[Bug tree-optimization/99954] [8/9 Regression] Copy loop over array of unions at -O3 generates memcpy instead of memmove, resulting in incorrect code

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99954

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:b091cb1efa1881e93fb2e264daaab8876acf6800

commit r9-9471-gb091cb1efa1881e93fb2e264daaab8876acf6800
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Apr 7 13:17:05 2021 +0200

    tree-optimization/99954 - fix loop distribution memcpy classification

    This fixes bogus classification of a copy as memcpy.  We cannot use
    plain dependence analysis to decide between memcpy and memmove when
    it computes no dependence.  Instead we have to try harder later which
    the patch does for the gcc.dg/tree-ssa/ldist-24.c testcase by resorting
    to tree-affine to compute the difference between src and dest and
    compare against the copy size.

    2021-04-07  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/99954
            * tree-loop-distribution.c: Include tree-affine.h.
            (generate_memcpy_builtin): Try using tree-affine to prove
            non-overlap.
            (loop_distribution::classify_builtin_ldst): Always classify
            as PKIND_MEMMOVE.

            * gcc.dg/torture/pr99954.c: New testcase.