Index: cfe/trunk/lib/Headers/xmmintrin.h
===================================================================
--- cfe/trunk/lib/Headers/xmmintrin.h
+++ cfe/trunk/lib/Headers/xmmintrin.h
@@ -924,6 +924,11 @@
   return __builtin_ia32_movmskps(__a);
 }
 
+
+#ifdef _MSC_VER
+#define _MM_ALIGN16 __declspec(align(16))
+#endif
+
 #define _MM_SHUFFLE(z, y, x, w) (((z) << 6) | ((y) << 4) | ((x) << 2) | (w))
 
 #define _MM_EXCEPT_INVALID    (0x0001)
Index: cfe/trunk/test/CodeGen/ms-mm-align.c
===================================================================
--- cfe/trunk/test/CodeGen/ms-mm-align.c
+++ cfe/trunk/test/CodeGen/ms-mm-align.c
@@ -0,0 +1,16 @@
+// 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
+
+// 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 capture_ptr(int* i);
+void test_mm_align16(int p) {
+  _MM_ALIGN16 int i;
+  capture_ptr(&i);
+}
+
+// CHECK: alloca i32, align 16