I wonder if a relatively easy starting point would be enabling the
declaration of do concurrent construct variables:

do concurrent (integer :: i = 1:n)

It’s a minor convenience and less exciting than adding locality specifiers
but possibly a good first exercise.


Damian

On Thu, Feb 23, 2023 at 07:08 Tobias Burnus <tobias@codesourcery.com> wrote:

> Hi,
>
> and welcome to the GCC / gfortran community.
>
> On 23.02.23 14:15, varma datla via Fortran wrote:
> > I am willing to contribute to the project idea "Fortran – DO CONCURRENT".
>
> I hope the following helps a bit – it is admittedly a bit chaotic, but I
> try to write something cleaner later.
>
> But to have something to think of and to startwith, it should be
> sufficient:
>
> I think there are two parts to it: First, to add the changes of newer
> Fortran to gfortran and then to actually use them to generate
> concurrently running code. (Internally, gfortran currently handles 'do
> concurrent' to run mostly like a normal loop – except that it annotates
> the loops are independent. – Real parallelization would be useful,
> however.)
>
> If you want to see examples, see do_concurrent_1.f90 to
> do_concurrent_6.f90 in gfortran's testsuite, i.e.
> gcc/testsuite/gfortran.dg/ in the GCC sources. That's at
>
> https://gcc.gnu.org/git/?p=gcc.git;a=tree;f=gcc/testsuite/gfortran.dg;hb=refs/heads/master
> / But it is best to download GCC yourself via Git as described at
> https://gcc.gnu.org/git.html
>
> I want to note that the DO CONCURRENT syntax also permits a mask
> argument, like in 'do concurrent (i=1:5, j=1:5, (i/=j))' where the last
> argument selects a subset.
>
> For the Fortran standard, see https://gcc.gnu.org/wiki/GFortranStandards
>
> Fortran 2018 (= 18-007r1) adds for locality specifiers: LOCAL,
> LOCAL_INIT, SHARED and DEFAULT(NONE).
>
> Fortran 202x alias 2023 adds 'reduce' as in 'do concurrent (i = 1, n)
> reduce(+:a, b, c) reduce(max:d, e, f)'
>
> I think the first step is to add parsing support for those new features,
> i.e. store them, check for issues (diagnostic) and then fail with a
> 'sorry not yet implemented'.
>
> The next step would be to implement LOCAL/LOCAL_INIT for running on the
> host.
>
> And then, finally, would be to translate into code which can then be run
> concurrently. I was thinking of mapping it internally to OpenMP or
> OpenACC, to be toggled via a commandline option like
> -fdo-concurrent=<openmp,openmp-target,openacc,...>.
>
> * * *
>
> I think the first step would be to download GCC and build it. Something
> like "git clone" as described above, then "mkdir build" (some
> directory); "cd build" and then "../configure --prefix=where-to-install"
> followed by "make -j12" and "make install". The "-j12" runs 12 build
> jobs in parallel. How much to use depends on your system.
>
> You probably need to install some development versions of libraries such
> as ISL, gmp, mpfr and mpc. If you don't have them readily, an option is
> to run ./contrib/download_prerequisites to download those and build them
> automatically alongside GCC.
>
> So far for now. If you have questions, please ask. — And I will try to
> write something more structured later.
>
> Tobias
>
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