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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/99396] std::rotl and std::rotr Does not convert into ROTATE on the gimple level Date: Fri, 05 Mar 2021 09:36:25 +0000 [thread overview] Message-ID: <bug-99396-4-sb0rYtyqaF@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-99396-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99396 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jakub at gcc dot gnu.org --- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- There is absolutely no reason why libstdc++ should use any intrinsics for the rotates, gcc recognizes a lot of patterns into rotates. Just not the extra verbose one used in libstdc++. The comment in gcc says: /* Recognize rotation patterns. Return true if a transformation applied, otherwise return false. We are looking for X with unsigned type T with bitsize B, OP being +, | or ^, some type T2 wider than T. For: (X << CNT1) OP (X >> CNT2) iff CNT1 + CNT2 == B ((T) ((T2) X << CNT1)) OP ((T) ((T2) X >> CNT2)) iff CNT1 + CNT2 == B transform these into: X r<< CNT1 Or for: (X << Y) OP (X >> (B - Y)) (X << (int) Y) OP (X >> (int) (B - Y)) ((T) ((T2) X << Y)) OP ((T) ((T2) X >> (B - Y))) ((T) ((T2) X << (int) Y)) OP ((T) ((T2) X >> (int) (B - Y))) (X << Y) | (X >> ((-Y) & (B - 1))) (X << (int) Y) | (X >> (int) ((-Y) & (B - 1))) ((T) ((T2) X << Y)) | ((T) ((T2) X >> ((-Y) & (B - 1)))) ((T) ((T2) X << (int) Y)) | ((T) ((T2) X >> (int) ((-Y) & (B - 1)))) transform these into: X r<< Y Or for: (X << (Y & (B - 1))) | (X >> ((-Y) & (B - 1))) (X << (int) (Y & (B - 1))) | (X >> (int) ((-Y) & (B - 1))) ((T) ((T2) X << (Y & (B - 1)))) | ((T) ((T2) X >> ((-Y) & (B - 1)))) ((T) ((T2) X << (int) (Y & (B - 1)))) \ | ((T) ((T2) X >> (int) ((-Y) & (B - 1)))) transform these into: X r<< (Y & (B - 1)) Note, in the patterns with T2 type, the type of OP operands might be even a signed type, but should have precision B. Expressions with & (B - 1) should be recognized only if B is a power of 2. */ but libstdc++ does e.g. constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits; const int __r = __s % _Nd; if (__r == 0) return __x; else if (__r > 0) return (__x << __r) | (__x >> ((_Nd - __r) % _Nd)); else return (__x >> -__r) | (__x << ((_Nd + __r) % _Nd)); // rotr(x, -r) So, can't it e.g. use constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits; const auto __r = static_cast<unsigned int>(__s); return (__x << (__r % _Nd)) | (__x >> ((-__r) % _Nd)); ?
next prev parent reply other threads:[~2021-03-05 9:36 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-04 23:09 [Bug libstdc++/99396] New: std::rotl and std::rotr do not invoke intrinsics, leading to serious performance issues unlvsur at live dot com 2021-03-05 0:05 ` [Bug tree-optimization/99396] " pinskia at gcc dot gnu.org 2021-03-05 0:06 ` [Bug tree-optimization/99396] std::rotl and std::rotr Does not convert into ROTATE on the gimple level pinskia at gcc dot gnu.org 2021-03-05 2:08 ` unlvsur at live dot com 2021-03-05 3:12 ` pinskia at gcc dot gnu.org 2021-03-05 3:18 ` unlvsur at live dot com 2021-03-05 8:25 ` redi at gcc dot gnu.org 2021-03-05 9:36 ` jakub at gcc dot gnu.org [this message] 2021-03-05 9:44 ` jakub at gcc dot gnu.org 2021-03-05 9:50 ` jakub at gcc dot gnu.org 2021-03-05 10:38 ` jakub at gcc dot gnu.org 2021-03-05 10:47 ` redi at gcc dot gnu.org 2021-03-05 10:52 ` jakub at gcc dot gnu.org 2021-03-05 11:02 ` jakub at gcc dot gnu.org 2021-03-05 11:59 ` unlvsur at live dot com 2021-03-05 12:03 ` jakub at gcc dot gnu.org 2021-03-05 12:04 ` jakub at gcc dot gnu.org 2021-03-05 12:08 ` unlvsur at live dot com 2021-03-05 12:09 ` unlvsur at live dot com 2021-03-05 12:12 ` unlvsur at live dot com 2021-03-06 10:12 ` cvs-commit at gcc dot gnu.org 2021-03-06 10:13 ` jakub at gcc dot gnu.org
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