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Re: libmvec in gcc to have vector math in fortran


On 10/04/18 14:27, Richard Biener wrote:
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:
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.

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?

Maybe we can also generate this module in a fixinlclude way?


ideally everything should work magically but i think
it's good to have a big hammer solution that's easy
to reason about.

the gcc vectorizer should be testable independently
of glibc, and users should be able to specify what
can be vectorized.

if this is via a per-frontend declaration syntax,
then i see implementation and usability issues, while
those are sorted out a single flag that requests every
function known to gcc to be vectorized sounds to me a
viable big hammer solution: easy to implement and
enables users to start experimenting with simd math.

(the implementation may use a preincluded fortran
module internally, but i think it makes sense to
have a single flag ui too)


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