Eagerly follow transitions to existing maps while json parsing.

src/objects-inl.h

 // Copyright 2012 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 1396 matching lines @@
   }
   MaybeObject* maybe_obj = GetElementsTransitionMap(GetIsolate(),
                                                     elements_kind);
   if (!maybe_obj->ToObject(&obj)) return maybe_obj;
   set_map(Map::cast(obj));
   initialize_elements();
   return this;
 }
 
 
+MaybeObject* JSObject::AddFastPropertyUsingMap(Map* map) {
+  ASSERT(this->map()->NumberOfOwnDescriptors() + 1 ==
+         map->NumberOfOwnDescriptors());
+  if (this->map()->unused_property_fields() == 0) {
+    int new_size = properties()->length() + map->unused_property_fields() + 1;
+    FixedArray* new_properties;
+    MaybeObject* maybe_properties = properties()->CopySize(new_size);
+    if (!maybe_properties->To(&new_properties)) return maybe_properties;
+    set_properties(new_properties);
+  }
+  set_map(map);
+  return this;
+}
+
+
+bool JSObject::TryTransitionToField(Handle<JSObject> object,
+                                    Handle<String> key) {
+  if (!object->map()->HasTransitionArray()) return false;
+  Handle<TransitionArray> transitions(object->map()->transitions());
+  int transition = transitions->Search(*key);
+  if (transition == TransitionArray::kNotFound) return false;
+  PropertyDetails target_details = transitions->GetTargetDetails(transition);
+  if (target_details.type() != FIELD) return false;
+  if (target_details.attributes() != NONE) return false;
+  Handle<Map> target(transitions->GetTarget(transition));
+  JSObject::AddFastPropertyUsingMap(object, target);
+  return true;
+}
+
+
 ACCESSORS(Oddball, to_string, String, kToStringOffset)
 ACCESSORS(Oddball, to_number, Object, kToNumberOffset)
 
 
 byte Oddball::kind() {
   return Smi::cast(READ_FIELD(this, kKindOffset))->value();
 }
 
 
 void Oddball::set_kind(byte value) {
@@ skipping 4113 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_