Swapped transition array and descriptor array.

src/objects.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 2173 matching lines @@
   // Copy the descriptors from the array.
   if (0 < descriptor_count) {
     for (int i = 0; i < descriptor_count; i++) {
       result->CopyFrom(i, *array, i, witness);
     }
   }
 
   // After this point the GC is not allowed to run anymore until the map is in a
   // consistent state again, i.e., all the descriptors are appended and the
   // descriptor array is trimmed to the right size.
-  map->set_instance_descriptors(*result);
+  Map::SetDescriptors(map, result);
 
   // Fill in new callback descriptors.  Process the callbacks from
   // back to front so that the last callback with a given name takes
   // precedence over previously added callbacks with that name.
   for (int i = nof_callbacks - 1; i >= 0; i--) {
     AccessorInfo* entry = AccessorInfo::cast(callbacks.get(i));
     String* key = String::cast(entry->name());
     // Check if a descriptor with this name already exists before writing.
     if (LinearSearch(*result, key, map->NumberOfSetDescriptors()) ==
         DescriptorArray::kNotFound) {
       CallbacksDescriptor desc(key, entry, entry->property_attributes());
       map->AppendDescriptor(&desc, witness);
     }
   }
 
   int new_number_of_descriptors = map->NumberOfSetDescriptors();
   // Reinstall the original descriptor array if no new elements were added.
   if (new_number_of_descriptors == descriptor_count) {
-    map->set_instance_descriptors(*array);
+    Map::SetDescriptors(map, array);
     return;
   }
 
   // If duplicates were detected, trim the descriptor array to the right size.
   int new_array_size = DescriptorArray::LengthFor(new_number_of_descriptors);
   if (new_array_size < result->length()) {
     RightTrimFixedArray<FROM_MUTATOR>(
         isolate->heap(), *result, result->length() - new_array_size);
   }
 }
@@ skipping 1871 matching lines @@
   { MaybeObject* maybe = NormalizeElements();
     if (!maybe->To<SeededNumberDictionary>(&dictionary)) return maybe;
   }
   ASSERT(HasDictionaryElements() || HasDictionaryArgumentsElements());
   // Make sure that we never go back to fast case.
   dictionary->set_requires_slow_elements();
 
   // Do a map transition, other objects with this map may still
   // be extensible.
   Map* new_map;
-  MaybeObject* maybe = map()->Copy(DescriptorArray::MAY_BE_SHARED);
+  MaybeObject* maybe = map()->Copy();
   if (!maybe->To(&new_map)) return maybe;
 
   new_map->set_is_extensible(false);
   set_map(new_map);
   ASSERT(!map()->is_extensible());
   return new_map;
 }
 
 
 // Tests for the fast common case for property enumeration:
@@ skipping 16 matching lines @@
     if (curr != this) {
       FixedArray* curr_fixed_array =
           FixedArray::cast(curr->map()->instance_descriptors()->GetEnumCache());
       if (curr_fixed_array->length() > 0) return false;
     }
   }
   return true;
 }
 
 
+void Map::SetDescriptors(Handle<Map> map,
+                         Handle<DescriptorArray> descriptors) {
+  Isolate* isolate = map->GetIsolate();
+  CALL_HEAP_FUNCTION_VOID(isolate, map->SetDescriptors(*descriptors));
+}
+
+
 int Map::NumberOfDescribedProperties(PropertyAttributes filter) {
   int result = 0;
   DescriptorArray* descs = instance_descriptors();
   for (int i = 0; i < descs->number_of_descriptors(); i++) {
     PropertyDetails details = descs->GetDetails(i);
     if ((details.attributes() & filter) == 0) {
       result++;
     }
   }
   return result;
@@ skipping 718 matching lines @@
                                          TransitionFlag flag) {
   Map* result;
   MaybeObject* maybe_result = CopyDropDescriptors();
   if (!maybe_result->To(&result)) return maybe_result;
 
   if (last_added == kNoneAdded) {
     ASSERT(descriptors->number_of_descriptors() == 0);
   } else {
     ASSERT(descriptors->GetDetails(last_added).index() ==
            descriptors->number_of_descriptors());
-    result->set_instance_descriptors(descriptors);
+    MaybeObject* maybe_failure = result->SetDescriptors(descriptors);
+    if (maybe_failure->IsFailure()) return maybe_failure;
     result->SetLastAdded(last_added);
   }
 
   if (flag == INSERT_TRANSITION && CanHaveMoreTransitions()) {
     TransitionArray* transitions;
     MaybeObject* maybe_transitions = AddTransition(name, result);
     if (!maybe_transitions->To(&transitions)) return maybe_transitions;
 
-    MaybeObject* maybe_set = set_transitions(transitions);
-    if (maybe_set->IsFailure()) return maybe_set;
-
+    set_transitions(transitions);
     result->SetBackPointer(this);
   }
 
   return result;
 }
 
 
 MaybeObject* Map::CopyAsElementsKind(ElementsKind kind, TransitionFlag flag) {
   // Create a new free-floating map only if we are not allowed to store it.
   Map* new_map = NULL;
-  MaybeObject* maybe_new_map = Copy(DescriptorArray::MAY_BE_SHARED);
+  MaybeObject* maybe_new_map = Copy();
   if (!maybe_new_map->To(&new_map)) return maybe_new_map;
   new_map->set_elements_kind(kind);
 
   if (flag == INSERT_TRANSITION) {
     ASSERT(!HasElementsTransition() ||
         ((elements_transition_map()->elements_kind() == DICTIONARY_ELEMENTS ||
           IsExternalArrayElementsKind(
               elements_transition_map()->elements_kind())) &&
          (kind == DICTIONARY_ELEMENTS ||
           IsExternalArrayElementsKind(kind))));
@@ skipping 11 matching lines @@
 }
 
 
 MaybeObject* Map::CopyWithPreallocatedFieldDescriptors() {
   if (pre_allocated_property_fields() == 0) return CopyDropDescriptors();
 
   // If the map has pre-allocated properties always start out with a descriptor
   // array describing these properties.
   ASSERT(constructor()->IsJSFunction());
   JSFunction* ctor = JSFunction::cast(constructor());
-  Map* initial_map = ctor->initial_map();
-  DescriptorArray* initial_descriptors = initial_map->instance_descriptors();
-  DescriptorArray* descriptors;
-  MaybeObject* maybe_descriptors =
-      initial_descriptors->Copy(DescriptorArray::MAY_BE_SHARED);
-  if (!maybe_descriptors->To(&descriptors)) return maybe_descriptors;
+  Map* map = ctor->initial_map();
+  DescriptorArray* descriptors = map->instance_descriptors();
 
-  int last_added = initial_map->LastAdded();
+  int last_added = map->LastAdded();
 
   return CopyReplaceDescriptors(descriptors, NULL, last_added, OMIT_TRANSITION);
 }
 
 
-MaybeObject* Map::Copy(DescriptorArray::SharedMode shared_mode) {
-  DescriptorArray* source_descriptors = instance_descriptors();
-  DescriptorArray* descriptors;
-  MaybeObject* maybe_descriptors = source_descriptors->Copy(shared_mode);
-  if (!maybe_descriptors->To(&descriptors)) return maybe_descriptors;
-
+MaybeObject* Map::Copy() {
+  DescriptorArray* descriptors = instance_descriptors();
   int last_added = LastAdded();
 
   return CopyReplaceDescriptors(descriptors, NULL, last_added, OMIT_TRANSITION);
 }
 
 
 static bool InsertionPointFound(String* key1, String* key2) {
   return key1->Hash() > key2->Hash() || key1 == key2;
 }
 
 
 MaybeObject* Map::CopyAddDescriptor(Descriptor* descriptor,
                                     TransitionFlag flag) {
   DescriptorArray* descriptors = instance_descriptors();
 
   // Ensure the key is a symbol.
   MaybeObject* maybe_failure = descriptor->KeyToSymbol();
   if (maybe_failure->IsFailure()) return maybe_failure;
 
   String* key = descriptor->GetKey();
   ASSERT(descriptors->Search(key) == DescriptorArray::kNotFound);
 
   int old_size = descriptors->number_of_descriptors();
   int new_size = old_size + 1;
 
   DescriptorArray* new_descriptors;
-  MaybeObject* maybe_descriptors =
-      DescriptorArray::Allocate(new_size, DescriptorArray::MAY_BE_SHARED);
+  MaybeObject* maybe_descriptors = DescriptorArray::Allocate(new_size);
   if (!maybe_descriptors->To(&new_descriptors)) return maybe_descriptors;
 
   FixedArray::WhitenessWitness witness(new_descriptors);
 
   // Copy the descriptors, inserting a descriptor.
   int insertion_index = -1;
   int to = 0;
   for (int from = 0; from < old_size; ++from) {
     if (insertion_index < 0 &&
         InsertionPointFound(descriptors->GetKey(from), key)) {
@@ skipping 40 matching lines @@
   ASSERT(0 <= insertion_index && insertion_index < size);
 
   // Ensure the key is a symbol.
   MaybeObject* maybe_failure = descriptor->KeyToSymbol();
   if (maybe_failure->IsFailure()) return maybe_failure;
 
   String* key = descriptor->GetKey();
   ASSERT(key == descriptors->GetKey(insertion_index));
 
   DescriptorArray* new_descriptors;
-  MaybeObject* maybe_descriptors =
-      DescriptorArray::Allocate(size, DescriptorArray::MAY_BE_SHARED);
+  MaybeObject* maybe_descriptors = DescriptorArray::Allocate(size);
   if (!maybe_descriptors->To(&new_descriptors)) return maybe_descriptors;
 
   FixedArray::WhitenessWitness witness(new_descriptors);
 
   // Copy the descriptors, replacing a descriptor.
   for (int index = 0; index < size; ++index) {
     if (index == insertion_index) continue;
     new_descriptors->CopyFrom(index, descriptors, index, witness);
   }
 
@@ skipping 200 matching lines @@
         IntrusivePrototypeTransitionIterator(GetPrototypeTransitions()).Start();
       }
 
       IntrusiveMapTransitionIterator(transitions()).Start();
     }
   }
 
   // If we have an unvisited child map, return that one and advance. If we have
   // none, return NULL and reset any destroyed FixedArray maps.
   TraversableMap* ChildIteratorNext() {
-    if (HasTransitionArray()) {
-      TransitionArray* transition_array = unchecked_transition_array();
+    TransitionArray* transition_array = unchecked_transition_array();
+    if (!transition_array->map()->IsSmi() &&
+        !transition_array->IsTransitionArray()) {
+      return NULL;
+    }
 
-      if (transition_array->HasPrototypeTransitions()) {
-        HeapObject* proto_transitions =
-            transition_array->UncheckedPrototypeTransitions();
-        IntrusivePrototypeTransitionIterator proto_iterator(proto_transitions);
-        if (proto_iterator.IsIterating()) {
-          Map* next = proto_iterator.Next();
-          if (next != NULL) return static_cast<TraversableMap*>(next);
-        }
-      }
-
-      IntrusiveMapTransitionIterator transition_iterator(transition_array);
-      if (transition_iterator.IsIterating()) {
-        Map* next = transition_iterator.Next();
+    if (transition_array->HasPrototypeTransitions()) {
+      HeapObject* proto_transitions =
+          transition_array->UncheckedPrototypeTransitions();
+      IntrusivePrototypeTransitionIterator proto_iterator(proto_transitions);
+      if (proto_iterator.IsIterating()) {
+        Map* next = proto_iterator.Next();
         if (next != NULL) return static_cast<TraversableMap*>(next);
       }
     }
 
+    IntrusiveMapTransitionIterator transition_iterator(transition_array);
+    if (transition_iterator.IsIterating()) {
+      Map* next = transition_iterator.Next();
+      if (next != NULL) return static_cast<TraversableMap*>(next);
+    }
+
     return NULL;
   }
 };
 
 
 // Traverse the transition tree in postorder without using the C++ stack by
 // doing pointer reversal.
 void Map::TraverseTransitionTree(TraverseCallback callback, void* data) {
   TraversableMap* current = static_cast<TraversableMap*>(this);
   current->ChildIteratorStart();
@@ skipping 529 matching lines @@
 bool FixedArray::IsEqualTo(FixedArray* other) {
   if (length() != other->length()) return false;
   for (int i = 0 ; i < length(); ++i) {
     if (get(i) != other->get(i)) return false;
   }
   return true;
 }
 #endif
 
 
-MaybeObject* DescriptorArray::Allocate(int number_of_descriptors,
-                                       SharedMode shared_mode) {
+MaybeObject* DescriptorArray::Allocate(int number_of_descriptors) {
   Heap* heap = Isolate::Current()->heap();
   // Do not use DescriptorArray::cast on incomplete object.
   FixedArray* result;
-  if (number_of_descriptors == 0 && shared_mode == MAY_BE_SHARED) {
-    return heap->empty_descriptor_array();
-  }
+  if (number_of_descriptors == 0) return heap->empty_descriptor_array();
   // Allocate the array of keys.
   MaybeObject* maybe_array =
       heap->AllocateFixedArray(LengthFor(number_of_descriptors));
   if (!maybe_array->To(&result)) return maybe_array;
 
   result->set(kEnumCacheIndex, Smi::FromInt(0));
-  result->set(kTransitionsIndex, Smi::FromInt(0));
   return result;
 }
 
 
 void DescriptorArray::SetEnumCache(FixedArray* bridge_storage,
                                    FixedArray* new_cache,
                                    Object* new_index_cache) {
   ASSERT(bridge_storage->length() >= kEnumCacheBridgeLength);
   ASSERT(new_index_cache->IsSmi() || new_index_cache->IsFixedArray());
   if (HasEnumCache()) {
@@ skipping 16 matching lines @@
                                DescriptorArray* src,
                                int src_index,
                                const WhitenessWitness& witness) {
   Object* value = src->GetValue(src_index);
   PropertyDetails details = src->GetDetails(src_index);
   Descriptor desc(src->GetKey(src_index), value, details);
   Set(dst_index, &desc, witness);
 }
 
 
-MaybeObject* DescriptorArray::Copy(SharedMode shared_mode) {
-  // Allocate the new descriptor array.
-  int number_of_descriptors = this->number_of_descriptors();
-  DescriptorArray* new_descriptors;
-  MaybeObject* maybe_result = Allocate(number_of_descriptors, shared_mode);
-  if (!maybe_result->To(&new_descriptors)) return maybe_result;
-
-  // Copy the content.
-  if (number_of_descriptors > 0) {
-    FixedArray::WhitenessWitness witness(new_descriptors);
-    for (int i = 0; i < number_of_descriptors; i++) {
-      new_descriptors->CopyFrom(i, this, i, witness);
-    }
-  }
-
-  return new_descriptors;
-}
-
-
 // We need the whiteness witness since sort will reshuffle the entries in the
 // descriptor array. If the descriptor array were to be black, the shuffling
 // would move a slot that was already recorded as pointing into an evacuation
 // candidate. This would result in missing updates upon evacuation.
 void DescriptorArray::Sort(const WhitenessWitness& witness) {
   // In-place heap sort.
   int len = number_of_descriptors();
   // Bottom-up max-heap construction.
   // Index of the last node with children
   const int max_parent_index = (len / 2) - 1;
@@ skipping 1332 matching lines @@
     // If there are no transitions to be cleared, return.
     // TODO(verwaest) Should be an assert, otherwise back pointers are not
     // properly cleared.
     if (transition_index == t->number_of_transitions()) return;
   }
 
   // If the final transition array does not contain any live transitions, remove
   // the transition array from the map.
   if (transition_index == 0 &&
       !t->HasElementsTransition() &&
-      !t->HasPrototypeTransitions()) {
+      !t->HasPrototypeTransitions() &&
+      t->descriptors()->IsEmpty()) {
     return ClearTransitions(heap);
   }
 
   int trim = t->number_of_transitions() - transition_index;
   if (trim > 0) {
     RightTrimFixedArray<FROM_GC>(
         heap, t, trim * TransitionArray::kTransitionSize);
   }
 }
 
@@ skipping 220 matching lines @@
     MaybeObject* ok = JSObject::cast(value)->OptimizeAsPrototype();
     if (ok->IsFailure()) return ok;
   }
 
   // Now some logic for the maps of the objects that are created by using this
   // function as a constructor.
   if (has_initial_map()) {
     // If the function has allocated the initial map
     // replace it with a copy containing the new prototype.
     Map* new_map;
-    MaybeObject* maybe_new_map =
-        initial_map()->Copy(DescriptorArray::MAY_BE_SHARED);
+    MaybeObject* maybe_new_map = initial_map()->Copy();
     if (!maybe_new_map->To(&new_map)) return maybe_new_map;
     new_map->set_prototype(value);
     MaybeObject* maybe_object = set_initial_map_and_cache_transitions(new_map);
     if (maybe_object->IsFailure()) return maybe_object;
   } else {
     // Put the value in the initial map field until an initial map is
     // needed.  At that point, a new initial map is created and the
     // prototype is put into the initial map where it belongs.
     set_prototype_or_initial_map(value);
   }
   heap->ClearInstanceofCache();
   return value;
 }
 
 
 MaybeObject* JSFunction::SetPrototype(Object* value) {
   ASSERT(should_have_prototype());
   Object* construct_prototype = value;
 
   // If the value is not a JSReceiver, store the value in the map's
   // constructor field so it can be accessed.  Also, set the prototype
   // used for constructing objects to the original object prototype.
   // See ECMA-262 13.2.2.
   if (!value->IsJSReceiver()) {
     // Copy the map so this does not affect unrelated functions.
     // Remove map transitions because they point to maps with a
     // different prototype.
     Map* new_map;
-    MaybeObject* maybe_new_map = map()->Copy(DescriptorArray::MAY_BE_SHARED);
+    MaybeObject* maybe_new_map = map()->Copy();
     if (!maybe_new_map->To(&new_map)) return maybe_new_map;
 
     Heap* heap = new_map->GetHeap();
     set_map(new_map);
     new_map->set_constructor(value);
     new_map->set_non_instance_prototype(true);
     construct_prototype =
         heap->isolate()->context()->global_context()->
             initial_object_prototype();
   } else {
@@ skipping 1273 matching lines @@
   // Nothing to do if prototype is already set.
   if (map->prototype() == value) return value;
 
   if (value->IsJSObject()) {
     MaybeObject* ok = JSObject::cast(value)->OptimizeAsPrototype();
     if (ok->IsFailure()) return ok;
   }
 
   Map* new_map = map->GetPrototypeTransition(value);
   if (new_map == NULL) {
-    MaybeObject* maybe_new_map = map->Copy(DescriptorArray::MAY_BE_SHARED);
+    MaybeObject* maybe_new_map = map->Copy();
     if (!maybe_new_map->To(&new_map)) return maybe_new_map;
 
     MaybeObject* maybe_new_cache =
         map->PutPrototypeTransition(value, new_map);
     if (maybe_new_cache->IsFailure()) return maybe_new_cache;
 
     new_map->set_prototype(value);
   }
   ASSERT(new_map->prototype() == value);
   real_receiver->set_map(new_map);
@@ skipping 3705 matching lines @@
     obj->set_map(new_map);
     obj->set_properties(heap->empty_fixed_array());
     // Check that it really works.
     ASSERT(obj->HasFastProperties());
     return obj;
   }
 
   // Allocate the instance descriptor.
   DescriptorArray* descriptors;
   MaybeObject* maybe_descriptors =
-      DescriptorArray::Allocate(instance_descriptor_length,
-                                DescriptorArray::MAY_BE_SHARED);
+      DescriptorArray::Allocate(instance_descriptor_length);
   if (!maybe_descriptors->To(&descriptors)) {
     return maybe_descriptors;
   }
 
   FixedArray::WhitenessWitness witness(descriptors);
 
   int number_of_allocated_fields =
       number_of_fields + unused_property_fields - inobject_props;
   if (number_of_allocated_fields < 0) {
     // There is enough inobject space for all fields (including unused).
@@ skipping 51 matching lines @@
       } else {
         UNREACHABLE();
       }
       ++next_descriptor;
     }
   }
   ASSERT(current_offset == number_of_fields);
 
   descriptors->Sort(witness);
 
+  MaybeObject* maybe_failure = new_map->InitializeDescriptors(descriptors);
+  if (maybe_failure->IsFailure()) return maybe_failure;
   new_map->set_unused_property_fields(unused_property_fields);
-  new_map->InitializeDescriptors(descriptors);
 
   // Transform the object.
   obj->set_map(new_map);
 
   obj->set_properties(fields);
   ASSERT(obj->IsJSObject());
 
   // Check that it really works.
   ASSERT(obj->HasFastProperties());
 
@@ skipping 498 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal