Array() in optimized code can create with wrong ElementsKind in corner cases.

src/objects-inl.h

 // Copyright 2012 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 7183 matching lines @@
   }
 }
 
 
 void JSArray::set_length(Smi* length) {
   // Don't need a write barrier for a Smi.
   set_length(static_cast<Object*>(length), SKIP_WRITE_BARRIER);
 }
 
 
+bool JSArray::SetElementsLengthWouldNormalize(
+    Heap* heap, Handle<Object> new_length_handle) {
+  // If the new array won't fit in a some non-trivial fraction of the max old
+  // space size, then force it to go dictionary mode.
+  int max_fast_array_size =
+      static_cast<int>((heap->MaxOldGenerationSize() / kDoubleSize) / 4);
+  return new_length_handle->IsNumber() &&
+         NumberToInt32(*new_length_handle) >= max_fast_array_size;
+}
+
+
 bool JSArray::AllowsSetElementsLength() {
   bool result = elements()->IsFixedArray() || elements()->IsFixedDoubleArray();
   DCHECK(result == !HasExternalArrayElements());
   return result;
 }
 
 
 void JSArray::SetContent(Handle<JSArray> array,
                          Handle<FixedArrayBase> storage) {
   EnsureCanContainElements(array, storage, storage->length(),
@@ skipping 317 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_