diff -r f7babf9d1592 -r 84743156e780 src/hotspot/cpu/x86/x86_64.ad
--- a/src/hotspot/cpu/x86/x86_64.ad	Wed Oct 03 11:43:39 2018 +0530
+++ b/src/hotspot/cpu/x86/x86_64.ad	Wed Oct 03 03:41:57 2018 -0400
@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
+// Copyright (c) 2003, 2018, Oracle and/or its affiliates. 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
@@ -2341,9 +2341,7 @@
 
   enc_class lock_prefix()
   %{
-    if (os::is_MP()) {
-      emit_opcode(cbuf, 0xF0); // lock
-    }
+    emit_opcode(cbuf, 0xF0); // lock
   %}
 
   enc_class REX_mem(memory mem)
@@ -6601,11 +6599,7 @@
 
   format %{
     $$template
-    if (os::is_MP()) {
-      $$emit$$"lock addl [rsp + #0], 0\t! membar_volatile"
-    } else {
-      $$emit$$"MEMBAR-volatile ! (empty encoding)"
-    }
+    $$emit$$"lock addl [rsp + #0], 0\t! membar_volatile"
   %}
   ins_encode %{
     __ membar(Assembler::StoreLoad);
@@ -7801,7 +7795,7 @@
   effect(KILL cr);
   format %{ "ADDB  [$mem],$add" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ addb($mem$$Address, $add$$constant);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7812,7 +7806,7 @@
   effect(KILL cr);
   format %{ "XADDB  [$mem],$newval" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ xaddb($mem$$Address, $newval$$Register);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7824,7 +7818,7 @@
   effect(KILL cr);
   format %{ "ADDW  [$mem],$add" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ addw($mem$$Address, $add$$constant);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7835,7 +7829,7 @@
   effect(KILL cr);
   format %{ "XADDW  [$mem],$newval" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ xaddw($mem$$Address, $newval$$Register);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7847,7 +7841,7 @@
   effect(KILL cr);
   format %{ "ADDL  [$mem],$add" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ addl($mem$$Address, $add$$constant);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7858,7 +7852,7 @@
   effect(KILL cr);
   format %{ "XADDL  [$mem],$newval" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ xaddl($mem$$Address, $newval$$Register);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7870,7 +7864,7 @@
   effect(KILL cr);
   format %{ "ADDQ  [$mem],$add" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ addq($mem$$Address, $add$$constant);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -7881,7 +7875,7 @@
   effect(KILL cr);
   format %{ "XADDQ  [$mem],$newval" %}
   ins_encode %{
-    if (os::is_MP()) { __ lock(); }
+    __ lock();
     __ xaddq($mem$$Address, $newval$$Register);
   %}
   ins_pipe( pipe_cmpxchg );
@@ -10898,7 +10892,7 @@
   ins_pipe(pipe_slow);
 %}
 
-instruct rep_stos_large(rcx_RegL cnt, rdi_RegP base, regD tmp, rax_RegI zero, 
+instruct rep_stos_large(rcx_RegL cnt, rdi_RegP base, regD tmp, rax_RegI zero,
                         Universe dummy, rFlagsReg cr)
 %{
   predicate(((ClearArrayNode*)n)->is_large());
@@ -10942,7 +10936,7 @@
     }
   %}
   ins_encode %{
-    __ clear_mem($base$$Register, $cnt$$Register, $zero$$Register, 
+    __ clear_mem($base$$Register, $cnt$$Register, $zero$$Register,
                  $tmp$$XMMRegister, true);
   %}
   ins_pipe(pipe_slow);