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Date: Sun, 22 Aug 2021 19:53:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94070

sandra at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |sandra at gcc dot g=
nu.org

--- Comment #8 from sandra at gcc dot gnu.org ---
In gfc_desc_to_cfi_desc (in libgfortran/runtime/ISO_Fortran_binding.c):

        /* Assumed size arrays have gfc ubound =3D=3D 0 and CFI extent =3D =
-1.  */
        if (n =3D=3D GFC_DESCRIPTOR_RANK (s) - 1
            && GFC_DESCRIPTOR_LBOUND(s, n) =3D=3D 1
            && GFC_DESCRIPTOR_UBOUND(s, n) =3D=3D 0)
          d->dim[n].extent =3D -1;
        else
          d->dim[n].extent =3D (CFI_index_t)GFC_DESCRIPTOR_UBOUND(s, n)
                             - (CFI_index_t)GFC_DESCRIPTOR_LBOUND(s, n) + 1;

The comment and test are only correct if the lower bound of the array dimen=
sion
either defaults to 1 or is explicitly specified as 1.  It does appear that =
the
ubound =3D=3D 0 part is true, but this means e.g. an array dimension specif=
ied as
-3:* is indistinguishable from -3:0.

I think this needs to be corrected at the point where the GFC descriptor is
created; perhaps set ubound =3D lbound - 1?  Or also set lbound =3D 1 as th=
e code
snippet above checks?  Assumed-size arrays can't be pointers or allocatable=
 so
their bounds don't need to be preserved across calls, but maybe GFC descrip=
tors
are used for other purposes where it matters?=