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

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 108f9f62489ad62b492ce22a748826a81baee62f..f3ac5717cd25bc9a56d811b10a2959352a02bfb8 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -5220,6 +5220,12 @@ LayoutDescriptor* Map::layout_descriptor_gc_safe() {
 }
 
 
+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);
@@ -7357,8 +7363,7 @@ 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 {
@@ -7371,8 +7376,7 @@ 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 {