From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable()
 	to compiler.h
Date: Mon, 14 Sep 2009 08:40:23 -0700
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To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Michael Buesch <mb@bu3sch.de>, linuxppc-dev@lists.ozlabs.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-mips@linux-mips.org, Heiko Carstens <heiko.carstens@de.ibm.com>, linuxppc-dev@ozlabs.org, Paul Mackerras <paulus@samba.org>, "H. Peter Anvin" <hpa@zytor.com>, linux-s390@vger.kernel.org, linux-am33-list@redhat.com, Helge Deller <deller@gmx.de>, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, Mike Frysinger <vapier@gentoo.org>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, uclinux-dist-devel@blackfin.uclinux.org, Thomas Gleixner <tglx@linutronix.de>, Richard Henderson <rth@twiddle.net>, Haavard Skinnemoen <hskinnemoen@atmel.com>, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, ralf@linux-mips.org, Kyle McMartin <kyle@mcmartin.ca>, linux-alpha@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, linux390@de.ibm.com, Koichi

Geert Uytterhoeven wrote:
> On Fri, Sep 11, 2009 at 17:58, David Daney<ddaney@caviumnetworks.com> wrote:
>> Michael Buesch wrote:
>>> On Friday 11 September 2009 01:56:42 David Daney wrote:
>>>> +/* Unreachable code */
>>>> +#ifndef unreachable
>>>> +# define unreachable() do { for (;;) ; } while (0)
>>>> +#endif
>>> # define unreachable() do { } while (1)
>>>
>>> ? :)
>> Clearly I was not thinking clearly when I wrote that part.  RTH noted the
>> same thing.  I will fix it.
> 
> However, people are so used to seeing the `do { } while (0)' idiom,
> that they might miss
> there's a `1' here, not a `0'.
> 
> So perhaps it's better to use plain `for (;;)' for infinite loops?
> 

I don't think so.  The only valid token that can follow 'do { } while 
(1)' is ';', any statement may follow 'for (;;)', so there is a greater 
possibility to silently screw things up with the for(;;) form.

David Daney