diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index d10f4ec..67a1540 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -343,8 +343,9 @@
   if (Subtarget->hasSSE1())
     setOperationAction(ISD::PREFETCH      , MVT::Other, Legal);
 
-  if (!Subtarget->hasSSE2())
-    setOperationAction(ISD::MEMBARRIER    , MVT::Other, Expand);
+  // We may not have a libcall for MEMBARRIER so we should lower this.
+  setOperationAction(ISD::MEMBARRIER    , MVT::Other, Custom);
+  
   // On X86 and X86-64, atomic operations are lowered to locked instructions.
   // Locked instructions, in turn, have implicit fence semantics (all memory
   // operations are flushed before issuing the locked instruction, and they
@@ -7508,6 +7509,16 @@
   return Sum;
 }
 
+SDValue X86TargetLowering::LowerMEMBARRIER(SDValue Op, SelectionDAG &DAG) const{
+  DebugLoc dl = Op.getDebugLoc();
+  
+  if (!Subtarget->hasSSE2())
+    return DAG.getNode(X86ISD::MEMBARRIER, dl, MVT::Other, Op.getOperand(0),
+                       DAG.getConstant(0, MVT::i32));
+                       
+  return DAG.getNode(X86ISD::MEMBARRIER, dl, MVT::Other, Op.getOperand(0));
+}
+
 SDValue X86TargetLowering::LowerCMP_SWAP(SDValue Op, SelectionDAG &DAG) const {
   EVT T = Op.getValueType();
   DebugLoc dl = Op.getDebugLoc();
@@ -7597,6 +7608,7 @@
 SDValue X86TargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   switch (Op.getOpcode()) {
   default: llvm_unreachable("Should not custom lower this!");
+  case ISD::MEMBARRIER:         return LowerMEMBARRIER(Op,DAG);
   case ISD::ATOMIC_CMP_SWAP:    return LowerCMP_SWAP(Op,DAG);
   case ISD::ATOMIC_LOAD_SUB:    return LowerLOAD_SUB(Op,DAG);
   case ISD::BUILD_VECTOR:       return LowerBUILD_VECTOR(Op, DAG);
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 4e4daa4..221fff2 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -265,7 +265,10 @@
       ATOMXOR64_DAG,
       ATOMAND64_DAG,
       ATOMNAND64_DAG,
-      ATOMSWAP64_DAG
+      ATOMSWAP64_DAG,
+      
+      // Memory barrier
+      MEMBARRIER
 
       // WARNING: Do not add anything in the end unless you want the node to
       // have memop! In fact, starting from ATOMADD64_DAG all opcodes will be
@@ -715,6 +718,7 @@
     SDValue LowerCMP_SWAP(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerLOAD_SUB(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerREADCYCLECOUNTER(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerMEMBARRIER(SDValue Op, SelectionDAG &DAG) const;
 
     virtual SDValue
       LowerFormalArguments(SDValue Chain,
diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index 6917a9d..d40ba69 100644
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -80,6 +80,14 @@
 
 def SDT_X86TCRET : SDTypeProfile<0, 2, [SDTCisPtrTy<0>, SDTCisVT<1, i32>]>;
 
+def SDT_X86MEMBARRIER : SDTypeProfile<0, 0, []>;
+def SDT_X86MEMBARRIERNoSSE : SDTypeProfile<0, 1, [SDTCisInt<0>]>;
+
+def X86MemBarrier : SDNode<"X86ISD::MEMBARRIER", SDT_X86MEMBARRIER,
+                            [SDNPHasChain]>;
+def X86MemBarrierNoSSE : SDNode<"X86ISD::MEMBARRIER", SDT_X86MEMBARRIERNoSSE,
+                                [SDNPHasChain]>;
+
 def X86bsf     : SDNode<"X86ISD::BSF",      SDTUnaryArithWithFlags>;
 def X86bsr     : SDNode<"X86ISD::BSR",      SDTUnaryArithWithFlags>;
 def X86shld    : SDNode<"X86ISD::SHLD",     SDTIntShiftDOp>;
@@ -3906,6 +3914,19 @@
 // Atomic support
 //
 
+// Memory barriers
+let hasSideEffects = 1 in {
+def Int_MemBarrier : I<0, Pseudo, (outs), (ins),
+                     "#MEMBARRIER",
+                     [(X86MemBarrier)]>, Requires<[HasSSE2]>;
+               
+let Uses = [ESP], isCodeGenOnly = 1 in
+def Int_MemBarrierNoSSE  : I<0x0B, Pseudo, (outs), (ins GR32:$zero),
+                           "lock\n\t"
+                           "or{l}\t{$zero, (%esp)|(%esp), $zero}",
+                           [(X86MemBarrierNoSSE GR32:$zero)]>, LOCK;
+}
+
 // Atomic swap. These are just normal xchg instructions. But since a memory
 // operand is referenced, the atomicity is ensured.
 let Constraints = "$val = $dst" in {