[Bug target/88963] gcc generates terrible code for vectors of 64+ length which are not natively supported

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88963

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 45489
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45489&action=edit
untested patch

forwprop patch I was playing with.