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

src/factory.cc

 // Copyright 2014 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/factory.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/base/bits.h"
 #include "src/conversions.h"
 #include "src/isolate-inl.h"
@@ skipping 2310 matching lines @@
   if (context->map_cache()->IsUndefined()) {
     // Allocate the new map cache for the native context.
     Handle<MapCache> new_cache = MapCache::New(isolate(), 24);
     context->set_map_cache(*new_cache);
   }
   // Check to see whether there is a matching element in the cache.
   Handle<MapCache> cache =
       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;
 }
 
 
 void Factory::SetRegExpAtomData(Handle<JSRegExp> regexp,
                                 JSRegExp::Type type,
                                 Handle<String> source,
                                 JSRegExp::Flags flags,
                                 Handle<Object> data) {
@@ skipping 50 matching lines @@
   return Handle<Object>::null();
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
 
 } }  // namespace v8::internal