Only mark the descriptor that is valid for the map in question. If this map

src/objects-inl.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 2124 matching lines @@
 
 
 Object** DescriptorArray::GetKeySlot(int descriptor_number) {
   ASSERT(descriptor_number < number_of_descriptors());
   return HeapObject::RawField(
       reinterpret_cast<HeapObject*>(this),
       OffsetOfElementAt(ToKeyIndex(descriptor_number)));
 }
 
 
+Object** DescriptorArray::GetDescriptorStartSlot(int descriptor_number) {
+  return GetKeySlot(descriptor_number);
+}
+
+
+Object** DescriptorArray::GetDescriptorEndSlot(int descriptor_number) {
+  return GetValueSlot(descriptor_number - 1) + 1;
+}
+
+
 String* DescriptorArray::GetKey(int descriptor_number) {
   ASSERT(descriptor_number < number_of_descriptors());
   return String::cast(get(ToKeyIndex(descriptor_number)));
 }
 
 
 int DescriptorArray::GetSortedKeyIndex(int descriptor_number) {
   return GetDetails(descriptor_number).pointer();
 }
 
@@ skipping 3725 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_