Re: Iterating over RTL in Graphite

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

On Fri, Feb 17, 2012 at 10:15 PM, Tobias Grosser <tobias@grosser.es> wrote:
> On 02/17/2012 08:34 PM, David Malcolm wrote:
>>
>> On Thu, 2012-02-16 at 19:17 -0400, Arnaldo wrote:
>>>
>>> Hello everyone,
>>>
>>> I'm working on an extension to the Graphite pass of GCC 4.4.0.  My
>>> intention is to associate costs to RTL instructions by adding them as
>>> RTX attributes to a machine description file, and to read them back
>>> during the Graphite pass by iterating through each basic block.
>>>
>>> Is the RTL available during this optimization pass? I'm not sure this
>>> is the case as I get a segfault when trying to iterate over the RTL
>>> with the code below ("internal compiler error: Segmentation fault"). I
>>> don't need the fully resolved RTL, just to be able to read the
>>> attribute given an RTL instruction.
>>>
>>> I've tried debugging the compiler with gdb but it can't find the
>>> debugging symbols even though they're there.  I'll keep trying to get
>>> gdb to work but any leads on reading these attributes from within
>>> Graphite is greatly appreciated.
>>
>> I don't know about GCC 4.4, but a while back I wrote a script using my
>> GCC Python plugin to draw a "subway map" of GCC 4.6's passes:
>> http://gcc.gnu.org/ml/gcc/2011-07/msg00157.html
>> which you can see here:
>> http://gcc-python-plugin.readthedocs.org/en/latest/tables-of-passes.html
>>
>> If I reading things correctly, the graphite passes happen whilst the
>> code is still in gimple form: the blocks are converted to RTL form in
>> the "expand" pass, which happens about 20 or so passes later.
>>
>> Caveat: I'm not familiar with the insides of the graphite, and am
>> relatively new to gcc's insides, so I could be wrong; also the script
>> relies on the pass flags, and they're not necessarily correct either...
>
>
> Yes, graphite works on GIMPLE. I believe I have never seen RTL when working
> on graphite, so I doubt it is easily available. (Maybe it is, but it is
> definitely not used within graphite).
>
> Cheers
> Tobi
>

Thanks David and Tobias, that helped.

I started looking into the expand pass (cfgexpand.c), there's an
interesting function there:
static basic_block expand_gimple_basic_block (basic_block bb)

When I get a change I'll make it 'public' and see if I can call it
from graphite.c

-Arnaldo