[mpich-discuss] Is it okay to remove F77 support?

Zhou, Hui zhouh at anl.gov
Wed Jan 27 08:14:13 CST 2021

Thanks! This type of response is the exact the kind of response we are looking for.

Okay, to clarify, there is no plan to stop support legacy f77 mpi applications that relies on `mpif.h` to work. We have a large set of test suites in F77 and we will always ensure these tests pass.

My question is really about simplifying the MPICH build. Currently we still assume there are Fortran compilers out there that will only compile (somewhat strict) F77 and our configure scripts checks for F77 compiler and F90 compiler separately, and our binding code have measures to ensure we don’t use features that legacy F77 compiler won’t accept. My question is, is there really such compilers out there? And if there is, is it okay for us not to support such compilers?

This is a similar question as moving our code base to C99, it is all about making code development easier and in the meantime ensure that we do not impose extra inconvenience for our user to build MPICH.

Hui Zhou

From: Gus Correa via discuss <discuss at mpich.org>
Date: Tuesday, January 26, 2021 at 9:09 PM
To: MPICH-Discuss <discuss at mpich.org>
Cc: Gus Correa <gus at ldeo.columbia.edu>
Subject: Re: [mpich-discuss] Is it okay to remove F77 support?
Is it okay to remove F77 support?
No, NO, NO!!!! NO!

Removing the support to Fortran 77 from MPI is a disastrous idea!
Sorry to say, but it is really stupid to suppose that only because compilers support F90
that you can remove F77 support from MPI.
A lot of people, academic institutions, and probably industry, continue to use,
and develop new code in F77.
What matters is if the CODE is written in Fortran 90 or in Fortran 77,
and whether it uses the Fortran 77 MPI API or the Fortran 90 MPI API,
not whether the compiler supports Fortran 90 (and yes, if not all, do).

There is an enormous Fortran 77 code base, written using MPI, and that is not likely to change for the foreseeable future.
That is true in the Atmospheric/Climate/Ocean sciences, where I work,
but would guess this is true in other areas of science as well.
Just one example: The MITgcm, which has an huge community of users,
is the backbone for many research projects, supports many PhD thesis,
is 100% written in Fortran-77 and will not be changed anytime soon,
as there is no financial support to do that.

Also, this type of inquiry to the MPICH community is way too narrow.
I don't think you should be using emails on a mailing list to base such a consequential decision.
Argonne should know better which community it supports, which codes out there use MPI.

Thank you,

Gus Correa
Lamont-Doherty Earth Observatory of Columbia University.

On Tue, Jan 26, 2021 at 6:12 PM Zhou, Hui via discuss <discuss at mpich.org<mailto:discuss at mpich.org>> wrote:
Dear MPICH community,

Can we assume at this point of time, that every Fortran compiler out there supports Fortran 90 at least?

Hui Zhou

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