Reland of "Enable inobject double fields unboxing for 64-bit archs."

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 5202 matching lines @@
   map->set_transitions(*transitions);
 }
 
 
 LayoutDescriptor* Map::layout_descriptor_gc_safe() {
   Object* layout_desc = READ_FIELD(this, kLayoutDecriptorOffset);
   return LayoutDescriptor::cast_gc_safe(layout_desc);
 }
 
 
+bool Map::HasFastPointerLayout() const {
+  Object* layout_desc = READ_FIELD(this, kLayoutDecriptorOffset);
+  return LayoutDescriptor::IsFastPointerLayout(layout_desc);
+}
+
+
 void Map::UpdateDescriptors(DescriptorArray* descriptors,
                             LayoutDescriptor* layout_desc) {
   set_instance_descriptors(descriptors);
   if (FLAG_unbox_double_fields) {
     if (layout_descriptor()->IsSlowLayout()) {
       set_layout_descriptor(layout_desc);
     }
     SLOW_DCHECK(layout_descriptor()->IsConsistentWithMap(this));
     DCHECK(visitor_id() == StaticVisitorBase::GetVisitorId(this));
   }
@@ skipping 2117 matching lines @@
       v->VisitPointer(HeapObject::RawField(object, offset));
     }
   }
 }
 
 
 template<int start_offset, int end_offset, int size>
 void FixedBodyDescriptor<start_offset, end_offset, size>::IterateBody(
     HeapObject* obj,
     ObjectVisitor* v) {
-  if (!FLAG_unbox_double_fields ||
-      obj->map()->layout_descriptor()->IsFastPointerLayout()) {

[Igor Sheludko, 2014/11/24 09:32:10]

It is not correct to call here layout_descriptor() because it could be moved by
GC, but for the purpose of checking if it is fast or not we could just compare
it with a Smi zero instead of involving heavy machinery like
layout_descriptor_gc_safe()->IsFastPointerLayout().

+  if (!FLAG_unbox_double_fields || obj->map()->HasFastPointerLayout()) {
     v->VisitPointers(HeapObject::RawField(obj, start_offset),
                      HeapObject::RawField(obj, end_offset));
   } else {
     IterateBodyUsingLayoutDescriptor(obj, start_offset, end_offset, v);
   }
 }
 
 
 template<int start_offset>
 void FlexibleBodyDescriptor<start_offset>::IterateBody(HeapObject* obj,
                                                        int object_size,
                                                        ObjectVisitor* v) {
-  if (!FLAG_unbox_double_fields ||
-      obj->map()->layout_descriptor()->IsFastPointerLayout()) {
+  if (!FLAG_unbox_double_fields || obj->map()->HasFastPointerLayout()) {
     v->VisitPointers(HeapObject::RawField(obj, start_offset),
                      HeapObject::RawField(obj, object_size));
   } else {
     IterateBodyUsingLayoutDescriptor(obj, start_offset, object_size, v);
   }
 }
 
 
 template<class Derived, class TableType>
 Object* OrderedHashTableIterator<Derived, TableType>::CurrentKey() {
@@ skipping 54 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_