Final vars and forced constants do not lazy-phi

Better comments on why a field is final

3 files changed, 33 insertions, 6 deletions

diff --git a/chapter18/src/main/java/com/seaofnodes/simple/Parser.java b/chapter18/src/main/java/com/seaofnodes/simple/Parser.java
index 3f4484f5..a6185aa0 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/Parser.java
@@ -694,10 +694,16 @@ public class Parser {
         Node expr;
         if( match("=") ) {
             expr = parseAsgn();
-            // `val` is always final
+            // TOP means val and val is always final
             xfinal = (t==Type.TOP) ||
-                // var is always not-final, final if no Bang AND TMP since primitives are not-final by default
-                (t!=Type.BOTTOM && !hasBang && (t instanceof TypeMemPtr));
+                // BOTTOM is var and var is always not-final
+                (t!=Type.BOTTOM &&
+                 // no Bang AND
+                 !hasBang &&
+                 // not-null (expecting null to be set to not-null)
+                 expr._type != Type.NIL &&
+                 // Pointers are final by default; int/flt are not-final by default.
+                 (t instanceof TypeNil));
             // var/val, then type comes from expression
             if( inferType ) {
                 if( expr._type==Type.NIL )
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
index 5620a2d2..d0d86b79 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -209,6 +209,7 @@ public class ScopeNode extends MemMergeNode {
                 : loop.setDef(v._idx,new PhiNode(v._name, v.lazyGLB(), loop.ctrl(), loop.in(loop.update(v,null)._idx),null).peephole());
             setDef(v._idx,old);
         }
+        assert !v._final || st==null;
         if( st!=null ) setDef(v._idx,st); // Set new value
         return v;
     }
@@ -258,7 +259,7 @@ public class ScopeNode extends MemMergeNode {
         for( int i=2; i<nIns(); i++ )
             // For lazy phis on loops we use a sentinel
             // that will trigger phi creation on update
-            dup.addDef(loop ? this : in(i));
+            dup.addDef(loop && !_vars.at(i)._final ? this : in(i));
         return dup;
     }
 
@@ -327,6 +328,8 @@ public class ScopeNode extends MemMergeNode {
     // Fill in the backedge of any inserted Phis
     void _endLoop( ScopeNode scope, Node back, Node exit ) {
         for( int i=2; i<nIns(); i++ ) {
+            if( _vars.at(i)._final ) continue; // Final vars did not get modified in the loop
+            if( _vars.at(i).type().isHighOrConst() ) continue; // Cannot lift higher than a constant, so no Phi
             if( back.in(i) != scope ) {
                 PhiNode phi = (PhiNode)in(i);
                 assert phi.region()==scope.ctrl() && phi.in(2)==null;
diff --git a/chapter18/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter18/src/test/java/com/seaofnodes/simple/Chapter18Test.java
index 39edb352..8852537b 100644
--- a/chapter18/src/test/java/com/seaofnodes/simple/Chapter18Test.java
+++ b/chapter18/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -13,7 +13,7 @@ public class Chapter18Test {
 """
 return 0;
 """);
-        code.parse().opto().typeCheck().GCM();
+        code.parse().opto().typeCheck().GCM().localSched();
         assertEquals("return 0;", code._stop.toString());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -179,6 +179,24 @@ return 2;
         assertEquals("1", Eval2.eval(code,  0));
     }
 
+    @Test
+    public void testFcn8() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? i2i = null;
+var id = {{int->int} f-> return f;};
+for(;;) {
+    if (i2i) return i2i(arg);
+    var x = {int i-> return i;};
+    arg = x(3);
+    i2i = id(x);
+}
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return x( Phi(Loop,arg,x( 3))); return Parm_i(x,int,3,Phi_arg); ]", code._stop.toString());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
 
     // Function break
     @Test
@@ -203,7 +221,7 @@ return 1;
     public void testErr2() {
         CodeGen code = new CodeGen(
 """
-{int -> int}? i2i = { int i -> return i; };
+{int -> int}? !i2i = { int i -> return i; };
 for(;;) {
     if (i2i(2) == arg) break;
     i2i = null;