Bug 841558 - Don't exactly mark tagged NULL pointers; r=sfink

--HG--
extra : rebase_source : 062760866d171948b2f866910ebd764521ed3f6f

js/src/gc/Marking.h

@@ -109,6 +109,13 @@ DeclMarker(TypeObject, types::TypeObject)
 
 #undef DeclMarker
 
+/* Return true if the pointer is NULL, or if it is a tagged pointer to NULL. */
+JS_ALWAYS_INLINE bool
+IsNullTaggedPointer(void *p)
+{
+    return uintptr_t(p) < 32;
+}
+
 /*** Externally Typed Marking ***/
 
 /*

js/src/gc/RootMarking.cpp

@@ -46,7 +46,7 @@ static inline void
 MarkExactStackRoot(JSTracer *trc, Rooted<void*> *rooter, ThingRootKind kind)
 {
     void **addr = (void **)rooter->address();
-    if (!*addr)
+    if (IsNullTaggedPointer(*addr))
         return;
 
     if (kind == THING_ROOT_OBJECT && *addr == Proxy::LazyProto)

js/src/vm/ObjectImpl-inl.h

@@ -359,7 +359,7 @@ js::ObjectImpl::writeBarrierPre(ObjectImpl *obj)
      * This would normally be a null test, but TypeScript::global uses 0x1 as a
      * special value.
      */
-    if (uintptr_t(obj) < 32)
+    if (IsNullTaggedPointer(obj))
         return;
 
     Zone *zone = obj->zone();
@@ -376,7 +376,7 @@ js::ObjectImpl::writeBarrierPre(ObjectImpl *obj)
 js::ObjectImpl::writeBarrierPost(ObjectImpl *obj, void *addr)
 {
 #ifdef JSGC_GENERATIONAL
-    if (uintptr_t(obj) < 32)
+    if (IsNullTaggedPointer(obj))
         return;
     obj->runtime()->gcStoreBuffer.putCell((Cell **)addr);
 #endif