Re: gcc Digest 26 Dec 2014 16:51:42 -0000 Issue 7953

[Andrew Senkevich <andrew dot n dot senkevich at gmail dot com>]

> From: Andrew Senkevich <andrew.n.senkevich@gmail.com>
> To: GCC Mailing List <gcc@gcc.gnu.org>, openmp-dev@dcs-maillist2.engr.illinois.edu, libc-alpha <libc-alpha@sourceware.org>
> Cc:
> Date: Fri, 26 Dec 2014 19:51:05 +0300
> Subject: OpenMP vector function ABI for x86_64
> ÂHi,
>
> during work on addition vector math functions to Glibc and discussions
> with community was found an issue with meaning of â#pragma omp declare
> simdâ (which will appear in math.h).
>
> Issue is there are no working way to specify ISA of vector function
> in GCC 5.0, and hence no way to determine exact vector function name.
>
> Here is description of exact meaning of â#pragma omp declare simdâ for x86_64.
>
> This is proposed as agreement between compilers supporting OpenMP.
>
> *************** OpenMP vector function ABI for x86_64 ***************
>
> Name of vector math function is based on Intel Vector Function ABI
> (http://www.cilkplus.org/sites/default/files/open_specifications/Intel-ABI-Vector-Function-2012-v0.9.5.pdf)
> with a little difference in part of name specifying ISA â namely
> letters b, c, d instead of x, y, Y.
>
> #pragma omp declare simd notinbranch simdlen(2) for some function
> âfuncâ means what the name of vector version is:
>
> _ZGVbN2v_func (it is SSE4 implementation).
>
> #pragma omp declare simd notinbranch simdlen(4) for some function
> âfuncâ means what the following names are available:
>
>  _ZGVcN4v_func (it is AVX implementation)
> and
> _ZGVdN4v_func (it is AVX2 implementation).
>
> Every vector function should be provided by math library for each
> supported ISA (currently SSE4, AVX and AVX2).
> Semantics of those pragmas are independent of the processor for which
> code is being generated.
> Those pragmas must not be interpreted as meaning version of other ISA
> of functions are available even if code is being built for a processor
> with such ISA support.
> Any future ABI extension that defines additional vector function
> versions will also define a different pragma to declare their
> availability.
>
> *********************************************************************
>
> Any feedback?

Hi, Jakub,

is this agreement OK?

Consensus is required to commit x86_64 vector math functions by Glibc
maintainer.


--
WBR,
Andrew