Our Solution Approach. We present OPPROX, a system for phase-aware optimization of approximate programs. OPPROX takes as inputs: a program with tunable approximable blocks and a user-provided accuracy specification, which consists of (1) a set of representative inputs that exercise the application’s desired functionality, (2) an accuracy metric that tells how to compute the difference between the results of the exact and the approximate execution, and (3) an error budget e b that specifies how much reduction in the accuracy metric in the final output the user is ready to tolerate