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 C1D163858C39 for ; Tue, 8 Nov 2022 14:42:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C1D163858C39 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=1667918568; 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; bh=wolUKzFfMmlXl19lNac5TPjczpf9H6nSwOzhoDdv2jw=; b=VRLBqTTJ1JChRT8j51m8YEiJmVh09a8UCsmPpD/fxVHTnxEXu4ZZrrLhqmpcvo39OyRvRC 0D/ZaltyuAfmPZatRY2J5pCuf7z+uXMR1bRPuD3Zwns6Vx0IA4SPgTjWtCqBZbtJE3FP3t k3tvAgV0rKTycQ3RXDi6CRHYn41Syiw= 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-88-w_bOdbMjNtOJmUIlDzK91w-1; Tue, 08 Nov 2022 09:42:47 -0500 X-MC-Unique: w_bOdbMjNtOJmUIlDzK91w-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D4CCF8001B8 for ; Tue, 8 Nov 2022 14:42:46 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.194.183]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 953EF2166B35; Tue, 8 Nov 2022 14:42:46 +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 2A8EghgN2244337 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Tue, 8 Nov 2022 15:42:44 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 2A8EghfN2244336; Tue, 8 Nov 2022 15:42:43 +0100 Date: Tue, 8 Nov 2022 15:42:43 +0100 From: Jakub Jelinek To: Jason Merrill Cc: gcc-patches@gcc.gnu.org Subject: [RFC PATCH] c++: Minimal handling of carries_dependency attribute Message-ID: Reply-To: Jakub Jelinek MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 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: Hi! A comment in D2552R1: "The only questionable (but still conforming) case we found was [[carries_dependency(some_argument)]] on GCC, where the emitted diagnostic said that the carries_dependency attribute is not supported, but did not specifically call out the syntax error in the argument clause." made me try the following patch, where we'll error at least for arguments to the attribute and for some uses of the attribute appertaining to something not mentioned in the standard warn with different diagnostics (or should that be an error?; clang++ does that, but I think we never do for any attribute, standard or not). The diagnostics on toplevel attribute declaration is still an attribute ignored warning and on empty statement different wording. The paper additionally mentions struct X { [[nodiscard]]; }; // no diagnostic on GCC and 2 cases of missing diagnostics on [[fallthrough]] (guess I should file a PR about those; one problem is that do { ... } while (0); there is replaced during genericization just by ... and another that [[fallthrough]] there is followed by a label, but not user/case/default label, but an artificial one created from while loop genericization. Thoughts on this? 2022-11-08 Jakub Jelinek * tree.cc (handle_carries_dependency_attribute): New function. (std_attribute_table): Add carries_dependency attribute. * parser.cc (cp_parser_check_std_attribute): Add carries_dependency attribute. * g++.dg/cpp0x/attr-carries_dependency1.C: New test. --- gcc/cp/tree.cc.jj 2022-11-07 10:30:42.758629740 +0100 +++ gcc/cp/tree.cc 2022-11-08 14:45:08.853864684 +0100 @@ -4923,6 +4923,32 @@ structural_type_p (tree t, bool explain) return true; } +/* Partially handle the C++11 [[carries_dependency]] attribute. + Just emit a different diagnostics when it is used on something the + spec doesn't allow vs. where it allows and we just choose to ignore + it. */ + +static tree +handle_carries_dependency_attribute (tree *node, tree name, + tree ARG_UNUSED (args), + int ARG_UNUSED (flags), + bool *no_add_attrs) +{ + if (TREE_CODE (*node) != FUNCTION_DECL + && TREE_CODE (*node) != PARM_DECL) + { + warning (OPT_Wattributes, "%qE attribute can only be applied to " + "functions or parameters", name); + *no_add_attrs = true; + } + else + { + warning (OPT_Wattributes, "%qE attribute ignored", name); + *no_add_attrs = true; + } + return NULL_TREE; +} + /* Handle the C++17 [[nodiscard]] attribute, which is similar to the GNU warn_unused_result attribute. */ @@ -5036,6 +5062,8 @@ const struct attribute_spec std_attribut handle_likeliness_attribute, attr_cold_hot_exclusions }, { "noreturn", 0, 0, true, false, false, false, handle_noreturn_attribute, attr_noreturn_exclusions }, + { "carries_dependency", 0, 0, true, false, false, false, + handle_carries_dependency_attribute, NULL }, { NULL, 0, 0, false, false, false, false, NULL, NULL } }; --- gcc/cp/parser.cc.jj 2022-11-04 18:11:41.523945997 +0100 +++ gcc/cp/parser.cc 2022-11-08 13:41:35.075135139 +0100 @@ -29239,8 +29239,7 @@ cp_parser_std_attribute (cp_parser *pars /* Warn if the attribute ATTRIBUTE appears more than once in the attribute-list ATTRIBUTES. This used to be enforced for certain - attributes, but the restriction was removed in P2156. Note that - carries_dependency ([dcl.attr.depend]) isn't implemented yet in GCC. + attributes, but the restriction was removed in P2156. LOC is the location of ATTRIBUTE. Returns true if ATTRIBUTE was not found in ATTRIBUTES. */ @@ -29249,7 +29248,7 @@ cp_parser_check_std_attribute (location_ { static auto alist = { "noreturn", "deprecated", "nodiscard", "maybe_unused", "likely", "unlikely", "fallthrough", - "no_unique_address" }; + "no_unique_address", "carries_dependency" }; if (attributes) for (const auto &a : alist) if (is_attribute_p (a, get_attribute_name (attribute)) --- gcc/testsuite/g++.dg/cpp0x/attr-carries_dependency1.C.jj 2022-11-08 15:17:43.168238390 +0100 +++ gcc/testsuite/g++.dg/cpp0x/attr-carries_dependency1.C 2022-11-08 15:16:39.695104787 +0100 @@ -0,0 +1,17 @@ +// { dg-do compile { target c++11 } } + +[[carries_dependency]] int *f1 (); // { dg-warning "attribute ignored" } +int f2 (int *x [[carries_dependency]]); // { dg-warning "attribute ignored" } +[[carries_dependency]] int f3 (); // { dg-warning "attribute ignored" } +int f4 (int x [[carries_dependency]]); // { dg-warning "attribute ignored" } +[[carries_dependency(1)]] int f5 (); // { dg-error "'carries_dependency' attribute does not take any arguments" } +[[carries_dependency]] int v; // { dg-warning "'carries_dependency' attribute can only be applied to functions or parameters" } +[[carries_dependency]]; // { dg-warning "attribute ignored" } +void +f6 () +{ + [[carries_dependency]]; // { dg-warning "attributes at the beginning of statement are ignored" } +} +#if __has_cpp_attribute(carries_dependency) +#error carries_dependency attribute is not actually implemented +#endif Jakub