infinite loop on array.sml

[Stephen Weeks]

> > > Yeah, I get that.  It's somewhere in main_0, so it's a pain to figure out.
> > > I mean to ask, could the new dominator version that doesn't care about
> > > the graph being connected and single rooted result in a dominator tree
> > > that has a cycle?
> > 
> > Maybe there is a bug in dominator computation causing the loop, but if
> > it terminates, we know from the tree type
> > 
> >       datatype 'a t = T of 'a * 'a t vector
> > 
> > that the tree really is acyclic.
> 
> O.k.  In any event, I'm fairly certain that after commonSubexp, there will
> be some dangling blocks in the cfg; particularly down the failure branches
> of repeated arithmetic computations.

I put in some print statements and Function.dominatorTree is  looping.
*scary*.  I will investigate.