Index: llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp
+++ llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp
@@ -116,6 +116,9 @@
   case RISCV::HWASAN_CHECK_MEMACCESS_SHORTGRANULES:
     LowerHWASAN_CHECK_MEMACCESS(*MI);
     return;
+  case RISCV::PseudoMemBarrier:
+    OutStreamer->emitRawComment("MEMBARRIER");
+    return;
   }
 
   MCInst TmpInst;
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -461,6 +461,8 @@
     setMaxAtomicSizeInBitsSupported(0);
   }
 
+  setOperationAction(ISD::ATOMIC_FENCE, MVT::Other, Custom);
+
   setBooleanContents(ZeroOrOneBooleanContent);
 
   if (Subtarget.hasVInstructions()) {
@@ -3667,11 +3669,29 @@
   return SDValue();
 }
 
+static SDValue LowerATOMIC_FENCE(SDValue Op, SelectionDAG &DAG) {
+  SDLoc dl(Op);
+  SyncScope::ID FenceSSID =
+      static_cast<SyncScope::ID>(Op.getConstantOperandVal(2));
+
+  // singlethread fences only synchronize with signal handles on the same
+  // thread and thus only need to preserve instruction order, not actually
+  // enforce memory ordering.
+  if (FenceSSID == SyncScope::SingleThread)
+    // MEMBARRIER is a compiler barrier; it codegens to a no-op.
+    return DAG.getNode(ISD::MEMBARRIER, dl, MVT::Other, Op.getOperand(0));
+
+  return Op;
+}
+
+
 SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
                                             SelectionDAG &DAG) const {
   switch (Op.getOpcode()) {
   default:
     report_fatal_error("unimplemented operand");
+  case ISD::ATOMIC_FENCE:
+    return LowerATOMIC_FENCE(Op, DAG);
   case ISD::GlobalAddress:
     return lowerGlobalAddress(Op, DAG);
   case ISD::BlockAddress:
Index: llvm/lib/Target/RISCV/RISCVInstrInfo.td
===================================================================
--- llvm/lib/Target/RISCV/RISCVInstrInfo.td
+++ llvm/lib/Target/RISCV/RISCVInstrInfo.td
@@ -1841,6 +1841,9 @@
                  (AddiPairImmSmall AddiPair:$rs2))>;
 }
 
+let hasSideEffects = 1, isMeta = 1 in
+def PseudoMemBarrier : Pseudo<(outs), (ins), [(membarrier)]>;
+
 //===----------------------------------------------------------------------===//
 // Standard extensions
 //===----------------------------------------------------------------------===//
Index: llvm/test/CodeGen/RISCV/atomic-fence.ll
===================================================================
--- llvm/test/CodeGen/RISCV/atomic-fence.ll
+++ llvm/test/CodeGen/RISCV/atomic-fence.ll
@@ -51,7 +51,7 @@
 define void @fence_singlethread_acquire() nounwind {
 ; CHECK-LABEL: fence_singlethread_acquire:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    fence r, rw
+; CHECK-NEXT:    #MEMBARRIER
 ; CHECK-NEXT:    ret
   fence syncscope("singlethread") acquire
   ret void
@@ -60,7 +60,7 @@
 define void @fence_singlethread_release() nounwind {
 ; CHECK-LABEL: fence_singlethread_release:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    fence rw, w
+; CHECK-NEXT:    #MEMBARRIER
 ; CHECK-NEXT:    ret
   fence syncscope("singlethread") release
   ret void
@@ -69,7 +69,7 @@
 define void @fence_singlethread_acq_rel() nounwind {
 ; CHECK-LABEL: fence_singlethread_acq_rel:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    fence.tso
+; CHECK-NEXT:    #MEMBARRIER
 ; CHECK-NEXT:    ret
   fence syncscope("singlethread") acq_rel
   ret void
@@ -78,7 +78,7 @@
 define void @fence_singlethread_seq_cst() nounwind {
 ; CHECK-LABEL: fence_singlethread_seq_cst:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    fence rw, rw
+; CHECK-NEXT:    #MEMBARRIER
 ; CHECK-NEXT:    ret
   fence syncscope("singlethread") seq_cst
   ret void