Comment by fwsgonzo

I compared against native:

  #define ITERATIONS 1000

  int main()
  {
    const size_t BUFFER_SIZE = 64ul \* 1024 \* 1024;
    __m128i\* data_buffer = (__m128i *)memalign(64, BUFFER_SIZE);

    const __m128i all_ones = _mm_set1_epi8(0xFF);

    for (size_t i = 0; i < ITERATIONS; i++)
    {
      __m128i* data = data_buffer;
      for (size_t b = 0; b < BUFFER_SIZE;) {
        _mm_stream_si128(&data[0], all_ones);
        _mm_stream_si128(&data[1], all_ones);
        _mm_stream_si128(&data[2], all_ones);
        _mm_stream_si128(&data[3], all_ones);
        data += 4;
        b += 16 * 4;
      }
    }
  }


  $ time ./fill_buffer.elf 
  real 0m1,832s


  $ time ./wasmer fill_buffer.wasm -i fillBufferWithSIMD 1000
  real 0m4,237s

I had to fixup the WAT because set_local and get_local don't exist anymore. They are called local.get and local.set now.

At higher number of iterations the C version converges on about 1.7 seconds per 1000, while the WASM version seems to remain the same at 4.2 secs per 1000. This leaves native 2.5x faster for this particular operation, on my machine.