Garbage collecting CAFs

I have seen numerous references to CAFs not used to being garbage collected in ghc leading to various contortions of the optimizer to keep from generating them and possible space leaks... then "something" was done and they are now collected.. I am curious what paper (or list message?) describes what that "something" is and what it entails in terms of tradeoffs. thanks. John -- John Meacham - ⑆repetae.net⑆john⑈