Abstract-- For embedded systems where neither energy nor reliability can be easily sacrificed, we present an energy efficient soft error protection scheme for register files (RF). Unlike previous approaches, our method explicitly optimizes for energy efficiency and exploits the fundamental tradeoff between reliability and energy. While even simple compiler-managed RF protection scheme is more energy efficient than hardware schemes, this work formulates and solves further compiler optimization problems to significantly enhance the energy efficiency of RF protection schemes by an additional 24%.