7114095: G1: assert(obj == oopDesc::load_decode_heap_oop(p)) failed: p should...

7114095: G1: assert(obj == oopDesc::load_decode_heap_oop(p)) failed: p should still be pointing to obj
Summary: As a result of  the changes for 4965777, the G1 reference field scanning closure could be applied to the discovered field of a reference object twice. The failing assert is too strong if the result of the first application of the closure is stolen, and the referenced object, evacuated by another worker thread.
Reviewed-by: ysr, tonyp

src/share/vm/gc_implementation/g1/g1OopClosures.inline.hpp

@@ -84,8 +84,11 @@ template <class T> inline void G1ParScanClosure::do_oop_nv(T* p) {
       // slightly paranoid test; I'm trying to catch potential
       // problems before we go into push_on_queue to know where the
       // problem is coming from
-      assert(obj == oopDesc::load_decode_heap_oop(p),
-             "p should still be pointing to obj");
+      assert((obj == oopDesc::load_decode_heap_oop(p)) ||
+             (obj->is_forwarded() &&
+                 obj->forwardee() == oopDesc::load_decode_heap_oop(p)),
+             "p should still be pointing to obj or to its forwardee");
+
       _par_scan_state->push_on_queue(p);
     } else {
       _par_scan_state->update_rs(_from, p, _par_scan_state->queue_num());