Removed recording of Target Slot in transition arrays since they only contain maps.

src/objects.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 7126 matching lines @@
 // TODO(mstarzinger): This method should be moved into MarkCompactCollector,
 // because it cannot be called from outside the GC and we already have methods
 // depending on the transitions layout in the GC anyways.
 void Map::ClearNonLiveTransitions(Heap* heap) {
   // If there are no transitions to be cleared, return.
   // TODO(verwaest) Should be an assert, otherwise back pointers are not
   // properly cleared.
   if (!HasTransitionArray()) return;
 
   TransitionArray* t = transitions();
+  MarkCompactCollector* collector = heap->mark_compact_collector();
 
   int transition_index = 0;
 
   // Compact all live descriptors to the left.
   for (int i = 0; i < t->number_of_transitions(); ++i) {
     if (!ClearBackPointer(heap, t->GetTarget(i))) {
       if (i != transition_index) {
         String* key = t->GetKey(i);
-        Map* target = t->GetTarget(i);
         t->SetKey(transition_index, key);
-        t->SetTarget(transition_index, target);
-        MarkCompactCollector* collector = heap->mark_compact_collector();
         Object** key_slot = t->GetKeySlot(transition_index);
         collector->RecordSlot(key_slot, key_slot, key);
-        Object** target_slot = t->GetTargetSlot(transition_index);
-        collector->RecordSlot(target_slot, target_slot, target);
+        // Target slots do not need to be recorded since maps are not compacted.
+        t->SetTarget(transition_index, t->GetTarget(i));
       }
       transition_index++;
     }
   }
 
   if (t->HasElementsTransition() &&
       ClearBackPointer(heap, t->elements_transition())) {
     t->ClearElementsTransition();
   } else {
     // If there are no transitions to be cleared, return.
@@ skipping 5868 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal