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From: "mikael at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/102043] Wrong array types used for negative stride
 accesses
Date: Wed, 10 Nov 2021 16:31:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102043

Mikael Morin <mikael at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikael at gcc dot gnu.org

--- Comment #8 from Mikael Morin <mikael at gcc dot gnu.org> ---
It comes from gfc_conv_expr_descriptor:

        /* Point the data pointer at the 1st element in the section.  */
        gfc_get_dataptr_offset (&loop.pre, parm, desc, base,
                                subref_array_target, expr);

where base has been calculated as the index of the first element.

I=E2=80=99ve tried doing a mere "if (forward) start else end" in the calcul=
ation of
base, but then I needed to add an offset (i.e. array index offset) to vector
subscript accesses, and then a delta was missing (i.e. loop index offset) as
the descriptor is one-based, but I don=E2=80=99t know how to fix the latter=
 without
impacting all the vector subscript handling which seems to rely on quite a =
few
assumptions (no delta, no offset, zero-based loop?, forward loop?).=