[Bug target/80846] auto-vectorized AVX2 horizontal sum should narrow to 128b right away, to be more efficient for Ryzen and Intel

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80846

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 41421
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41421&action=edit
WIP patch