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 39D013858C74 for ; Mon, 15 Aug 2022 11:47:45 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 39D013858C74 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-178-RbJgFkueOzirN65WS9XG9A-1; Mon, 15 Aug 2022 07:47:42 -0400 X-MC-Unique: RbJgFkueOzirN65WS9XG9A-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A6D0A29AB418; Mon, 15 Aug 2022 11:47:41 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 449B3492C3B; Mon, 15 Aug 2022 11:47:41 +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 27FBlb5k1241683 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 15 Aug 2022 13:47:38 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 27FBlaub1241682; Mon, 15 Aug 2022 13:47:36 +0200 Date: Mon, 15 Aug 2022 13:47:36 +0200 From: Jakub Jelinek To: Richard Biener Cc: "Joseph S. Myers" , Jeff Law , gcc-patches@gcc.gnu.org, FX Subject: Re: [PATCH] Implement __builtin_issignaling Message-ID: Reply-To: Jakub Jelinek References: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 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=-3.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, LOTS_OF_MONEY, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) 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, 15 Aug 2022 11:47:46 -0000 On Mon, Aug 15, 2022 at 11:24:14AM +0000, Richard Biener wrote: > Unlike the issignalling macro from glibc the builtin will return > false for sNaN arguments when -fno-signalling-nans is used (similar > to isinf, isnan, etc.). I think this deserves mentioning in the > documentation (and I have my reservations about this long-time > behavior of FP classification builtins we have). I have actually tried to make the builtin working even with -fno-signaling-nans (i.e. the default). That is why the folding is done only if the argument is REAL_CST or if !tree_expr_maybe_nan_p (arg). At one point I was doing the folding when tree_expr_signaling_nan_p (arg) (to true) or !tree_expr_maybe_signaling_nan_p (arg) (to false) and in that case indeed -fsignaling-nans was a requirement. -fsignaling-nans is used in the tests nevertheless because the tests really do care about sNaNs, so I've turned on the option that says they should be honored. > Generally it looks OK - what does it do to size optimized code? The problem is that except for the glibc __issignaling{f,,l,f128} entrypoints, other C libraries don't implement it, so there is nothing to fallback to (unless we want to also implement it in libgcc.a). For float/double, it is relatively short: movd %xmm0, %eax xorl $4194304, %eax andl $2147483647, %eax cmpl $2143289344, %eax seta %al movzbl %al, %eax which e.g. for if (__builtin_issignaling (arg)) could be even simplified further by just doing ja or jna, resp. movabsq $9221120237041090560, %rdx movq %xmm0, %rax btcq $51, %rax btrq $63, %rax cmpq %rax, %rdx setb %al movzbl %al, %eax For long double (especially Intel) / _Float128 it is larger (26 insns for XFmode, 15 for _Float128), sure. > glibc 2.31 seems to silently accept > > #include > > int foo(_Complex double x) > { > return issignaling (x); > } That seems like a glibc bug/weird feature in the __MATH_TG macro or _Generic. When compiled with C++ it is rejected. Jakub