Reapply descriptor array sharing.

src/transitions.cc

 // 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 17 matching lines @@
 #include "v8.h"
 
 #include "objects.h"
 #include "transitions-inl.h"
 #include "utils.h"
 
 namespace v8 {
 namespace internal {
 
 
-MaybeObject* TransitionArray::Allocate(int number_of_transitions) {
+MaybeObject* TransitionArray::Allocate(int number_of_transitions,
+                                       JSGlobalPropertyCell* descriptors_cell) {
   Heap* heap = Isolate::Current()->heap();
+
+  if (descriptors_cell == NULL) {
+    MaybeObject* maybe_cell =
+        heap->AllocateJSGlobalPropertyCell(heap->empty_descriptor_array());
+    if (!maybe_cell->To(&descriptors_cell)) return maybe_cell;
+  }
+
   // Use FixedArray to not use DescriptorArray::cast on incomplete object.
   FixedArray* array;
   MaybeObject* maybe_array =
       heap->AllocateFixedArray(ToKeyIndex(number_of_transitions));
   if (!maybe_array->To(&array)) return maybe_array;
 
+  array->set(kDescriptorsPointerIndex, descriptors_cell);
   array->set(kElementsTransitionIndex, Smi::FromInt(0));
   array->set(kPrototypeTransitionsIndex, Smi::FromInt(0));
   return array;
 }
 
 
 void TransitionArray::NoIncrementalWriteBarrierCopyFrom(TransitionArray* origin,
                                                         int origin_transition,
                                                         int target_transition) {
   NoIncrementalWriteBarrierSet(target_transition,
                                origin->GetKey(origin_transition),
                                origin->GetTarget(origin_transition));
 }
 
 
 static bool InsertionPointFound(String* key1, String* key2) {
   return key1->Hash() > key2->Hash();
 }
 
 
-MaybeObject* TransitionArray::NewWith(String* name, Map* target) {
+MaybeObject* TransitionArray::NewWith(
+    String* name,
+    Map* target,
+    JSGlobalPropertyCell* descriptors_pointer,
+    Object* back_pointer) {
   TransitionArray* result;
 
-  MaybeObject* maybe_array = TransitionArray::Allocate(1);
+  MaybeObject* maybe_array = TransitionArray::Allocate(1, descriptors_pointer);
   if (!maybe_array->To(&result)) return maybe_array;
 
   result->NoIncrementalWriteBarrierSet(0, name, target);
+  result->set_back_pointer_storage(back_pointer);
   return result;
 }
 
 
 MaybeObject* TransitionArray::CopyInsert(String* name, Map* target) {
   TransitionArray* result;
 
   int number_of_transitions = this->number_of_transitions();
   int new_size = number_of_transitions;
 
   int insertion_index = this->Search(name);
   if (insertion_index == kNotFound) ++new_size;
 
   MaybeObject* maybe_array;
-  maybe_array = TransitionArray::Allocate(new_size);
+  maybe_array = TransitionArray::Allocate(new_size, descriptors_pointer());
   if (!maybe_array->To(&result)) return maybe_array;
 
   if (HasElementsTransition()) {
     result->set_elements_transition(elements_transition());
   }
 
   if (HasPrototypeTransitions()) {
     result->SetPrototypeTransitions(GetPrototypeTransitions());
   }
 
@@ skipping 14 matching lines @@
         this, insertion_index, insertion_index);
   }
 
   result->NoIncrementalWriteBarrierSet(insertion_index, name, target);
 
   for (; insertion_index < number_of_transitions; ++insertion_index) {
     result->NoIncrementalWriteBarrierCopyFrom(
         this, insertion_index, insertion_index + 1);
   }
 
+  result->set_back_pointer_storage(back_pointer_storage());
   return result;
 }
 
 
 } }  // namespace v8::internal