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Date: Tue, 20 May 2008 16:14:49 -0700 (PDT)
From: Trent Piepho <tpiepho@freescale.com>
To: Andreas Schwab <schwab@suse.de>
Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code
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Cc: Scott Wood <scottwood@freescale.com>, linuxppc-dev@ozlabs.org,
	linux-kernel@vger.kernel.org
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On Wed, 21 May 2008, Andreas Schwab wrote:
> Trent Piepho <tpiepho@freescale.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)

into the desired:
         stwbrx 0, 0, 3