I'm sitting on old patches that implemented predicated value numbering in GCC by combining the algorithms from http://portal.acm.org/citation.cfm?id=512529.512536 "A sparse algorithm for predicated global value numbering" and http://www.springerlink.com/content/v1421878255577n5/ "An Efficient SSA-Based Algorithm for Complete Global Value Numbering"

The patches are more than three years old, and not totally complete. My project will be to update them to current GCC, and complete them to be eventually in a mergeable state.