Reapply change to GVN all HFieldGet instructions.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
diff --git a/lib/compiler/implementation/ssa/optimize.dart b/lib/compiler/implementation/ssa/optimize.dart
index af319b4b597f770c952586141180811c68b5f503..79deacf0a2e6a60de79240522fd98b00cfc158dd 100644
--- a/lib/compiler/implementation/ssa/optimize.dart
+++ b/lib/compiler/implementation/ssa/optimize.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
@@ -711,12 +711,11 @@ class SsaDeadCodeEliminator extends HGraphVisitor implements OptimizationPhase {
   final String name = "SsaDeadCodeEliminator";
 
   static bool isDeadCode(HInstruction instruction) {
-    // TODO(ngeoffray): the way we handle side effects is not right
-    // (e.g. branching instructions have side effects).
     return !instruction.hasSideEffects()
            && instruction.usedBy.isEmpty()
            && instruction is !HCheck
-           && instruction is !HTypeGuard;
+           && instruction is !HTypeGuard
+           && !instruction.isControlFlow();
   }
 
   void visitGraph(HGraph graph) {
@@ -904,13 +903,16 @@ class SsaGlobalValueNumberer implements OptimizationPhase {
 
   void visitBasicBlock(HBasicBlock block, ValueSet values) {
     HInstruction instruction = block.first;
+    if (block.isLoopHeader()) {
+      int flags = loopChangesFlags[block.id];
+      values.kill(flags);
+    }
     while (instruction !== null) {
       HInstruction next = instruction.next;
       int flags = instruction.getChangesFlags();
-      if (flags != 0) {
-        assert(!instruction.useGvn());
-        values.kill(flags);
-      } else if (instruction.useGvn()) {
+      assert(flags == 0 || !instruction.useGvn());
+      values.kill(flags);
+      if (instruction.useGvn()) {
         HInstruction other = values.lookup(instruction);
         if (other !== null) {
           assert(other.gvnEquals(instruction) && instruction.gvnEquals(other));