public inbox for libstdc++-cvs@sourceware.org help / color / mirror / Atom feed
From: Ian Lance Taylor <ian@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc/devel/gccgo] libstdc++: std::includes performance tweak Date: Sun, 12 Jul 2020 19:55:03 +0000 (GMT) [thread overview] Message-ID: <20200712195503.6E1323890402@sourceware.org> (raw) https://gcc.gnu.org/g:465520e3eb45d83ad18394aa537150bfa6bdf117 commit 465520e3eb45d83ad18394aa537150bfa6bdf117 Author: Marc Glisse <marc.glisse@inria.fr> Date: Fri Jun 19 13:03:45 2020 +0100 libstdc++: std::includes performance tweak A small tweak to the implementation of __includes, which in my application saves 20% of the running time. I noticed it because using range-v3 was giving unexpected performance gains. Some of the gain comes from pulling the 2 calls ++__first1 out of the condition so there is just one call. And most of the gain comes from replacing the resulting if (__comp(__first1, __first2)) ; else ++__first2; with if (!__comp(__first1, __first2)) ++__first2; I was very surprised that the code ended up being so different for such a change, and I still don't really understand where the extra time is going... Anyway, while I blame the compiler for not generating very good code with the current implementation, I believe the change can be seen as a simplification. libstdc++-v3/ChangeLog: * include/bits/stl_algo.h (__includes): Simplify the code. Diff: --- libstdc++-v3/include/bits/stl_algo.h | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h index fd6edd0d5f4..550a15f2b3b 100644 --- a/libstdc++-v3/include/bits/stl_algo.h +++ b/libstdc++-v3/include/bits/stl_algo.h @@ -2783,15 +2783,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _Compare __comp) { while (__first1 != __last1 && __first2 != __last2) - if (__comp(__first2, __first1)) - return false; - else if (__comp(__first1, __first2)) - ++__first1; - else - { - ++__first1; + { + if (__comp(__first2, __first1)) + return false; + if (!__comp(__first1, __first2)) ++__first2; - } + ++__first1; + } return __first2 == __last2; }
reply other threads:[~2020-07-12 19:55 UTC|newest] Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20200712195503.6E1323890402@sourceware.org \ --to=ian@gcc.gnu.org \ --cc=gcc-cvs@gcc.gnu.org \ --cc=libstdc++-cvs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).