[Bug target/71921] missed vectorization optimization

[arjan at linux dot intel.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71921

--- Comment #7 from Arjan van de Ven <arjan at linux dot intel.com> ---
Created attachment 40416
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40416&action=edit
prototype patch