https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104005
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 trunk
when shared libraries are used from -O2 when two or more thread-MPI are used. 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.sandif...@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 avoid
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 right
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.
