Swapped transition array and descriptor 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 23 matching lines @@
 #include "objects.h"
 #include "v8checks.h"
 
 namespace v8 {
 namespace internal {
 
 
 // TransitionArrays are fixed arrays used to hold map transitions for property,
 // constant, and element changes.
 // The format of the these objects is:
-// [0] Elements transition
-// [1] First transition
+// [0] Descriptor array
+// [1] Undefined or back pointer map
+// [2] Smi(0) or elements transition map
+// [3] Smi(0) or fixed array of prototype transitions
+// [4] First transition
 // [length() - kTransitionSize] Last transition
 class TransitionArray: public FixedArray {
  public:
   // Accessors for fetching instance transition at transition number.
   inline String* GetKey(int transition_number);
   inline void SetKey(int transition_number, String* value);
   inline Object** GetKeySlot(int transition_number);
 
   inline Map* GetTarget(int transition_number);
   inline void SetTarget(int transition_number, Map* target);
 
   inline PropertyDetails GetTargetDetails(int transition_number);
 
   inline Map* elements_transition();
   inline void set_elements_transition(
       Map* target,
       WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
   inline bool HasElementsTransition();
   inline void ClearElementsTransition();
 
+  inline DescriptorArray* descriptors();
+  inline void set_descriptors(DescriptorArray* descriptors,
+                              WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+  inline Object** GetDescriptorsSlot();
+
+  inline Object* back_pointer_storage();
+  inline void set_back_pointer_storage(
+      Object* back_pointer,
+      WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+
   inline FixedArray* GetPrototypeTransitions();
   inline void SetPrototypeTransitions(
       FixedArray* prototype_transitions,
       WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
   inline Object** GetPrototypeTransitionsSlot();
   inline bool HasPrototypeTransitions();
   inline HeapObject* UncheckedPrototypeTransitions();
 
   // Returns the number of transitions in the array.
   int number_of_transitions() {
@@ skipping 23 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 kPrototypeTransitionsIndex = 1;
-  static const int kFirstIndex = 2;
+  static const int kDescriptorsIndex = 0;
+  static const int kBackPointerStorageIndex = 1;
+  static const int kElementsTransitionIndex = 2;
+  static const int kPrototypeTransitionsIndex = 3;
+  static const int kFirstIndex = 4;
 
   // Layout transition array header.
-  static const int kElementsTransitionOffset = FixedArray::kHeaderSize;
+  static const int kDescriptorsOffset = FixedArray::kHeaderSize;
+  static const int kBackPointerStorageOffset = kDescriptorsOffset +
+                                               kPointerSize;
+  static const int kElementsTransitionOffset = kBackPointerStorageOffset +
+                                               kPointerSize;
   static const int kPrototypeTransitionsOffset = kElementsTransitionOffset +
                                                  kPointerSize;
-  static const int kFirstOffset = kPrototypeTransitionsOffset + kPointerSize;
 
   // Layout of map transition.
   static const int kTransitionKey = 0;
   static const int kTransitionTarget = 1;
   static const int kTransitionSize = 2;
 
 #ifdef OBJECT_PRINT
   // Print all the transitions.
   inline void PrintTransitions() {
     PrintTransitions(stdout);
@@ skipping 30 matching lines @@
                   Map* target,
                   const WhitenessWitness&);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_H_