src/share/vm/opto/matcher.cpp

*** 273,282 ****
--- 273,296 ----
    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. Reuse existing ConP node only if it is shared.
+   Node* new_idealConP0 = ConNode::make(C, TypePtr::NULL_PTR);
+   Node* old_idealConP0 = NULL;
+   for( DUIterator_Fast jmax, j = C->root()->fast_outs(jmax); j < jmax; j++ ) {
+     Node* n = C->root()->fast_out(j);
+     if (n->Opcode() == Op_ConP && n->bottom_type() == TypePtr::NULL_PTR) {
+       old_idealConP0 = n;
+       break;
+     }
+   }
+ 
    // 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 ****
--- 328,351 ----
            --j;
            --jmax;
          }
        }
  
+       // Generate new mach node for ConP #NULL or use already generated.
+       if (old_idealConP0 != NULL && has_new_node(old_idealConP0)) {
+         _machConP0 = new_node(old_idealConP0)->as_Mach();
+       } else {
+         assert(new_idealConP0 != NULL, "sanity");
+         _machConP0 = match_tree(new_idealConP0);
+         // 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(_machConP0 != NULL, "");
+ 
        C->set_root(xroot->is_Root() ? xroot->as_Root() : NULL);
+ 
  #ifdef ASSERT
        verify_new_nodes_only(xroot);
  #endif
      }
    }