Move DescriptorArray into the map

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 21 matching lines @@
 #include "heap.h"
 #include "isolate.h"
 #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] 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
+// constant, and element changes. They can either be simple transition arrays
+// that store a single property transition, or a full transition array that has
+// space for elements transitions, prototype transitions and multiple property
+// transitons. The details related to property transitions are accessed in the
+// descriptor array of the target map. In the case of a simple transition, the
+// key is also read from the descriptor array of the target map.
+//
+// The simple format of the these objects is:
+// [0] Undefined or back pointer map
+// [1] Single transition
+//
+// The full format is:
+// [0] Undefined or back pointer map
+// [1] Smi(0) or elements transition map
+// [2] Smi(0) or fixed array of prototype transitions
+// [3] 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);
   int GetSortedKeyIndex(int transition_number) { return transition_number; }
 
   String* GetSortedKey(int transition_number) {
     return GetKey(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 Object** GetDescriptorsSlot();
-  inline DescriptorArray* descriptors();
-  inline void set_descriptors(DescriptorArray* descriptors);
-
   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() {
     if (IsSimpleTransition()) return 1;
     int len = length();
     return len <= kFirstIndex ? 0 : (len - kFirstIndex) / kTransitionSize;
   }
 
   inline int number_of_entries() { return number_of_transitions(); }
 
   // Allocate a new transition array with a single entry.
   static MUST_USE_RESULT MaybeObject* NewWith(
       SimpleTransitionFlag flag,
       String* key,
       Map* target,
-      DescriptorArray* descriptors,
       Object* back_pointer);
 
-  static MUST_USE_RESULT MaybeObject* AllocateDescriptorsHolder();
-
   MUST_USE_RESULT MaybeObject* ExtendToFullTransitionArray();
 
   // Copy the transition array, inserting a new transition.
   // TODO(verwaest): This should not cause an existing transition to be
   // overwritten.
   MUST_USE_RESULT MaybeObject* CopyInsert(String* name, Map* target);
 
   // Copy a single transition from the origin array.
   inline void NoIncrementalWriteBarrierCopyFrom(TransitionArray* origin,
                                                 int origin_transition,
                                                 int target_transition);
 
   // Search a transition for a given property name.
   inline int Search(String* name);
 
   // Allocates a TransitionArray.
   MUST_USE_RESULT static MaybeObject* Allocate(int number_of_transitions);
 
-  bool IsDescriptorsHolder() { return length() == kDescriptorsHolderSize; }
   bool IsSimpleTransition() { return length() == kSimpleTransitionSize; }
   bool IsFullTransitionArray() { return length() >= kFirstIndex; }
 
   // Casting.
   static inline TransitionArray* cast(Object* obj);
 
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
-  static const int kDescriptorsIndex = 0;
-  static const int kBackPointerStorageIndex = 1;
-  static const int kDescriptorsHolderSize = 2;
+  static const int kBackPointerStorageIndex = 0;
 
   // Layout for full transition arrays.
-  static const int kElementsTransitionIndex = 2;
-  static const int kPrototypeTransitionsIndex = 3;
-  static const int kFirstIndex = 4;
+  static const int kElementsTransitionIndex = 1;
+  static const int kPrototypeTransitionsIndex = 2;
+  static const int kFirstIndex = 3;
 
   // Layout for simple transition arrays.
-  static const int kSimpleTransitionTarget = 2;
-  static const int kSimpleTransitionSize = 3;
+  static const int kSimpleTransitionTarget = 1;
+  static const int kSimpleTransitionSize = 2;
   static const int kSimpleTransitionIndex = 0;
   STATIC_ASSERT(kSimpleTransitionIndex != kNotFound);
 
-  static const int kDescriptorsOffset = FixedArray::kHeaderSize;
-  static const int kBackPointerStorageOffset = kDescriptorsOffset +
-                                               kPointerSize;
+  static const int kBackPointerStorageOffset = FixedArray::kHeaderSize;
 
   // Layout for the full transition array header.
   static const int kElementsTransitionOffset = kBackPointerStorageOffset +
                                                kPointerSize;
   static const int kPrototypeTransitionsOffset = kElementsTransitionOffset +
                                                  kPointerSize;
 
   // Layout of map transition entries in full transition arrays.
   static const int kTransitionKey = 0;
   static const int kTransitionTarget = 1;
@@ skipping 35 matching lines @@
                                            String* key,
                                            Map* target);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_H_