c - Getting started with Intel x86 SSE SIMD instructions

Question

I want to learn more about using the SSE.

What ways are there to learn, besides the obvious reading the Intel? 64 and IA-32 Architectures Software Developer's Manuals?

Mainly I'm interested to work with the GCC X86 Built-in Functions.

Answer 1

First, I don't recommend on using the built-in functions - they are not portable (across compilers of the same arch).

Use intrinsics, GCC does a wonderful job optimizing SSE intrinsics into even more optimized code. You can always have a peek at the assembly and see how to use SSE to it's full potential.

Intrinsics are easy - just like normal function calls:

#include <immintrin.h>  // portable to all x86 compilers

int main()
{
    __m128 vector1 = _mm_set_ps(4.0, 3.0, 2.0, 1.0); // high element first, opposite of C array order.  Use _mm_setr_ps if you want "little endian" element order in the source.
    __m128 vector2 = _mm_set_ps(7.0, 8.0, 9.0, 0.0);

    __m128 sum = _mm_add_ps(vector1, vector2); // result = vector1 + vector 2

    vector1 = _mm_shuffle_ps(vector1, vector1, _MM_SHUFFLE(0,1,2,3));
    // vector1 is now (1, 2, 3, 4) (above shuffle reversed it)
    return 0;
}

Use _mm_load_ps or _mm_loadu_ps to load data from arrays.

Of course there are way more options, SSE is really powerful and in my opinion relatively easy to learn.

See also https://stackoverflow.com/tags/sse/info for some links to guides.