Array.concat: properly go to dictionary mode when required

BUG=chromium:387031
LOG=y
R=danno@chromium.org

Review URL: https://codereview.chromium.org/342333002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21903 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/runtime.cc

@@ -10040,7 +10040,7 @@ class ArrayConcatVisitor {
       // getters on the arrays increasing the length of later arrays
       // during iteration.
       // This shouldn't happen in anything but pathological cases.
-      SetDictionaryMode(index);
+      SetDictionaryMode();
       // Fall-through to dictionary mode.
     }
     ASSERT(!fast_elements_);
@@ -10061,6 +10061,14 @@ class ArrayConcatVisitor {
     } else {
       index_offset_ += delta;
     }
+    // If the initial length estimate was off (see special case in visit()),
+    // but the array blowing the limit didn't contain elements beyond the
+    // provided-for index range, go to dictionary mode now.
+    if (fast_elements_ &&
+        index_offset_ >= static_cast<uint32_t>(
+            FixedArrayBase::cast(*storage_)->length())) {
+      SetDictionaryMode();
+    }
   }
 
   bool exceeds_array_limit() {
@@ -10082,7 +10090,7 @@ class ArrayConcatVisitor {
 
  private:
   // Convert storage to dictionary mode.
-  void SetDictionaryMode(uint32_t index) {
+  void SetDictionaryMode() {
     ASSERT(fast_elements_);
     Handle<FixedArray> current_storage(*storage_);
     Handle<SeededNumberDictionary> slow_storage(

test/mjsunit/regress/regress-crbug-387031.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 = [1];
+b = [];
+a.__defineGetter__(0, function () {
+  b.length = 0xffffffff;
+});
+c = a.concat(b);
+for (var i = 0; i < 20; i++) {
+  assertEquals(undefined, (c[i]));
+}