Avoid some unnecessary variables for phis.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index 8784c2b9ffda835e34308f2dc83adf128a451fe9..fc2b1717ff3f0b13fc4347947c15b3045514b1c9 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -85,6 +85,7 @@ class SsaCodeGenerator implements HVisitor {
   final Map<HPhi, String> logicalOperations;
   final Map<Element, ElementAction> breakAction;
   final Map<Element, ElementAction> continueAction;
+  final Equivalence<HPhi> phiEquivalence;
 
   Element equalsNullElement;
   int indent = 0;
@@ -125,7 +126,8 @@ class SsaCodeGenerator implements HVisitor {
       generateAtUseSite = new Set<HInstruction>(),
       logicalOperations = new Map<HPhi, String>(),
       breakAction = new Map<Element, ElementAction>(),
-      continueAction = new Map<Element, ElementAction>() {
+      continueAction = new Map<Element, ElementAction>(),
+      phiEquivalence = new Equivalence<HPhi>() {
 
     for (final name in parameterNames.getValues()) {
       prefixes[name] = 0;
@@ -167,6 +169,7 @@ class SsaCodeGenerator implements HVisitor {
     new SsaInstructionMerger(generateAtUseSite).visitGraph(graph);
     new SsaConditionMerger(generateAtUseSite,
                            logicalOperations).visitGraph(graph);
+    new PhiEquivalator(phiEquivalence, logicalOperations).analyzeGraph(graph);
   }
 
   visitGraph(HGraph graph) {
@@ -570,6 +573,7 @@ class SsaCodeGenerator implements HVisitor {
             addIndentation();
             buffer.add("}\n");
           } else {
+            addIndentation();
             buffer.add(") {\n");
             indent++;
             wrapLoopBodyForContinue(info);
@@ -633,15 +637,27 @@ class SsaCodeGenerator implements HVisitor {
             // In case the phi is being generated by another
             // instruction.
             if (isLogicalOperation && isGenerateAtUseSite(phi)) return;
+            HPhi canonicalPhi = phiEquivalence.getRepresentative(phi);
+            HInstruction input = phi.inputs[index];
+            if (input is HPhi) {
+              HPhi inputPhi = input;
+              HPhi canonicalInput = phiEquivalence.getRepresentative(inputPhi);
+              // If we use the same variable, we don't need to create an
+              // assingment.

[floitsch, 2012/04/11 11:44:39]

assignment

[Lasse Reichstein Nielsen, 2012/04/11 11:55:26]

Done.

+              if (canonicalInput == canonicalPhi) {
+                assert(!isLogicalOperation);
+                return;
+              }
+            }
             if (isGeneratingExpression()) {
               addExpressionSeparator();
             } else {
               addIndentation();
             }
-            if (!temporaryExists(phi)) {
-              declareVariable(temporary(phi));
+            if (!temporaryExists(canonicalPhi)) {
+              declareVariable(temporary(canonicalPhi));
             } else {
-              buffer.add(temporary(phi));
+              buffer.add(temporary(canonicalPhi));
             }
             buffer.add(" = ");
             if (isLogicalOperation) {
@@ -1179,7 +1195,8 @@ class SsaCodeGenerator implements HVisitor {
     if (operation !== null) {
       emitLogicalOperation(node, operation);
     } else {
-      buffer.add('${temporary(node)}');
+      HPhi canonicalPhi = phiEquivalence.getRepresentative(node);
+      buffer.add('${temporary(canonicalPhi)}');
     }
   }