| Message ID | 20210305203745.GB1837485@tucnak |
|---|---|
| State | New |
| Headers | show |
| Series | libstdc++: Improve std::rot[lr] [PR99396] | expand |
On Fri, 5 Mar 2021, 22:32 Jakub Jelinek via Libstdc++, < libstdc++@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. > >
--- libstdc++-v3/include/std/bit.jj 2021-03-05 10:37:36.108378753 +0100 +++ libstdc++-v3/include/std/bit 2021-03-05 12:01:57.926310110 +0100 @@ -68,6 +68,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __rotl(_Tp __x, int __s) noexcept { constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits; + if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0) + { + // Variant for power of two _Nd which the compiler can + // easily pattern match. + constexpr unsigned __uNd = _Nd; + const unsigned __r = __s; + return (__x << (__r % __uNd)) | (__x >> ((-__r) % __uNd)); + } const int __r = __s % _Nd; if (__r == 0) return __x; @@ -82,6 +90,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __rotr(_Tp __x, int __s) noexcept { constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits; + if _GLIBCXX17_CONSTEXPR ((_Nd & (_Nd - 1)) == 0) + { + // Variant for power of two _Nd which the compiler can + // easily pattern match. + constexpr unsigned __uNd = _Nd; + const unsigned __r = __s; + return (__x >> (__r % __uNd)) | (__x << ((-__r) % __uNd)); + } const int __r = __s % _Nd; if (__r == 0) return __x;
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? 2021-03-05 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. Jakub