Keep maps when resetting elements.

src/objects.cc

 // Copyright 2013 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/accessors.h"
 #include "src/allocation-site-scopes.h"
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 4839 matching lines @@
 
   object->set_properties(*fields);
   ASSERT(object->IsJSObject());
 
   // Check that it really works.
   ASSERT(object->HasFastProperties());
 }
 
 
 void JSObject::ResetElements(Handle<JSObject> object) {
-  if (object->map()->is_observed()) {
-    // Maintain invariant that observed elements are always in dictionary mode.
-    Isolate* isolate = object->GetIsolate();
-    Factory* factory = isolate->factory();
-    Handle<SeededNumberDictionary> dictionary =
-        SeededNumberDictionary::New(isolate, 0);
-    if (object->map() == *factory->sloppy_arguments_elements_map()) {
-      FixedArray::cast(object->elements())->set(1, *dictionary);
-    } else {
-      object->set_elements(*dictionary);
-    }
-    return;
-  }
-
-  ElementsKind elements_kind = GetInitialFastElementsKind();
-  if (!FLAG_smi_only_arrays) {
-    elements_kind = FastSmiToObjectElementsKind(elements_kind);
-  }
-  Handle<Map> map = JSObject::GetElementsTransitionMap(object, elements_kind);
-  DisallowHeapAllocation no_gc;
-  Handle<FixedArrayBase> elements(map->GetInitialElements());
-  JSObject::SetMapAndElements(object, map, elements);
+  Heap* heap = object->GetIsolate()->heap();
+  CHECK(object->map() != heap->sloppy_arguments_elements_map());
+  object->set_elements(object->map()->GetInitialElements());
 }
 
 
 static Handle<SeededNumberDictionary> CopyFastElementsToDictionary(
     Handle<FixedArrayBase> array,
     int length,
     Handle<SeededNumberDictionary> dictionary) {
   Isolate* isolate = array->GetIsolate();
   Factory* factory = isolate->factory();
   bool has_double_elements = array->IsFixedDoubleArray();
@@ skipping 12202 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal