--- a/src/share/vm/ci/ciTypeFlow.cpp	Fri Feb 24 18:30:42 2012 -0800
+++ b/src/share/vm/ci/ciTypeFlow.cpp	Mon Feb 27 13:10:13 2012 +0100
@@ -1589,7 +1589,7 @@
   _next = NULL;
   _on_work_list = false;
   _backedge_copy = false;
-  _exception_entry = false;
+  _has_monitorenter = false;
   _trap_bci = -1;
   _trap_index = 0;
   df_init();
@@ -2182,6 +2182,10 @@
         !head->is_clonable_exit(lp))
       continue;
 
+    // Avoid BoxLock merge.
+    if (EliminateNestedLocks && head->has_monitorenter())
+      continue;
+
     // check not already cloned
     if (head->backedge_copy_count() != 0)
       continue;
@@ -2322,6 +2326,10 @@
     // Watch for bailouts.
     if (failing())  return;
 
+    if (str.cur_bc() == Bytecodes::_monitorenter) {
+      block->set_has_monitorenter();
+    }
+
     if (res) {
 
       // We have encountered a trap.  Record it in this block.