Promoting elements transitions to their own field.

src/property.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 93 matching lines @@
 // A pointer from a map to the new map that is created by adding
 // a named property.  These are key to the speed and functioning of V8.
 // The two maps should always have the same prototype, since
 // MapSpace::CreateBackPointers depends on this.
 class MapTransitionDescriptor: public Descriptor {
  public:
   MapTransitionDescriptor(String* key, Map* map, PropertyAttributes attributes)
       : Descriptor(key, map, attributes, MAP_TRANSITION) { }
 };
 
-class ElementsTransitionDescriptor: public Descriptor {
- public:
-  ElementsTransitionDescriptor(String* key,
-                               Object* map_or_array)
-      : Descriptor(key, map_or_array, PropertyDetails(NONE,
-                                                      ELEMENTS_TRANSITION)) { }
-};
-
 // Marks a field name in a map so that adding the field is guaranteed
 // to create a FIELD descriptor in the new map.  Used after adding
 // a constant function the first time, creating a CONSTANT_FUNCTION
 // descriptor in the new map.  This avoids creating multiple maps with
 // the same CONSTANT_FUNCTION field.
 class ConstTransitionDescriptor: public Descriptor {
  public:
   explicit ConstTransitionDescriptor(String* key, Map* map)
       : Descriptor(key, map, NONE, CONSTANT_TRANSITION) { }
 };
@@ skipping 41 matching lines @@
     case CALLBACKS: {
       Object* callback_object = desc->GetCallbackObject();
       // Non-JavaScript (i.e. native) accessors are always a property, otherwise
       // either the getter or the setter must be an accessor. Put another way:
       // If we only see map transitions and holes in a pair, this is not a
       // property.
       return (!callback_object->IsAccessorPair() ||
               AccessorPair::cast(callback_object)->ContainsAccessor());
     }
     case MAP_TRANSITION:
-    case ELEMENTS_TRANSITION:
     case CONSTANT_TRANSITION:
     case NULL_DESCRIPTOR:
       return false;
   }
   UNREACHABLE();  // keep the compiler happy
   return false;
 }
 
 
 class LookupResult BASE_EMBEDDED {
@@ skipping 110 matching lines @@
         return GetConstantFunction();
       default:
         return Smi::FromInt(0);
     }
   }
 
 
   Map* GetTransitionMap() {
     ASSERT(lookup_type_ == DESCRIPTOR_TYPE);
     ASSERT(type() == MAP_TRANSITION ||
-           type() == ELEMENTS_TRANSITION ||
            type() == CONSTANT_TRANSITION);
     return Map::cast(GetValue());
   }
 
   Map* GetTransitionMapFromMap(Map* map) {
     ASSERT(lookup_type_ == DESCRIPTOR_TYPE);
     ASSERT(type() == MAP_TRANSITION);
     return Map::cast(map->instance_descriptors()->GetValue(number_));
   }
 
@@ skipping 68 matching lines @@
   JSReceiver* holder_;
   int number_;
   bool cacheable_;
   PropertyDetails details_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_H_