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From: "pmblakely at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/111719] New: Omitting data-sharing attribute for
 function return value in OpenMP does not raise an error.
Date: Sat, 07 Oct 2023 13:13:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111719

            Bug ID: 111719
           Summary: Omitting data-sharing attribute for function return
                    value in OpenMP does not raise an error.
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pmblakely at googlemail dot com
  Target Milestone: ---

In the following Fortran90 example:

program prog

contains
  function b(arr)
    implicit none
    integer :: i, xCells
    real(kind =3D 8) :: dx, a, dc, b, dt
    real(kind =3D 8), allocatable, dimension(:), intent(in) :: arr

    b =3D 1d300
    dc =3D 1d300
!$OMP parallel do default(none) reduction(min:dt) firstprivate(xCells, dx, =
a)
shared(arr)
    do i =3D 0, xCells=20
       a =3D arr(i)
       b =3D min(b, 1d0 / a)
    end do=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  end function b
end program prog

the return value for function 'b' is the intended reduction value in the
do-loop, but is not mentioned in the OpenMP reduction clause (dt is incorre=
ctly
mentioned instead). Due to the default(none) clause, this should be a
compile-time error.
However:
gfortran test.f90 -o test -fopenmp
compiles this without warnings or errors (versions 13.1.0, 8.4.0, 9.4.0, 11=
.2.0
and 12.1.0 all tested).

If "b =3D min(b, 1d0 / a)" is replaced by "dc =3D min(dc, 1d0/a)"
then gfortran gives: "Error: 'dc' not specified in enclosing =E2=80=98paral=
lel=E2=80=99"

I would expect this error to be generated in the original case as well.

Note that the OpenMP standard at
https://www.openmp.org/spec-html/5.2/openmpsu33.html does not give an
implicitly determined data-sharing attribute for the function return value.
Also the Intel Fortran ifort (2021.8.0) does raise the expected error on the
above test-code.=