Reduce space usage of simple transitions and descriptors holders.

src/transitions-inl.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 51 matching lines @@
   return Map::cast(transition_map);
 }
 
 
 void TransitionArray::ClearElementsTransition() {
   WRITE_FIELD(this, kElementsTransitionOffset, Smi::FromInt(0));
 }
 
 
 bool TransitionArray::HasElementsTransition() {
-  return get(kElementsTransitionIndex) != Smi::FromInt(0);
+  return IsFullTransitionArray() &&
+      get(kElementsTransitionIndex) != Smi::FromInt(0);
 }
 
 
 void TransitionArray::set_elements_transition(Map* transition_map,
                                               WriteBarrierMode mode) {
+  ASSERT(IsFullTransitionArray());
   Heap* heap = GetHeap();
   WRITE_FIELD(this, kElementsTransitionOffset, transition_map);
   CONDITIONAL_WRITE_BARRIER(
       heap, this, kElementsTransitionOffset, transition_map, mode);
 }
 
 
 DescriptorArray* TransitionArray::descriptors() {
   return DescriptorArray::cast(descriptors_pointer()->value());
 }
@@ skipping 26 matching lines @@
 void TransitionArray::set_back_pointer_storage(Object* back_pointer,
                                                WriteBarrierMode mode) {
   Heap* heap = GetHeap();
   WRITE_FIELD(this, kBackPointerStorageOffset, back_pointer);
   CONDITIONAL_WRITE_BARRIER(
       heap, this, kBackPointerStorageOffset, back_pointer, mode);
 }
 
 
 bool TransitionArray::HasPrototypeTransitions() {
-  Object* prototype_transitions = get(kPrototypeTransitionsIndex);
-  return prototype_transitions != Smi::FromInt(0);
+  return IsFullTransitionArray() &&
+      get(kPrototypeTransitionsIndex) != Smi::FromInt(0);
 }
 
 
 FixedArray* TransitionArray::GetPrototypeTransitions() {
+  ASSERT(IsFullTransitionArray());
   Object* prototype_transitions = get(kPrototypeTransitionsIndex);
   return FixedArray::cast(prototype_transitions);
 }
 
 
 HeapObject* TransitionArray::UncheckedPrototypeTransitions() {
   ASSERT(HasPrototypeTransitions());
   return reinterpret_cast<HeapObject*>(get(kPrototypeTransitionsIndex));
 }
 
 
 void TransitionArray::SetPrototypeTransitions(FixedArray* transitions,
                                               WriteBarrierMode mode) {
-  ASSERT(this != NULL);
+  ASSERT(IsFullTransitionArray());
   ASSERT(transitions->IsFixedArray());
   Heap* heap = GetHeap();
   WRITE_FIELD(this, kPrototypeTransitionsOffset, transitions);
   CONDITIONAL_WRITE_BARRIER(
       heap, this, kPrototypeTransitionsOffset, transitions, mode);
 }
 
 
 Object** TransitionArray::GetPrototypeTransitionsSlot() {
   return HeapObject::RawField(reinterpret_cast<HeapObject*>(this),
                               kPrototypeTransitionsOffset);
 }
 
 
 Object** TransitionArray::GetKeySlot(int transition_number) {
+  ASSERT(!IsSimpleTransition());
   ASSERT(transition_number < number_of_transitions());
   return HeapObject::RawField(
       reinterpret_cast<HeapObject*>(this),
       OffsetOfElementAt(ToKeyIndex(transition_number)));
 }
 
 
 String* TransitionArray::GetKey(int transition_number) {
+  if (IsSimpleTransition()) {
+    Map* target = GetTarget(kSimpleTransitionIndex);
+    int descriptor = target->LastAdded();
+    String* key = target->instance_descriptors()->GetKey(descriptor);
+    return key;
+  }
   ASSERT(transition_number < number_of_transitions());
   return String::cast(get(ToKeyIndex(transition_number)));
 }
 
 
 void TransitionArray::SetKey(int transition_number, String* key) {
+  ASSERT(!IsSimpleTransition());
   ASSERT(transition_number < number_of_transitions());
   set(ToKeyIndex(transition_number), key);
 }
 
 
 Map* TransitionArray::GetTarget(int transition_number) {
+  if (IsSimpleTransition()) {
+    ASSERT(transition_number == kSimpleTransitionIndex);
+    return Map::cast(get(kSimpleTransitionTarget));
+  }
   ASSERT(transition_number < number_of_transitions());
   return Map::cast(get(ToTargetIndex(transition_number)));
 }
 
 
 void TransitionArray::SetTarget(int transition_number, Map* value) {
+  if (IsSimpleTransition()) {
+    ASSERT(transition_number == kSimpleTransitionIndex);
+    return set(kSimpleTransitionTarget, value);
+  }
   ASSERT(transition_number < number_of_transitions());
   set(ToTargetIndex(transition_number), value);
 }
 
 
 PropertyDetails TransitionArray::GetTargetDetails(int transition_number) {
   Map* map = GetTarget(transition_number);
   DescriptorArray* descriptors = map->instance_descriptors();
   int descriptor = map->LastAdded();
   return descriptors->GetDetails(descriptor);
@@ skipping 16 matching lines @@
 
 
 #undef FIELD_ADDR
 #undef WRITE_FIELD
 #undef CONDITIONAL_WRITE_BARRIER
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_INL_H_