Re: Iterating over RTL in Graphite

[Arnaldo <arnaldo.cruz@upr.edu>]

On Mon, Mar 5, 2012 at 10:00 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Mon, 5 Mar 2012, Arnaldo wrote:
>
>> I couldn't get cfgexpand.c:basic_block expand_gimple_basic_block
>> (basic_block bb) to work by calling it directly because there is some
>> preprocessing in gimple_expand_cfg() that has to be done first.  But
>> calling gimple_expand_cfg() modifies the CFG and asserts will fail later
>> on during compilation.
>>
>> I think the only way to solve this would be to somehow duplicate the
>> current cfun structure when entering the part of Graphite I'm extending,
>> then calling push_cfun(), gimple_expand_cfg(), extracting the BBs with
>> the RTL and calling pop_cfun() before continuing.
>
> Really, you're barking up the wrong tree.  graphite doesn't work on the
> RTL IL, it'll work only on gimple.  expanding is what we call the process
> of transforming gimple to RTL, and that process destroys gimple.  Hence
> you can't do that when still at the gimple side of things as there are
> still passes to run that run in gimple.
>
> Whatever you want to do with graphite, you have to do it at the gimple
> level.
>
>
> Ciao,
> Michael.

Richard, Michael,

I have to find a way to generate the RTL because I have profiled an
instruction set and I need access to these costs during my extension
to the Graphite pass.  I planed to add these costs as attributes to
the RTX patterns in the machine description file and read the back
from Graphite.  Gimple seems to be too high-level to associate its
statements to machine costs.

I know this is not the way GCC was designed but the optimization I'm
working on needs access to the profile.  Maybe there's a better way of
doing this?  What I'm attempting to do now is to duplicate the current
cfun so that I can expand and read the RTL attributes and then discard
this cfun before continuing with the compilation.

-Arnaldo