https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109780
--- Comment #12 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Eh, that commit sneakily changed avx2 tuning without explaining that in the
Changelog. Anyway, it should possible to "workaround" that by compiling with
-O2 -mavx2 -mtune=skylake-avx512
instead, in which case the bisect will likely point to commit
r12-2666-g29f0e955c97 ("x86: Update piecewise move and store") (before that,
expansion of memcpy via store-by-pieces wouldn't use avx2).
Also, PR 109093 looks very related.
