[Bug tree-optimization/81346] Missed constant propagation into comparison

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81346

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 41707
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41707&action=edit
gcc8-pr81346-wip.patch

Untested WIP patch.  Still no idea how to handle the build_range_check stuff at
GIMPLE, that function is pretty huge.  Shall I just always generate the cast to
utype and (acmp (minus (convert:utype @0) { lo; }) { himinuslo; })
after doing the etype/utype computation and verification in (with {...}) and
hope rest of match.pd optimizes that or add matchers for the various
optimizations in there?