Statically safe speculative execution for real-time systems

Deterministic worst-case execution for satisfying hard-real-time constraint s, and speculative execution with rollback for improving average-case throu ghput, appear to lie on opposite ends of a spectrum of performance requirem ents and strategies. Nonetheless, we show that there are situations in whic h speculative execution can improve the performance of a hard real-time sys tem, either by enhancing average performance while not affecting the worst- case, or by actually decreasing the worst-case execution time. The paper pr oposes a set of compiler transformation rules to identify opportunities for speculative execution and transform the code. Moreover, we have conducted an extensive experiment using simulation of randomly generated real-time pr ograms to evaluate applicability and profitability of speculative execution . The simulation results indicate that speculative execution improves avera ge execution time and program timeliness. Finally, a prototype implementati on is described in which these transformations have been evaluated for real istic applications.