Your LLVM email

I believe it’s “Dotty”, I simply output “opt -view-regions-only”.

It's a .dot file as used by the graphviz package. The default viewer, provided by graphviz is called 'dotty'. I normally use xdot.py [1].

Cheers
Tobi

http://code.google.com/p/jrfonseca/wiki/XDot