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From: David Brown <david@westcontrol.com>
To: gcc@gcc.gnu.org
Subject: Re: avr compilation
Date: Fri, 18 Mar 2011 12:11:00 -0000	[thread overview]
Message-ID: <ilvi4e$br0$1@dough.gmane.org> (raw)
In-Reply-To: <ilvbbf$69u$1@dough.gmane.org>

On 18/03/2011 11:15, Paulo J. Matos wrote:
> On 18/03/11 10:08, WANG.Jiong wrote:
>> This may related with subreg regmove finding
>> Suggest specifiy -fdump-rtl-regmove to see what happen after this pass
>> Maybe avr need a target dependent regmove pass to handle this
>>
>
> It doesn't look like it's regmove, whose result looks pretty sane:

As far as I can see, you are correct - avr-gcc generates subobtimal code 
here, and your version is better.

There are only a few people who work with the AVR backend, and while 
these people are both clever and dedicated, they are limited in how much 
they can do - correct code generation and support for newer devices or 
features rightly takes priority over optimisation issues.  Thus there 
are a fair number of "missed optimisation" issues filed for the AVR 
backend, and many more cases like this of suboptimal code that don't 
even have issues filed.

There are also a number of patches that are generally applied to avr-gcc 
builds (most of which eventually make it into the main FSF tree).  I 
could not say if any of these are relevant here.

If you are digging through the AVR backend and find ways to improve code 
sequences like this, the avr-gcc community would be very grateful.

There is an avr-gcc mailing list at 
<http://lists.nongnu.org/mailman/listinfo/avr-gcc-list>, which may be of 
interest to you.

  reply	other threads:[~2011-03-18 12:11 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-18  8:48 Paulo J. Matos
2011-03-18 10:08 ` WANG.Jiong
2011-03-18 10:15   ` Paulo J. Matos
2011-03-18 12:11     ` David Brown [this message]
2011-03-18 13:37       ` Paulo J. Matos
2011-03-18 13:26 ` Georg-Johann Lay
2011-03-18 13:40   ` Paulo J. Matos
2011-03-18 14:20     ` Ian Lance Taylor
2011-03-18 14:50       ` Paulo J. Matos

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