[PATCH 1/N] x86_64 vectorization support: vectorized math functions addition to Glibc

[Carlos O'Donell]

On 09/11/2014 06:11 AM, Matthew Fortune wrote:
> Joseph S. Myers <joseph@codesourcery.com> writes:
>> On Wed, 10 Sep 2014, Andrew Senkevich wrote:
>>
>>> Hi all,
>>>
>>> this is the first patch in the series of patches which will add Intel
>>> vectorized math functions to Glibc.
>>
>> Please start by raising general design questions on libc-alpha before
>> sending any patches; only send patches once there is consensus on the
>> general questions and that consensus has been written up on a wiki page.
>> For example:
> 
> FWIW I had envisaged vectorised math functions looking more generic such
> that they were not dependent on vector size:
> 
> void sin_simd (float* dst, float* src, int count)
> {
>   while (count > 0)
>   {
>     *dst = sinf (*src);
>     dst++;
>     src++;
>     count--;
>   }
> }
> 
> With this pattern, the precise SIMD ISA extension is not important to the
> caller. The additional cost of loading/storing the data compared with the
> number of instructions required to perform the vectorised operation does
> not seem significant. Ifunc is then the obvious way to select the widest
> SIMD available at runtime.

This isn't going to happen right now. It might be a distinct API, but right
now we are talking about existing API's created by Intel, and IBM, that
developers have already been using or know how to use.

A new GNU API for vectorized math functions is a distinct topic that we can
talk about, and talk about in generalities.

Cheers,
Carlos.