From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id A77063AAB446; Fri, 7 May 2021 14:35:53 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A77063AAB446 From: "StevenSun2021 at hotmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/99686] ICE when using both concepts and full specialization Date: Fri, 07 May 2021 14:35:53 +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: 11.1.0 X-Bugzilla-Keywords: ice-on-valid-code X-Bugzilla-Severity: normal X-Bugzilla-Who: StevenSun2021 at hotmail dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: 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: Fri, 07 May 2021 14:35:53 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99686 --- Comment #8 from Steven Sun --- under c++17 Step 4 needs `types_match =3D=3D 1` [at 1] but, its value is zero, which is= caused by `function_requirements_equivalent_p` [at 3] returns 0 [at 2] . [1] https://gcc.gnu.org/git?p=3Dgcc.git;a=3Dblob;f=3Dgcc/cp/decl.c;h=3D316ad4c1= 426940bd4f51197a6297eefc24064fec;hb=3DHEAD#l1481 [2] https://gcc.gnu.org/git?p=3Dgcc.git;a=3Dblob;f=3Dgcc/cp/decl.c;h=3D316ad4c1= 426940bd4f51197a6297eefc24064fec;hb=3DHEAD#l1052 [3] https://gcc.gnu.org/git?p=3Dgcc.git;a=3Dblob;f=3Dgcc/cp/decl.c;h=3D316ad4c1= 426940bd4f51197a6297eefc24064fec;hb=3DHEAD#l944 [4] https://gcc.gnu.org/git?p=3Dgcc.git;a=3Dblob;f=3Dgcc/cp/pt.c;h=3D36a8cb5df5= d36337c18e1547e775b747f59a087f;hb=3DHEAD#l3510 In `function_requirements_equivalent_p` [at 3], the comparison is different= for cxx20 and before. According to the comments, before c++20, only the combined constraints are compaired. -------------------------------------------------------------- By the way, for those two primary function templates in comment 1. Before cxx20, they are regard as=20 equivalent heads [at 4] inequivalent requirements [at 3] Since cxx20, they are regard as=20 inequivalent heads [at 4] equivalent requirements [at 3] If I change both [3], [4], forcing cxx17 using cxx20 standard, everything works. ------------------------------------------------------------- Many invariants are broken here. They cause this bug together: A failure in requirements comparison caused no reregistration, which leads = to overload between implicit instatntiation. The full specialzation is already parsed, leaving a null `cfun` state. Then it tries to instatiate the functi= on body and everything crashes, They are all `by design` in a sense. How to fix it is not only a technical issue, but a design choice. If any senior gcc developer sees this, help me. ------------------------------------------------------------- By the way, I don't think this bug would matter too much, since no one real= ly uses concepts before c++20. I am just curious.=