From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id CF317395B062 for ; Wed, 16 Nov 2022 14:46:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org CF317395B062 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668609980; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2cIyTdZtjIaQlYABghMhVKtUKGlHZyIrcqE++NZx4nA=; b=VrYYcCInOjblbKwGE751+eZI1xZtbRSpEs1PfRJvI9PA6YiMWqwuEU44qN+p77EAdFpIDZ xv4Smw6oC3nDS3srOIRNSu5EL3ClKxRO7NbzMcIV0iOoZDTZYJCl1TdSLhTdYacme7vL0K Tw5LG6OFgtBm2NWvPAR5t9djN3fwbQ8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-458-CT-8VjcGMX2JksO1s0Iz7Q-1; Wed, 16 Nov 2022 09:46:18 -0500 X-MC-Unique: CT-8VjcGMX2JksO1s0Iz7Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A6B0E811E67 for ; Wed, 16 Nov 2022 14:46:18 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.193.99]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5E5DB40C83AA; Wed, 16 Nov 2022 14:46:18 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 2AGEkE3d2465823 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 16 Nov 2022 15:46:14 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 2AGEkDV82465822; Wed, 16 Nov 2022 15:46:13 +0100 Date: Wed, 16 Nov 2022 15:46:13 +0100 From: Jakub Jelinek To: Jason Merrill Cc: Jonathan Wakely , gcc-patches@gcc.gnu.org, Marek Polacek Subject: Re: [PATCH] c++, v2: Implement C++23 P2647R1 - Permitting static constexpr variables in constexpr functions Message-ID: Reply-To: Jakub Jelinek References: <016f168b-f143-baff-5f71-c48d4611ae11@redhat.com> MIME-Version: 1.0 In-Reply-To: <016f168b-f143-baff-5f71-c48d4611ae11@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-3.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Wed, Nov 16, 2022 at 09:33:27AM -0500, Jason Merrill wrote: > > and at that point I fear decl_maybe_constant_var_p will not work > > properly. Shall this hunk be moved somewhere else (cp_finish_decl?) > > where we can already call it, or do the above in start_decl for > > cxx_dialect < cxx20 and add a cxx_dialect == cxx20 hunk in cp_finish_decl? > > Hmm, I'd expect decl_maybe_constant_var_p to work fine at this point. For static constexpr vars sure, but what about static const where start_decl doesn't know the initializer? Sure, decl_maybe_constant_var_p will not crash in that case, but it will return true even if the static const var doesn't have a constant initializer. Sure, we'd catch that later on when actually trying to constexpr evaluate the function and hitting there the spots added for C++23 in potential_constant_expression*/cxx_eval_*, but it would mean that we don't reject it when nothing calls the functions. I meant something like: constexpr int bar (int x) { if (x) throw 1; return 0; } constexpr int foo () { static const int a = bar (1); return 0; } with -std=c++20 IMHO shouldn't be accepted, while in C++23 it should. With constexpr int a = foo (); added we reject it in C++23 (correct), but the diagnostics is too weird: test.C:3:23: in ‘constexpr’ expansion of ‘foo()’ test.C:3:24: error: ‘__atomic_load_1((& _ZGVZ3foovE1a), 2)’ is not a constant expression 3 | constexpr int a = foo (); | ^ Jakub