[Bug middle-end/121453] [OpenMP] 'omp simd' with 'collapse' – variable '.count' uninitialized, but used as 'if (.iter.14 == .count.15)'

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121453

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-15 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:cb24799a21dae86162e418c6baa44f4e32b8e7cc

commit r15-10359-gcb24799a21dae86162e418c6baa44f4e32b8e7cc
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Aug 26 00:28:10 2025 +0200

    omp-expand: Initialize fd->loop.n2 if needed for the zero iter case
[PR121453]

    When expand_omp_for_init_counts is called from expand_omp_for_generic,
    zero_iter1_bb is NULL and the code always creates a new bb in which it
    clears fd->loop.n2 var (if it is a var), because it can dominate code
    with lastprivate guards that use the var.
    When called from other places, zero_iter1_bb is non-NULL and so we don't
    insert the clearing (and can't, because the same bb is used also for the
    non-zero iterations exit and in that case we need to preserve the iteration
    count).  Clearing is also not necessary when e.g. outermost collapsed
    loop has constant non-zero number of iterations, in that case we initialize
the
    var to something already earlier.  The following patch makes sure to clear
    it if it hasn't been initialized yet before the first check for zero
iterations.

    2025-08-26  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/121453
            * omp-expand.cc (expand_omp_for_init_counts): Clear fd->loop.n2
            before first zero count check if zero_iter1_bb is non-NULL upon
            entry and fd->loop.n2 has not been written yet.

            * gcc.dg/gomp/pr121453.c: New test.

    (cherry picked from commit 948f20cc520e50968f8759b173096358dcbba3de)