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

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Date:	Wed, 21 May 2008 10:03:54 +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:

> On Wed, 21 May 2008, Andreas Schwab wrote:
>> Trent Piepho <tpiepho@...escale.com> writes:
>>
>>> It's the _le versions that have a problem, since we can't get gcc to just use
>>> the register indexed mode.  It seems like an obvious thing to have a
>>> constraint for, but I guess there weren't enough instructions that only come
>>> in 'x' versions to bother with it.  There is a 'Z' constraint, "Memory operand
>>> that is an indexed or indirect from a register", but I tried it and it can use
>>> both "rb,ri" and "disp(rb)" forms.  Actually, I'm not sure how 'Z' is any
>>> different than "m"?
>>
>> 'Z' will never emit a non-zero constant displacement.
>
> It's too bad gas doesn't appear to be smart enough to turn:
>         stwbrx 0, 0(3)   -or-   stwbr 0, 0(3)

Use the %y modifier when substituting the operand.

Andreas.

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