Re: [Patch] Edit contrib/ files to download gfortran prerequisites

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Oct 24, 2017 at 12:02 AM, Damian Rouson
<damian@sourceryinstitute.org> wrote:
>
>
> On October 23, 2017 at 3:54:22 AM, Richard Biener
> (richard.guenther@gmail.com) wrote:
>
> On Sat, Oct 21, 2017 at 2:26 AM, Damian Rouson
> <damian@sourceryinstitute.org> wrote:
>>
>> Hi Richard,
>>
>> Attached is a revised patch that makes the downloading of Fortran
>> prerequisites optional via a new --no-fortran flag that can be passed to
>> contrib/download_prerequisites as requested in your reply below.
>>
>> As Jerry mentioned in his response, he has been working on edits to the
>> top-level build machinery, but we need additional guidance to complete his
>> work. Given that there were no responses to his request for guidance and
>> it’s not clear when that work will complete, I’m hoping this minor change
>> can be approved independently so that this patch doesn’t suffer bit rot in
>> the interim.
>
> But the change doesn't make sense without the build actually picking up
> things.
>
> Each prerequisite tar ball contains build scripts so the change is useful
> even without the ultimate integration into the GCC build system.  Our first
> step was to get the tar balls onto the GCC ftp server.  Our next step was to
> set up for the files to be downloaded automatically with this patch.  For
> now, users can use the build scripts in the prerequisite tar balls.  Our
> final step will be to finish the integration into the GCC build system.
> Jerry has requested guidance on this mailing list, but I don’t think there
> have been any replies to his request.  In the interim, I’m stuck updating
> this patch indefinitely.  I’ve already updated it several times because the
> files it patches are changing.

What I am completely missing is documentation on the Coarrays feature.
doc/install.texi doesn't list any install requirements like for example
where GCC will look for and for what libraries (and headers?) and what
the constraints on the libraries are (like mpich vs. openmpi).

Simply downloading a tarball from download_prerequesites doesn't
sound useful.  People can simply follow URLs listed in install.texi
to get at those.

> Most importantly, the features these prerequisites enable are part of the
> Fortran standard so they are necessary for full access to the language —
> namely access to any Fortran 2008 or Fortran 2015 parallel features.  I hope
> I’ve made a case for the benefit of the patch. Is there a way in which the
> patch is harmful?

It will unconditionally download stuff and the user doesn't know he needs
to do sth "manual" to enable -fcoarrays=lib(?)?  From what I gather
from the scattered information on the wiki there's nothing one needs to
strictly do at GCC _build_ time.  Just when one wants to use
-fcoarrays=lib you need to manually add -lXYZ (why's that not done
with GCCs driver specs processing?) and have that library available
somewhere in the search path.

It looks then this is a similar level of integration as -mveclibabi={acml,svml}
where we don't download or build/install a vector math library either.

So - can you - as a first step - add something about Fortran Coarray
requirements to doc/install.texi?  Just put it in an item after 'isl Library'.
I presume the MPI library is a requirement of OpenCoarrays and  not
of GFortran?  If so people should refer to OpenCoarrays documentation
to figure out that requirement (and decide themselves what MPI library
to use?)

Thanks,
Richard.

>
> Damian