propagate_freq enormous performance hit in 3.1

[Jan Hubicka]

> Jan:
> 
> >From examining the sources, it seems that predict.c is your baby,
> and it seems to have a serious performance problem in propagate_freq
> for large flow graphs, see
> 
> http://gcc.gnu.org/ml/gcc-prs/2001-08/msg00184.html
> 
> Do you have any idea of what's going on here?
It can have problems with large graphs with many irregular regions (see the
comment inside function).
I will take a look - in meantime I made code to find back edges, so I can
discover irregular regions easilly.

Can you please try to take a look at debug output and let me know if it
complains about the irregular regions?

Otherwise the time complexity should be OK.  I will try to prepare patch for
better irregular regions handling overnight, but my time is somewhat limited, so
it may take longer.

Thanks for letting me know.

Honza
> 
> BTW, I apologize for the large, useless inclusion in that GNAT PR.  The real
> source code I tested it on is at
> 
> http://www.math.purdue.edu/~lucier/all.i.gz
> 
> Brad Lucier