Moving prototype transitions into the header of the transition array.

src/transitions.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 34 matching lines @@
 // [1] First transition
 // [length() - kTransitionSize] Last transition
 class TransitionArray: public FixedArray {
  public:
   inline Map* elements_transition();
   inline void set_elements_transition(
       Map* value,
       WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
   inline void ClearElementsTransition();
   inline bool HasElementsTransition();
+  inline FixedArray* prototype_transitions();
+  inline void set_prototype_transitions(
+      FixedArray* prototype_transitions,
+      WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+  inline HeapObject* unchecked_prototype_transitions();
+  inline bool HasPrototypeTransitions();
   // Accessors for fetching instance transition at transition number.
   inline String* GetKey(int transition_number);
   inline Object** GetKeySlot(int transition_number);
   inline void SetKey(int transition_number, String* value);
   inline Object* GetValue(int transition_number);
   inline Object** GetValueSlot(int transition_number);
   inline void SetValue(int transition_number, Object* value);
   inline Map* GetTargetMap(int transition_number);
   inline PropertyDetails GetTargetDetails(int transition_number);
   inline Object** GetElementsSlot();
+  inline Object** GetPrototypeTransitionsSlot();

[Michael Starzinger, 2012/07/06 13:53:18]

Can we group these accessors somehow, this is becoming a rather large block.

[Toon Verwaest, 2012/07/09 12:45:27]

Done.

+  bool TransitionsTo(Object* target);
 
   // Returns the number of transitions in the array.
   int number_of_transitions() {
     ASSERT(length() >= kFirstIndex);
     int len = length();
     return len <= kFirstIndex ? 0 : (len - kFirstIndex) / kTransitionSize;
   }
 
   inline int number_of_entries() { return number_of_transitions(); }
 
@@ skipping 17 matching lines @@
   // Allocates a TransitionArray.
   MUST_USE_RESULT static MaybeObject* Allocate(int number_of_transitions);
 
   // Casting.
   static inline TransitionArray* cast(Object* obj);
 
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
   static const int kElementsTransitionIndex = 0;
-  static const int kFirstIndex = 1;
+  static const int kPrototypeTransitionsIndex = 1;
+  static const int kFirstIndex = 2;
 
   // Layout transition array header.
   static const int kElementsTransitionOffset = FixedArray::kHeaderSize;
-  static const int kFirstOffset = kElementsTransitionOffset + kPointerSize;
+  static const int kPrototypeTransitionsOffset = kElementsTransitionOffset +

[Michael Starzinger, 2012/07/06 13:53:18]

Better break that after the "=", to be consistent with objects.h

+                                                 kPointerSize;
+  static const int kFirstOffset = kPrototypeTransitionsOffset + kPointerSize;
 
   // Layout of map transition.
   static const int kTransitionKey = 0;
   static const int kTransitionValue = 1;
   static const int kTransitionSize = 2;
 
 #ifdef OBJECT_PRINT
   // Print all the transitions.
   inline void PrintTransitions() {
     PrintTransitions(stdout);
@@ skipping 30 matching lines @@
                   Object* value,
                   const WhitenessWitness&);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_H_