DescriptorArray::CopyFrom should always drop transitions for CALLBACKS.

src/objects.h

 // 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 2416 matching lines @@
    private:
     IncrementalMarking* marking_;
   };
 
   // Accessor for complete descriptor.
   inline void Get(int descriptor_number, Descriptor* desc);
   inline void Set(int descriptor_number,
                   Descriptor* desc,
                   const WhitenessWitness&);
 
-  // Transfer complete descriptor from another descriptor array to
-  // this one.
-  inline void CopyFrom(int index,
-                       DescriptorArray* src,
+  // Transfer complete descriptor from src descriptor array to dst, dropping map
+  // transitions in CALLBACKS.
+  static void CopyFrom(Handle<DescriptorArray> dst,
+                       int dst_index,
+                       Handle<DescriptorArray> src,
                        int src_index,
-                       const WhitenessWitness&);
+                       const WhitenessWitness& witness);
+
+  MUST_USE_RESULT MaybeObject* CopyFrom(int dst_index,

[Michael Starzinger, 2012/02/13 14:04:17]

Could you add a similar comment like above to this function? It really helps
because most editors have the ability to quickly display those comments.

+                                        DescriptorArray* src,
+                                        int src_index,
+                                        const WhitenessWitness&);
 
   // Copy the descriptor array, insert a new descriptor and optionally
   // remove map transitions.  If the descriptor is already present, it is
   // replaced.  If a replaced descriptor is a real property (not a transition
   // or null), its enumeration index is kept as is.
   // If adding a real property, map transitions must be removed.  If adding
   // a transition, they must not be removed.  All null descriptors are removed.
   MUST_USE_RESULT MaybeObject* CopyInsert(Descriptor* descriptor,
                                           TransitionFlag transition_flag);
 
@@ skipping 5322 matching lines @@
 //   * undefined: considered an accessor by the spec, too, strangely enough
 //   * the hole: an accessor which has not been set
 //   * a pointer to a map: a transition used to ensure map sharing
 class AccessorPair: public Struct {
  public:
   DECL_ACCESSORS(getter, Object)
   DECL_ACCESSORS(setter, Object)
 
   static inline AccessorPair* cast(Object* obj);
 
+  MaybeObject* CopyWithoutTransitions();

[Michael Starzinger, 2012/02/13 14:10:25]

This needs a MUST_USE_RESULT.

+
 #ifdef OBJECT_PRINT
   void AccessorPairPrint(FILE* out = stdout);
 #endif
 #ifdef DEBUG
   void AccessorPairVerify();
 #endif
 
   static const int kGetterOffset = HeapObject::kHeaderSize;
   static const int kSetterOffset = kGetterOffset + kPointerSize;
   static const int kSize = kSetterOffset + kPointerSize;
@@ skipping 491 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_