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From: "igor.gayday at mu dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/97046] New: Bad interaction between lbound/ubound,
 allocatable arrays and bind(C) subroutine with dimension(..) parameter
Date: Mon, 14 Sep 2020 15:42:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97046

            Bug ID: 97046
           Summary: Bad interaction between lbound/ubound, allocatable
                    arrays and bind(C) subroutine with dimension(..)
                    parameter
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: igor.gayday at mu dot edu
  Target Milestone: ---

Consider the following code:

MODULE FOO
INTERFACE
SUBROUTINE dummyc(x0) BIND(C, name=3D"sync")
type(*), dimension(..) :: x0
END SUBROUTINE
END INTERFACE
contains
SUBROUTINE dummy(x0)
type(*), dimension(..) :: x0
call dummyc(x0)
END SUBROUTINE
END MODULE

PROGRAM main
    USE FOO
    IMPLICIT NONE
    integer :: before(2), after(2)

    INTEGER, parameter :: n =3D 1

    DOUBLE PRECISION, ALLOCATABLE :: buf(:)
    DOUBLE PRECISION :: buf2(n)

    ALLOCATE(buf(n))
    before(1) =3D LBOUND(buf,1)
    before(2) =3D UBOUND(buf,1)
    CALL dummy (buf)
    after(1) =3D LBOUND(buf,1)
    after(2) =3D UBOUND(buf,1)

    if (before(1) .NE. after(1)) stop 1
    if (before(2) .NE. after(2)) stop 2

    before(1) =3D LBOUND(buf2,1)
    before(2) =3D UBOUND(buf2,1)
    CALL dummy (buf2)
    after(1) =3D LBOUND(buf2,1)
    after(2) =3D LBOUND(buf2,1)

    if (before(1) .NE. after(1)) stop 3
    if (before(2) .NE. after(2)) stop 4

END PROGRAM

lbound() and ubound() of an allocatable array return different values=20
before and after a Fortran subroutine with dimension(..) parameter (that=20
in turns invokes a bind(C) subroutine) is invoked.

Note that if the main program directly CALL dummyc(buf) (instead of=20
dummy(buf)), then the error does not occur.

gcc versions 9.2.0, 10.2.0 and the latest master branch are all affected.

In particular, this causes issues with mpi_f08 module, see:
https://stackoverflow.com/questions/63824065/lbound-of-an-array-changes-aft=
er-call-to-mpi-gatherv-when-using-mpi-f08-module

This might be a duplicate of Bug #94070.=