Index: include/clang/Basic/BuiltinsX86_64.def
===================================================================
--- include/clang/Basic/BuiltinsX86_64.def
+++ include/clang/Basic/BuiltinsX86_64.def
@@ -40,6 +40,7 @@
 TARGET_HEADER_BUILTIN(_InterlockedIncrement64,   "LLiLLiD*",    "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 TARGET_HEADER_BUILTIN(_InterlockedOr64,          "LLiLLiD*LLi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 TARGET_HEADER_BUILTIN(_InterlockedXor64,         "LLiLLiD*LLi", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(_InterlockedCompareExchange128, "UcLLiD*LLiLLiLLi*", "nh", "intrin.h", ALL_MS_LANGUAGES, "cx16")
 
 TARGET_BUILTIN(__builtin_ia32_readeflags_u64, "ULLi", "n", "")
 TARGET_BUILTIN(__builtin_ia32_writeeflags_u64, "vULLi", "n", "")
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -8432,6 +8432,45 @@
     return EmitMSVCBuiltinExpr(MSVCIntrin::_InterlockedDecrement, E);
   case X86::BI_InterlockedIncrement64:
     return EmitMSVCBuiltinExpr(MSVCIntrin::_InterlockedIncrement, E);
+  case X86::BI_InterlockedCompareExchange128: {
+    // InterlockedCompareExchange128 doesn't directly refer to 128bit ints,
+    // instead it takes pointers to 64bit ints for Destination and
+    // ComparandResult, and exchange is taken as two 64bit ints (high & low).
+    // The previous value is written to ComparandResult, and success is
+    // returned.
+
+    llvm::Type *Int128Ty = Builder.getInt128Ty();
+    llvm::Type *Int128PtrTy = Int128Ty->getPointerTo();
+
+    Value *Destination =
+        Builder.CreateBitCast(EmitScalarExpr(E->getArg(0)), Int128PtrTy);
+    Value *ExchangeHigh128 =
+        Builder.CreateZExt(EmitScalarExpr(E->getArg(1)), Int128Ty);
+    Value *ExchangeLow128 =
+        Builder.CreateZExt(EmitScalarExpr(E->getArg(2)), Int128Ty);
+    Address ComparandResult(
+        Builder.CreateBitCast(EmitScalarExpr(E->getArg(3)), Int128PtrTy),
+        getContext().toCharUnitsFromBits(128));
+
+    Value *Exchange = Builder.CreateOr(
+        Builder.CreateShl(ExchangeHigh128, 64, "", false, false),
+        ExchangeLow128);
+
+    Value *Comparand = Builder.CreateLoad(ComparandResult);
+
+    AtomicCmpXchgInst *CXI =
+        Builder.CreateAtomicCmpXchg(Destination, Comparand, Exchange,
+                                    AtomicOrdering::SequentiallyConsistent,
+                                    AtomicOrdering::SequentiallyConsistent);
+    CXI->setVolatile(true);
+
+    // Write the result back to the inout pointer.
+    Builder.CreateStore(Builder.CreateExtractValue(CXI, 0), ComparandResult);
+
+    // Get the success boolean and zero extend it to i8.
+    Value *Success = Builder.CreateExtractValue(CXI, 1);
+    return Builder.CreateZExt(Success, ConvertType(E->getType()));
+  }
 
   case X86::BI_AddressOfReturnAddress: {
     Value *F = CGM.getIntrinsic(Intrinsic::addressofreturnaddress);
Index: test/CodeGen/ms-intrinsics.c
===================================================================
--- test/CodeGen/ms-intrinsics.c
+++ test/CodeGen/ms-intrinsics.c
@@ -5,7 +5,7 @@
 // RUN:         -triple thumbv7--windows -Oz -emit-llvm %s -o - \
 // RUN:         | FileCheck %s --check-prefixes CHECK,CHECK-ARM,CHECK-ARM-X64
 // RUN: %clang_cc1 -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:         -triple x86_64--windows -Oz -emit-llvm %s -o - \
+// RUN:         -triple x86_64--windows -Oz -emit-llvm -target-feature +cx16 %s -o - \
 // RUN:         | FileCheck %s --check-prefixes CHECK,CHECK-X64,CHECK-ARM-X64,CHECK-INTEL
 
 // intrin.h needs size_t, but -ffreestanding prevents us from getting it from
@@ -329,6 +329,27 @@
 // CHECK: ret i64 [[RESULT]]
 // CHECK: }
 
+#if defined(__x86_64__)
+unsigned char test_InterlockedCompareExchange128(__int64 volatile *Destination, __int64 ExchangeHigh, __int64 ExchangeLow, __int64* ComparandResult) {
+  return _InterlockedCompareExchange128(Destination, ExchangeHigh, ExchangeLow, ComparandResult);
+}
+// CHECK-X64: define{{.*}}i8 @test_InterlockedCompareExchange128(i64*{{[a-z_ ]*}}%Destination, i64{{[a-z_ ]*}}%ExchangeHigh, i64{{[a-z_ ]*}}%ExchangeLow, i64*{{[a-z_ ]*}}%ComparandResult){{.*}}{
+// CHECK-X64: [[DST:%[0-9]+]] = bitcast i64* %Destination to i128*
+// CHECK-X64: [[EH:%[0-9]+]] = zext i64 %ExchangeHigh to i128
+// CHECK-X64: [[EL:%[0-9]+]] = zext i64 %ExchangeLow to i128
+// CHECK-X64: [[CNR:%[0-9]+]] = bitcast i64* %ComparandResult to i128*
+// CHECK-X64: [[EHS:%[0-9]+]] = shl nuw i128 [[EH]], 64
+// CHECK-X64: [[EXP:%[0-9]+]] = or i128 [[EHS]], [[EL]]
+// CHECK-X64: [[ORG:%[0-9]+]] = load i128, i128* [[CNR]], align 16
+// CHECK-X64: [[RES:%[0-9]+]] = cmpxchg volatile i128* [[DST]], i128 [[ORG]], i128 [[EXP]] seq_cst seq_cst
+// CHECK-X64: [[OLD:%[0-9]+]] = extractvalue { i128, i1 } [[RES]], 0
+// CHECK-X64: store i128 [[OLD]], i128* [[CNR]], align 16
+// CHECK-X64: [[SUC1:%[0-9]+]] = extractvalue { i128, i1 } [[RES]], 1
+// CHECK-X64: [[SUC8:%[0-9]+]] = zext i1 [[SUC1]] to i8
+// CHECK-X64: ret i8 [[SUC8]]
+// CHECK-X64: }
+#endif
+
 short test_InterlockedIncrement16(short volatile *Addend) {
   return _InterlockedIncrement16(Addend);
 }