Index: cfe/trunk/lib/Basic/Targets/X86.cpp
===================================================================
--- cfe/trunk/lib/Basic/Targets/X86.cpp
+++ cfe/trunk/lib/Basic/Targets/X86.cpp
@@ -1121,6 +1121,8 @@
 
 bool X86TargetInfo::isValidFeatureName(StringRef Name) const {
   return llvm::StringSwitch<bool>(Name)
+      .Case("3dnow", true)
+      .Case("3dnowa", true)
       .Case("aes", true)
       .Case("avx", true)
       .Case("avx2", true)
Index: cfe/trunk/test/Headers/mm3dnow.c
===================================================================
--- cfe/trunk/test/Headers/mm3dnow.c
+++ cfe/trunk/test/Headers/mm3dnow.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only -ffreestanding %s -verify
+// RUN: %clang_cc1 -fsyntax-only -ffreestanding -x c++ %s -verify
+// expected-no-diagnostics
+
+#if defined(i386) || defined(__x86_64__)
+#include <mm3dnow.h>
+
+int __attribute__((__target__(("3dnow")))) foo(int a) {
+  _m_femms();
+  return 4;
+}
+
+__m64 __attribute__((__target__(("3dnowa")))) bar(__m64 a) {
+  return _m_pf2iw(a);
+}
+#endif