Statically Safe Speculative Execution for Real-Time Systems

Deterministic worst-case execution for satisfying hard-real-time constraints, and speculative execution with rollback for improving average-case throughput, appear to lie on opposite ends of a spectrum of performance requirements and strategies. Nonetheless, we show that there are situations in which speculative execution can improve the performance of a hard real-time system, either by enhancing average performance while not affecting the worst-case, or by actually decreasing the worst-case execution time. The paper proposes 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 programs to evaluate applicability and profitability of speculative execution. The simulation results indicate that speculative execution improves average execution time and program timeliness. Finally, a prototype implementation is described in which these transformations have been evaluated for realistic applications.