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Date:      Tue, 11 Sep 2012 10:04:12 -0700
From:      Steve Kargl <sgk@troutmask.apl.washington.edu>
To:        Mark Felder <feld@feld.me>
Cc:        Christer Solskogen <christer.solskogen@gmail.com>, toolchain@freebsd.org, Michael Butler <imb@protected-networks.net>, current@freebsd.org
Subject:   Re: Clang as default compiler November 4th
Message-ID:  <20120911170412.GA96297@troutmask.apl.washington.edu>
In-Reply-To: <op.wkhcpr0n34t2sn@me-pc>
References:  <20120910211207.GC64920@lor.one-eyed-alien.net> <20120911104518.GF37286@deviant.kiev.zoral.com.ua> <20120911120649.GA52235@freebsd.org> <20120911122122.GJ37286@deviant.kiev.zoral.com.ua> <20120911123833.GA54483@freebsd.org> <848C813E-E6EC-4FAF-9374-B5583A077404@cederstrand.dk> <20120911133215.GB87126@troutmask.apl.washington.edu> <CAMVU60ZVmCaYr=MyLsnz9tqD9O5m9Y8bgYiqtqvUXcYcXj-RmQ@mail.gmail.com> <504F4650.9090700@protected-networks.net> <op.wkhcpr0n34t2sn@me-pc>

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On Tue, Sep 11, 2012 at 11:42:53AM -0500, Mark Felder wrote:
> On Tue, 11 Sep 2012 09:10:24 -0500, Michael Butler  
> <imb@protected-networks.net> wrote:
> 
> >- From the link (http://math-atlas.sourceforge.net/errata.html#WhatComp)
> >that Steve Kargl referenced (dated July 2012).
> 
> 
> I don't know where this guy is getting his info, but CLANG is /more/  
> standards compliant and doesn't have an issue producing "correct" code.  
> Though it might not be the fastest (yet).
> 
> And if Apple (probably one of the largest commercial CLANG users) doesn't  
> have an issue with it producing "incorrect" code why should we believe  
> this guy?


Who does 'this guy' refer to?  If it is me, then I get
my information from the developer of ATLAS.  The issue
isn't conformance to a standard.  The issue is whether
clang generates correct code when floating point is
concerned.  From the ATLAS installation guide date 
10 Jul 2012:

   In most cases, switching these compilers will get you worse
   performance and accuracy, even when you are absolutely sure
   it is a better compiler and flag combination!  In particular,
   our timings indicated that clang was always slower on all
   platforms that gcc, and that it very often produced incorrect
   code.

If 'this guy' refers to the author of ATLAS, then 'this
guy' is R. Clint Whaley.  It is fairly easy to find his
home page and thus his credentials.

-- 
Steve



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