What's new in compiler optimization techniques over last few years?
I'm not sure how novel it is, or if it's too much on the applied side for your interest, but Hoopl shows how a control/data flow optimization can be modularised, with propagation of facts about control-graph vertices being independent of the language and specific optimization.

They reference a 2002 algorithm of Lerner, Grove and Chambers which composes simple optimizations into a "superoptimization".