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To: Tom Rini <trini@kernel.crashing.org>
Cc: Jakub Jelinek <jakub@redhat.com>, Paul Mackerras <paulus@samba.org>,
        Gabriel Dos Reis <gdr@codesourcery.com>,
        mike stump <mrs@windriver.com>, dewar@gnat.com, gcc@gcc.gnu.org,
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Subject: Re: [PATCH] C undefined behavior fix
In-Reply-To: <200201061824.KAA19536@kankakee.wrs.com>
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From: Alexandre Oliva <aoliva@redhat.com>
Organization: GCC Team, Red Hat
Date: 06 Jan 2002 23:40:28 -0200
In-Reply-To: Tom Rini's message of "Sun, 6 Jan 2002 17:09:54 -0700"
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On Jan  6, 2002, Tom Rini <trini@kernel.crashing.org> wrote:

> On Sun, Jan 06, 2002 at 11:19:40PM +0100, Jakub Jelinek wrote:
>> On Mon, Jan 07, 2002 at 08:59:47AM +1100, Paul Mackerras wrote:

>> > 	asm("" : "=r" (x) : "0" (y));

>> Even if gcc learned to analyze asm statements (and use it in something other
>> than scheduling), I'm sure this wouldn't be optimized away exactly because
>> this construct is used by various projects exactly for this purpose (make
>> gcc think it can have any value allowed for the type in question).

> Yes, but there's no gaurentee of that.  It'd probably break a few things
> if they did, but there's nothing stopping them from doing it.

If we documented this side effect of such asm statements, one would
have to come up with a very strong case to change it.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist    *Please* write to mailing lists, not to me
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