https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99396
--- Comment #19 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:84185598dc7470bad4e7f8c22b64e3c944efb670 commit r11-7542-g84185598dc7470bad4e7f8c22b64e3c944efb670 Author: Jakub Jelinek <ja...@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 = 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. 2021-03-06 Jakub Jelinek <ja...@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.
