[Bug tree-optimization/126085] If a in (-CST, 1-CST), then a + CST to a == (CST + 1)

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126085

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
I think we should do the opposite way around and convert `(type)(a == (CST +
1))` into `a+CST` instead. Adding is almost always simplier than comparsion.