Also in ClearNonLiveTransitions we have to check if there still is a...

Also in ClearNonLiveTransitions we have to check if there still is a transition array before we access it.
This should never happen in the long run, but will happen when maps still have a back-pointer while the forward pointer (the transition) was overwritten.

Review URL: https://chromiumcodereview.appspot.com/10704109

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12000 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/objects-inl.h

@@ -1997,7 +1997,7 @@ int DescriptorArray::SearchWithCache(String* name) {
 
 
 TransitionArray* DescriptorArray::transitions() {
-  if (!this->MayContainTransitions()) return NULL;
+  ASSERT(MayContainTransitions());
   Object* array = get(kTransitionsIndex);
   return TransitionArray::cast(array);
 }

src/objects.cc

@@ -7366,11 +7366,12 @@ static bool ClearNonLiveTransition(Heap* heap,
 // 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) {
-  TransitionArray* t = transitions();
   // If there are no transitions to be cleared, return.
   // TODO(verwaest) Should be an assert, otherwise back pointers are not
   // properly cleared.
-  if (t == NULL) return;
+  if (!HasTransitionArray()) return;
+
+  TransitionArray* t = transitions();
 
   int transition_index = 0;