[Bug tree-optimization/92420] [8/9 Regression] Vectorization miscompilation with negative strides since r238039

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92420

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Richard Sandiford
<rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:2d8ea3a0a6095a56b7c59c50b1068d602cde934a

commit r9-8248-g2d8ea3a0a6095a56b7c59c50b1068d602cde934a
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Mon Nov 11 19:43:52 2019 +0000

    Fix SLP downward group access classification [PR92420]

    This PR was caused by the SLP handling in get_group_load_store_type
    returning VMAT_CONTIGUOUS rather than VMAT_CONTIGUOUS_REVERSE for
    downward groups.

    A more elaborate fix would be to try to combine the reverse permutation
    into SLP_TREE_LOAD_PERMUTATION for loads, but that's really a follow-on
    optimisation and not backport material.  It might also not necessarily
    be a win, if the target supports (say) reversing and odd/even swaps
    as independent permutes but doesn't recognise the combined form.

    2020-02-18  Richard Sandiford  <richard.sandiford@arm.com>

    gcc/
        Backport from mainline
        2019-11-11  Richard Sandiford  <richard.sandiford@arm.com>

        PR tree-optimization/92420
        * tree-vect-stmts.c (get_negative_load_store_type): Move further
        up file.
        (get_group_load_store_type): Use it for reversed SLP accesses.

    gcc/testsuite/
        PR tree-optimization/92420
        * gcc.dg/vect/pr92420.c: New test.