From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by sourceware.org (Postfix) with ESMTP id 4FCFF3858406 for ; Wed, 10 Aug 2022 17:17:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 4FCFF3858406 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=kernel.crashing.org Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 27AHElFO014265; Wed, 10 Aug 2022 12:14:47 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 27AHEjA5014264; Wed, 10 Aug 2022 12:14:45 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 10 Aug 2022 12:14:45 -0500 From: Segher Boessenkool To: Michael Meissner , GCC Development , "Kewen.Lin" , David Edelsohn , Peter Bergner , Will Schmidt , Jason Merrill , Nathan Sidwell , Mike Stump , Iain Sandoe , Joseph Myers , Tulio Magno Quites Machado Filho , Alan Modra , Nick Clifton , Jeff Law , Jakub Jelinek , Richard Biener , "David S. Miller" , "Carlos O'Donell" , libc-alpha@sourceware.org Subject: Re: Resend: Potential upcoming changes in mangling to PowerPC GCC Message-ID: <20220810171445.GB25951@gate.crashing.org> References: <20220804205355.GO25951@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-Spam-Status: No, score=-3.0 required=5.0 tests=BAYES_00, JMQ_SPF_NEUTRAL, KAM_DMARC_STATUS, KAM_MANYTO, SPF_HELO_PASS, SPF_PASS, 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@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: Wed, 10 Aug 2022 17:17:10 -0000 On Mon, Aug 08, 2022 at 05:44:36PM -0400, Michael Meissner wrote: > On Thu, Aug 04, 2022 at 03:53:55PM -0500, Segher Boessenkool wrote: > > On Thu, Aug 04, 2022 at 01:48:51PM -0400, Michael Meissner wrote: > > It would be a lot simpler and less roundabout and inside out if we could > > do this the other way around: start with the QP float and double-double > > types and modes, and point the long double type and TFmode at that. But > > alas. > > Yes if we could go back 5 years it would have been simpler to do that way. It does not require time machines: we can change the current code *now*. > > > These 3 tests use the > > > 'nanqs' built-in function, which is mapped to 'nanf128s' and it delivers a > > > _Float128 signaling NaN. But since __float128 uses a different type, the > > > signaling NaN is converted and it loses the signaling property. > > > > So you are saying __float128 and _Float128 should *not* be separate > > types? Or, the testcases are buggy, make unwarranted assumptions? > > I am saying right now, they are separate types when -mabi=ieeelongdouble is > used. They are the same type when -mabi=ibmlongdouble is used. I think they > should be the same type, no matter which way long double is defined. Ah, good. > But there are a bunch of assumptions within the compiler that need to be > changed due to these assumptions. > > > In addition, it would be nice if we could refine the setting of bits in the ELF > > > header so that if you pass an explicit __float128 or __ibm128 object, it > > > doesn't set the bits that you used long double of the appropriate type. But > > > the code that sets these bits is done in the RTL stages, and it only looks at > > > modes, not at types. > > > > So fix that? It is a clear bug. > > It isn't so simple, Yes it is. It *is* a clear bug. Solving it might be some work, but it has to be done, it can not be avoided. > > It cannot always use IFmode? Generic code uses TFmode for long double > > (which can be double-double). > > My point is __ibm128 can potentionally be separate and always use IFmode. > Hence my question. It cannot be. Generic code (on double-double configs) uses TFmode. It is a good idea for us to use IFmode in the backend code, certainly. Segher