Horizontal minimum and maximum using SSE

Question

I have a function using SSE to do a lot of stuff, and the profiler shows me that the code portion I use to compute the horizontal minimum and maximum consumes most of the ti

Answer 1

I suggest two changes:

• Replace ((int8_t*) ((void *) &buffer))[0] with _mm_cvtsi128_si32.

• Replace _mm_shuffle_epi8 with _mm_shuffle_epi32/_mm_shufflelo_epi16 which have lower latency on recent AMD processors and Intel Atom, and will save you memory load operations:

  static inline int16_t hMin(__m128i buffer)
  {
      buffer = _mm_min_epi8(buffer, _mm_shuffle_epi32(buffer, _MM_SHUFFLE(3, 2, 3, 2)));
      buffer = _mm_min_epi8(buffer, _mm_shuffle_epi32(buffer, _MM_SHUFFLE(1, 1, 1, 1)));
      buffer = _mm_min_epi8(buffer, _mm_shufflelo_epi16(buffer, _MM_SHUFFLE(1, 1, 1, 1)));
      buffer = _mm_min_epi8(buffer, _mm_srli_epi16(buffer, 8));
      return (int8_t)_mm_cvtsi128_si32(buffer);
  }