Index: lib/Headers/intrin.h
===================================================================
--- lib/Headers/intrin.h
+++ lib/Headers/intrin.h
@@ -566,6 +566,16 @@
 long _InterlockedAdd(long volatile *Addend, long Value);
 int _ReadStatusReg(int);
 void _WriteStatusReg(int, int);
+
+static inline unsigned short _byteswap_ushort (unsigned short val) {
+  return __builtin_bswap16(val);
+}
+static inline unsigned long _byteswap_ulong (unsigned long val) {
+  return __builtin_bswap32(val);
+}
+static inline unsigned __int64 _byteswap_uint64 (unsigned __int64 val) {
+  return __builtin_bswap64(val);
+}
 #endif
 
 /*----------------------------------------------------------------------------*\
Index: test/Headers/ms-arm64-intrin.cpp
===================================================================
--- test/Headers/ms-arm64-intrin.cpp
+++ test/Headers/ms-arm64-intrin.cpp
@@ -1,9 +1,15 @@
+// REQUIRES: aarch64-registered-target
+
 // RUN: %clang_cc1 -triple arm64-windows \
 // RUN: -fms-compatibility -fms-compatibility-version=17.00 \
 // RUN: -ffreestanding -fsyntax-only -Werror \
 // RUN: -isystem %S/Inputs/include %s -S -o - 2>&1 | FileCheck %s
 
-// REQUIRES: aarch64-registered-target
+// RUN: %clang_cc1 -triple arm64-windows -O1 \
+// RUN: -fms-compatibility -fms-compatibility-version=17.00 \
+// RUN: -ffreestanding -fsyntax-only -Werror \
+// RUN: -isystem %S/Inputs/include %s -S -o - -emit-llvm 2>&1 \
+// RUN: | FileCheck %s --check-prefix CHECK-IR
 
 #include <intrin.h>
 
@@ -11,3 +17,18 @@
 // CHECK: nop
   __nop();
 }
+
+unsigned short check_byteswap_ushort(unsigned short val) {
+// CHECK-IR: call i16 @llvm.bswap.i16(i16 %val)
+  return _byteswap_ushort(val);
+}
+
+unsigned long check_byteswap_ulong(unsigned long val) {
+// CHECK-IR: call i32 @llvm.bswap.i32(i32 %val)
+  return _byteswap_ulong(val);
+}
+
+unsigned __int64 check_byteswap_uint64(unsigned __int64 val) {
+// CHECK-IR: call i64 @llvm.bswap.i64(i64 %val)
+  return _byteswap_uint64(val);
+}