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 ESMTP id 2D5183858C2C for ; Wed, 22 Sep 2021 16:33:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 2D5183858C2C Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-490-XygPvTIUORy-2Lfew-tR6w-1; Wed, 22 Sep 2021 12:33:19 -0400 X-MC-Unique: XygPvTIUORy-2Lfew-tR6w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9742C362FB; Wed, 22 Sep 2021 16:33:18 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.34]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 35658970EC; Wed, 22 Sep 2021 16:33:18 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.16.1/8.16.1) with ESMTPS id 18MGXEcW373820 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 22 Sep 2021 18:33:15 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 18MGXDt9373819; Wed, 22 Sep 2021 18:33:13 +0200 Date: Wed, 22 Sep 2021 18:33:13 +0200 From: Jakub Jelinek To: Bill Schmidt , GCC Patches , Segher Boessenkool , David Edelsohn , willschm@linux.ibm.com Subject: Re: [PATCH] rs6000: Add psabi diagnostic for C++ zero-width bit field ABI change (PR102024) Message-ID: <20210922163313.GF304296@tucnak> Reply-To: Jakub Jelinek References: <676699df-01c3-690a-d49f-8d00d1891246@linux.ibm.com> <189f5cfa4f77fc71a12f5d57df6320256dc57cd7.camel@vnet.ibm.com> <20210922150215.GE304296@tucnak> MIME-Version: 1.0 In-Reply-To: <20210922150215.GE304296@tucnak> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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=-6.3 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Sep 2021 16:33:22 -0000 On Wed, Sep 22, 2021 at 05:02:15PM +0200, Jakub Jelinek via Gcc-patches wrote: > > > > @@ -6298,7 +6298,8 @@ rs6000_aggregate_candidate (const_tree type, machine_mode *modep, > > > > return -1; > > > > count = rs6000_aggregate_candidate (TREE_TYPE (type), modep, > > > > - empty_base_seen); > > > > + empty_base_seen, > > > > + zero_width_bf_seen); > > > > if (count == -1 > > > > || !index > > > > || !TYPE_MAX_VALUE (index) > > > > @@ -6336,6 +6337,12 @@ rs6000_aggregate_candidate (const_tree type, machine_mode *modep, > > > > if (TREE_CODE (field) != FIELD_DECL) > > > > continue; > > > > + if (DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (field)) > > > > + { > > > > + *zero_width_bf_seen = 1; > > > > + continue; > > > > + } > > So, from what you wrote, :0 in the ppc* psABIs the intent is that :0 is not > ignored, right? > In that case I don't really understand the above (the continue in > particular). Because the continue means it is ignored for C++ and not > ignored for C, so basically you return to the 4.5-11 ABI incompatibility > between C and C++. > C++ :0 will have DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD set, C :0 will not... To be more precise, I'd expect what most targets want to do for the actual ABI decisions not to use DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD at all. I.e. do: if (TREE_CODE (field) != FIELD_DECL) continue; if (DECL_BIT_FIELD (field) && integer_zerop (DECL_SIZE (field))) { // :0 // in some psABIs, ignore it, i.e. continue; // in others psABIs, take them into account, i.e. do nothing. } and use DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD only for the -Wpsabi purposes. The only exception would be for targets that decide to keep GCC 4.5-11 compatibility with the C incompatible with C++. Jakub