Only use custom SSE FMUL and FMAC with non-clang compilers.

media/base/vector_math.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/vector_math.h"
 #include "media/base/vector_math_testing.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "build/build_config.h"
 
 // NaCl does not allow intrinsics.
 #if defined(ARCH_CPU_X86_FAMILY) && !defined(OS_NACL)
 #include <xmmintrin.h>
+// Don't use custom SSE versions where the auto-vectorized C version performs
+// better, which is anywhere clang is used.
+#if !defined(__clang__)
 #define FMAC_FUNC FMAC_SSE
 #define FMUL_FUNC FMUL_SSE
+#else
+#define FMAC_FUNC FMAC_C
+#define FMUL_FUNC FMUL_C
+#endif
 #define EWMAAndMaxPower_FUNC EWMAAndMaxPower_SSE
 #elif defined(ARCH_CPU_ARM_FAMILY) && defined(USE_NEON)
 #include <arm_neon.h>
 #define FMAC_FUNC FMAC_NEON
 #define FMUL_FUNC FMUL_NEON
 #define EWMAAndMaxPower_FUNC EWMAAndMaxPower_NEON
 #else
 #define FMAC_FUNC FMAC_C
 #define FMUL_FUNC FMUL_C
 #define EWMAAndMaxPower_FUNC EWMAAndMaxPower_C
@@ skipping 247 matching lines @@
     result.first += sample_squared * smoothing_factor;
     result.second = std::max(result.second, sample_squared);
   }
 
   return result;
 }
 #endif
 
 }  // namespace vector_math
 }  // namespace media