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

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

2015-01-12 19:46 GMT+03:00 Jakub Jelinek <jakub@redhat.com>:
> On Mon, Jan 12, 2015 at 07:38:10PM +0300, Andrew Senkevich wrote:
>> > 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?
>>
>> is this agreement OK?
>>
>> Consensus is required to commit x86_64 vector math functions by Glibc
>> maintainer.
>
> With the difference that b stands for SSE2, not SSE4, and the fact
> that those functions do not use the __regcall calling conventions, but
> normal psABI calling conventions after replacing the arguments/return values
> with the vectors documented in the 0.9.5 pdf (and/or adding the vector mask
> arg) it describes what has been implemented, yes.

But which name use for SSE4?
Gcc generates the same as for SSE2, and we now have SSE4 implementations.


--
WBR,
Andrew