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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id EFFE63852C66 for ; Fri, 18 Nov 2022 16:34:32 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org EFFE63852C66 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=1668789272; 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:in-reply-to:in-reply-to: references:references; bh=XYbJS9FbL3LuXLdn/Oah/pHyuzCK/lEobFEhYAmrLR4=; b=OEal45YHCLL2mocQUFBtCxmOW5LyjQlOE6dRWnoqOv+dwYw+fjlfWGQ9ZgO7hqPIuAhWgP JCg3XelrnT+Y5fDy3oJP8t08Zdt+gQa3V+3AHqT5PpJ64x+CPXMcEBRXfdFSx3UREkR3OG X8Ee38+inGHdu/+L154xwUsTqvPQ+sE= 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-359-UDA9bOG6OCiI57V1SmhFvQ-1; Fri, 18 Nov 2022 11:34:31 -0500 X-MC-Unique: UDA9bOG6OCiI57V1SmhFvQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id ADC75185A792 for ; Fri, 18 Nov 2022 16:34:30 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 51674C2C7D9; Fri, 18 Nov 2022 16:34:30 +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 2AIGYPkA1903535 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Fri, 18 Nov 2022 17:34:26 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 2AIGYPA71903533; Fri, 18 Nov 2022 17:34:25 +0100 Date: Fri, 18 Nov 2022 17:34:24 +0100 From: Jakub Jelinek To: Jason Merrill Cc: Marek Polacek , Jonathan Wakely , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++, v4: Implement C++23 P2647R1 - Permitting static constexpr variables in constexpr functions Message-ID: Reply-To: Jakub Jelinek References: <740b5e1e-7143-c291-5594-af937867fbc3@redhat.com> <529c47ee-b6ff-b5dd-8d4b-1844c46ddbd6@redhat.com> MIME-Version: 1.0 In-Reply-To: <529c47ee-b6ff-b5dd-8d4b-1844c46ddbd6@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 Fri, Nov 18, 2022 at 11:24:45AM -0500, Jason Merrill wrote: > > Right, that's the C++17 implicit constexpr for lambdas, finish_function: > > > > /* Lambda closure members are implicitly constexpr if possible. */ > > if (cxx_dialect >= cxx17 > > && LAMBDA_TYPE_P (CP_DECL_CONTEXT (fndecl))) > > DECL_DECLARED_CONSTEXPR_P (fndecl) > > = ((processing_template_decl > > || is_valid_constexpr_fn (fndecl, /*complain*/false)) > > && potential_constant_expression (DECL_SAVED_TREE (fndecl))); > > Yeah, I guess potential_constant_expression needs to be stricter in a > lambda. Or perhaps any function that isn't already > DECL_DECLARED_CONSTEXPR_P? potential_constant_expression can't be relied on that it catches up everything if it, even a simple if statement with a condition not yet known to be 0 or non-0 results in just a requirement that at least one of the substatements is potential constant, etc. Similarly switch statements etc. If there is a way to distinguish between functions with user specified constexpr/consteval and DECL_DECLARED_CONSTEXPR_P set through the above if condition, sure, cp_finish_decl -> check_static_in_constexpr could be perhaps silent about those, but then we want to diagnose it during constexpr evaluation at least. But in that case having it a pedwarn rather than "this is a constant expression" vs. "this is not a constant expression, if !ctx->quiet emit an error" is something I don't see how to handle. Because something needs to be returned, it is a constant expression or it is not. Jakub