Protect the emptiness of Array prototype elements with a PropertyCell.

src/builtins.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 181 matching lines @@
       return false;
     }
   }
   return true;
 }
 
 
 static inline bool IsJSArrayFastElementMovingAllowed(Heap* heap,
                                                      JSArray* receiver) {
   DisallowHeapAllocation no_gc;
-  PrototypeIterator iter(heap->isolate(), receiver);
+  Isolate* isolate = heap->isolate();
+  if (!isolate->IsFastArrayConstructorPrototypeChainIntact()) {
+    return false;
+  }
+
+  // If the array prototype chain is intact (and free of elements), and if the
+  // receiver's prototype is the array prototype, then we are done.
+  Object* prototype = receiver->map()->prototype();
+  if (prototype->IsJSArray() &&
+      isolate->is_initial_array_prototype(JSArray::cast(prototype))) {
+    return true;
+  }
+
+  // Slow case.
+  PrototypeIterator iter(isolate, receiver);
   return ArrayPrototypeHasNoElements(heap, &iter);
 }
 
 
 // Returns empty handle if not applicable.
 MUST_USE_RESULT
 static inline MaybeHandle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
     Isolate* isolate,
     Handle<Object> receiver,
     Arguments* args,
@@ skipping 16 matching lines @@
     elms = JSObject::EnsureWritableFastElements(array);
     if (args == NULL || array->HasFastObjectElements()) return elms;
   } else if (map == heap->fixed_double_array_map()) {
     if (args == NULL) return elms;
   } else {
     return MaybeHandle<FixedArrayBase>();
   }
 
   // Adding elements to the array prototype would break code that makes sure
   // it has no elements. Handle that elsewhere.
-  if (array->GetIsolate()->is_initial_array_prototype(*array)) {
+  if (isolate->IsAnyInitialArrayPrototype(array)) {
     return MaybeHandle<FixedArrayBase>();
   }
 
   // Need to ensure that the arguments passed in args can be contained in
   // the array.
   int args_length = args->length();
   if (first_added_arg >= args_length) return handle(array->elements(), isolate);
 
   ElementsKind origin_kind = array->map()->elements_kind();
   DCHECK(!IsFastObjectElementsKind(origin_kind));
@@ skipping 1408 matching lines @@
 }
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 } }  // namespace v8::internal