Fix for a smi stores optimization on x64 with a regression test.

test/mjsunit/regress/regress-crbug-345715.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
 
+a = {y:1.5};
+a.y = 0;
+b = a.y;
+c = {y:{}};
+
 function f() {
-  var o = {x:1};
-  var y = {y:2.5, x:0};
-  var result;
-  for (var i = 0; i < 2; i++) {
-    result = o.x + 3;
-    o = y;
-  }
-  return result;
+  return 1;
 }
 
-f();
-f();
-%OptimizeFunctionOnNextCall(f);
-assertEquals(3, f());
+function g() {
+  var e = {y: b};
+  var d = {x:f()};
+  var d = {x:f()};
+  return [e, d];
+}
+
+g();
+g();
+%OptimizeFunctionOnNextCall(g);
+assertEquals(1, g()[1].x);