Chapter 17: Syntax Sugarlinear-chapter17

21 files changed, 309 insertions, 214 deletions

diff --git a/src/main/java/com/seaofnodes/simple/node/AddNode.java b/src/main/java/com/seaofnodes/simple/node/AddNode.java
index f3b213fb..0834a381 100644
--- a/src/main/java/com/seaofnodes/simple/node/AddNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/AddNode.java
@@ -36,7 +36,7 @@ public class AddNode extends Node {
         return TypeInteger.BOT;
     }
 
-    private static boolean overflow( long x, long y ) {
+    static boolean overflow( long x, long y ) {
         if( (x ^    y ) < 0 ) return false; // unequal signs, never overflow
         return (x ^ (x + y)) < 0; // sum has unequal signs, so overflow
     }
diff --git a/src/main/java/com/seaofnodes/simple/node/CFGNode.java b/src/main/java/com/seaofnodes/simple/node/CFGNode.java
index 9e9d6970..052ad8fc 100644
--- a/src/main/java/com/seaofnodes/simple/node/CFGNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/CFGNode.java
@@ -28,15 +28,6 @@ public abstract class CFGNode extends Node {
     // Block head is Start, Region, CProj, but not e.g. If, Return, Stop
     public boolean blockHead() { return false; }
 
-    // Should be exactly 1 tail from a block head
-    public CFGNode blockTail() {
-        assert blockHead();
-        for( Node n : _outputs )
-            if( n instanceof CFGNode cfg )
-                return cfg;
-        return null;
-    }
-
     // ------------------------------------------------------------------------
     /**
      * Immediate dominator tree depth, used to approximate a real IDOM during
@@ -64,27 +55,78 @@ public abstract class CFGNode extends Node {
         return lhs;
     }
 
-    // Loop nesting depth
-    public int _loopDepth;
-    public int loopDepth() { return _loopDepth==0 ? (_loopDepth = cfg(0).loopDepth()) : _loopDepth; }
-
     // Anti-dependence field support
     public int _anti;           // Per-CFG field to help find anti-deps
 
     // ------------------------------------------------------------------------
-    // Support routines for Global Code Motion
+    // Loop nesting
+    public LoopNode loop() { return _ltree._head; }
+    public int loopDepth() { return _ltree==null ? 0 : _ltree.depth(); }
+
+    LoopTree _ltree;
+    int _pre;                   // Pre-order numbers for loop tree finding
+    private static class LoopTree {
+        LoopTree _par;
+        final LoopNode _head;
+        int _depth;
+        LoopTree(LoopNode head) { _head = head; }
+        @Override public String toString() { return "LOOP"+_head._nid; }
+        int depth() {
+            return _depth==0 ? (_par==null ? 0 : (_depth = _par.depth()+1)) : _depth;
+        }
+    }
 
-    // Tik-tok recursion pattern.  This method is final, and every caller does
-    // this work.
-    public final void walkUnreach( BitSet visit, HashSet<CFGNode> unreach ) {
-        if( visit.get(_nid) ) return;
-        visit.set(_nid);
-        _walkUnreach(visit,unreach);
-        unreach.remove(this); // Since we reached here... Node was not unreachable
+    // ------------------------------------------------------------------------
+    // Tag all CFG Nodes with their containing LoopNode; LoopNodes themselves
+    // also refer to *their* containing LoopNode, as well as have their depth.
+    // Start is a LoopNode which contains all at depth 1.
+    public void buildLoopTree(StopNode stop) {
+        _ltree = stop._ltree = Parser.XCTRL._ltree = new LoopTree((StartNode)this);
+        _bltWalk(2,stop, new BitSet());
     }
+    private int _bltWalk(int pre, StopNode stop, BitSet post) {
+        // Pre-walked?
+        if( _pre!=0 ) return pre;
+        _pre = pre++;
+        // Pre-walk
+        for( Node use : _outputs )
+            if( use instanceof CFGNode usecfg )
+                pre = usecfg._bltWalk(pre,stop,post);
 
-    // Tik-tok recursion pattern; not-final; callers override this.
-    void _walkUnreach( BitSet visit, HashSet<CFGNode> unreach ) {
-        cfg(0).walkUnreach(visit,unreach);
+        // Post-order work: find innermost loop
+        LoopTree inner = null, ltree;
+        for( Node use : _outputs ) {
+            if( !(use instanceof CFGNode usecfg) ) continue;
+            // Child visited but not post-visited?
+            if( !post.get(usecfg._nid) ) {
+                // Must be a backedge to a LoopNode then
+                ltree = usecfg._ltree = new LoopTree((LoopNode)usecfg);
+            } else {
+                // Take child's loop choice, which must exist
+                ltree = usecfg._ltree;
+                // If falling into a loop, use the target loop's parent instead
+                if( ltree._head == usecfg ) {
+                    if( ltree._par == null )
+                        // This loop never had an If test choose to take its
+                        // exit, i.e. it is a no-exit infinite loop.
+                        ltree._par = ltree._head.forceExit(stop)._ltree;
+                    ltree = ltree._par;
+                }
+            }
+            // Sort inner loops.  The decision point is some branch far removed
+            // from either loop head OR either backedge so requires pre-order
+            // numbers to figure out innermost.
+            if( inner == null ) { inner = ltree; continue; }
+            if( inner == ltree ) continue; // No change
+            LoopTree outer = ltree._head._pre > inner._head._pre ? inner : ltree;
+            inner =          ltree._head._pre > inner._head._pre ? ltree : inner;
+            inner._par = outer;
+        }
+        // Set selected loop
+        if( inner!=null )
+            _ltree = inner;
+        // Tag as post-walked
+        post.set(_nid);
+        return pre;
     }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/CProjNode.java b/src/main/java/com/seaofnodes/simple/node/CProjNode.java
index 3d6fd1fa..d2f1bbe1 100644
--- a/src/main/java/com/seaofnodes/simple/node/CProjNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/CProjNode.java
@@ -52,10 +52,6 @@ public class CProjNode extends CFGNode {
     }
 
     @Override
-    public Node getBlockStart() {
-        return ctrl() instanceof IfNode ? this : ctrl().getBlockStart();
-    }
-    @Override
     boolean eq( Node n ) { return _idx == ((CProjNode)n)._idx; }
 
     @Override
diff --git a/src/main/java/com/seaofnodes/simple/node/IfNode.java b/src/main/java/com/seaofnodes/simple/node/IfNode.java
index 3cce89ab..513b4721 100644
--- a/src/main/java/com/seaofnodes/simple/node/IfNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/IfNode.java
@@ -43,6 +43,9 @@ public class IfNode extends CFGNode implements MultiNode {
         // Else true branch is reachable
         if( t.isConstant() )
             return t.makeInit()==t ? TypeTuple.IF_FALSE : TypeTuple.IF_TRUE;
+        // Integers allow non-zero ranges: "1-65535"
+        if( t.makeZero().meet(t) != t )
+            return TypeTuple.IF_TRUE;
 
         return TypeTuple.IF_BOTH;
     }
@@ -60,12 +63,4 @@ public class IfNode extends CFGNode implements MultiNode {
         return null;
     }
 
-    @Override void _walkUnreach( BitSet visit, HashSet<CFGNode> unreach ) {
-        for( Node proj : _outputs )
-            if( ((CProjNode)proj)._loopDepth == 0 )
-                unreach.add((CProjNode)proj);
-        super._walkUnreach(visit,unreach);
-    }
-
-    @Override public Node getBlockStart() { return ctrl().getBlockStart(); }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/src/main/java/com/seaofnodes/simple/node/LoadNode.java
index d15d4f83..1528f2e9 100644
--- a/src/main/java/com/seaofnodes/simple/node/LoadNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -33,10 +33,13 @@ public class LoadNode extends MemOpNode {
 
     @Override
     public Type compute() {
-        if( mem()._type instanceof TypeMem mem &&
-            // No constant folding if ptr might null-check
-            _declaredType != mem._t && err()==null ) {
-            return  _declaredType.join(mem._t);
+        if( mem()._type instanceof TypeMem mem ) {
+            // Update declared forward ref to the actual
+            if( _declaredType.isFRef() && mem._t instanceof TypeMemPtr tmp && !tmp.isFRef() )
+                _declaredType = tmp;
+            // No lifting if ptr might null-check
+            if( err()==null )
+                return _declaredType.join(mem._t);
         }
         return _declaredType;
     }
@@ -60,13 +63,15 @@ public class LoadNode extends MemOpNode {
         // Load-after-Store on same address, but bypassing provably unrelated
         // stores.  This is a more complex superset of the above two peeps.
         // "Provably unrelated" is really weak.
+        if( ptr instanceof ReadOnlyNode ro )
+            ptr = ro.in(1);
         Node mem = mem();
         outer:
         while( true ) {
             switch( mem ) {
             case StoreNode st:
                 if( ptr == st.ptr() && off() == st.off() )
-                    return st.val(); // Proved equal
+                    return castRO(st.val()); // Proved equal
                 // Can we prove unequal?  Offsets do not overlap?
                 if( !off()._type.join(st.off()._type).isHigh() && // Offsets overlap
                     !neverAlias(ptr,st.ptr()) )                   // And might alias
@@ -79,11 +84,13 @@ public class LoadNode extends MemOpNode {
             case ProjNode mproj:
                 if( mproj.in(0) instanceof NewNode nnn1 ) {
                     if( ptr instanceof ProjNode pproj && pproj.in(0) == mproj.in(0) )
-                        return nnn1.in(nnn1.findAlias(_alias)); // Load from New init
+                        return castRO(nnn1.in(nnn1.findAlias(_alias))); // Load from New init
                     if( !(ptr instanceof ProjNode pproj && pproj.in(0) instanceof NewNode nnn2) )
                         break outer; // Cannot tell, ptr not related to New
                     mem = nnn1.in(_alias);// Bypass unrelated New
                     break;
+                } else if( mproj.in(0) instanceof StartNode ) {
+                    break outer;
                 } else throw Utils.TODO();
             default:
                 throw Utils.TODO();
@@ -98,7 +105,11 @@ public class LoadNode extends MemOpNode {
         //   else       ptr.x = e1;                    : e1;
         //   val = ptr.x;                   ptr.x = val;
         if( mem() instanceof PhiNode memphi && memphi.region()._type == Type.CONTROL && memphi.nIns()== 3 &&
-            off() instanceof ConstantNode ) {
+            // Offset can be hoisted
+            off() instanceof ConstantNode &&
+            // Pointer can be hoisted
+            hoistPtr(ptr,memphi)  ) {
+
             // Profit on RHS/Loop backedge
             if( profit(memphi,2) ||
                 // Else must not be a loop to count profit on LHS.
@@ -111,10 +122,12 @@ public class LoadNode extends MemOpNode {
 
         return null;
     }
+
     private Node ld( int idx ) {
         Node mem = mem(), ptr = ptr();
         return new LoadNode(_name,_alias,_declaredType,mem.in(idx),ptr instanceof PhiNode && ptr.in(0)==mem.in(0) ? ptr.in(idx) : ptr, off()).peephole();
     }
+
     private static boolean neverAlias( Node ptr1, Node ptr2 ) {
         return ptr1.in(0) != ptr2.in(0) &&
             // Unrelated allocations
@@ -122,6 +135,25 @@ public class LoadNode extends MemOpNode {
             ptr2 instanceof ProjNode && ptr2.in(0) instanceof NewNode;
     }
 
+    private static boolean hoistPtr(Node ptr, PhiNode memphi ) {
+        // Can I hoist ptr above the Region?
+        if( !(memphi.region() instanceof RegionNode r) )
+            return false;       // Dead or dying Region/Phi
+        // If ptr from same Region, then yes, just use hoisted split pointers
+        if( ptr instanceof PhiNode pphi && pphi.region() == r )
+            return true;
+
+        // No, so can we lift this ptr?
+        CFGNode cptr = ptr.cfg0();
+        if( cptr != null )
+            // Pointer is controlled high
+            // TODO: Really needs to be the LCA of all inputs is high
+            return cptr.idepth() <= r.idepth();
+
+        // Dunno without a longer walk
+        return false;
+    }
+
     // Profitable if we find a matching Store on this Phi arm.
     private boolean profit(PhiNode phi, int idx) {
         Node px = phi.in(idx);
@@ -130,4 +162,11 @@ public class LoadNode extends MemOpNode {
         if( px instanceof StoreNode st1 && ptr()==st1.ptr() && off()==st1.off() ) { px.addDep(this); return true; }
         return false;
     }
+
+    // Read-Only is a deep property, and cannot be cast-away
+    private Node castRO(Node rez) {
+        if( ptr()._type.isFinal() && !rez._type.isFinal() )
+            return new ReadOnlyNode(rez).peephole();
+        return rez;
+    }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/LoopNode.java b/src/main/java/com/seaofnodes/simple/node/LoopNode.java
index 22862cb9..ecda9c63 100644
--- a/src/main/java/com/seaofnodes/simple/node/LoopNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/LoopNode.java
@@ -32,38 +32,18 @@ public class LoopNode extends RegionNode {
     // Bypass Region idom, same as the default idom() using use in(1) instead of in(0)
     @Override public CFGNode idom(Node dep) { return entry(); }
 
-    @Override public int loopDepth() {
-        if( _loopDepth!=0 ) return _loopDepth; // Was already set
-        _loopDepth = entry()._loopDepth+1;     // Entry depth plus one
-        // One-time tag loop exits
-        for( CFGNode idom = back(); idom!=this; idom = idom.idom() ) {
-            // Walk idom in loop, setting depth
-            idom._loopDepth = _loopDepth;
-            // Loop exit hits the CProj before the If, instead of jumping from
-            // Region directly to If.
-            if( idom instanceof CProjNode proj ) {
-                assert proj.in(0) instanceof IfNode; // Loop exit test
-                // Find the loop exit CProj, and set loop_depth
-                for( Node use : proj.in(0)._outputs )
-                    if( use instanceof CProjNode proj2 && proj2 != idom )
-                        proj2._loopDepth = _loopDepth-1;
-            }
-        }
-        return _loopDepth;
-    }
-
     // If this is an unreachable loop, it may not have an exit.  If it does not
     // (i.e., infinite loop), force an exit to make it reachable.
-    public void forceExit( StopNode stop ) {
+    public StopNode forceExit( StopNode stop ) {
         // Walk the backedge, then immediate dominator tree util we hit this
         // Loop again.  If we ever hit a CProj from an If (as opposed to
         // directly on the If) we found our exit.
         CFGNode x = back();
         while( x != this ) {
             if( x instanceof CProjNode exit && exit.in(0) instanceof IfNode iff ) {
-                Node other = iff.cproj(1-exit._idx);
-                if( !(other.out(0) instanceof LoopNode loop) || loop.entry()==exit )
-                    return;         // Found an exit, not an infinite loop
+                CFGNode other = iff.cproj(1-exit._idx);
+                if( other.loopDepth() < loopDepth() )
+                    return stop; // Found an exit, not an infinite loop
             }
             x = x.idom();
         }
@@ -76,5 +56,6 @@ public class LoopNode extends RegionNode {
         CProjNode f = new CProjNode(iff,1,"False");
         setDef(2,f);
         stop.addDef(new ReturnNode(t,Parser.ZERO,null));
+        return stop;
     }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/MemOpNode.java b/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
index c7a1efec..82aab8ac 100644
--- a/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/MemOpNode.java
@@ -1,6 +1,5 @@
 package com.seaofnodes.simple.node;
 
-import com.seaofnodes.simple.type.Field;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeMemPtr;
 
@@ -11,7 +10,9 @@ public abstract class MemOpNode extends Node {
 
     public final String _name;
     public final int _alias;
-    public final Type _declaredType;
+    // Declared type; not final because it might be a forward-reference
+    // which will be lazily improved when the reference is declared.
+    public Type _declaredType;
 
     public MemOpNode(String name, int alias, Type glb, Node mem, Node ptr, Node off) {
         super(null, mem, ptr, off);
diff --git a/src/main/java/com/seaofnodes/simple/node/MinusNode.java b/src/main/java/com/seaofnodes/simple/node/MinusNode.java
index 8a2c9406..760a4274 100644
--- a/src/main/java/com/seaofnodes/simple/node/MinusNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/MinusNode.java
@@ -2,6 +2,7 @@ package com.seaofnodes.simple.node;
 
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
+import com.seaofnodes.simple.Utils;
 
 import java.util.BitSet;
 
@@ -22,7 +23,9 @@ public class MinusNode extends Node {
     public Type compute() {
         if( in(1)._type instanceof TypeInteger i0 ) {
             if( i0.isHigh() ) return TypeInteger.TOP;
-            return i0==TypeInteger.BOT ? TypeInteger.BOT : TypeInteger.make(-i0._max,-i0._min);
+            if( i0==TypeInteger.BOT || i0._min == Long.MIN_VALUE || i0._max == Long.MIN_VALUE )
+                return TypeInteger.BOT;
+            return TypeInteger.make(-i0._max,-i0._min);
         }
         return TypeInteger.TOP.meet(in(1)._type);
     }
diff --git a/src/main/java/com/seaofnodes/simple/node/Node.java b/src/main/java/com/seaofnodes/simple/node/Node.java
index 462a403c..3827fdac 100644
--- a/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -153,7 +153,7 @@ public abstract class Node implements OutNode {
      * @param new_def the new definition
      * @return new_def for flow coding
      */
-    public Node setDef(int idx, Node new_def ) {
+    public <N extends Node> N setDef(int idx, N new_def ) {
         unlock();
         Node old_def = in(idx);
         if( old_def == new_def ) return new_def; // No change
@@ -267,6 +267,10 @@ public abstract class Node implements OutNode {
     }
     // Test "keep" status
     public boolean iskeep() { return _outputs.find(null) != -1; }
+    public void unkill() {
+        if( unkeep().isUnused() )
+            kill();
+    }
 
 
     // Replace self with nnn in the graph, making 'this' go dead
@@ -278,6 +282,7 @@ public abstract class Node implements OutNode {
             int idx = n._inputs.find(this);
             n._inputs.set(idx,nnn);
             nnn.addUse(n);
+            IterPeeps.addAll(n._outputs);
         }
         kill();
     }
@@ -419,7 +424,7 @@ public abstract class Node implements OutNode {
      * And more folding:
      * <pre>   ary + ((idx<<2) + 16)</pre>
      * And during code-gen:
-     * <pre>   MOV4 Rary,Ridx,16 // or some such hardware-specific notation </pre>
+     * <pre>   MOV4 Rary,[Ridx<<2 +16] // or some such hardware-specific notation </pre>
      * <p>
      * {@link #idealize} has a very specific calling convention:
      * <ul>
@@ -542,9 +547,6 @@ public abstract class Node implements OutNode {
     /** Is this Node Memory related */
     public boolean isMem() { return false; }
 
-    /** Return block start from a isCFG() */
-    public Node getBlockStart() { return null; }
-
     /** Pinned in the schedule; these are data nodes whose input#0 is not allowed to change */
     public boolean isPinned() { return false; }
 
diff --git a/src/main/java/com/seaofnodes/simple/node/NotNode.java b/src/main/java/com/seaofnodes/simple/node/NotNode.java
index ffd3e01e..664d7c7b 100644
--- a/src/main/java/com/seaofnodes/simple/node/NotNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/NotNode.java
@@ -28,15 +28,14 @@ public class NotNode extends Node {
             // top->top, bot->bot, null->1, *void->0, not-null ptr->0, ptr/nil->bot
             // If input in null then true
             // If input is not null ptr then false
-            if( p0 == TypeMemPtr.TOP  )    return TypeInteger.TOP;
-            if( p0 == TypeMemPtr.NULLPTR ) return TypeInteger.constant(1);
-            if( !p0._nil )                 return TypeInteger.constant(0);
-            return TypeInteger.BOT;
+            if( p0 == TypeMemPtr.NULLPTR ) return TypeInteger.TRUE;
+            if( !p0._nil )                 return TypeInteger.FALSE;
+            return TypeInteger.BOOL;
         case Type t:
             if( t0.getClass() != Type.class )
                 // Only doing NOT on ints and ptrs
                 throw Utils.TODO();
-            return t0==Type.TOP ? Type.TOP : Type.BOTTOM;
+            return TypeInteger.BOOL;
         }
     }
 
diff --git a/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/src/main/java/com/seaofnodes/simple/node/PhiNode.java
index f0140ce6..cb266ca3 100644
--- a/src/main/java/com/seaofnodes/simple/node/PhiNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -47,7 +47,7 @@ public class PhiNode extends Node {
         // During parsing Phis have to be computed type pessimistically.
         if( r.inProgress() ) return _declaredType;
         // Set type to local top of the starting type
-        Type t = _declaredType.glb().dual();
+        Type t = _declaredType.lub();
         for (int i = 1; i < nIns(); i++)
             // If the region's control input is live, add this as a dependency
             // to the control because we can be peeped should it become dead.
@@ -101,7 +101,7 @@ public class PhiNode extends Node {
             if( in(2)._type == in(2)._type.makeInit() ) nullx = 2;
             if( nullx != -1 ) {
                 Node val = in(3-nullx);
-                if( r.idom(this) instanceof IfNode iff && iff.pred().addDep(this)==val ) {
+                if( r.idom(this).addDep(this) instanceof IfNode iff && iff.pred().addDep(this)==val ) {
                     // Must walk the idom on the null side to make sure we hit False.
                     CFGNode idom = (CFGNode)r.in(nullx);
                     while( idom.nIns() > 0 && idom.in(0) != iff ) idom = idom.idom();
diff --git a/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java b/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
new file mode 100644
index 00000000..fddcaa67
--- /dev/null
+++ b/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
@@ -0,0 +1,29 @@
+package com.seaofnodes.simple.node;
+
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeMemPtr;
+
+import java.util.BitSet;
+
+/**
+ * Cast a pointer to read-only
+ */
+public class ReadOnlyNode extends Node {
+    public ReadOnlyNode( Node n ) { super(null,n); }
+    @Override public String label() { return "ReadOnly"; }
+
+    @Override
+    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+        return in(1)._print0(sb.append("(const)"),visited);
+    }
+    @Override public Type compute() {
+        Type t = in(1)._type;
+        return t instanceof TypeMemPtr tmp ? tmp.makeRO() : t;
+    }
+
+    @Override public Node idealize() {
+        if( in(1)._type instanceof TypeMemPtr tmp && tmp.isFinal() )
+            return in(1);
+        return null;
+    }
+}
diff --git a/src/main/java/com/seaofnodes/simple/node/RegionNode.java b/src/main/java/com/seaofnodes/simple/node/RegionNode.java
index 941de76b..fb39af17 100644
--- a/src/main/java/com/seaofnodes/simple/node/RegionNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/RegionNode.java
@@ -18,7 +18,7 @@ public class RegionNode extends CFGNode {
 
     @Override
     StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return sb.append(label()).append(_nid);
+        return sb.append(label());
     }
 
     @Override public boolean isMultiHead() { return true; }
@@ -72,65 +72,9 @@ public class RegionNode extends CFGNode {
             p1.in(0) instanceof IfNode iff )
             return iff.ctrl();
 
-
-        // Look for direct uses of a guarded expression, and replace with the guard result.
-        if( !(idom() instanceof StartNode) && // Dead or dying
-            !(this instanceof LoopNode) ) {
-            VISIT.clear();
-            boolean progress = false;
-            outer:
-            for( int i=1; i<nIns(); i++ ) {
-                CFGNode idom = cfg(i);
-                while( !(idom instanceof CProjNode cproj) ) {
-                    idom = idom.idom();
-                    if( idom==null || idom.idepth() < idom().idepth() )
-                        continue outer;
-                }
-                if( cproj.cfg0() instanceof IfNode iff && cproj.compute()==Type.CONTROL ) {
-                    VISIT.set(iff.pred()._nid);
-                    for( Node out : _outputs )
-                        if( out instanceof PhiNode phi )
-                            progress |= walk(iff,cproj,phi.in(i));
-                }
-            }
-            if( progress )
-                return this;
-        }
-
         return null;
     }
 
-    // A walk that can be cutoff early
-    private static final BitSet VISIT = new BitSet();
-    private boolean walk( IfNode iff, CProjNode cproj, Node n ) {
-        if( VISIT.get(n._nid) ) return false;
-        VISIT.set(n._nid);
-        if( n instanceof CFGNode ) return false;
-        if( n.in(0)!=null && n.cfg0().idepth() < iff.idepth() )
-            return false;
-        boolean progress = false;
-        Node pred = iff.pred();
-        if( pred._type.isHighOrConst() ) return false; // This will collapse the IF already
-        for( int i=1; i<n.nIns(); i++ ) {
-            // Using a tested value
-            if( n.in(i) == pred && !(n instanceof CastNode) ) {
-                // Checking pred for T/F
-                Type t = pred._type;
-                Type tcast = cproj._idx==0 ? t.nonZero() : t.makeInit();
-                if( t!=tcast ) { // Progress to cast
-                    Node cast = new CastNode( tcast, cproj, pred ).peephole();
-                    n.setDef( i, cast );
-                    IterPeeps.add(n);
-                    progress = true;
-                } else pred.addDep( this );
-            }
-            if( n.in(i)!=null )
-                progress |= walk(iff,cproj,n.in(i));
-        }
-        return progress;
-    }
-
-
     private int findDeadInput() {
         for( int i=1; i<nIns(); i++ )
             if( in(i)._type==Type.XCONTROL )
@@ -164,13 +108,6 @@ public class RegionNode extends CFGNode {
         return lca;
     }
 
-    @Override void _walkUnreach( BitSet visit, HashSet<CFGNode> unreach ) {
-        for( int i=1; i<nIns(); i++ )
-            cfg(i).walkUnreach(visit,unreach);
-    }
-
-    @Override public int loopDepth() { return _loopDepth==0 ? (_loopDepth = cfg(1).loopDepth()) : _loopDepth; }
-
     // True if last input is null
     public final boolean inProgress() {
         return nIns()>1 && in(nIns()-1) == null;
@@ -180,6 +117,4 @@ public class RegionNode extends CFGNode {
     @Override boolean eq( Node n ) {
         return !inProgress();
     }
-
-    @Override public Node getBlockStart() { return this; }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/ReturnNode.java b/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
index de4eba52..b586a44f 100644
--- a/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
@@ -47,6 +47,4 @@ public class ReturnNode extends CFGNode {
             return ctrl();
         return null;
     }
-
-    @Override public Node getBlockStart() { return ctrl().getBlockStart(); }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/ScopeMinNode.java b/src/main/java/com/seaofnodes/simple/node/ScopeMinNode.java
index e4874e15..9134f9c3 100644
--- a/src/main/java/com/seaofnodes/simple/node/ScopeMinNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/ScopeMinNode.java
@@ -14,16 +14,29 @@ public class ScopeMinNode extends Node {
     /** The tracked fields are now complex enough to deserve a array-of-structs layout
      */
     public static class Var {
-        public final int _idx;
-        public final String _name;
-        public final Type _type;
-        public final boolean _final;
+        public final int _idx;       // index in containing scope
+        public final String _name;   // Declared name
+        private Type _type;          // Declared type
+        public final boolean _final; // Final field
         public Var(int idx, String name, Type type, boolean xfinal) {
             _idx = idx;
             _name = name;
             _type = type;
             _final = xfinal;
         }
+        public Type type() {
+            if( !_type.isFRef() ) return _type;
+            // Update self to no longer use the forward ref type
+            Type def = Parser.TYPES.get(((TypeMemPtr)_type)._obj._name);
+            return (_type=_type.meet(def));
+        }
+        public Type lazyGLB() {
+            Type t = type();
+            return t instanceof TypeMemPtr ? t : t.glb();
+        }
+        @Override public String toString() {
+            return _type.toString()+(_final ? " ": " !")+_name;
+        }
     }
 
     public ScopeMinNode() { _type = TypeMem.BOT; }
diff --git a/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
index 11e54d82..86aa7665 100644
--- a/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -1,8 +1,6 @@
 package com.seaofnodes.simple.node;
 
 import com.seaofnodes.simple.IterPeeps;
-import com.seaofnodes.simple.Parser;
-import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.Ary;
 import com.seaofnodes.simple.type.*;
 import java.util.*;
@@ -29,13 +27,22 @@ public class ScopeNode extends ScopeMinNode {
     // Since of each nested lexical scope
     public final Ary<Integer> _lexSize;
 
+    // True if parsing inside of a constructor
+    public final Ary<Boolean> _inCons;
+
+    // Extra guards; tested predicates and casted results
+    private final Ary<Node> _guards;
 
     // A new ScopeNode
-    public ScopeNode() { _vars = new Ary<>(Var.class); _lexSize = new Ary<>(Integer.class); }
+    public ScopeNode() {
+        _vars   = new Ary<>(Var    .class);
+        _lexSize= new Ary<>(Integer.class);
+        _inCons = new Ary<>(Boolean.class);
+        _guards = new Ary<>(Node   .class);
+    }
 
     @Override public String label() { return "Scope"; }
 
-
     @Override
     StringBuilder _print1(StringBuilder sb, BitSet visited) {
         sb.append("Scope[ ");
@@ -43,7 +50,7 @@ public class ScopeNode extends ScopeMinNode {
         for( int i=0; i<nIns(); i++ ) {
             if( j < _lexSize._len && i == _lexSize.at(j) ) { sb.append("| "); j++; }
             Var v = _vars.get(i);
-            v._type.print(sb);
+            v.type().print(sb);
             sb.append(" ");
             if( v._final ) sb.append("!");
             sb.append(v._name);
@@ -75,17 +82,24 @@ public class ScopeNode extends ScopeMinNode {
      *
      * @return Node that was bound
      */
-    public Node ctrl(Node n) { return setDef(0,n); }
+    public <N extends Node> N ctrl(N n) { return setDef(0,n); }
 
-    public void push() {
+    public void push() { push(false); }
+    public void push(boolean inCon) {
+        assert _lexSize._len==_inCons._len;
         _lexSize.push(_vars.size());
+        _inCons.push(inCon);
     }
     public void pop() {
+        assert _lexSize._len==_inCons._len;
         int n = _lexSize.pop();
+        _inCons.pop();
         popUntil(n);
         _vars.setLen(n);
     }
 
+    public boolean inCon() { return _inCons.last(); }
+
     // Find name in reverse, return an index into _vars or -1.  Linear scan
     // instead of hashtable, but probably doesn't matter until the scan
     // typically hits many dozens of variables.
@@ -125,7 +139,7 @@ public class ScopeNode extends ScopeMinNode {
     public Var lookup( String name ) {
         int idx = find(name);
         // -1 is missed in all scopes, not found
-        return idx == -1 ? null : _update(_vars.at(idx),null);
+        return idx == -1 ? null : update(_vars.at(idx),null);
     }
 
     /**
@@ -137,10 +151,10 @@ public class ScopeNode extends ScopeMinNode {
     public void update( String name, Node n ) {
         int idx = find(name);
         assert idx>=0;
-        _update(_vars.at(idx),n);
+        update(_vars.at(idx),n);
     }
 
-    Var _update( ScopeNode.Var v, Node st ) {
+    public Var update( ScopeNode.Var v, Node st ) {
         Node old = in(v._idx);
         if( old instanceof ScopeNode loop ) {
             // Lazy Phi!
@@ -151,7 +165,7 @@ public class ScopeNode extends ScopeMinNode {
                 // Set real Phi in the loop head
                 // The phi takes its one input (no backedge yet) from a recursive
                 // lookup, which might have insert a Phi in every loop nest.
-                : loop.setDef(v._idx,new PhiNode(v._name, v._type instanceof TypeMemPtr ? v._type : v._type.glb(), loop.ctrl(), loop.in(loop._update(v,null)._idx),null).peephole());
+                : loop.setDef(v._idx,new PhiNode(v._name, v.lazyGLB(), loop.ctrl(), loop.in(loop.update(v,null)._idx),null).peephole());
             setDef(v._idx,old);
         }
         if( st!=null ) setDef(v._idx,st); // Set new value
@@ -178,8 +192,15 @@ public class ScopeNode extends ScopeMinNode {
         // 1) duplicate the name bindings of the ScopeNode across all stack levels
         // 2) Make the new ScopeNode a user of all the nodes bound
         // 3) Ensure that the order of defs is the same to allow easy merging
-        dup._vars.addAll(_vars);
+        dup._vars   .addAll(_vars   );
         dup._lexSize.addAll(_lexSize);
+        dup._inCons .addAll(_inCons );
+        dup._guards .addAll(_guards );
+        // The dup'd guards all need dup'd keepers, to keep proper accounting
+        // when later removing all guards
+        for( Node n : _guards )
+            if( !(n instanceof CFGNode) )
+                n.keep();
         dup.addDef(ctrl());     // Control input is just copied
 
         // Memory input is a shallow copy
@@ -208,13 +229,13 @@ public class ScopeNode extends ScopeMinNode {
      * @param that The ScopeNode to be merged into this
      * @return A new node representing the merge point
      */
-    public Node mergeScopes(ScopeNode that) {
+    public RegionNode mergeScopes(ScopeNode that) {
         RegionNode r = (RegionNode) ctrl(new RegionNode(null,ctrl(), that.ctrl()).keep());
         mem()._merge(that.mem(),r);
         this ._merge(that      ,r);
         that.kill();            // Kill merged scope
         IterPeeps.add(r);
-        return r.unkeep().peephole();
+        return r.unkeep();
     }
 
     private void _merge(ScopeNode that, RegionNode r) {
@@ -223,9 +244,9 @@ public class ScopeNode extends ScopeMinNode {
                 // If we are in lazy phi mode we need to a lookup
                 // by name as it will trigger a phi creation
                 Var v = _vars.at(i);
-                Node lhs = this.in(this._update(v,null));
-                Node rhs = that.in(that._update(v,null));
-                setDef(i, new PhiNode(v._name, v._type, r, lhs, rhs).peephole());
+                Node lhs = this.in(this.update(v,null));
+                Node rhs = that.in(that.update(v,null));
+                setDef(i, new PhiNode(v._name, v.type(), r, lhs, rhs).peephole());
             }
     }
 
@@ -264,42 +285,78 @@ public class ScopeNode extends ScopeMinNode {
 
     // Up-casting: using the results of an If to improve a value.
     // E.g. "if( ptr ) ptr.field;" is legal because ptr is known not-null.
-
-    // This Scope looks for direct variable uses, or certain simple
-    // combinations, and replaces the variable with the upcast variant.
-    public Node upcast( Node ctrl, Node pred, boolean invert ) {
+    public void addGuards( Node ctrl, Node pred, boolean invert ) {
+        assert ctrl instanceof CFGNode;
+        _guards.add(ctrl);      // Marker to distinguish 0,1,2 guards
+        // add pred & its cast to the normal input list, with special Vars
+        if( ctrl._type == Type.XCONTROL || pred==null || pred.isDead() )
+            return;           // Dead, do not add any guards
         // Invert the If conditional
         if( invert )
             pred = pred instanceof NotNode not ? not.in(1) : IterPeeps.add(new NotNode(pred).peephole());
-
-        // Direct use of a value as predicate.  This is a zero/null test.
-        if( _inputs.find(pred) != -1 ) {
-            if( !(pred._type instanceof TypeMemPtr tmp) )
-                // Must be an `int`, since int and ptr are the only two value types
-                // being tested. No representation for a generic not-null int, so no upcast.
-                return null;
-            if( tmp.isa(TypeMemPtr.VOIDPTR) )
-                return null;    // Already not-null, no reason to upcast
-            // Upcast the ptr to not-null ptr, and replace in scope
-            return replace(pred,new CastNode(TypeMemPtr.VOIDPTR,ctrl,pred).peephole());
+        // This is a zero/null test.
+        // Compute the positive test type.
+        Type tnz   = pred._type.nonZero();
+        Type tcast = tnz.join(pred._type);
+        if( tcast != pred._type ) {
+            Node cast = new CastNode(tnz,ctrl,pred.keep()).peephole().keep();
+            _guards.add(pred);
+            _guards.add(cast);
+            replace(pred,cast);
         }
 
+        // Compute the negative test type.
         if( pred instanceof NotNode not ) {
-            // Direct use of a !value as predicate.  This is a zero/null test.
-            if( _inputs.find(not.in(1)) != -1 ) {
-                Type tinit = not.in(1)._type.makeInit();
-                if( not.in(1)._type.isa(tinit) ) return null; // Already zero/null, no reason to upcast
-                return replace(not.in(1), new ConstantNode(tinit).peephole());
+            Node npred = not.in(1);
+            Type tzero = npred._type.makeZero();
+            Type tzcast= tzero.join(npred._type);
+            if( tzcast != npred._type ) {
+                Node cast = new CastNode(tzero,ctrl,npred.keep()).peephole().keep();
+                _guards.add(npred);
+                _guards.add( cast);
+                replace(npred,cast);
             }
         }
-        // Apr/9/2024: Attempted to replace X with Y if guarded by a test of
-        // X==Y.  This didn't seem to help very much, or at least in the test
-        // cases seen so far was a very minor help.
+    }
+
+    // Remove matching pred/cast pairs from this guarded region.
+    public void removeGuards( Node ctrl ) {
+        assert ctrl instanceof CFGNode;
+        // 0,1 or 2 guards
+        while( true ) {
+            Node g = _guards.pop();
+            if( g == ctrl ) break;
+            if( g instanceof CFGNode ) continue;
+            g            .unkill(); // Pop/kill cast
+            _guards.pop().unkill(); // Pop/kill pred
+        }
+    }
 
-        // No upcast
-        return null;
+    // If we find a guarded instance of pred, replace with the upcasted version
+    public Node upcastGuard( Node pred ) {
+        // If finding an instanceof pred, replace with cast.
+        // Otherwise, just pred itself.
+        int i = _guards._len;
+        while( i > 0 ) {
+            Node  cast = _guards.at(--i);
+            if( cast instanceof CFGNode ) continue; // Marker between guard sets
+            Node xpred = _guards.at(--i);
+            if( xpred == pred )
+                return cast;
+        }
+        return pred;
     }
 
+    // Kill guards also
+    @Override public void kill() {
+        for( Node n : _guards )
+            if( !(n instanceof CFGNode) )
+                n.unkill();
+        _guards.clear();
+        super.kill();
+    }
+
+
     private Node replace( Node old, Node cast ) {
         assert old!=null && old!=cast;
         for( int i=0; i<nIns(); i++ )
diff --git a/src/main/java/com/seaofnodes/simple/node/ShlNode.java b/src/main/java/com/seaofnodes/simple/node/ShlNode.java
index b67d985a..6fd951e4 100644
--- a/src/main/java/com/seaofnodes/simple/node/ShlNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/ShlNode.java
@@ -44,7 +44,7 @@ public class ShlNode extends Node {
             if( (shl.value()&63)==0 )
                 return lhs;
             // (x + c) << i  =>  (x << i) + (c << i)
-            if( lhs instanceof AddNode add && add.in(2)._type instanceof TypeInteger c && c.isConstant() && c!=TypeInteger.ZERO ) {
+            if( lhs instanceof AddNode add && add.addDep(this).in(2)._type instanceof TypeInteger c && c.isConstant() && c!=TypeInteger.ZERO ) {
                 long sum = c.value() << shl.value();
                 if( Integer.MIN_VALUE <= sum  && sum <= Integer.MAX_VALUE )
                     return new AddNode( new ShlNode(add.in(1),rhs).peephole(), Parser.con(sum) );
diff --git a/src/main/java/com/seaofnodes/simple/node/StartNode.java b/src/main/java/com/seaofnodes/simple/node/StartNode.java
index c03a4b06..ab6e4931 100644
--- a/src/main/java/com/seaofnodes/simple/node/StartNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/StartNode.java
@@ -14,11 +14,11 @@ import static com.seaofnodes.simple.Utils.TODO;
  * In ch10 we also add mem aliases as structs get defined; each field in struct
  * adds a distinct alias to Start's tuple.
  */
-public class StartNode extends CFGNode implements MultiNode {
+public class StartNode extends LoopNode implements MultiNode {
 
     final Type _arg;
 
-    public StartNode(Type arg) { super(); _arg = arg; _type = compute(); }
+    public StartNode(Type arg) { super(null); _arg = arg; _type = compute(); }
 
     @Override public String label() { return "Start"; }
 
@@ -41,9 +41,4 @@ public class StartNode extends CFGNode implements MultiNode {
     @Override public int idepth() { return 0; }
     @Override public CFGNode idom(Node dep) { return null; }
 
-    @Override void _walkUnreach( BitSet visit, HashSet<CFGNode> unreach ) { }
-
-    @Override public int loopDepth() { return (_loopDepth=1); }
-
-    @Override public Node getBlockStart() { return this; }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/StopNode.java b/src/main/java/com/seaofnodes/simple/node/StopNode.java
index 0eacc1f4..867225cb 100644
--- a/src/main/java/com/seaofnodes/simple/node/StopNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/StopNode.java
@@ -1,6 +1,7 @@
 package com.seaofnodes.simple.node;
 
 import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.GlobalCodeMotion;
 import com.seaofnodes.simple.GraphVisualizer;
@@ -63,8 +64,6 @@ public class StopNode extends CFGNode {
     }
     @Override public CFGNode idom(Node dep) { return null; }
 
-    @Override public int loopDepth() { return (_loopDepth=1); }
-
     public Node addReturn(Node node) {
         return addDef(node);
     }
@@ -77,13 +76,10 @@ public class StopNode extends CFGNode {
         return this;
     }
     StopNode GCM(boolean show) {
-        // Break infinite loops, forcing a Never-branch to exit
-        GlobalCodeMotion.fixLoops(this);
+        Parser.START.buildLoopTree(this);
         if( show )
             System.out.println(new GraphVisualizer().generateDotOutput(this,null,null));
         GlobalCodeMotion.buildCFG(this);
         return this;
     }
-
-    @Override public Node getBlockStart() { return this; }
 }
diff --git a/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index 7b1bddd5..62b49a1a 100644
--- a/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -42,9 +42,15 @@ public class StoreNode extends MemOpNode {
     public Type compute() {
         Type val = val()._type;
         TypeMem mem = (TypeMem)mem()._type; // Invariant
-        Type t = mem._alias==_alias
-            ? val.meet(mem._t)  // Meet into existing memory
-            : Type.BOTTOM;
+        Type t = Type.BOTTOM;               // No idea on field contents
+        // Same alias, lift val to the declared type and then meet into other fields
+        if( mem._alias == _alias ) {
+            // Update declared forward ref to the actual
+            if( _declaredType.isFRef() && val instanceof TypeMemPtr tmp && !tmp.isFRef() )
+                _declaredType = tmp;
+            val = val.join(_declaredType);
+            t = val.meet(mem._t);
+        }
         return TypeMem.make(_alias,t);
     }
 
@@ -108,6 +114,9 @@ public class StoreNode extends MemOpNode {
     String err() {
         String err = super.err();
         if( err != null ) return err;
+        TypeMemPtr tmp = (TypeMemPtr)ptr()._type;
+        if( tmp._obj.field(_name)._final )
+            return "Cannot modify final field '"+_name+"'";
         Type t = val()._type;
         return _init || t.isa(_declaredType) ? null : "Cannot store "+t+" into field "+_declaredType+" "+_name;
     }
diff --git a/src/main/java/com/seaofnodes/simple/node/SubNode.java b/src/main/java/com/seaofnodes/simple/node/SubNode.java
index 009fb30e..5d6c2643 100644
--- a/src/main/java/com/seaofnodes/simple/node/SubNode.java
+++ b/src/main/java/com/seaofnodes/simple/node/SubNode.java
@@ -29,6 +29,11 @@ public class SubNode extends Node {
             t2 instanceof TypeInteger i2 ) {
             if (i1.isConstant() && i2.isConstant())
                 return TypeInteger.constant(i1.value()-i2.value());
+            // Fold ranges like {2-3} - {0-1} into {1-3}.
+            if( !AddNode.overflow(i1._min,-i2._max) &&
+                !AddNode.overflow(i1._max,-i2._min) &&
+                i2._min != Long.MIN_VALUE  )
+                return TypeInteger.make(i1._min-i2._max,i1._max-i2._min);
         }
         // Sub of same is 0
         if( in(1)==in(2) )