Return descriptor ownership after TrimDescriptorArray to allow resharing of descriptor arrays

src/objects.cc

 // Copyright 2013 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 9228 matching lines @@
   int number_of_descriptors = descriptors->number_of_descriptors_storage();
   int to_trim = number_of_descriptors - number_of_own_descriptors;
   if (to_trim == 0) return;
 
   RightTrimFixedArray<FROM_GC>(
       heap, descriptors, to_trim * DescriptorArray::kDescriptorSize);
   descriptors->SetNumberOfDescriptors(number_of_own_descriptors);
 
   if (descriptors->HasEnumCache()) TrimEnumCache(heap, map, descriptors);
   descriptors->Sort();
+
+  map->set_owns_descriptors(true);

[Michael Starzinger, 2013/10/16 09:34:06]

nit: Can we hoist this out of this helper into Map::ClearNonLiveTransitions()?
Otherwise the semantics of TrimDescriptorArray get blurred and it magically does
other things.

[rmcilroy, 2013/10/16 10:44:01]

Makes sense, done.

 }
 
 
 // Clear a possible back pointer in case the transition leads to a dead map.
 // Return true in case a back pointer has been cleared and false otherwise.
 static bool ClearBackPointer(Heap* heap, Map* target) {
   if (Marking::MarkBitFrom(target).Get()) return false;
   target->SetBackPointer(heap->undefined_value(), SKIP_WRITE_BARRIER);
   return true;
 }
@@ skipping 7002 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal