[Bug tree-optimization/112736] [14 Regression] vectorizer is introducing out of bounds memory access

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112736

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:6d0b0806eb638447c3184c59d996c2f178553d45

commit r14-6459-g6d0b0806eb638447c3184c59d996c2f178553d45
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Dec 11 14:39:48 2023 +0100

    tree-optimization/112736 - avoid overread with non-grouped SLP load

    The following aovids over/under-read of storage when vectorizing
    a non-grouped load with SLP.  Instead of forcing peeling for gaps
    use a smaller load for the last vector which might access excess
    elements.  This builds upon the existing optimization avoiding
    peeling for gaps, generalizing it to all gap widths leaving a
    power-of-two remaining number of elements (but it doesn't replace
    or improve that particular case at this point).

    I wonder if the poly relational compares I set up are good enough
    to guarantee /* remain should now be > 0 and < nunits.  */.

    There is existing test coverage that runs into /* DR will be unused.  */
    always when the gap is wider than nunits.  Compared to the
    existing gap == nunits/2 case this only adjusts the load that will
    cause the overrun at the end, not every load.  Apart from the
    poly relational compares it should reliably cover these cases but
    I'll leave it for stage1 to remove.

            PR tree-optimization/112736
            * tree-vect-stmts.cc (vectorizable_load): Extend optimization
            to avoid peeling for gaps to handle single-element non-groups
            we now allow with SLP.

            * gcc.dg/torture/pr112736.c: New testcase.