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 0d6bb70f794abbcb31a2ea8f7c1da901b83f25c2..d48e813aacf316904219d1146d1efac457e80127 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.
@@ -1076,6 +1079,9 @@ class HConditionalBranch extends HControlFlow {
 class HControlFlow extends HInstruction {
   HControlFlow(inputs) : super(inputs);
   abstract toString();
+  void prepareGvn() {
+    // Control flow does not have side-effects.
+  }
   bool isControlFlow() => true;
   bool isStatement() => true;
 }
@@ -1261,12 +1267,8 @@ class HFieldGet extends HFieldAccess {
   accept(HVisitor visitor) => visitor.visitFieldGet(this);
 
   void prepareGvn() {
-    if (isFinalOrConst) {
-      assert(!hasSideEffects());
-      setUseGvn();
-    } else {
-      clearAllSideEffects();
-    }
+    setUseGvn();
+    if (!isFinalOrConst) setDependsOnSomething();
   }
 
   int typeCode() => 27;