Do not eliminate bounds checks for "<const> - x".

Before this change, bounds check elimination treated "<const> - x" as
"x - <const>".

R=yangguo@chromium.org
BUG=385054
TEST=test/mjsunit/regress/regress-385054.js
LOG=N

Review URL: https://codereview.chromium.org/339583003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21859 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-bce.cc

@@ -47,10 +47,7 @@ class BoundsCheckKey : public ZoneObject {
     } else if (check->index()->IsSub()) {
       HSub* index = HSub::cast(check->index());
       is_sub = true;
-      if (index->left()->IsConstant()) {
-        constant = HConstant::cast(index->left());
-        index_base = index->right();
-      } else if (index->right()->IsConstant()) {
+      if (index->right()->IsConstant()) {
         constant = HConstant::cast(index->right());
         index_base = index->left();
       }

test/mjsunit/regress/regress-385054.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
+
+function f(x) {
+  var a = [1, 2];
+  a[x];
+  return a[0 - x];
+}
+
+f(0);
+f(0);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(undefined, f(1));