Re: Iterating over RTL in Graphite

[David Malcolm <dmalcolm at redhat dot com>]

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...

Hope this is helpful
Dave