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From: "unlvsur at live dot com" <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 03:18:18 +0000	[thread overview]
Message-ID: <bug-99396-4-2HWlgzmZMr@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

--- Comment #4 from cqwrteur <unlvsur at live dot com> ---
(In reply to Andrew Pinski from comment #3)
> (In reply to cqwrteur from comment #2)
> > I would like to see __builtin_cpp_rotl and __builtin_cpp_rotr to allow more
> > aggressive optimizations since rotl and rotr are so important for
> > cryptography.
> 
> You don't need them.
> The following code will already produce the rotate instruction:
> auto f3(std::size_t v, int t)
> {
>   return (v<<t) | (v>>(sizeof(v)*8 - t));
> }
> 
> Note std::rotl/std::rotr has specific behavior dealing with 0 and negative
> values and all.

but if it is constant, it would get optimized to just ror or rol

  parent reply	other threads:[~2021-03-05  3:18 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 [this message]
2021-03-05  8:25 ` redi at gcc dot gnu.org
2021-03-05  9:36 ` jakub at gcc dot gnu.org
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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