Serious performance regression -- some tree optimizer questions

[David Edelsohn]

	The new tree-level loop optimizations are, well, new.  They are a
work in progress and need some more tuning.  I believe that there are some
more patches in the wings that can help loop performance further.
However, there is a delicate balance between fixing performance
regressions and not introducing new bugs.  We need to see what changes the
fixes entail.

David