From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=2biq=4N=mentor.com=joseph_myers@sourceware.org>
Received: from esa3.mentor.iphmx.com (esa3.mentor.iphmx.com [68.232.137.180])
	by sourceware.org (Postfix) with ESMTPS id A57A3388B683;
	Thu, 15 Dec 2022 18:28:30 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A57A3388B683
Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=codesourcery.com
Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=mentor.com
X-IronPort-AV: E=Sophos;i="5.96,248,1665475200"; 
   d="scan'208";a="89698525"
Received: from orw-gwy-02-in.mentorg.com ([192.94.38.167])
  by esa3.mentor.iphmx.com with ESMTP; 15 Dec 2022 10:28:25 -0800
IronPort-SDR: Dwk5SMrFxWaheNbKjpgpRNfXBt0pLLsaeRvoUlWTHLYkIBDS9M+aEiuayuNv5x5TO3jXz57bCx
 4z2g7YHjFkD3VqO+H6LF2+AbvXusY2XnMFkGsrjniuHzzSif4NP8Pr92ZIbxyyOzFWhfQZsFpY
 t8Hpn+EOct7eu9uEkenqhG1G2V2DWvtfovZpCCnvpf91AFy0XAD/8+wqtuIsQY0wSsNJ3oI7Bp
 5squi9d+PWD/gNApzKFqFDiiVm00WCdSlGv1OLALFb5QGwW5wJCElS1uLCcf/MVASnPbhuqKMw
 XQg=
Date: Thu, 15 Dec 2022 18:28:19 +0000
From: Joseph Myers <joseph@codesourcery.com>
To: Kewen.Lin <linkw@linux.ibm.com>
CC: Jakub Jelinek <jakub@redhat.com>, Michael Meissner
	<meissner@linux.ibm.com>, <gcc-patches@gcc.gnu.org>, Segher Boessenkool
	<segher@kernel.crashing.org>, Peter Bergner <bergner@linux.ibm.com>, David
 Edelsohn <dje.gcc@gmail.com>, Will Schmidt <will_schmidt@vnet.ibm.com>,
	William Seurer <seurer@gcc.gnu.org>
Subject: Re: [PATCH 2/3] Make __float128 use the _Float128 type, PR
 target/107299
In-Reply-To: <df19711b-8648-0141-5fb9-336f8c8afa4d@linux.ibm.com>
Message-ID: <c160a07d-b9c-01d-3b4-91c77436adb8@codesourcery.com>
References: <Y2HYSM7z8b5jDCZG@toto.the-meissners.org> <Y2HZFlHH8HuvhGL4@toto.the-meissners.org> <e96ce199-348d-7446-102c-8d2b037a7286@linux.ibm.com> <6b7325c6-6416-d64f-89a8-7341aeb8226c@linux.ibm.com> <Y5mZA32qGS2Lbk04@tucnak> <3cbaa3d2-4327-c62a-2904-eac5ca506d20@linux.ibm.com>
 <df19711b-8648-0141-5fb9-336f8c8afa4d@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
X-Originating-IP: [137.202.0.90]
X-ClientProxiedBy: svr-ies-mbx-12.mgc.mentorg.com (139.181.222.12) To
 svr-ies-mbx-10.mgc.mentorg.com (139.181.222.10)
X-Spam-Status: No, score=-3109.2 required=5.0 tests=BAYES_00,HEADER_FROM_DIFFERENT_DOMAINS,KAM_DMARC_STATUS,KAM_NUMSUBJECT,SPF_HELO_PASS,SPF_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org
List-Id: <gcc-patches.gcc.gnu.org>

On Thu, 15 Dec 2022, Kewen.Lin via Gcc-patches wrote:

> By investigating the exposed NaN failures, I found it's due to that it wants
> to convert _Float128 type constant to long double type constant, it goes
> through function real_convert which clears the signalling bit in the context
> of !HONOR_SNANS (arg).
> 
>   if (r->cl == rvc_nan)
>     r->signalling = 0;
> 
> The test cases don't have the explicit option -fsignaling-nans, I'm inclined
> to believe it's intentional since there is only a sNaN generation.  If so,
> we don't want this kind of conversion which is useless and can clear signalling
> bit unexpectedly, one shortcut is to just copy the corresponding REAL_VALUE_TYPE
> and rebuild with the given type if the modes are the same.

I think this approach - treating floating-point conversions to a type with 
the same mode consistently as a copy rather than a convertFormat operation 
- is reasonable.

-- 
Joseph S. Myers
joseph@codesourcery.com