diff -r 0edda524b58c -r 1ee8caae33af src/share/vm/opto/lcm.cpp
--- a/src/share/vm/opto/lcm.cpp	Wed Aug 06 11:57:31 2008 -0400
+++ b/src/share/vm/opto/lcm.cpp	Thu Aug 21 23:36:31 2008 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright 1998-2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 1998-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -322,7 +322,7 @@
   uint choice  = 0; // Bigger is most important
   uint latency = 0; // Bigger is scheduled first
   uint score   = 0; // Bigger is better
-  uint idx;         // Index in worklist
+  int idx = -1;     // Index in worklist
 
   for( uint i=0; i<cnt; i++ ) { // Inspect entire worklist
     // Order in worklist is used to break ties.
@@ -412,9 +412,10 @@
     }
   } // End of for all ready nodes in worklist
 
-  Node *n = worklist[idx];      // Get the winner
+  assert(idx >= 0, "index should be set");
+  Node *n = worklist[(uint)idx];      // Get the winner
 
-  worklist.map(idx,worklist.pop());     // Compress worklist
+  worklist.map((uint)idx, worklist.pop());     // Compress worklist
   return n;
 }
 
@@ -599,7 +600,14 @@
           assert(cfg->_bbs[oop_store->_idx]->_dom_depth <= this->_dom_depth, "oop_store must dominate card-mark");
         }
       }
-      if( n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_MemBarAcquire ) {
+      if( n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_MemBarAcquire &&
+          n->req() > TypeFunc::Parms ) {
+        // MemBarAcquire could be created without Precedent edge.
+        // del_req() replaces the specified edge with the last input edge
+        // and then removes the last edge. If the specified edge > number of
+        // edges the last edge will be moved outside of the input edges array
+        // and the edge will be lost. This is why this code should be
+        // executed only when Precedent (== TypeFunc::Parms) edge is present.
         Node *x = n->in(TypeFunc::Parms);
         n->del_req(TypeFunc::Parms);
         n->add_prec(x);