[Bug libstdc++/120428] [15/16 regression] Suboptimal autovec involving blocked permutation and std::copy

[shawn at shawnxu dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120428

--- Comment #3 from Shawn Xu <shawn at shawnxu dot org> ---
Seems to only matter when -mavx or -mavx512f is on. Otherwise the generated
assemblies are identical