non-tail returns

[Matthew Fluet]

> > On the other hand, for a return, there is no interference when moving the
> > return values into their return location below the top of the stack.
> 
> I guess it would help to have the callee do a little lookahead and use
> some negative stack offsets to store its results directly in the right
> place.

That might help in some cases.

> I agree with your conclusions.  I also observe from those numbers that
> I really want -native-live-stack true.  Those are some nice speedups.
> Maybe we could put some hack in that uses -native-live-stack true for
> programs with fewer than N statements (where N =~ 10000)?

We could try it.  I haven't tried a self compile with -native-live-stack
true in a while, so I'll see how slow it is.