[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 48453
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48453&action=edit
gcc11-pr94921.patch

Untested fix.