Re: libmvec in gcc to have vector math in fortran

[Richard Biener <richard.guenther@gmail.com>]

On April 10, 2018 3:06:55 PM GMT+02:00, Jakub Jelinek <jakub@redhat.com> wrote:
>On Tue, Apr 10, 2018 at 02:55:43PM +0200, Richard Biener wrote:
>> > And the easiest solution is in the Fortran FE based on some flag
>> > (e.g. -mveclibabi=glibc) through a target hook add
>> > __attribute__((__simd__ ("notinbranch")))
>> > to the builtins like __builtin_sin etc. that have them in the
>> > glibc header (x86_64 -m64 and -ffast-math only):
>> >
>> > #  undef __DECL_SIMD_cos
>> > #  define __DECL_SIMD_cos __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_cosf
>> > #  define __DECL_SIMD_cosf __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_sin
>> > #  define __DECL_SIMD_sin __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_sinf
>> > #  define __DECL_SIMD_sinf __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_sincos
>> > #  define __DECL_SIMD_sincos __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_sincosf
>> > #  define __DECL_SIMD_sincosf __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_log
>> > #  define __DECL_SIMD_log __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_logf
>> > #  define __DECL_SIMD_logf __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_exp
>> > #  define __DECL_SIMD_exp __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_expf
>> > #  define __DECL_SIMD_expf __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_pow
>> > #  define __DECL_SIMD_pow __DECL_SIMD_x86_64
>> > #  undef __DECL_SIMD_powf
>> > #  define __DECL_SIMD_powf __DECL_SIMD_x86_64
>> >
>> > The sincos/sincosf stuff is questionable, because some glibc
>versions
>> > implement it incorrectly and the simd ("notinbranch") attribute
>isn't that
>> > useful for it anyway, we'd want to use extra clauses so that it
>doesn't need
>> > to do scatter stores.
>> 
>> I wonder if it is possible for glibc to ship a "module" for fortran
>instead
>> containing the appropriate declarations and gfortran auto-include
>that
>> (if present).
>
>Then we'd run into module binary format changing every release, so hard
>for
>glibc to ship that.

It's just nobody bothered to implement version dependent parsing (it's plain text after all). 

>Another thing is how would we express it in the module,
>we could just use OpenMP syntax,
>      interface
>        function sin(x) bind(C,name="__builtin_sin") result(res)
>          import
>	  !$omp declare simd notinbranch
>          real(c_double) :: res
>          real(c_double),value :: x
>        end function
>      end interface
>but we'd need to temporarily enable OpenMP while parsing that module.
>I see Fortran now supports already
>!GCC$ attributes stdcall, fastcall::test
>Could we support
>!GCC$ attributes simd
>and
>!GCC$ attributes simd('notinbranch')
>too?

I guess that would be useful indeed. 

Richard. 

>	Jakub