Transition ownership back if the descriptors were shared via elements transitions.

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 7413 matching lines @@
 
 
 void String::PrintOn(FILE* file) {
   int length = this->length();
   for (int i = 0; i < length; i++) {
     fprintf(file, "%c", Get(i));
   }
 }
 
 
-// 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;
-}
-
-
 static void TrimEnumCache(Heap* heap, Map* map, DescriptorArray* descriptors) {
   int live_enum = map->EnumLength();
   if (live_enum == Map::kInvalidEnumCache) {
     live_enum = map->NumberOfDescribedProperties(OWN_DESCRIPTORS, DONT_ENUM);
   }
   if (live_enum == 0) return descriptors->ClearEnumCache();
 
   FixedArray* enum_cache = descriptors->GetEnumCache();
 
   int to_trim = enum_cache->length() - live_enum;
@@ skipping 25 matching lines @@
   if (to_trim > keep) {
     RightTrimFixedArray<FROM_GC>(heap, descriptors, to_trim - keep);
   }
   descriptors->SetNumberOfDescriptors(number_of_own_descriptors);
 
   if (descriptors->HasEnumCache()) TrimEnumCache(heap, map, descriptors);
   descriptors->Sort();
 }
 
 
+// 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,
+                             DescriptorArray* descriptors,
+                             bool* descriptors_owner_died) {
+  if (Marking::MarkBitFrom(target).Get()) return false;
+  if (target->instance_descriptors() == descriptors) {
+    *descriptors_owner_died = true;
+  }
+  target->SetBackPointer(heap->undefined_value(), SKIP_WRITE_BARRIER);
+  return true;
+}
+
+
 // 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;
 
   DescriptorArray* descriptors = t->descriptors();
   bool descriptors_owner_died = false;
 
   // Compact all live descriptors to the left.
   for (int i = 0; i < t->number_of_transitions(); ++i) {
     Map* target = t->GetTarget(i);
-    if (ClearBackPointer(heap, target)) {
-      ASSERT(!Marking::IsGrey(Marking::MarkBitFrom(target)));
-      DescriptorArray* target_descriptors = target->instance_descriptors();
-      if ((target_descriptors->number_of_descriptors() == 0 &&
-           target->NumberOfOwnDescriptors() > 0) ||
-          target_descriptors == descriptors) {
-        descriptors_owner_died = true;
-      }
-    } else {
+    if (!ClearBackPointer(heap, target, descriptors, &descriptors_owner_died)) {
       if (i != transition_index) {
         String* key = t->GetKey(i);
         t->SetKey(transition_index, key);
         Object** key_slot = t->GetKeySlot(transition_index);
         collector->RecordSlot(key_slot, key_slot, key);
         // 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())) {
-    if (t->elements_transition()->instance_descriptors() == descriptors) {
-      descriptors_owner_died = true;
-    }
+      ClearBackPointer(heap,
+                       t->elements_transition(),
+                       descriptors,
+                       &descriptors_owner_died)) {
     t->ClearElementsTransition();
   } else {
     // If there are no transitions to be cleared, return.
     // TODO(verwaest) Should be an assert, otherwise back pointers are not
     // properly cleared.
     if (transition_index == t->number_of_transitions()) return;
   }
 
   int number_of_own_descriptors = NumberOfOwnDescriptors();
 
@@ skipping 5983 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