Index: include/clang/Basic/BuiltinsX86.def
===================================================================
--- include/clang/Basic/BuiltinsX86.def
+++ include/clang/Basic/BuiltinsX86.def
@@ -2071,6 +2071,10 @@
 TARGET_BUILTIN(__builtin_ia32_monitorx, "vv*UiUi", "", "mwaitx")
 TARGET_BUILTIN(__builtin_ia32_mwaitx, "vUiUiUi", "", "mwaitx")
 
+TARGET_HEADER_BUILTIN(_ReadWriteBarrier, "v", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(_ReadBarrier,      "v", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(_WriteBarrier,     "v", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+
 #undef BUILTIN
 #undef TARGET_BUILTIN
 #undef TARGET_HEADER_BUILTIN
Index: include/clang/Basic/BuiltinsX86_64.def
===================================================================
--- include/clang/Basic/BuiltinsX86_64.def
+++ include/clang/Basic/BuiltinsX86_64.def
@@ -21,5 +21,8 @@
 TARGET_HEADER_BUILTIN(__mulh,  "LLiLLiLLi",    "nch", "intrin.h", ALL_MS_LANGUAGES, "")
 TARGET_HEADER_BUILTIN(__umulh, "ULLiULLiULLi", "nch", "intrin.h", ALL_MS_LANGUAGES, "")
 
+TARGET_HEADER_BUILTIN(__faststorefence, "v", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+
+
 #undef BUILTIN
 #undef TARGET_HEADER_BUILTIN
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -7599,7 +7599,18 @@
     HigherBits = Builder.CreateIntCast(HigherBits, ResType, IsSigned);
     return HigherBits;
   }
+
+  case X86::BI__faststorefence: {
+    return Builder.CreateFence(llvm::AtomicOrdering::SequentiallyConsistent,
+                               llvm::CrossThread);
   }
+  case X86::BI_ReadWriteBarrier:
+  case X86::BI_ReadBarrier:
+  case X86::BI_WriteBarrier: {
+    return Builder.CreateFence(llvm::AtomicOrdering::SequentiallyConsistent,
+                               llvm::SingleThread);
+  }
+  }
 }
 
 
Index: lib/Headers/intrin.h
===================================================================
--- lib/Headers/intrin.h
+++ lib/Headers/intrin.h
@@ -254,11 +254,13 @@
 unsigned long __cdecl _lrotl(unsigned long, int);
 static __inline__
 unsigned long __cdecl _lrotr(unsigned long, int);
+static __inline__ void
+__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
+_ReadBarrier(void);
+static __inline__ void
+__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
+_ReadWriteBarrier(void);
 static __inline__
-void _ReadBarrier(void);
-static __inline__
-void _ReadWriteBarrier(void);
-static __inline__
 void *_ReturnAddress(void);
 unsigned int _rorx_u32(unsigned int, const unsigned int);
 static __inline__
@@ -286,8 +288,9 @@
 void _Store_HLERelease(long volatile *, long);
 void _Store64_HLERelease(__int64 volatile *, __int64);
 void _StorePointer_HLERelease(void *volatile *, void *);
-static __inline__
-void _WriteBarrier(void);
+static __inline__ void
+__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
+_WriteBarrier(void);
 unsigned __int32 xbegin(void);
 void _xend(void);
 static __inline__
@@ -1063,30 +1066,6 @@
 }
 #endif
 /*----------------------------------------------------------------------------*\
-|* Barriers
-\*----------------------------------------------------------------------------*/
-static __inline__ void __DEFAULT_FN_ATTRS
-__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
-_ReadWriteBarrier(void) {
-  __atomic_signal_fence(__ATOMIC_SEQ_CST);
-}
-static __inline__ void __DEFAULT_FN_ATTRS
-__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
-_ReadBarrier(void) {
-  __atomic_signal_fence(__ATOMIC_SEQ_CST);
-}
-static __inline__ void __DEFAULT_FN_ATTRS
-__attribute__((__deprecated__("use other intrinsics or C++11 atomics instead")))
-_WriteBarrier(void) {
-  __atomic_signal_fence(__ATOMIC_SEQ_CST);
-}
-#ifdef __x86_64__
-static __inline__ void __DEFAULT_FN_ATTRS
-__faststorefence(void) {
-  __atomic_thread_fence(__ATOMIC_SEQ_CST);
-}
-#endif
-/*----------------------------------------------------------------------------*\
 |* readfs, readgs
 |* (Pointers in address space #256 and #257 are relative to the GS and FS
 |* segment registers, respectively.)
Index: test/CodeGen/ms-barriers-intrinsics.c
===================================================================
--- /dev/null
+++ test/CodeGen/ms-barriers-intrinsics.c
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
+// RUN:         -triple i686--windows -emit-llvm %s -o - \
+// RUN:         | FileCheck %s -check-prefix=CHECK -check-prefix=CHECK-I386
+// RUN: %clang_cc1 -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
+// RUN:         -triple x86_64--windows -emit-llvm %s -o - \
+// RUN:         | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-X64
+
+// intrin.h needs size_t, but -ffreestanding prevents us from getting it from
+// stddef.h.  Work around it with this typedef.
+typedef __SIZE_TYPE__ size_t;
+
+#include <intrin.h>
+
+void test_ReadWriteBarrier() { _ReadWriteBarrier(); }
+// CHECK-LABEL: define void @test_ReadWriteBarrier
+// CHECK:   fence singlethread seq_cst
+// CHECK:   ret void
+// CHECK: }
+
+void test_ReadBarrier() { _ReadBarrier(); }
+// CHECK-LABEL: define void @test_ReadBarrier
+// CHECK:   fence singlethread seq_cst
+// CHECK:   ret void
+// CHECK: }
+
+void test_WriteBarrier() { _WriteBarrier(); }
+// CHECK-LABEL: define void @test_WriteBarrier
+// CHECK:   fence singlethread seq_cst
+// CHECK:   ret void
+// CHECK: }
+
+#if defined(__x86_64__)
+void test__faststorefence() { __faststorefence(); }
+// CHECK-X64-LABEL: define void @test__faststorefence
+// CHECK-X64:   fence seq_cst
+// CHECK-X64:   ret void
+// CHECK-X64: }
+#endif
+