linux-kernel - Re: [PATCH] [POWERPC] Improve (in|out)

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Message-ID: <jeiqx83ab0.fsf@sykes.suse.de>
Date:	Wed, 21 May 2008 00:00:51 +0200
From:	Andreas Schwab <schwab@...e.de>
To:	Trent Piepho <tpiepho@...escale.com>
Cc:	linuxppc-dev@...abs.org, Scott Wood <scottwood@...escale.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code

Trent Piepho <tpiepho@...escale.com> writes:

> For the LE versions, eventually they boil down to an asm that will look
> something like this:
> asm("sync; stwbrx %1,0,%2" : "=m" (*addr) : "r" (val), "r" (addr));
>
> While not perfect, this appears to be the best one can do.  The issue is
> that the "stwbrx" instruction only comes in an indexed, or 'x', version, in
> which the address is represented by the sum of two registers (the "0,%2").
> Unfortunately, gcc doesn't have a constraint for an indexed memory
> reference.

There is the "Z" constraint, which matches either an indirect or an
indexed memory address.  That should fit here.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@...e.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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