From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 5DD553858D32; Thu, 7 Jul 2022 09:25:16 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 5DD553858D32 From: "nimrodcowboy at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/106223] difference in behaviour between no optimization and -O for specialization of std::forward Date: Thu, 07 Jul 2022 09:25:16 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 12.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: nimrodcowboy at gmail dot com X-Bugzilla-Status: RESOLVED X-Bugzilla-Resolution: INVALID X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 07 Jul 2022 09:25:16 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106223 --- Comment #4 from Nimrod --- Ok, that somehow makes sense to me. I agree with the forwarding part, as a normal case, is doing nothing and keep the type. But I don't find any wordings about "value" or "internal state" in terms of "(perfect) forwarding", I believe it's only about the types? (If so, the example does conforms it.)=20 https://timsong-cpp.github.io/cppwp/n4659/forward#1 The standard states std::forward as a helper function to simplify forwardin= g. "The library provides templated helper functions to simplify applying move semantics to an lvalue and to simplify the implementation of forwarding functions. All functions specified in this subclause are signal-safe ([csignal.syn])." https://timsong-cpp.github.io/cppwp/n4659/func.require#3 "...A forwarding call wrapper is a call wrapper that can be called with an arbitrary argument list and delivers the arguments to the wrapped callable object as references. This forwarding step shall ensure that rvalue argumen= ts are delivered as rvalue references and lvalue arguments are delivered as lv= alue references...." https://timsong-cpp.github.io/cppwp/n4659/temp.deduct.call#3 "A forwarding reference is an rvalue reference to a cv-unqualified template parameter that does not represent a template parameter of a class template (during class template argument deduction). If P is a forwarding reference = and the argument is an lvalue, the type =E2=80=9Clvalue reference to A=E2=80=9D= is used in place of A for type deduction."=