Revert "GVN fix, preventing loads hoisting above stores to the same field when...

Revert "GVN fix, preventing loads hoisting above stores to the same field when HObjectAccess's representation is not the same."

This reverts commit r21830 for tanking performance on Deltablue.

TBR=ishell@chromium.org

Review URL: https://codereview.chromium.org/336223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21857 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-gvn.cc

@@ -466,7 +466,7 @@ bool SideEffectsTracker::ComputeGlobalVar(Unique<Cell> cell, int* index) {
 bool SideEffectsTracker::ComputeInobjectField(HObjectAccess access,
                                               int* index) {
   for (int i = 0; i < num_inobject_fields_; ++i) {
-    if (access.SameField(inobject_fields_[i])) {
+    if (access.Equals(inobject_fields_[i])) {
       *index = i;
       return true;
     }

src/hydrogen-instructions.h

@@ -6202,14 +6202,7 @@ class HObjectAccess V8_FINAL {
   void PrintTo(StringStream* stream) const;
 
   inline bool Equals(HObjectAccess that) const {
-    return value_ == that.value_;
-  }
-
-  // Returns true if |this| access refers to the same field as |that|, which
-  // means that both have same |offset| and |portion| values.
-  inline bool SameField(HObjectAccess that) const {
-    uint32_t mask = PortionField::kMask | OffsetField::kMask;
-    return (value_ & mask) == (that.value_ & mask);
+    return value_ == that.value_;  // portion and offset must match
   }
 
  protected:

test/mjsunit/regress/regress-gvn-ftt.js

-// Copyright 2014 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --allow-natives-syntax --track-field-types --use-gvn
-
-function A(id) {
-  this.id = id;
-}
-
-var a1 = new A(1);
-var a2 = new A(2);
-
-
-var g;
-function f(o, value) {
-  g = o.o;
-  o.o = value;
-  return o.o;
-}
-
-var obj = {o: a1};
-
-f(obj, a1);
-f(obj, a1);
-%OptimizeFunctionOnNextCall(f);
-assertEquals(a2.id, f(obj, a2).id);