Fix optimistic BCE to back off after deopt

BUG=v8:3176
LOG=n
R=danno@chromium.org

Review URL: https://codereview.chromium.org/177523002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19530 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-bce.cc

@@ -375,7 +375,8 @@ BoundsCheckBbData* HBoundsCheckEliminationPhase::PreProcessBlock(
       check->DeleteAndReplaceWith(check->ActualValue());
     } else if (data->BasicBlock() == bb) {
       data->CoverCheck(check, offset);
-    } else {
+    } else if (graph()->use_optimistic_licm() ||
+               bb->IsLoopSuccessorDominator()) {
       int32_t new_lower_offset = offset < data->LowerOffset()
           ? offset
           : data->LowerOffset();

test/mjsunit/regress/regress-3176.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 foo(a) {
+  var sum = 0;
+  for (var i = 0; i < 10; i++) {
+    sum += a[i];
+
+    if (i > 6) {
+      sum -= a[i - 4];
+      sum -= a[i - 5];
+    }
+  }
+  return sum;
+}
+
+var a = new Int32Array(10);
+
+foo(a);
+foo(a);
+%OptimizeFunctionOnNextCall(foo);
+foo(a);
+%OptimizeFunctionOnNextCall(foo);
+foo(a);
+assertOptimized(foo);