[Bug middle-end/100471] #pragma omp taskloop with custom reduction

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100471

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:49bfa539e240cd769179751f18c472f9a4ea2248

commit r10-10608-g49bfa539e240cd769179751f18c472f9a4ea2248
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue May 11 09:07:47 2021 +0200

    openmp: Fix up taskloop reduction ICE if taskloop has no iterations
[PR100471]

    When a taskloop doesn't have any iterations, GOMP_taskloop* takes an early
    return, doesn't create any tasks and more importantly, doesn't create
    a taskgroup and doesn't register task reductions.  But, the code emitted
    in the callers assumes task reductions have been registered and performs
    the reduction handling and task reduction unregistration.  The pointer
    to the task reduction private variables is reused, on input it is the
alignment
    and only on output it is the pointer, so in the case taskloop with no
iterations
    the caller attempts to dereference the alignment value as if it was a
pointer
    and crashes.  We could in the early returns register the task reductions
    only to have them looped over and unregistered in the caller, but I think
    it is better to tell the caller there is nothing to task reduce and bypass
    all that.

    2021-05-11  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/100471
            * omp-low.c (lower_omp_task_reductions): For OMP_TASKLOOP, if data
            is 0, bypass the reduction loop including
            GOMP_taskgroup_reduction_unregister call.

            * taskloop.c (GOMP_taskloop): If GOMP_TASK_FLAG_REDUCTION and not
            GOMP_TASK_FLAG_NOGROUP, when doing early return clear the task
            reduction pointer.
            * testsuite/libgomp.c/task-reduction-4.c: New test.

    (cherry picked from commit 98acbb3111fcb5e57d5e63d46c0d92f4e53e3c2a)