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 551253858D28 for ; Mon, 31 Jan 2022 09:43:01 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 551253858D28 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-277-7HFzRenKMyeXZSdOoQXgbg-1; Mon, 31 Jan 2022 04:42:57 -0500 X-MC-Unique: 7HFzRenKMyeXZSdOoQXgbg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4411746861; Mon, 31 Jan 2022 09:42:56 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.125]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ACE3F749BE; Mon, 31 Jan 2022 09:42:55 +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 20V9gqI03417262 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 31 Jan 2022 10:42:53 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 20V9gp9x3417261; Mon, 31 Jan 2022 10:42:51 +0100 Date: Mon, 31 Jan 2022 10:42:51 +0100 From: Jakub Jelinek To: Jonathan Wakely Cc: Theodore Papadopoulo , "gcc@gcc.gnu.org" Subject: Re: Enquiry Message-ID: <20220131094251.GH2646553@tucnak> Reply-To: Jakub Jelinek References: <20220130104145.GC2646553@tucnak> <20220130105822.GD2646553@tucnak> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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=-5.2 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_H2, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE 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@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 31 Jan 2022 09:43:02 -0000 On Sun, Jan 30, 2022 at 11:11:15AM +0000, Jonathan Wakely wrote: > On Sun, 30 Jan 2022, 10:58 Jakub Jelinek, wrote: > > > On Sun, Jan 30, 2022 at 10:50:56AM +0000, Jonathan Wakely wrote: > > > We could put a trap instruction at the end of the function though, which > > > would make the result a bit less arbitrary. > > > > > > I've come around to thinking that's preferable for cases like this. > > > > Depends on which exact cases. > > Because for > > int foo (int s) { if (s == 123) return 1; } > > we want to optimize it into > > return 1; > > rather than if (s == 123) return 1; else __builtin_trap (); > > For debugging we have -fsanitize=undefined > > > What if we inserted the trap for -O0? Adding a trap for -O0 looks reasonable to me, after all, we aren't going to do too many optimizations with __builtin_unreachable at -O0 anyway. Jakub