On Monday, June 20, 2022 at 3:48:29 AM UTC-7, mies wrote:
> schrieb am Samstag, 18. Juni 2022 um 16:14:29 UTC+2:
> > Thomas Koenig schrieb am Freitag, 17. Juni 2022 um 17:01:36 UTC+2:
> > > schrieb:
> > > > Thomas Koenig schrieb am Sonntag, 12. Juni 2022 um 13:53:27 UTC+2:
> > > >> I recently had an e-mail from somebody who ran into trouble
> > > >> with old code on gfortran - gfortran 9 did not have the
> > > >> -fallow-argument-mismatch flag, but gfortran 11 required it due
> > > >> to issues in the code.
> > > >>
> > > >> The solution I proposed was to add something like
> > > >>
> > > >> FC_OPTIONS="-O2"
> > > >> cat > optiontest.f90 <<EOF
> > > >> end
> > > >> EOF
> > > >> gfortran -fallow-argument-mismatch -fsyntax-only optiontest.f90 \
> > > >> 2>/dev/null && FC_OPTIONS="$FC_OPTIONS -fallow-argument-mismatch"
> > > >> echo $FC_OPTIONS
> > > >> rm optiontest.f90
> > > >>
> > > >> to his build scripts, which will add the flag to the FC_OPTIONS
> > > >> variable if it is supported, and I thought I'd share it.
> > > >
> > > > It is certainly an MPICH issue, but I am still using gfortran
> > > > version 9.2.1 just to avoid this -fallow-argument-mismatch flag
> > > > when compiling MPICH for use with gfortran and OpenCoarrays. To me,
> > > > it appears that this flag is somehow related to severe performance
> > > > issues with MPICH and coarray programming.
> > > I can assure you it is not - the change in question is purely something
> > > that will downgrade a newly introduced error to a warning.
> > >
> > > Any Performance issues you are seeing may be related to the
> > > interplay of the OpenCoarrays library with MPICH. Since
> > > I know neither well, I cannot really comment on that.
> > My personal guess is that this performance issue is not due to gfortran, not due to OpenCoarrays, and not due to ifort, but only due to MPICH. Recent releases of gfortran/OpenCoarrays and ifort show the exactly same (poor) run-time performance pattern. And Intel MPI is MPICH. Earlier releases of ifort did perform as fast as my setup with gfortran 9.2 and OpenCoarrays.
> > And, for reasons that I can’t understand, the poor performance pattern with gfortran/OpenCoarrays occurs whenever the compilation of MPICH leads to:
> >
> > mpich 4.0.1 ./configure
> > checking whether gfortran allows mismatched arguments... yes, with -fallow-argument-mismatch
> > configure: error: The Fortran compiler gfortran does not accept programs that call the same routine with arguments of different types without the option -fallow-argument-mismatch. Rerun configure with FFLAGS=-fallow-argument-mismatch and FCFLAGS=-fallow-argument-mismatch
> Just to make this more complete:
> From what I did see, the poor performance pattern is not necessarily a poor performance of the image-to-image data transfers with synchronization (through MPICH), but may rather be a poor performance of executing the purely local codes (and in my case with oversubscribing cores, i.e. using more coarray images than hardware cores are available).
I was examining the docs (https://gcc.gnu.org/onlinedocs/gfortran/Fortran-Dialect-Options.html) and it turns out that -fallow-argument-mismatch is implied by -std=legacy. -std=legacy is allowed by at least some versions that will reject -fallow-argument-mismatch. Switching to -std=legacy worked for my use case, removing the need for a compatibility test. Just be careful in case -std=legacy has other, less desirable, effects.

Wyatt Spear <wjspear@gmail.com> schrieb:
> I was examining the docs
>(https://gcc.gnu.org/onlinedocs/gfortran/Fortran-Dialect-Options.html)
> and it turns out that -fallow-argument-mismatch is implied by
> -std=legacy.

That is correct.

>-std=legacy is allowed by at least some versions that
> will reject -fallow-argument-mismatch.

That was the idea, for backwards compatibility.

> Switching to -std=legacy
> worked for my use case, removing the need for a compatibility
> test.

That can be done.

I would still recommend using the test because

>Just be careful in case -std=legacy has other, less desirable,
>effects.

you are right there: -std=legacy accepts a lot of code that is
not in the user's best interest to have :-)