*** old/src/share/vm/opto/parse1.cpp	Thu Jan  7 16:01:56 2010
--- new/src/share/vm/opto/parse1.cpp	Thu Jan  7 16:01:56 2010

*** 1381,1390 ****
--- 1381,1394 ----
   
      // Learn the current bci from the iterator:
      set_parse_bci(iter().cur_bci());
  
      if (bci() == block()->limit()) {
+       //insert a predicate if it falls through to a loop head block
+       if(should_add_predicate(bci())){
+         add_predicate();
+       }
        // Do not walk into the next block until directed by do_all_blocks.
        merge(bci());
        break;
      }
      assert(bci() < block()->limit(), "bci still in block");

*** 2081,2090 ****
--- 2085,2125 ----
      assert(C->root() != NULL, "Expect parse is still valid");
      C->root()->add_prec(transformed_sfpnt);
    }
  }
  
+ //------------------------------should_add_predicate--------------------------
+ bool Parse::should_add_predicate(int target_bci) {
+   if (!UseLoopPredicate) return false;
+   Block* target = successor_for_bci(target_bci);
+   if (target != NULL          && 
+       target->is_loop_head()  &&
+       block()->rpo() < target->rpo()) {
+     return true;
+   }
+   return false;
+ }
+ 
+ //------------------------------add_predicate---------------------------------
+ void Parse::add_predicate() {
+   assert(UseLoopPredicate,"use only for loop predicate");
+   Node *cont    = _gvn.intcon(1);
+   Node* opq     = _gvn.transform(new (C, 2) Opaque1Node(C, cont));
+   Node *bol     = _gvn.transform(new (C, 2) Conv2BNode(opq));
+   IfNode* iff   = create_and_map_if(control(), bol, PROB_MAX, COUNT_UNKNOWN);
+   Node* iffalse = _gvn.transform(new (C, 1) IfFalseNode(iff));
+   C->add_predicate_opaq(opq);
+   {
+     PreserveJVMState pjvms(this);
+     set_control(iffalse);
+     uncommon_trap(Deoptimization::Reason_predicate,
+                   Deoptimization::Action_maybe_recompile);
+   }
+   Node* iftrue = _gvn.transform(new (C, 1) IfTrueNode(iff));
+   set_control(iftrue);
+ }
+ 
  #ifndef PRODUCT
  //------------------------show_parse_info--------------------------------------
  void Parse::show_parse_info() {
    InlineTree* ilt = NULL;
    if (C->ilt() != NULL) {