On Fri, 5 Mar 2021, 22:32 Jakub Jelinek via Libstdc++, <
libstd...@gcc.gnu.org> wrote:
> Hi!
>
> As can be seen on:
> #include <bit>
>
> 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 = std::rotl (1234U, 0);
> constexpr auto b = std::rotl (1234U, 5);
> constexpr auto c = std::rotl (1234U, -5);
> constexpr auto d = std::rotl (1234U, -__INT_MAX__ - 1);
> the current <bit> definitions of std::__rot[lr] aren't pattern recognized
> 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 that
> 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.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
OK, thanks.
>
>
