Use the initial map of the Object function for empty object literals

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/586673002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24088 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/bootstrapper.cc

@@ -483,12 +483,14 @@ Handle<JSFunction> Genesis::CreateEmptyFunction(Isolate* isolate) {
 
   {  // --- O b j e c t ---
     Handle<JSFunction> object_fun = factory->NewFunction(object_name);
+    int unused = JSObject::kInitialGlobalObjectUnusedPropertiesCount;
+    int instance_size = JSObject::kHeaderSize + kPointerSize * unused;
     Handle<Map> object_function_map =
-        factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+        factory->NewMap(JS_OBJECT_TYPE, instance_size);
+    object_function_map->set_inobject_properties(unused);
     JSFunction::SetInitialMap(object_fun, object_function_map,
                               isolate->factory()->null_value());
-    object_function_map->set_unused_property_fields(
-        JSObject::kInitialGlobalObjectUnusedPropertiesCount);
+    object_function_map->set_unused_property_fields(unused);
 
     native_context()->set_object_function(*object_fun);
 
@@ -1153,11 +1155,8 @@ void Genesis::InitializeGlobal(Handle<GlobalObject> global_object,
   {  // Set up the iterator result object
     STATIC_ASSERT(JSGeneratorObject::kResultPropertyCount == 2);
     Handle<JSFunction> object_function(native_context()->object_function());
-    DCHECK(object_function->initial_map()->inobject_properties() == 0);
     Handle<Map> iterator_result_map =
         Map::Create(object_function, JSGeneratorObject::kResultPropertyCount);
-    DCHECK(iterator_result_map->inobject_properties() ==
-           JSGeneratorObject::kResultPropertyCount);
     Map::EnsureDescriptorSlack(iterator_result_map,
                                JSGeneratorObject::kResultPropertyCount);
 
@@ -1171,7 +1170,12 @@ void Genesis::InitializeGlobal(Handle<GlobalObject> global_object,
                                NONE, Representation::Tagged());
     iterator_result_map->AppendDescriptor(&done_descr);
 
+    iterator_result_map->set_instance_size(JSGeneratorObject::kResultSize);
     iterator_result_map->set_unused_property_fields(0);
+    iterator_result_map->set_inobject_properties(
+        JSGeneratorObject::kResultPropertyCount);
+    iterator_result_map->set_pre_allocated_property_fields(
+        JSGeneratorObject::kResultPropertyCount);
     DCHECK_EQ(JSGeneratorObject::kResultSize,
               iterator_result_map->instance_size());
     native_context()->set_iterator_result_map(*iterator_result_map);

src/factory.cc

@@ -2328,9 +2328,12 @@ Handle<Map> Factory::ObjectLiteralMapFromCache(Handle<Context> context,
       Handle<MapCache>(MapCache::cast(context->map_cache()));
   Handle<Object> result = Handle<Object>(cache->Lookup(*keys), isolate());
   if (result->IsMap()) return Handle<Map>::cast(result);
-  // Create a new map and add it to the cache.
-  Handle<Map> map = Map::Create(
-      handle(context->object_function()), keys->length());
+  int length = keys->length();
+  // Create a new map and add it to the cache. Reuse the initial map of the
+  // Object function if the literal has no predeclared properties.
+  Handle<Map> map =
+      length == 0 ? handle(context->object_function()->initial_map())
+                  : Map::Create(handle(context->object_function()), length);
   AddToMapCache(context, keys, map);
   return map;
 }

src/hydrogen.cc

@@ -11001,7 +11001,8 @@ HInstruction* HOptimizedGraphBuilder::BuildFastLiteral(
   }
 
   // Copy in-object properties.
-  if (boilerplate_object->map()->NumberOfFields() != 0) {
+  if (boilerplate_object->map()->NumberOfFields() != 0 ||
+      boilerplate_object->map()->unused_property_fields() > 0) {
     BuildEmitInObjectProperties(boilerplate_object, object, site_context,
                                 pretenure_flag);
   }