*** old/src/share/vm/opto/matcher.cpp	Wed Apr 22 15:01:17 2009
--- new/src/share/vm/opto/matcher.cpp	Wed Apr 22 15:01:17 2009

*** 273,282 ****
--- 273,288 ----
    find_shared( C->root() );
    find_shared( C->top() );
  
    C->print_method("Before Matching");
  
+   // Create new ideal node ConP #NULL even if it does exist in old space
+   // to avoid false sharing if the corresponding mach node is not used.
+   // The corresponding mach node is only used in rare cases for derived
+   // pointers.
+   Node* new_ideal_null = ConNode::make(C, TypePtr::NULL_PTR);
+ 
    // Swap out to old-space; emptying new-space
    Arena *old = C->node_arena()->move_contents(C->old_arena());
  
    // Save debug and profile information for nodes in old space:
    _old_node_note_array = C->node_note_array();

*** 314,324 ****
--- 320,339 ----
            --j;
            --jmax;
          }
        }
  
+       // Generate new mach node for ConP #NULL
+       assert(new_ideal_null != NULL, "sanity");
+       _mach_null = match_tree(new_ideal_null);
+       // Don't set control, it will confuse GCM since there are no uses.
+       // The control will be set when this node is used first time
+       // in find_base_for_derived().
+       assert(_mach_null != NULL, "");
+ 
        C->set_root(xroot->is_Root() ? xroot->as_Root() : NULL);
+ 
  #ifdef ASSERT
        verify_new_nodes_only(xroot);
  #endif
      }
    }