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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/108741] New: [OpenMP] Wrong code for lastprivate with
 pointer iteration variable
Date: Thu, 09 Feb 2023 12:35:48 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: fortran
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: burnus at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108741

            Bug ID: 108741
           Summary: [OpenMP] Wrong code for lastprivate with pointer
                    iteration variable
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

The motivation is Fortran code, based on
  libgomp/testsuite/libgomp.fortran/non-rectangular-loop-3.f90
for PR107424 and with the patch applied from
  https://gcc.gnu.org/pipermail/gcc-patches/2023-January/610584.html

However, the issue is preexisting and probably fails already since
ever.

It shows also up with a questionable C code, which tries to mimic the Fortr=
an
code. The problem is that '**a0' in the loop body points to invalid memory.

//----- (questionable) C testcase ------

void foo(int **a1) {
  int j, a0;
  #pragma omp simd collapse(2) lastprivate(a0,a1,j)
  for (a0 =3D 1; a0 <=3D 10; a0++)
    for (j =3D 1; j <=3D 20; j++)
      **a1 =3D a0;    /// Segfaults here as *a0 points to invalid memory
  if (**a1 !=3D 10 || j !=3D 21 || a0 !=3D 11)
    __builtin_abort ();
}

int main() {
  int *a1, a2;
  a2 =3D 5;
  a1 =3D &a2;
  foo (&a1);
  return 0;
}


! Fortran testcase
  implicit none
  integer, pointer :: a1
  allocate(a1)
  call o(a1)
contains
  subroutine o(a1)
    implicit none
    integer :: j
    integer, pointer :: a1
    !$omp simd collapse(2) lastprivate(a1,j)
      do a1 =3D 1, 10
        do j =3D 1, 20
        end do
      end do
    if (a1 /=3D 11 .or. j /=3D 21) error stop
  end
end=