Decoupling MarkDescriptorArray as much as possible from the ContentArray.

src/mark-compact.cc

 // 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 1854 matching lines @@
 template <class T>
 void Marker<T>::MarkDescriptorArray(DescriptorArray* descriptors) {
   // Empty descriptor array is marked as a root before any maps are marked.
   ASSERT(descriptors != descriptors->GetHeap()->empty_descriptor_array());
 
   // The DescriptorArray contains a pointer to its contents array, but the
   // contents array will be marked black and hence not be visited again.
   if (!base_marker()->MarkObjectAndPush(descriptors)) return;
   FixedArray* contents = FixedArray::cast(
       descriptors->get(DescriptorArray::kContentArrayIndex));
-  ASSERT(contents->length() >= 2);
   ASSERT(Marking::IsWhite(Marking::MarkBitFrom(contents)));
   base_marker()->MarkObjectWithoutPush(contents);
 
-  // Contents contains (value, details) pairs.  If the descriptor contains a
-  // transition (value is a Map), we don't mark the value as live.  It might
-  // be set to the NULL_DESCRIPTOR in ClearNonLiveTransitions later.
-  for (int i = 0; i < contents->length(); i += 2) {
-    PropertyDetails details(Smi::cast(contents->get(i + 1)));
+  // If the descriptor contains a transition (value is a Map), we don't mark the
+  // value as live. It might be set to the NULL_DESCRIPTOR in
+  // ClearNonLiveTransitions later.
+  for (int i = 0; i < descriptors->number_of_descriptors(); ++i) {
+    PropertyDetails details(descriptors->GetDetails(i));
+    Object** slot = descriptors->GetValueSlot(i);
 
-    Object** slot = contents->data_start() + i;
     if (!(*slot)->IsHeapObject()) continue;
     HeapObject* value = HeapObject::cast(*slot);
 
     mark_compact_collector()->RecordSlot(slot, slot, *slot);
 
     switch (details.type()) {
       case NORMAL:
       case FIELD:
       case CONSTANT_FUNCTION:
       case HANDLER:
@@ skipping 2206 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal