[Bug tree-optimization/108757] We do not simplify (a - (N*M)) / N + M -> a / N

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108757

--- Comment #24 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
(In reply to Jiu Fu Guo from comment #23)
> /* Simplify ((t + -N*M) / N + M) -> t / N: (t + -C) >> N + (C>>N) ==> t >> N
> */
> (for div (trunc_div exact_div)
div was not used in this matcher, yet.  Here rshift is used:  t/(1<<N) could be
optimized to "t>>N".

>  (simplify
>   (plus (rshift (plus @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3)
>   (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type) &&
>        (wi::to_wide (@3) << wi::to_wide (@2)) == -wi::to_wide (@1))
>    (if (TYPE_OVERFLOW_UNDEFINED (type))
>     (div @0 @2)
This should be "(rshift @0 @2)", otherwise it will be error if relax
"TYPE_UNSIGNED (type)"