Optimize clearing of map transitions.

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 2062 matching lines @@
 
 
 void WeakCell::set_next(Object* val, WriteBarrierMode mode) {
   WRITE_FIELD(this, kNextOffset, val);
   if (mode == UPDATE_WRITE_BARRIER) {
     WRITE_BARRIER(GetHeap(), this, kNextOffset, val);
   }
 }
 
 
-void WeakCell::clear_next(Heap* heap) {
-  set_next(heap->the_hole_value(), SKIP_WRITE_BARRIER);
+void WeakCell::clear_next(Object* the_hole_value) {
+  set_next(the_hole_value, SKIP_WRITE_BARRIER);

[Hannes Payer (out of office), 2015/12/08 14:19:41]

Let's DCHECK that the_hole_value is the hole value.

[ulan, 2015/12/08 16:25:04]

Done.

 }
 
 
 bool WeakCell::next_cleared() { return next()->IsTheHole(); }
 
 
 int JSObject::GetHeaderSize() { return GetHeaderSize(map()->instance_type()); }
 
 
 int JSObject::GetHeaderSize(InstanceType type) {
@@ skipping 3404 matching lines @@
 void Map::set_prototype_info(Object* value, WriteBarrierMode mode) {
   DCHECK(is_prototype_map());
   WRITE_FIELD(this, Map::kTransitionsOrPrototypeInfoOffset, value);
   CONDITIONAL_WRITE_BARRIER(
       GetHeap(), this, Map::kTransitionsOrPrototypeInfoOffset, value, mode);
 }
 
 
 void Map::SetBackPointer(Object* value, WriteBarrierMode mode) {
   DCHECK(instance_type() >= FIRST_JS_RECEIVER_TYPE);
-  DCHECK((value->IsUndefined() && GetBackPointer()->IsMap()) ||
-         (value->IsMap() && GetBackPointer()->IsUndefined()));
+  DCHECK((value->IsMap() && GetBackPointer()->IsUndefined()));
   DCHECK(!value->IsMap() ||
          Map::cast(value)->GetConstructor() == constructor_or_backpointer());
   set_constructor_or_backpointer(value, mode);
 }
 
 
 ACCESSORS(Map, code_cache, Object, kCodeCacheOffset)
 ACCESSORS(Map, dependent_code, DependentCode, kDependentCodeOffset)
 ACCESSORS(Map, weak_cell_cache, Object, kWeakCellCacheOffset)
 ACCESSORS(Map, constructor_or_backpointer, Object,
@@ skipping 2348 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_