[new-regalloc] Dataflow too slow...

[Geert Bosch]

One of the things I'm stumbling on now is that df_rd_global_compute
takes way too much time to allow me to bootstrap the Ada compiler.

For example, one unit that usually just takes 0.8 seconds to compile on 
a 1.1GH Athlon, takes more then 10 minutes now. Memory usage is around
30 MB, not outrageous. One invocation of this function takes a few
minutes to return... 

I killed the compiler after it was munching for 40 minutes on a (bit)
more complex file. Of course, it is too early to be concerned about a 
factor of ten in performance, but even for testing this is a bit too slow...
What complexity should these dataflow calculations be? 

  -Geert