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 [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id EDFF9385782A for ; Mon, 4 Jan 2021 20:48:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org EDFF9385782A 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-481-d7_6vP01OQyStE_EFwYJ3A-1; Mon, 04 Jan 2021 15:48:24 -0500 X-MC-Unique: d7_6vP01OQyStE_EFwYJ3A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DFD0E10082E1 for ; Mon, 4 Jan 2021 20:48:23 +0000 (UTC) Received: from tucnak.zalov.cz (ovpn-112-11.ams2.redhat.com [10.36.112.11]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7BB9F60BE5; Mon, 4 Jan 2021 20:48:23 +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 104KmKWk725492 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 4 Jan 2021 21:48:20 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 104KmKNU725491; Mon, 4 Jan 2021 21:48:20 +0100 Date: Mon, 4 Jan 2021 21:48:20 +0100 From: Jakub Jelinek To: Jason Merrill Cc: gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: Fix ICE with __builtin_bit_cast [PR98469] Message-ID: <20210104204820.GB725145@tucnak> Reply-To: Jakub Jelinek References: <20201230091343.GU3788@tucnak> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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=-6.2 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_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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: Mon, 04 Jan 2021 20:48:28 -0000 On Mon, Jan 04, 2021 at 03:44:46PM -0500, Jason Merrill wrote: > This change is OK, but part of the problem is that we're trying to do > overload resolution for an S copy/move constructor, which we shouldn't be > because bit_cast is a prvalue, so in C++17 and up we should use it to > directly initialize the target without any implied constructor call. > > It seems we're mishandling this because the code in > build_special_member_call specifically looks for TARGET_EXPR or CONSTRUCTOR, > and BIT_CAST_EXPR is neither of those. > > Wrapping a BIT_CAST_EXPR of aggregate type in a TARGET_EXPR would address > this, and any other places that expect a class prvalue to come in the form > of a TARGET_EXPR. I can try that tomorrow. Won't that cause copying through extra temporary in some cases though, or is that guaranteed to be optimized? Jakub