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

src/spaces.h

 // Copyright 2011 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 315 matching lines @@
     }
   }
 
   void set_owner(Space* space) {
     ASSERT((reinterpret_cast<intptr_t>(space) & kFailureTagMask) == 0);
     owner_ = reinterpret_cast<Address>(space) + kFailureTag;
     ASSERT((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
            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_;
   }
 
   void InitializeReservedMemory() {
     reservation_.Reset();
   }
 
   void set_reserved_memory(VirtualMemory* reservation) {
     ASSERT_NOT_NULL(reservation);
@@ skipping 2473 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_