[Bug target/86731] [8/9 Regression] Miscompiles vec_sl at -O3 with -fwrapv on ppc64el

[willschm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86731

--- Comment #1 from Will Schmidt <willschm at gcc dot gnu.org> ---
Created attachment 44542
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44542&action=edit
preliminary patch to resolve the problem

preliminary/rfc patch.