From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 4B2B6385840B; Thu, 13 Jan 2022 11:41:59 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4B2B6385840B
From: "gilles.gouaillardet at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/104005] New: Regression on arm+sve with -O2 -fPIC
Date: Thu, 13 Jan 2022 11:41:59 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: gilles.gouaillardet at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-104005-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Thu, 13 Jan 2022 11:41:59 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104005

            Bug ID: 104005
           Summary: Regression on arm+sve with -O2 -fPIC
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gilles.gouaillardet at gmail dot com
  Target Milestone: ---

The GROMACS (2021.3) non regression test suite now hangs with the latest tr=
unk
when shared libraries are used from -O2 when two or more thread-MPI are use=
d. I
only tried 512 bit SVE vectors.

I ran a git bisect and it pointed to the following commit:

commit 526e1639aa76b0a8496b0dc3a3ff2c450229544e (refs/bisect/bad)
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Fri Nov 12 17:33:00 2021 +0000

    aarch64: Detect more consecutive MEMs


When investigating this issue, I found out that rebuilding the
src/gromacs/domdec/redistribute.cpp file **without** -fPIC is enough to avo=
id
the issue (a crash or a hang depending on the test cases).

FWIW, thread-MPI is a "fake" MPI implementation that used threads instead
processes. In this case, that means two threads. Then each thread enter its=
 own
#pragma omp parallel section (and each thread-MPI thread has a unique OpenMP
thread)


The attached tarball includes preprocessed source (redistribute.cpp.i) and
assembly with -fPIC (redistribute.cpp.PIC.s) and without -fPIC
(redistribute.cpp.noPIC.s) for the commit mentioned above and the commit ri=
ght
before.


Please let me know if this is enough for you to make sense of this bug,
otherwise I will provide instructions on how to build GROMACS from sources =
and
manually workaround the issue by "removing" the -fPIC flags for the
redistribute.cpp file.=