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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99396] std::rotl and std::rotr do not invoke
 intrinsics, leading to serious performance issues
Date: Fri, 05 Mar 2021 00:05:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99396

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |tree-optimization
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-03-05

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
    return std::rotr(v,((unsigned int)t)&63);
Fixes the problem ....
    int a =3D std::abs(t);
    a &=3D 63;
    return std::rotr(v,a);

Also improves the situtation.
I am thinking the std::rotr could be rewritten or we could optimize this at=
 the
tree level into the almost the intrinsics.
Note I think I Might have gotten the above incorrect a little bit.=