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From: "guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108757] We do not simplify (a - (N*M)) / N +
 M -> a / N
Date: Fri, 12 May 2023 09:35:05 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108757

--- 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) =3D=3D>=
 t >> N
> */
> (for div (trunc_div exact_div)
div was not used in this matcher, yet.  Here rshift is used:  t/(1<<N) coul=
d 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)) =3D=3D -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)"=