Work around a bug in Clang that optimizes away a NULL check

Review URL: https://codereview.chromium.org/12090072

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13562 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/spaces.cc

@@ -711,7 +711,7 @@ LargePage* MemoryAllocator::AllocateLargePage(intptr_t object_size,
 
 void MemoryAllocator::Free(MemoryChunk* chunk) {
   LOG(isolate_, DeleteEvent("MemoryChunk", chunk));
-  if (chunk->owner() != NULL) {
+  if (chunk->has_owner()) {
     ObjectSpace space =
         static_cast<ObjectSpace>(1 << chunk->owner()->identity());
     PerformAllocationCallback(space, kAllocationActionFree, chunk->size());

src/spaces.h

@@ -333,6 +333,14 @@ class MemoryChunk {
            kFailureTag);
   }
 
+  // Workaround for a bug in Clang-3.3 which in some situations optimizes away
+  // an "if (chunk->owner() != NULL)" check.
+  bool has_owner() {
+    if (owner_ == 0) return false;
+    if (reinterpret_cast<intptr_t>(owner_) == kFailureTag) return false;
+    return true;
+  }
+
   VirtualMemory* reserved_memory() {
     return &reservation_;
   }