From 41e9d916c45b98da1270b265e9121474ec5ef65b Mon Sep 17 00:00:00 2001
From: "ishell@chromium.org"
 <ishell@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Fri, 13 Jun 2014 07:51:45 +0000
Subject: [PATCH] GVN fix, preventing loads hoisting above stores to the same
 field when HObjectAccess's representation is not the same.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/331493006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21830 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/hydrogen-gvn.cc                     |  2 +-
 src/hydrogen-instructions.h             |  9 ++++++++-
 test/mjsunit/regress/regress-gvn-ftt.js | 27 +++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 test/mjsunit/regress/regress-gvn-ftt.js

diff --git a/src/hydrogen-gvn.cc b/src/hydrogen-gvn.cc
index e6f1ae90f3..385947d754 100644
--- a/src/hydrogen-gvn.cc
+++ b/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.Equals(inobject_fields_[i])) {
+    if (access.SameField(inobject_fields_[i])) {
       *index = i;
       return true;
     }
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index f1720f4442..fce5d681a9 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -6202,7 +6202,14 @@ class HObjectAccess V8_FINAL {
   void PrintTo(StringStream* stream) const;
 
   inline bool Equals(HObjectAccess that) const {
-    return value_ == that.value_;  // portion and offset must match
+    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);
   }
 
  protected:
diff --git a/test/mjsunit/regress/regress-gvn-ftt.js b/test/mjsunit/regress/regress-gvn-ftt.js
new file mode 100644
index 0000000000..d2cb44381d
--- /dev/null
+++ b/test/mjsunit/regress/regress-gvn-ftt.js
@@ -0,0 +1,27 @@
+// 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);