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.
