Index: lib/Frontend/InitPreprocessor.cpp
===================================================================
--- lib/Frontend/InitPreprocessor.cpp
+++ lib/Frontend/InitPreprocessor.cpp
@@ -882,14 +882,16 @@
     // The value written by __atomic_test_and_set.
     // FIXME: This is target-dependent.
     Builder.defineMacro("__GCC_ATOMIC_TEST_AND_SET_TRUEVAL", "1");
+  }
 
+  auto addLockFreeMacros = [&](const llvm::Twine &Prefix) {
     // Used by libc++ and libstdc++ to implement ATOMIC_<foo>_LOCK_FREE.
     unsigned InlineWidthBits = TI.getMaxAtomicInlineWidth();
-#define DEFINE_LOCK_FREE_MACRO(TYPE, Type) \
-    Builder.defineMacro("__GCC_ATOMIC_" #TYPE "_LOCK_FREE", \
-                        getLockFreeValue(TI.get##Type##Width(), \
-                                         TI.get##Type##Align(), \
-                                         InlineWidthBits));
+#define DEFINE_LOCK_FREE_MACRO(TYPE, Type)                                     \
+  Builder.defineMacro(Prefix + "_" #TYPE "_LOCK_FREE",                         \
+                      getLockFreeValue(TI.get##Type##Width(),                  \
+                                       TI.get##Type##Align(),                  \
+                                       InlineWidthBits));
     DEFINE_LOCK_FREE_MACRO(BOOL, Bool);
     DEFINE_LOCK_FREE_MACRO(CHAR, Char);
     DEFINE_LOCK_FREE_MACRO(CHAR16_T, Char16);
@@ -899,12 +901,15 @@
     DEFINE_LOCK_FREE_MACRO(INT, Int);
     DEFINE_LOCK_FREE_MACRO(LONG, Long);
     DEFINE_LOCK_FREE_MACRO(LLONG, LongLong);
-    Builder.defineMacro("__GCC_ATOMIC_POINTER_LOCK_FREE",
+    Builder.defineMacro(Prefix + "_POINTER_LOCK_FREE",
                         getLockFreeValue(TI.getPointerWidth(0),
                                          TI.getPointerAlign(0),
                                          InlineWidthBits));
 #undef DEFINE_LOCK_FREE_MACRO
-  }
+  };
+  addLockFreeMacros("__CLANG_ATOMIC");
+  if (!LangOpts.MSVCCompat)
+    addLockFreeMacros("__GCC_ATOMIC");
 
   if (LangOpts.NoInlineDefine)
     Builder.defineMacro("__NO_INLINE__");
Index: test/Preprocessor/init.c
===================================================================
--- test/Preprocessor/init.c
+++ test/Preprocessor/init.c
@@ -8846,6 +8846,16 @@
 // WEBASSEMBLY32-NEXT:#define __CHAR32_TYPE__ unsigned int
 // WEBASSEMBLY32-NEXT:#define __CHAR_BIT__ 8
 // WEBASSEMBLY32-NOT:#define __CHAR_UNSIGNED__
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_BOOL_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_CHAR16_T_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_CHAR32_T_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_CHAR_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_INT_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_LLONG_LOCK_FREE 1
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_LONG_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_POINTER_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_SHORT_LOCK_FREE 2
+// WEBASSEMBLY32-NEXT:#define __CLANG_ATOMIC_WCHAR_T_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __CONSTANT_CFSTRINGS__ 1
 // WEBASSEMBLY32-NEXT:#define __DBL_DECIMAL_DIG__ 17
 // WEBASSEMBLY32-NEXT:#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
@@ -9162,6 +9172,16 @@
 // WEBASSEMBLY64-NEXT:#define __CHAR32_TYPE__ unsigned int
 // WEBASSEMBLY64-NEXT:#define __CHAR_BIT__ 8
 // WEBASSEMBLY64-NOT:#define __CHAR_UNSIGNED__
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_BOOL_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_CHAR16_T_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_CHAR32_T_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_CHAR_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_INT_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_LLONG_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_LONG_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_POINTER_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_SHORT_LOCK_FREE 2
+// WEBASSEMBLY64-NEXT:#define __CLANG_ATOMIC_WCHAR_T_LOCK_FREE 2
 // WEBASSEMBLY64-NEXT:#define __CONSTANT_CFSTRINGS__ 1
 // WEBASSEMBLY64-NEXT:#define __DBL_DECIMAL_DIG__ 17
 // WEBASSEMBLY64-NEXT:#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
@@ -9637,3 +9657,36 @@
 // AVR:#define __WCHAR_MAX__ 32767
 // AVR:#define __WCHAR_TYPE__ int
 // AVR:#define __WINT_TYPE__ int
+
+
+// RUN: %clang_cc1 -E -dM -ffreestanding \
+// RUN:    -triple i686-windows-msvc -fms-compatibility < /dev/null \
+// RUN:  | FileCheck -match-full-lines -check-prefix MSVC-X32 %s
+
+// RUN: %clang_cc1 -E -dM -ffreestanding \
+// RUN:    -triple x86_64-windows-msvc -fms-compatibility < /dev/null \
+// RUN:  | FileCheck -match-full-lines -check-prefix MSVC-X64 %s
+
+// MSVC-X32:#define __CLANG_ATOMIC_BOOL_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_CHAR16_T_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_CHAR32_T_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_CHAR_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_INT_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_LLONG_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_LONG_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_POINTER_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_SHORT_LOCK_FREE 2
+// MSVC-X32-NEXT:#define __CLANG_ATOMIC_WCHAR_T_LOCK_FREE 2
+// MSVC-X32-NOT:#define __GCC_ATOMIC{{.*}}
+
+// MSVC-X64:#define __CLANG_ATOMIC_BOOL_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_CHAR16_T_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_CHAR32_T_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_CHAR_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_INT_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_LLONG_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_LONG_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_POINTER_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_SHORT_LOCK_FREE 2
+// MSVC-X64-NEXT:#define __CLANG_ATOMIC_WCHAR_T_LOCK_FREE 2
+// MSVC-X86-NOT:#define __GCC_ATOMIC{{.*}}
Index: test/Sema/atomic-ops.c
===================================================================
--- test/Sema/atomic-ops.c
+++ test/Sema/atomic-ops.c
@@ -7,19 +7,29 @@
 struct S { char c[3]; };
 
 _Static_assert(__GCC_ATOMIC_BOOL_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_BOOL_LOCK_FREE == __CLANG_ATOMIC_BOOL_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_CHAR_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_CHAR_LOCK_FREE == __CLANG_ATOMIC_CHAR_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_CHAR16_T_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_CHAR16_T_LOCK_FREE == __CLANG_ATOMIC_CHAR16_T_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_CHAR32_T_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_CHAR32_T_LOCK_FREE == __CLANG_ATOMIC_CHAR32_T_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_WCHAR_T_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_WCHAR_T_LOCK_FREE == __CLANG_ATOMIC_WCHAR_T_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_SHORT_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_SHORT_LOCK_FREE == __CLANG_ATOMIC_SHORT_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_INT_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_INT_LOCK_FREE == __CLANG_ATOMIC_INT_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_LONG_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_LONG_LOCK_FREE == __CLANG_ATOMIC_LONG_LOCK_FREE, "");
 #ifdef __i386__
 _Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 1, "");
 #else
 _Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == 2, "");
 #endif
+_Static_assert(__GCC_ATOMIC_LLONG_LOCK_FREE == __CLANG_ATOMIC_LLONG_LOCK_FREE, "");
 _Static_assert(__GCC_ATOMIC_POINTER_LOCK_FREE == 2, "");
+_Static_assert(__GCC_ATOMIC_POINTER_LOCK_FREE == __CLANG_ATOMIC_POINTER_LOCK_FREE, "");
 
 _Static_assert(__c11_atomic_is_lock_free(1), "");
 _Static_assert(__c11_atomic_is_lock_free(2), "");