Reapply change to GVN all HFieldGet instructions.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
diff --git a/lib/compiler/implementation/ssa/nodes.dart b/lib/compiler/implementation/ssa/nodes.dart
index 3c205251de1b983a6d07d4a73b82db366c4d02d6..cc27a5b23f864689f299b619711b09fb4f006c7f 100644
--- a/lib/compiler/implementation/ssa/nodes.dart
+++ b/lib/compiler/implementation/ssa/nodes.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.
 
@@ -740,6 +740,9 @@ class HInstruction implements Hashable {
   void setAllSideEffects() { flags |= ((1 << FLAG_CHANGES_COUNT) - 1); }
   void clearAllSideEffects() { flags &= ~((1 << FLAG_CHANGES_COUNT) - 1); }
 
+  bool dependsOnSomething() => getFlag(FLAG_DEPENDS_ON_SOMETHING);
+  void setDependsOnSomething() { setFlag(FLAG_DEPENDS_ON_SOMETHING); }
+
   bool useGvn() => getFlag(FLAG_USE_GVN);
   void setUseGvn() { setFlag(FLAG_USE_GVN); }
   // Does this node potentially affect control flow.
@@ -1075,6 +1078,9 @@ class HConditionalBranch extends HControlFlow {
 class HControlFlow extends HInstruction {
   HControlFlow(inputs) : super(inputs);
   abstract toString();
+  void prepareGvn() {
+    clearAllSideEffects();

[ngeoffray, 2012/06/15 19:45:33]

Do you need to do this? I think by default insturctions don't have side effects.

[Mads Ager (google), 2012/06/18 07:45:23]

You are right, we don't need to clear side effects here, we just have to
override the method so nothing is set. Done.

+  }
   bool isControlFlow() => true;
   bool isStatement() => true;
 }
@@ -1260,12 +1266,9 @@ class HFieldGet extends HFieldAccess {
   accept(HVisitor visitor) => visitor.visitFieldGet(this);
 
   void prepareGvn() {
-    if (isFinalOrConst) {
-      assert(!hasSideEffects());
-      setUseGvn();
-    } else {
-      clearAllSideEffects();
-    }
+    clearAllSideEffects();

[ngeoffray, 2012/06/15 19:45:33]

ditto

[Mads Ager (google), 2012/06/18 07:45:23]

Done.

+    setUseGvn();
+    if (!isFinalOrConst) setDependsOnSomething();
   }
 
   int typeCode() => 27;