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Subject: [Bug tree-optimization/99396] std::rotl and std::rotr Does not
 convert into ROTATE on the gimple level
Date: Sat, 06 Mar 2021 10:12:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99396

--- Comment #19 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:84185598dc7470bad4e7f8c22b64e3c944efb670

commit r11-7542-g84185598dc7470bad4e7f8c22b64e3c944efb670
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Mar 6 11:11:30 2021 +0100

    libstdc++: Improve std::rot[lr] [PR99396]

    As can be seen on:

    unsigned char f1 (unsigned char x, int y) { return std::rotl (x, y); }
    unsigned char f2 (unsigned char x, int y) { return std::rotr (x, y); }
    unsigned short f3 (unsigned short x, int y) { return std::rotl (x, y); }
    unsigned short f4 (unsigned short x, int y) { return std::rotr (x, y); }
    unsigned int f5 (unsigned int x, int y) { return std::rotl (x, y); }
    unsigned int f6 (unsigned int x, int y) { return std::rotr (x, y); }
    unsigned long int f7 (unsigned long int x, int y) { return std::rotl (x,
y); }
    unsigned long int f8 (unsigned long int x, int y) { return std::rotr (x,
y); }
    unsigned long long int f9 (unsigned long long int x, int y) { return
std::rotl (x, y); }
    unsigned long long int f10 (unsigned long long int x, int y) { return
std::rotr (x, y); }
    //unsigned __int128 f11 (unsigned __int128 x, int y) { return std::rotl=
 (x,
y); }
    //unsigned __int128 f12 (unsigned __int128 x, int y) { return std::rotr=
 (x,
y); }

    constexpr auto a =3D std::rotl (1234U, 0);
    constexpr auto b =3D std::rotl (1234U, 5);
    constexpr auto c =3D std::rotl (1234U, -5);
    constexpr auto d =3D std::rotl (1234U, -__INT_MAX__ - 1);
    the current <bit> definitions of std::__rot[lr] aren't pattern recogniz=
ed
    as rotates, they are too long/complex for that, starting with signed
modulo,
    special case for 0 and different cases for positive and negative.

    For types with power of two bits the following patch adds definitions t=
hat
    the compiler can pattern recognize and turn e.g. on x86_64 into
ro[lr][bwlq]
    instructions.  For weirdo types like unsigned __int20 etc. it keeps the
    current definitions.

    2021-03-06  Jakub Jelinek  <jakub@redhat.com>

            PR libstdc++/99396
            * include/std/bit (__rotl, __rotr): Add optimized variants for
power of
            two _Nd which the compiler can pattern match the rotates.=