From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <sgk@troutmask.apl.washington.edu>
Received: from troutmask.apl.washington.edu (troutmask.apl.washington.edu
 [128.95.76.21])
 by sourceware.org (Postfix) with ESMTPS id 094313858004
 for <fortran@gcc.gnu.org>; Sat,  3 Apr 2021 17:28:47 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 094313858004
Received: from troutmask.apl.washington.edu (localhost [127.0.0.1])
 by troutmask.apl.washington.edu (8.16.1/8.16.1) with ESMTPS id 133HSkMg014172
 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO)
 for <fortran@gcc.gnu.org>; Sat, 3 Apr 2021 10:28:46 -0700 (PDT)
 (envelope-from sgk@troutmask.apl.washington.edu)
Received: (from sgk@localhost)
 by troutmask.apl.washington.edu (8.16.1/8.16.1/Submit) id 133HSkuP014171
 for fortran@gcc.gnu.org; Sat, 3 Apr 2021 10:28:46 -0700 (PDT)
 (envelope-from sgk)
Date: Sat, 3 Apr 2021 10:28:46 -0700
From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: fortran@gcc.gnu.org
Subject: RANDOM_INIT() and coarray Fortran 
Message-ID: <20210403172846.GA14134@troutmask.apl.washington.edu>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS,
 KAM_LAZY_DOMAIN_SECURITY, KAM_SHORT, SPF_HELO_NONE, SPF_NONE,
 TXREP autolearn=no autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: fortran@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Fortran mailing list <fortran.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/fortran>,
 <mailto:fortran-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/fortran/>
List-Help: <mailto:fortran-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/fortran>,
 <mailto:fortran-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Sat, 03 Apr 2021 17:28:49 -0000

What to do about RANDOM_INIT() and coarray Fortran?

The main issue is that if one compiles with -fcoarray=lib
(or the WIP -fcoarray=shared), then RANDOM_INIT() may
require communication between images.  Thus, RANDOM_INIT()
cannot live in libgfortran for at least -fcoarray=lib.

Consider the simple code:

subroutine foo
   call random_init(.true., .false.)
end subroutine foo

I have updated the patch for
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98301
to use a stub routine for -fcoarray=lib and -fcoarray=shared.
Anyone, who knows how to use git, is encouraged to commit the patch.

For -fcoarray=none (default option) and -fcoarray=single, the
patch will cause gfortran to generate

__attribute__((fn spec (". ")))
void foo ()
{
  _gfortran_random_init (1, 0, 0);
}

_gfortran_random_init() live in libgfortran and it has been updated
to meet the intended requires of the Fortran standard.

With -fcoarray=lib and -fcoarray=shared, gfortran will now generate

__attribute__((fn spec (". ")))
void foo ()
{
  _gfortran_random_init_foobar (1, 0);
}

where _gfortran_random_init_foobar() lives in libgfortran.  It prints
an error message that RANDOM_INIT() is not yet supported for coarray
Fortran and exits.  Someone, who cares about coarray Fortran, can fix
-fcoarray=lib and -fcoarray=shared by updating trans-decl.c (see the
FIXME for random_init()) to emit 

__attribute__((fn spec (". ")))
void foo ()
{
  _gfortran_caf_random_init (1, 0);
}

or

__attribute__((fn spec (". ")))
void foo ()
{
  _gfortran_cas_random_init (1, 0);
}

-- 
Steve