--- old/src/hotspot/cpu/x86/x86.ad	2018-09-26 10:02:37.454071170 -0400
+++ new/src/hotspot/cpu/x86/x86.ad	2018-09-26 10:02:35.897980644 -0400
@@ -2797,11 +2797,7 @@
 
   format %{
     $$template
-    if (os::is_MP()) {
-      $$emit$$"pause\t! membar_onspinwait"
-    } else {
-      $$emit$$"MEMBAR-onspinwait ! (empty encoding)"
-    }
+    $$emit$$"pause\t! membar_onspinwait"
   %}
   ins_encode %{
     __ pause();