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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109767] New: [OpenMP][5.2] Missing loop-variable
 privatization inside 'teams'
Date: Mon, 08 May 2023 09:10:05 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: openmp, wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109767

            Bug ID: 109767
           Summary: [OpenMP][5.2] Missing loop-variable privatization
                    inside 'teams'
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: openmp, wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
  Target Milestone: ---

Cf. https://github.com/SOLLVE/sollve_vv/issues/731

OpenMP 5.1 had:
* "Loop iteration variables inside 'parallel' or task generating constructs=
 are
private in the innermost such construct that encloses the loop."

OpenMP 5.2 added 'teams':
* "Loop iteration variables inside 'parallel', 'teams', or task generating
constructs are private in the innermost such construct that encloses the lo=
op."


In GCC, the 'j' is shared, causing race issues. Testcases:

=3D=3D> teams-loop-var.c <=3D=3D
#define N 10
int
main ()
{
  int x[N][N], y[N][N];
  int j;

  #pragma omp teams  // in GCC implied: shared(j)  <<< (!) >>>
                     // [but 'private(j) with gfortran]
    for (int i =3D 0; i < N; i++)
      for (j =3D 0; j < N; j++)
        // TR12: #pragma omp atomic write
        x[i][j] =3D 2*j;

  #pragma omp teams   // in GCC implied: shared(j)  <<< (!) >>>
                      // [but 'private(j) with gfortran]
    #pragma omp loop  // in GCC implied: omp parallel shared(j)  <<< (!) >>>
    for (int i =3D 0; i < N; i++)
      for (j =3D 0; j < N; j++)
        // TR12: #pragma omp atomic write
        y[i][j] =3D j + x[i][j];

  for (int i =3D 0; i < N; i++)
    for (j =3D 0; j < N; j++)
      if (y[i][j] !=3D j + 2*j)
        __builtin_abort ();
  return 0;
}


=3D=3D> teams-loop-var.f90 <=3D=3D
implicit none
integer, parameter :: N =3D 10
integer :: x(N,N), y(N,N)
integer :: i, j

!$omp teams  ! in GCC implied: private(j)  [but shared(j) with gcc/g++]
  do i =3D 1, N
    do j =3D 1, N
      ! TR12: !$omp atomic write
      x(j,i) =3D 2*j
    end do
  end do
!$omp end teams

!$omp teams   ! in GCC implied: private(j)  [but shared(j) with gcc/g++]
  !$omp loop  ! gcc generated: omp parallel shared(j) <<< (!) >>>
  do i =3D 1, N
    do j =3D 1, N
      ! TR12: !$omp atomic write
      y(j,i) =3D j + x(j, i)
    end do
  end do
!$omp end teams

do i =3D 1, N
  do j =3D 1, N
    if (y(j,i) /=3D j + 2*j)  &
      stop 1
  end do
end do
end=