src/cpu/x86/vm/x86_64.ad

*** 6338,6347 ****
--- 6338,6366 ----
    format %{ "MEMBAR-release (a FastUnlock follows so empty encoding)" %}
    ins_encode();
    ins_pipe(empty);
  %}
  
+ instruct onspinwait()
+ %{
+   match(OnSpinWait);
+   ins_cost(200);
+ 
+   format %{
+     $$template
+     if (os::is_MP()) {
+       $$emit$$"pause\t! membar_onspinwait"
+     } else {
+       $$emit$$"MEMBAR-onspinwait ! (empty encoding)"
+     }
+   %}
+   ins_encode %{
+     __ pause();
+   %}
+   ins_pipe(pipe_slow);
+ %}
+ 
  instruct membar_volatile(rFlagsReg cr) %{
    match(MemBarVolatile);
    effect(KILL cr);
    ins_cost(400);