public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "nimrodcowboy at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/106223] New: difference in behaviour between no optimization and -O for specialization of std::forward Date: Thu, 07 Jul 2022 08:37:52 +0000 [thread overview] Message-ID: <bug-106223-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106223 Bug ID: 106223 Summary: difference in behaviour between no optimization and -O for specialization of std::forward Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: nimrodcowboy at gmail dot com Target Milestone: --- Consider the following C++17 code, I make a specialization of std::forward for user-defined type A. #include <iostream> #include <utility> struct A{ constexpr A(int val) : val(val) {} int val = 0; }; namespace std { template<> A&& forward(A& a) noexcept { a.val += 1; return std::move(a); } template<> constexpr A& forward(A& a) noexcept { a.val += 1; return a; } } void foo(A a) { std::cout << a.val << "\n"; } template <typename T> void f(T&& arg) { foo(std::forward<T>(arg)); } int main() { A a{1}; f(a); f(std::move(a)); } Output: no optimization: 2 3 -O: 1 1 See https://godbolt.org/z/sMKdEj1d5 It seems a regression introduced in GCC 12. I believe it's not UB, since it's legal to do so in C++17.
next reply other threads:[~2022-07-07 8:37 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-07-07 8:37 nimrodcowboy at gmail dot com [this message] 2022-07-07 8:40 ` [Bug c++/106223] " pinskia at gcc dot gnu.org 2022-07-07 8:51 ` nimrodcowboy at gmail dot com 2022-07-07 8:55 ` pinskia at gcc dot gnu.org 2022-07-07 9:25 ` nimrodcowboy at gmail dot com 2022-07-07 9:58 ` redi at gcc dot gnu.org 2022-07-07 11:01 ` redi at gcc dot gnu.org 2022-07-07 15:53 ` nimrodcowboy at gmail dot com 2022-07-07 16:02 ` nimrodcowboy at gmail dot com 2022-07-07 16:03 ` nimrodcowboy at gmail dot com 2022-07-07 16:59 ` redi at gcc dot gnu.org
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=bug-106223-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@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).