Reapply change to GVN all HFieldGet instructions.

lib/compiler/implementation/ssa/nodes.dart

-// 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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
   R visitBoolify(HBoolify node);
@@ skipping 721 matching lines @@
 
   static int computeDependsOnFlags(int flags) => flags << FLAG_CHANGES_COUNT;
 
   int getChangesFlags() => flags & ((1 << FLAG_CHANGES_COUNT) - 1);
   bool hasSideEffects() => getChangesFlags() != 0;
   void prepareGvn() { setAllSideEffects(); }
 
   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.
   bool isControlFlow() => false;
 
   // All isFunctions work on the propagated types.
   bool isArray() => propagatedType.isArray();
   bool isReadableArray() => propagatedType.isReadableArray();
   bool isMutableArray() => propagatedType.isMutableArray();
   bool isExtendableArray() => propagatedType.isExtendableArray();
@@ skipping 316 matching lines @@
   HConditionalBranch(inputs) : super(inputs);
   HInstruction get condition() => inputs[0];
   HBasicBlock get trueBranch() => block.successors[0];
   HBasicBlock get falseBranch() => block.successors[1];
   abstract toString();
 }
 
 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;
 }
 
 class HInvoke extends HInstruction {
   /**
     * The first argument must be the target: either an [HStatic] node, or
     * the receiver of a method-call. The remaining inputs are the arguments
     * to the invocation.
     */
@@ skipping 165 matching lines @@
   HFieldGet(Element element, HInstruction receiver,
             [this.isFinalOrConst = false])
       : super(element, <HInstruction>[receiver]);
   HFieldGet.fromActivation(receiver) : this(null, receiver);
 
   HInstruction get receiver() => inputs.length == 1 ? inputs[0] : null;
 
   accept(HVisitor visitor) => visitor.visitFieldGet(this);
 
   void prepareGvn() {
-    if (isFinalOrConst) {
-      assert(!hasSideEffects());
-      setUseGvn();
-    } else {
-      clearAllSideEffects();
-    }
+    setUseGvn();
+    if (!isFinalOrConst) setDependsOnSomething();
   }
 
   int typeCode() => 27;
   bool typeEquals(other) => other is HFieldGet;
   bool dataEquals(HFieldGet other) => element == other.element;
 }
 
 class HFieldSet extends HFieldAccess {
   HFieldSet(Element element, HInstruction receiver, HInstruction value)
       : super(element, <HInstruction>[receiver, value]);
@@ skipping 1313 matching lines @@
   HBasicBlock get start() => expression.start;
   HBasicBlock get end() {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }