(In reply to comment #13)
> (In reply to comment #12)
> > Created attachment 105630 [details] [review] [review] [review]
> > another debugging patch
> > 
> > Ok, it looks like the problem is that node 0's q_total is bogus, which means
> > it never even gets considered for optimistic coloring. To help me figure out
> > why this is, can you apply this patch to master (not on top of the other
> > patch) and tell me the output of the piglit test now?
> 
> On (In reply to comment #12)
> > Created attachment 105630 [details] [review] [review] [review]
> > another debugging patch
> > 
> > Ok, it looks like the problem is that node 0's q_total is bogus, which means
> > it never even gets considered for optimistic coloring. To help me figure out
> > why this is, can you apply this patch to master (not on top of the other
> > patch) and tell me the output of the piglit test now?
> 
> I'm not sure if this matters, but r300g pre-allocates the input registers
> before calling ra_allocate_no_spills().

I think there are no input registers in this case (there's a NumInputs = 0
somewhere in the backtrace) so there aren't any pre-allocated nodes here.