SIMD c = a op b

[Guillaume Piolat]

On Sunday, 18 June 2023 at 05:01:16 UTC, Cecil Ward wrote:
> On Sunday, 18 June 2023 at 04:54:08 UTC, Cecil Ward wrote:
>> Is it true that this doesn’t always work (in either branch)?
>>
>> float4 a,b;
>> static if (__traits(compiles, a/b))
>>     c = a / b;
>> else
>>     c[] = a[] / b[];
>>

It's because SIMD stuff doesn't always works that 
intel-intrinsics was created. It insulates you from the compiler 
underneath.


import inteli.emmintrin;

void main()
{
     float4 a, b, c;
     c = a / b;            // _always_ works
     c = _mm_div_ps(a, b); // _always_ works
}

Sure in some case it may emulate those vectors, but for vector of 
float it's only in DMD -m32. It relies on excellent __vector work 
made a long time ago, and supplements it.

For 32-byte vectors such as __vector(float[8]), you will have 
trouble on GDC when -mavx isn't there, or with DMD.

Do you think the builtin __vector support the same operations 
across the compilers? The answer is "it's getting there", in the 
meanwhile using intel-intrinsics will lower your exposure to the 
compiler woes.
If you want to use DMD and -O -inline, you should also expect 
much more problems unless working extra in order to have SIMD.