Index: include/clang/Basic/BuiltinsX86.def
===================================================================
--- include/clang/Basic/BuiltinsX86.def
+++ include/clang/Basic/BuiltinsX86.def
@@ -30,6 +30,12 @@
 // can use it?
 BUILTIN(__builtin_cpu_supports, "bcC*", "nc")
 
+// Undefined Values
+//
+TARGET_BUILTIN(__builtin_ia32_undef128, "V2d", "nc", "")
+TARGET_BUILTIN(__builtin_ia32_undef256, "V4d", "nc", "")
+TARGET_BUILTIN(__builtin_ia32_undef512, "V8d", "nc", "")
+
 // 3DNow!
 //
 TARGET_BUILTIN(__builtin_ia32_femms, "v", "", "3dnow")
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -6090,6 +6090,10 @@
     Value *F = CGM.getIntrinsic(Intrinsic::prefetch);
     return Builder.CreateCall(F, {Address, RW, Locality, Data});
   }
+  case X86::BI__builtin_ia32_undef128:
+  case X86::BI__builtin_ia32_undef256:
+  case X86::BI__builtin_ia32_undef512:
+    return UndefValue::get(ConvertType(E->getType()));
   case X86::BI__builtin_ia32_vec_init_v8qi:
   case X86::BI__builtin_ia32_vec_init_v4hi:
   case X86::BI__builtin_ia32_vec_init_v2si:
Index: lib/Headers/avx512fintrin.h
===================================================================
--- lib/Headers/avx512fintrin.h
+++ lib/Headers/avx512fintrin.h
@@ -57,6 +57,30 @@
   return (__m512i)(__v8di){ 0, 0, 0, 0, 0, 0, 0, 0 };
 }
 
+static __inline__ __m512d __DEFAULT_FN_ATTRS
+_mm512_undefined_pd()
+{
+  return (__m512d)__builtin_ia32_undef512();
+}
+
+static __inline__ __m512 __DEFAULT_FN_ATTRS
+_mm512_undefined()
+{
+  return (__m512)__builtin_ia32_undef512();
+}
+
+static __inline__ __m512 __DEFAULT_FN_ATTRS
+_mm512_undefined_ps()
+{
+  return (__m512)__builtin_ia32_undef512();
+}
+
+static __inline__ __m512i __DEFAULT_FN_ATTRS
+_mm512_undefined_epi32()
+{
+  return (__m512i)__builtin_ia32_undef512();
+}
+
 static __inline __m512i __DEFAULT_FN_ATTRS
 _mm512_maskz_set1_epi32(__mmask16 __M, int __A)
 {
Index: lib/Headers/avxintrin.h
===================================================================
--- lib/Headers/avxintrin.h
+++ lib/Headers/avxintrin.h
@@ -900,6 +900,24 @@
 }
 
 /* Create vectors */
+static __inline__ __m256d __DEFAULT_FN_ATTRS
+_mm256_undefined_pd()
+{
+  return (__m256d)__builtin_ia32_undef256();
+}
+
+static __inline__ __m256 __DEFAULT_FN_ATTRS
+_mm256_undefined_ps()
+{
+  return (__m256)__builtin_ia32_undef256();
+}
+
+static __inline__ __m256i __DEFAULT_FN_ATTRS
+_mm256_undefined_si256()
+{
+  return (__m256i)__builtin_ia32_undef256();
+}
+
 static __inline __m256d __DEFAULT_FN_ATTRS
 _mm256_set_pd(double __a, double __b, double __c, double __d)
 {
Index: lib/Headers/emmintrin.h
===================================================================
--- lib/Headers/emmintrin.h
+++ lib/Headers/emmintrin.h
@@ -523,6 +523,12 @@
 }
 
 static __inline__ __m128d __DEFAULT_FN_ATTRS
+_mm_undefined_pd()
+{
+  return (__m128d)__builtin_ia32_undef128();
+}
+
+static __inline__ __m128d __DEFAULT_FN_ATTRS
 _mm_set_sd(double __w)
 {
   return (__m128d){ __w, 0 };
@@ -1116,6 +1122,12 @@
 }
 
 static __inline__ __m128i __DEFAULT_FN_ATTRS
+_mm_undefined_si128()
+{
+  return (__m128i)__builtin_ia32_undef128();
+}
+
+static __inline__ __m128i __DEFAULT_FN_ATTRS
 _mm_set_epi64x(long long q1, long long q0)
 {
   return (__m128i){ q0, q1 };
Index: lib/Headers/xmmintrin.h
===================================================================
--- lib/Headers/xmmintrin.h
+++ lib/Headers/xmmintrin.h
@@ -577,6 +577,12 @@
 }
 
 static __inline__ __m128 __DEFAULT_FN_ATTRS
+_mm_undefined_ps()
+{
+  return (__m128)__builtin_ia32_undef128();
+}
+
+static __inline__ __m128 __DEFAULT_FN_ATTRS
 _mm_set_ss(float __w)
 {
   return (__m128){ __w, 0, 0, 0 };
Index: test/CodeGen/sse-undefined.c
===================================================================
--- test/CodeGen/sse-undefined.c
+++ test/CodeGen/sse-undefined.c
@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -o - | not grep "xmm"
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -o - | not grep "ymm"
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -o - | not grep "zmm"
+
+// Don't include mm_malloc.h, it's system specific.
+#define __MM_MALLOC_H
+
+#include <x86intrin.h>
+
+__m128 test_mm_undefined_ps() {
+  return _mm_undefined_ps();
+}
+
+__m128d test_mm_undefined_pd() {
+  return _mm_undefined_pd();
+}
+
+__m128i test_mm_undefined_si128() {
+  return _mm_undefined_si128();
+}
+
+__m256 test_mm256_undefined_ps() {
+  return _mm256_undefined_ps();
+}
+
+__m256d test_mm256_undefined_pd() {
+  return _mm256_undefined_pd();
+}
+
+__m256i test_mm256_undefined_si256() {
+  return _mm256_undefined_si256();
+}
+
+__m512 test_mm512_undefined() {
+  return _mm512_undefined();
+}
+
+__m512 test_mm512_undefined_ps() {
+  return _mm512_undefined_ps();
+}
+
+__m512d test_mm512_undefined_pd() {
+  return _mm512_undefined_pd();
+}
+
+__m512i test_mm512_undefined_epi32() {
+  return _mm512_undefined_epi32();
+}
+