Date: Tue, 11 Sep 2012 19:19:48 +0200 From: Roman Divacky <rdivacky@freebsd.org> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: toolchain@FreeBSD.org, Tijl Coosemans <tijl@coosemans.org>, Dimitry Andric <dim@FreeBSD.org>, current@FreeBSD.org Subject: Re: Clang as default compiler November 4th Message-ID: <20120911171948.GA81334@freebsd.org> In-Reply-To: <20120911151230.GB87526@troutmask.apl.washington.edu> References: <20120910211207.GC64920@lor.one-eyed-alien.net> <20120911104518.GF37286@deviant.kiev.zoral.com.ua> <20120911120649.GA52235@freebsd.org> <20120911132410.GA87126@troutmask.apl.washington.edu> <504F4645.4070900@FreeBSD.org> <504F4A6B.4010001@coosemans.org> <20120911151230.GB87526@troutmask.apl.washington.edu>
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On Tue, Sep 11, 2012 at 08:12:30AM -0700, Steve Kargl wrote: > On Tue, Sep 11, 2012 at 04:27:55PM +0200, Tijl Coosemans wrote: > > On 11-09-2012 16:10, Dimitry Andric wrote: > > > On 2012-09-11 15:24, Steve Kargl wrote: > > >> What is important is whether software built with clang functions > > >> correctly. See for example, > > >> > > >> http://math-atlas.sourceforge.net/errata.html#WhatComp > > > > > > Yes, maths support, specifically precision, is admittedly still one of > > > clang's (really llvm's) weaker points. It is currently not really a > > > high priority item for upstream. > > > > > > This is obviously something that a certain part of our userbase will > > > care a lot about, while most of the time they won't care so much about > > > licensing or politics. So those people are probably better off using > > > gcc for the time being. > > > > Does it affect the accuracy of libm functions? > > > > I'm not sure if anyone has done any extensive testing. > I've started to run some of my test codes to compare > certain functions in a clang-compiled libm, gcc-compiled > libm, and reference solutions generated from math/mpfr. > For a locally patched j0f, I found that clang gave > much worse accuracy. If I revert the local patch, > clang and gcc are to give the same results. Unfortnately, > an unpatched j0f gives 500000 ULP errors. Steve, Can you please provide a small self contained test case that shows that clang is doing worse on accuracy than gcc? So that we can analyze it and decide if it's a bug in the code or in the compiler. So far we know absolutely nothing. Thank you, Roman
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