From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22450 invoked by alias); 20 Nov 2009 21:53:25 -0000 Received: (qmail 22127 invoked by uid 22791); 20 Nov 2009 21:53:24 -0000 X-SWARE-Spam-Status: No, hits=-2.0 required=5.0 tests=AWL,BAYES_00,SPF_FAIL X-Spam-Check-By: sourceware.org Received: from mx20.gnu.org (HELO mx20.gnu.org) (199.232.41.8) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 20 Nov 2009 21:52:20 +0000 Received: from mail.codesourcery.com ([38.113.113.100]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NBbOs-0004vw-7R for gcc@gcc.gnu.org; Fri, 20 Nov 2009 16:52:18 -0500 Received: (qmail 14829 invoked from network); 20 Nov 2009 21:52:17 -0000 Received: from unknown (HELO digraph.polyomino.org.uk) (joseph@127.0.0.2) by mail.codesourcery.com with ESMTPA; 20 Nov 2009 21:52:17 -0000 Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.69) (envelope-from ) id 1NBbOp-0002Je-Cl; Fri, 20 Nov 2009 21:52:15 +0000 Date: Fri, 20 Nov 2009 21:53:00 -0000 From: "Joseph S. Myers" To: Rainer Orth cc: gcc@gcc.gnu.org Subject: Re: Supporting decimal float on additional platforms In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-detected-operating-system: by mx20.gnu.org: GNU/Linux 2.6, seldom 2.4 (older, 4) Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org X-SW-Source: 2009-11/txt/msg00588.txt.bz2 On Fri, 20 Nov 2009, Rainer Orth wrote: > > Much the same applies if anyone wishes to add fixed point (TR 18037) > > support for more targets. > > I'll have a look at the last draft (N1169) for now. Right now, only > MIPS support is in GCC, so there seems to be less traction so far. Each of these extensions is aimed at a specific class of programs, and users of such programs are much more likely to use some processors than others - various embedded processors have fixed point instructions of one form or another (not necessarily all mapping neatly to the TR 18037 types), while some Power and S390 processors have hardware support for decimal floating point. The TRs may eventually result in those classes of programs becoming more portable, in which case people might eventually want to include free software using these extensions in general-purpose operating system distributions - which may drive porting the feature as people wish to build those distributions for many different processors - but the limited application domains for these features seem likely to exacerbate the chicken-and-egg effect that applies to any new language feature (no demand for the feature in compilers without applications using it, no applications using it without compilers implementing it). Implementing a feature without having any applications for it is of course one way of addressing that effect, as is implementing a feature you'd like to use yourself in programs you write in future; it seems a fine improvement to the compiler to contribute as long as you work with any ABI maintainers to avoid it causing future compatibility problems. (Though I made decimal floating point work on e500 processors - to eliminate the test failures seen in such configurations given that it's enabled by default for Power GNU/Linux and already worked for other Power processors - it's quite possible that no-one has ever used that functionality other than for testcases. There were no ABI compatibility issues there since e500 uses the same ABI as soft-float Power processors.) Note that the fixed point implementation for MIPS substantially slows down the build of libgcc for MIPS targets because of a huge number of libgcc functions for fixed point that need to be built, so people may not care for their libgcc builds being slowed down for other targets without any applications for the new feature. -- Joseph S. Myers joseph@codesourcery.com