);
+        code._obs = new GraphObserver<Node>() {
+            @Override public void before(Node n) {}
+            @Override public void after(Node n, Node repl, boolean applied) {}
+            @Override public void phase(String phase) { phases.add(phase); }
+        };
+        code.driver(Phase.TypeCheck);
+        code.driver(Phase.TypeCheck); // A repeated request does not rerun anything.
+        code.driver(Phase.LocalSched);
+        assertEquals("Parse Iter Opto IterPostOpto FinalizeIR TypeCheck Lower LoopTree Unlink Schedule LocalSched",
+                     String.join(" ",phases));
+        assertNull(code._serial);
+        assertNull(code._mach);
+        assertEquals("45",Eval2.eval(code,10));
+    }
+
+    @Test public void testEncodingWithoutSerialization() {
+        for( String cpu : new String[]{"x86_64_v2","arm","riscv"} ) {
+            CodeGen code = new CodeGen(SRC).driver(Phase.TypeCheck);
+            code.driver(Phase.Unlink,cpu,"SystemV");
+            code.driver(Phase.Select,cpu,"SystemV");
+            code.driver(Phase.Encoding,cpu,"SystemV");
+            assertNull(code._serial);
+            byte[] staged = code._encoding._bits.toByteArray();
+            CodeGen direct = new CodeGen(SRC).driver(Phase.Encoding,cpu,"SystemV");
+            assertArrayEquals(staged,direct._encoding._bits.toByteArray());
+        }
+    }
+
+    @Test public void testExplicitSerializationAndMemoryExport() {
+        CodeGen code = new CodeGen(SRC).driver(Phase.Serialize);
+        assertNotNull(code._serial);
+        assertEquals(Phase.Serialize,code._phase);
+        code.driver(Phase.Encoding,"riscv","SystemV");
+        assertNotNull(code._serial);
+
+        CodeGen memory = new CodeGen(SRC).driver("riscv","SystemV",true,false);
+        assertNull(memory._serial);
+        assertEquals(Phase.Export,memory._phase);
+
+        CodeGen late = new CodeGen(SRC).driver(Phase.Encoding,"riscv","SystemV");
+        try {
+            late.exportELF(false,false);
+            fail("Cannot recover ideal IR after lowering and instruction selection");
+        } catch( IllegalStateException expected ) {
+            assertTrue(expected.getMessage().contains("Serialize before Lower"));
+        }
+    }
+}
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Simple.java b/chapter25/src/test/java/com/seaofnodes/simple/Simple.java
index 9078a33a..2d688bbe 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Simple.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Simple.java
@@ -49,6 +49,7 @@ Options:
   --dump-after-iter-post-opto - dump after SCCP-driven peepholes and inlining
   --dump-after-finalize-ir - dump after field layout and IR finalization
   --dump-after-type-check  - dump intermediate representation after type check pass
+  --dump-after-lower       - dump expanded class initialization before loop trees
   --dump-after-select      - dump intermediate representation after instruction selection pass
   --dump-after-gcm         - dump intermediate representation after GCM pass
   --dump-after-local-sched - dump intermediate representation after local scheduling pass
@@ -119,6 +120,7 @@ Options:
             case "--dump-after-iter-post-opto": dump |= 1<<Phase.IterPostOpto.ordinal(); break;
             case "--dump-after-finalize-ir":  dump |=  1<<Phase.FinalizeIR.ordinal()   ; break;
             case "--dump-after-type-check":   dump |=  1<<Phase.TypeCheck .ordinal()   ; break;
+            case "--dump-after-lower":        dump |=  1<<Phase.Lower     .ordinal()   ; break;
             case "--dump-after-loop-tree":    dump |=  1<<Phase.LoopTree  .ordinal()   ; break;
             case "--dump-after-select":       dump |=  1<<Phase.Select    .ordinal()   ; break;
             case "--dump-after-gcm":          dump |=  1<<Phase.Schedule  .ordinal()   ; break;
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/StaticDataTest.java b/chapter25/src/test/java/com/seaofnodes/simple/StaticDataTest.java
index 070b7a9e..03df05a7 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/StaticDataTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/StaticDataTest.java
@@ -2,6 +2,9 @@ package com.seaofnodes.simple;
 
 import com.seaofnodes.simple.codegen.CodeGen;
 import com.seaofnodes.simple.codegen.StaticData;
+import com.seaofnodes.simple.node.ConstantNode;
+import com.seaofnodes.simple.node.StoreNode;
+import com.seaofnodes.simple.type.TypeMem;
 import com.seaofnodes.simple.type.TypeStruct;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.util.Ary;
@@ -16,14 +19,25 @@ public class StaticDataTest {
     private static final String SRC="val n=42; val f={int x -> x+n;}; return 0;";
 
     private static StaticData.ObjectData root(CodeGen code) {
-        return code._encoding._data.entries().stream()
-            .filter(obj -> obj.symbol.endsWith("Test.$class")).findFirst().orElseThrow();
+        for( var obj : code._encoding._data.entries() )
+            if( obj.symbol.endsWith("Test.$class") ) return obj;
+        throw new AssertionError("Missing Test class object");
     }
 
     // Read the image before <clinit>, then call the function through its data slot.
     @Test public void testEmulatorImage() {
         for( String cpu : new String[]{"arm","riscv"} ) {
-            CodeGen code=new CodeGen(SRC).driver(cpu,"SystemV",true,false);
+            CodeGen code=new CodeGen(SRC).driver(CodeGen.Phase.TypeCheck);
+            assertNull("Constant fields fold before instruction selection",
+                       code._stop.walk(n -> n instanceof StoreNode st &&
+                           (st._name.equals("n") || st._name.equals("f")) ? n : null));
+            assertNotNull(code._stop.walk(n -> n instanceof ConstantNode &&
+                n._type instanceof TypeMem mem && mem.isConstant() &&
+                mem._t==TypeInteger.constant(42) ? n : null));
+            assertNotNull("The runtime initialization flag still needs its Store",
+                          code._stop.walk(n -> n instanceof StoreNode st &&
+                              st._name.equals("$init") ? n : null));
+            code.driver(cpu,"SystemV",true,false);
             var e=code._encoding;
             var obj=root(code);
             TypeStruct ts=(TypeStruct)obj.type;
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/codegen/FlagSpillTestSupport.java b/chapter25/src/test/java/com/seaofnodes/simple/codegen/FlagSpillTestSupport.java
new file mode 100644
index 00000000..445acb61
--- /dev/null
+++ b/chapter25/src/test/java/com/seaofnodes/simple/codegen/FlagSpillTestSupport.java
@@ -0,0 +1,141 @@
+package com.seaofnodes.simple.codegen;
+
+import com.seaofnodes.isa.X86;
+import com.seaofnodes.isa.eval.EvalArm64;
+import com.seaofnodes.simple.TestC;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.node.cpus.arm.arm;
+import com.seaofnodes.simple.node.cpus.x86_64_v2.x86_64_v2;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import static org.junit.Assert.*;
+
+// Force overlapping flags, then force every GPR unavailable across the gap.
+public class FlagSpillTestSupport {
+    private static class Op extends MachConcreteNode {
+        final RegMask _def, _use, _kill;
+        Op(RegMask def,RegMask use,RegMask kill,Node... ins) {
+            super(ins); _def=def; _use=use; _kill=kill; _type=TypeInteger.BOT;
+        }
+        @Override public String op() { return "flagsProbe"; }
+        @Override public RegMask outregmap() { return _def; }
+        @Override public RegMask regmap(int i) { return _use; }
+        @Override public RegMask killmap() { return _kill; }
+        @Override public void encoding(Encoding enc) { throw new AssertionError(); }
+    }
+
+    public static void run() throws IOException {
+        StringBuilder asm = new StringBuilder(".text\n");
+        for( boolean isArm : new boolean[]{false,true} )
+            for( boolean stack : new boolean[]{false,true} ) {
+                CodeGen code = new CodeGen("");
+                code._callingConv="SystemV";
+                code._mach=isArm ? new arm(code) : new x86_64_v2(code);
+                RegionNode block = new RegionNode(null,code._start,code._start);
+                code._cfg.add(block);
+                int flagsReg=isArm ? 64 : 32, firstStack=flagsReg+1;
+                RegMask flags = new RegMask(flagsReg);
+                Op def = new Op(flags,null,null,block);
+                RegMask killMask = stack ? (isArm ? new RegMask(0x7fffffffL,1L) : new RegMask(0x1ffffffefL)) : flags;
+                Op kill = new Op(null,null,killMask,block);
+                new Op(null,flags,null,block,def);
+                RegAlloc alloc = new RegAlloc(code);
+                alloc.regAlloc();
+
+                int splits=0, slots=0;
+                for( Node n : block._outputs ) if( n instanceof SplitNode split ) {
+                    int dst=alloc.regnum(n), src=alloc.regnum(n.in(1));
+                    assertTrue(split.outregmap().test(dst));
+                    assertTrue(split.regmap(1).test(src));
+                    for( int fp=isArm ? 32 : 16; fp<flagsReg; fp++ ) {
+                        assertFalse("FP output allowed",split.outregmap().test(fp));
+                        assertFalse("FP input allowed",split.regmap(1).test(fp));
+                    }
+                    if( dst>=firstStack || src>=firstStack ) slots++;
+                    splits++;
+                }
+                assertTrue(splits>=2);
+                assertEquals(stack,slots!=0);
+
+                // Keep the allocated registers, supplying a frame for encoding stack offsets.
+                FunNode frame = new FunNode(null,null,"flags",null,(Node)null);
+                code._regAlloc=new RegAlloc(code);
+                for( Node n : block._outputs )
+                    if( alloc.regnum(n)>=0 ) code._regAlloc.newLRG(n,frame)._reg=alloc.regnum(n);
+                Encoding save = new Encoding(code), restore = new Encoding(code);
+                Encoding enc = save;
+                for( Node n : block._outputs ) {
+                    if( n==kill ) enc=restore;
+                    if( n instanceof SplitNode split ) split.encoding(enc);
+                }
+                if( isArm ) {
+                    for( int bits=0; bits<16; bits++ ) {
+                        EvalArm64 cpu = new EvalArm64(new byte[1024],512);
+                        System.arraycopy(save._bits.buf(),0,cpu._buf,0,save._bits.size());
+                        System.arraycopy(restore._bits.buf(),0,cpu._buf,save._bits.size(),restore._bits.size());
+                        cpu.N=(bits&8)!=0; cpu.Z=(bits&4)!=0; cpu.C=(bits&2)!=0; cpu.V=(bits&1)!=0;
+                        assertEquals(0,cpu.step(save._bits.size()/4));
+                        cpu.N=cpu.Z=cpu.C=cpu.V=false;
+                        if( stack ) for( int r=0; r<31; r++ ) cpu.regs[r]=0;
+                        assertEquals(0,cpu.step(restore._bits.size()/4));
+                        assertEquals((bits&8)!=0,cpu.N); assertEquals((bits&4)!=0,cpu.Z);
+                        assertEquals((bits&2)!=0,cpu.C); assertEquals((bits&1)!=0,cpu.V);
+                        assertEquals(512,cpu.regs[31]);
+                    }
+                } else {
+                    Encoding body = new Encoding(code);
+                    int[] preserved={3,5,6,7,12,13,14,15};
+                    for( int r : preserved ) pushPop(body,r,false);
+                    X86.imm(body,0x81,5,4,16); // Reserve spill storage.
+                    X86.flags(body,TestC.OS.startsWith("Windows") ? 1 : 7,true);
+                    bytes(body,save);
+                    if( stack ) {
+                        for( int r=0; r<16; r++ ) if( r!=4 ) X86.constant(body,r,0);
+                    } else X86.reg(body,0x39,0,0); // CMP rax,rax clobbers only flags.
+                    bytes(body,restore);
+                    X86.flags(body,0,false); // Return the restored flags.
+                    X86.imm(body,0x81,0,4,16);
+                    for( int i=preserved.length-1; i>=0; i-- ) pushPop(body,preserved[i],true);
+                    X86.ret(body);
+                    String name=stack ? "flags_stack" : "flags_reg";
+                    asm.append(".globl ").append(name).append('\n').append(name).append(":\n.byte ");
+                    for( int i=0; i<body._bits.size(); i++ ) {
+                        if( i!=0 ) asm.append(',');
+                        asm.append(body._bits.buf()[i]&255);
+                    }
+                    asm.append('\n');
+                }
+            }
+        Path dir=Files.createTempDirectory(Path.of("build/objs"),"flag_spills_");
+        Files.writeString(dir.resolve("flags.s"),asm);
+        Files.writeString(dir.resolve("flags.c"),"""
+            typedef unsigned long long u64;
+            u64 __attribute__((CALL_CONV)) flags_reg(u64);
+            u64 __attribute__((CALL_CONV)) flags_stack(u64);
+            int main(void) {
+                const int positions[]={0,2,4,6,7,11};
+                for(int bits=0; bits<64; bits++) {
+                    u64 flags=0x202;
+                    for(int i=0;i<6;i++) if(bits&(1<<i)) flags|=1ULL<<positions[i];
+                    if((flags_reg(flags)&0x8d5)!=(flags&0x8d5)) return 1;
+                    if((flags_stack(flags)&0x8d5)!=(flags&0x8d5)) return 2;
+                }
+                return 0;
+            }
+            """);
+        String exe=dir.resolve(TestC.OS.startsWith("Windows") ? "flags.exe" : "flags").toString();
+        TestC.exec("gcc","-DCALL_CONV="+(TestC.OS.startsWith("Windows") ? "ms_abi" : "sysv_abi"),
+            "-o",exe,dir.resolve("flags.c").toString(),dir.resolve("flags.s").toString());
+        TestC.exec(exe);
+    }
+
+    private static void bytes(Encoding dst,Encoding src) {
+        for( int i=0; i<src._bits.size(); i++ ) dst.add1(src._bits.buf()[i]&255);
+    }
+    private static void pushPop(Encoding enc,int reg,boolean pop) {
+        if( reg>=8 ) enc.add1(0x41);
+        enc.add1((pop ? 0x58 : 0x50)+(reg&7));
+    }
+}
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java b/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
index 93380c87..292f1ae7 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
@@ -29,6 +29,12 @@ public class RegAllocTestSupport {
         return code;
     }
 
+    private static SplitNode testSplit(CodeGen code, MachNode def) {
+        LRG lrg = new LRG((short)0,null);
+        lrg._machDef = def;
+        return code._mach.split(lrg,"test",(byte)0);
+    }
+
     public static void uncoloredFixedNeighbor() throws Exception {
         CodeGen code = graph();
         RegAlloc alloc = new RegAlloc(code);
@@ -225,11 +231,11 @@ public class RegAllocTestSupport {
             RegAlloc alloc = new RegAlloc(code);
             Op def = new Op(A,null,null,false,code._start);
             alloc.newLRG(def,null)._reg=0;
-            SplitNode hi = code._mach.split(null,"test",(byte)0);
+            SplitNode hi = testSplit(code,def);
             hi.setDef(0,code._start); hi.setDef(1,def);
             alloc.newLRG(hi,null)._reg=1;
             new Op(null,null,killed ? A : null,false,code._start);
-            SplitNode lo = code._mach.split(null,"test",(byte)0);
+            SplitNode lo = testSplit(code,hi);
             lo.setDef(0,code._start); lo.setDef(1,hi);
             alloc.newLRG(lo,null)._reg=0;
             Op use = new Op(null,A,null,false,code._start,lo);
@@ -243,7 +249,7 @@ public class RegAllocTestSupport {
         uncolored.newLRG(def0,null)._mask=A;
         Op fixed = new Op(A,null,null,false,pre._start);
         uncolored.newLRG(fixed,null)._mask=A;
-        SplitNode copy = pre._mach.split(null,"test",(byte)0);
+        SplitNode copy = testSplit(pre,def0);
         copy.setDef(0,pre._start); copy.setDef(1,def0);
         assertFalse("A fixed definition clobbers even before coloring",uncolored.sameBlockNoClobber(copy));
     }
@@ -284,7 +290,7 @@ public class RegAllocTestSupport {
             RegAlloc alloc = new RegAlloc(code);
             Op def = new Op(A,null,null,false,code._start);
             alloc.newLRG(def,null)._reg=0;
-            SplitNode copy = code._mach.split(null,"test",(byte)0);
+            SplitNode copy = testSplit(code,def);
             copy.setDef(0,code._start); copy.setDef(1,def);
             alloc.newLRG(copy,null)._reg=1;
             if( kind==3 ) new Op(null,null,A,false,code._start);
@@ -307,7 +313,7 @@ public class RegAllocTestSupport {
             CodeGen code = graph();
             RegAlloc alloc = new RegAlloc(code);
             Op def = new Op(new RegMask(3L),null,null,false,code._start);
-            SplitNode copy = code._mach.split(null,"test",(byte)0);
+            SplitNode copy = testSplit(code,def);
             copy.setDef(0,code._start); copy.setDef(1,def);
             Op use = new Op(null,new RegMask(3L),null,false,code._start,copy);
             LRG from = alloc.newLRG(def,null), to = alloc.newLRG(copy,null);