Specialize ScavengingVisitor for the case when all logging and profiling is disabled.

src/objects-visiting.h

 // Copyright 2006-2009 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 123 matching lines @@
         base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords);
 
     return Min(specialization, generic);
   }
 };
 
 
 template<typename Callback>
 class VisitorDispatchTable {
  public:
+  void CopyFrom(VisitorDispatchTable* other) {
+    // We are not using memcpy to guarantee that during update
+    // every element of callbacks_ array will remain correct
+    // pointer (memcpy might be implemented as a byte copying loop).
+    for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
+      NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
+    }
+  }
+
   inline Callback GetVisitor(Map* map) {
-    return callbacks_[map->visitor_id()];
+    return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
   }
 
   void Register(StaticVisitorBase::VisitorId id, Callback callback) {
     ASSERT(id < StaticVisitorBase::kVisitorIdCount);  // id is unsigned.
-    callbacks_[id] = callback;
+    callbacks_[id] = reinterpret_cast<AtomicWord>(callback);
   }
 
   template<typename Visitor,
            StaticVisitorBase::VisitorId base,
            StaticVisitorBase::VisitorId generic,
            int object_size_in_words>
   void RegisterSpecialization() {
     static const int size = object_size_in_words * kPointerSize;
     Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size),
              &Visitor::template VisitSpecialized<size>);
@@ skipping 11 matching lines @@
     RegisterSpecialization<Visitor, base, generic, 4>();
     RegisterSpecialization<Visitor, base, generic, 5>();
     RegisterSpecialization<Visitor, base, generic, 6>();
     RegisterSpecialization<Visitor, base, generic, 7>();
     RegisterSpecialization<Visitor, base, generic, 8>();
     RegisterSpecialization<Visitor, base, generic, 9>();
     Register(generic, &Visitor::Visit);
   }
 
  private:
-  Callback callbacks_[StaticVisitorBase::kVisitorIdCount];
+  AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
 };
 
 
 template<typename StaticVisitor>
 class BodyVisitorBase : public AllStatic {
  public:
   INLINE(static void IteratePointers(Heap* heap,
                                      HeapObject* object,
                                      int start_offset,
                                      int end_offset)) {
@@ skipping 211 matching lines @@
 
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_H_