Re: [PATCH] C undefined behavior fix

Alexandre Oliva
2002-01-07T01:41:35Z

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}
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