*** old/src/share/vm/opto/macro.cpp	Tue Feb  7 16:22:54 2012
--- new/src/share/vm/opto/macro.cpp	Tue Feb  7 16:22:54 2012

*** 232,246 ****
--- 232,255 ----
        assert(mem->is_Store(), "store required");
        _igvn.replace_node(mem, mem->in(MemNode::Memory));
      }
    } else {
      // G1 pre/post barriers
!     assert(p2x->outcnt() == 2, "expects 2 users: Xor and URShift nodes");
!     assert(p2x->outcnt() <= 2, "expects 1 or 2 users: Xor and URShift nodes");
      // It could be only one user, URShift node, in Object.clone() instrinsic
      // but the new allocation is passed to arraycopy stub and it could not
      // be scalar replaced. So we don't check the case.
  
+     // An other case of only one user (Xor) is when the value check for NULL
+     // in G1 post barrier is folded after CCP so the code which used URShift
+     // is removed.
+ 
+     // Take Region node before eliminating post barrier since it also
+     // eliminates CastP2X node when it has only one user.
+     Node* this_region = p2x->in(0);
+     assert(this_region != NULL, "");
+ 
      // Remove G1 post barrier.
  
      // Search for CastP2X->Xor->URShift->Cmp path which
      // checks if the store done to a different from the value's region.
      // And replace Cmp with #0 (false) to collapse G1 post barrier.

*** 261,272 ****
--- 270,279 ----
      _igvn.replace_node(cmpx, makecon(TypeInt::CC_EQ));
  
      // Remove G1 pre barrier.
  
      // Search "if (marking != 0)" check and set it to "false".
      Node* this_region = p2x->in(0);
      assert(this_region != NULL, "");
      // There is no G1 pre barrier if previous stored value is NULL
      // (for example, after initialization).
      if (this_region->is_Region() && this_region->req() == 3) {
        int ind = 1;
        if (!this_region->in(ind)->is_IfFalse()) {

*** 290,300 ****
--- 297,307 ----
          }
        }
      }
      // Now CastP2X can be removed since it is used only on dead path
      // which currently still alive until igvn optimize it.
!     assert(p2x->outcnt() == 0 || p2x->unique_out()->Opcode() == Op_URShiftX, "");
      _igvn.replace_node(p2x, top());
    }
  }
  
  // Search for a memory operation for the specified memory slice.