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From: "hewillk at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/100104] New: std::transform is 1.5 times faster than std::copy with -O3 Date: Thu, 15 Apr 2021 18:06:45 +0000 [thread overview] Message-ID: <bug-100104-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100104 Bug ID: 100104 Summary: std::transform is 1.5 times faster than std::copy with -O3 Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hewillk at gmail dot com Target Milestone: --- Consider: std::vector<double> v1(100, 0); // copy using copy std::vector<int> v2; std::copy(v1.begin(), v1.end(), std::back_inserter(v2)); // copy using transform std::vector<int> v2; std::transform(v1.begin(), v1.end(), std::back_inserter(v2), [](auto x) { return x; }); Those two will generate similar assembly code under -O2, but is very different under -O3/-Ofast, and transform will be 1.5 times faster than the copy. I don’t know if this is a bug since these two represent the same thing, and correct me if I am wrong. quick-bench with -O2: https://quick-bench.com/q/uKT8QEmPkS1wr153s3P-DRt90eY quick-bench with -O3: https://quick-bench.com/q/syuBCQYVtCoVwT2MRtLT25P-MQI goldbot: https://godbolt.org/z/7ee77cs8W
next reply other threads:[~2021-04-15 18:06 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-15 18:06 hewillk at gmail dot com [this message] 2021-04-15 19:30 ` [Bug middle-end/100104] " pinskia at gcc dot gnu.org 2021-04-16 1:42 ` hewillk at gmail dot com 2021-04-16 1:43 ` hewillk at gmail dot com 2021-04-16 1:51 ` hewillk at gmail dot com 2021-04-18 17:30 ` hewillk at gmail dot com
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