Share Maps for ElementsKind transitions

src/api.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3292 matching lines @@
 
 
 void PrepareExternalArrayElements(i::Handle<i::JSObject> object,
                                   void* data,
                                   ExternalArrayType array_type,
                                   int length) {
   i::Isolate* isolate = object->GetIsolate();
   i::Handle<i::ExternalArray> array =
       isolate->factory()->NewExternalArray(length, array_type, data);
 
-  // If the object already has external elements, create a new, unique
-  // map if the element type is now changing, because assumptions about
-  // generated code based on the receiver's map will be invalid.
-  i::Handle<i::HeapObject> elements(object->elements());
-  bool cant_reuse_map =
-      elements->map()->IsUndefined() ||
-      !elements->map()->has_external_array_elements() ||
-      elements->map() != isolate->heap()->MapForExternalArrayType(array_type);
-  if (cant_reuse_map) {
-    i::Handle<i::Map> external_array_map =
-        isolate->factory()->GetElementsTransitionMap(
-            i::Handle<i::Map>(object->map()),
-            GetElementsKindFromExternalArrayType(array_type),
-            object->HasFastProperties());
-    object->set_map(*external_array_map);
-  }
+  i::Handle<i::Map> external_array_map =
+      isolate->factory()->GetElementsTransitionMap(
+          object,
+          GetElementsKindFromExternalArrayType(array_type));
+
+  object->set_map(*external_array_map);
   object->set_elements(*array);
 }
 
 }  // namespace
 
 
 void v8::Object::SetIndexedPropertiesToPixelData(uint8_t* data, int length) {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   ON_BAILOUT(isolate, "v8::SetElementsToPixelData()", return);
   ENTER_V8(isolate);
@@ skipping 2737 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* scope_implementer =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   scope_implementer->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal