Re: Iterating over RTL in Graphite

[Richard Guenther <richard.guenther@gmail.com>]

On Mon, Mar 5, 2012 at 3:52 PM, Arnaldo <arnaldo.cruz@upr.edu> wrote:
> 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.

Graphite (polyhedral form) is even more high-level, how do you expect
RTX costs to be meaningful there at all?

> 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.

I don't even see how you could compute a reliable mapping of Graphite
(or GIMPLE) to the RTL you generate that way.

Richard.

> -Arnaldo