Difficulties in Computing the WCET for Processors with Speculative Execution

In real-time applications, the Worst-Case Execution Time often needs to be estimated to check that deadlines will be respected. With the trend of using up-to-date processors, WCET computation techniques continuously have to evolve in order to take into account the most recent hardware features. In this paper, we show that ignoring speculative execution can lead to underestimated execution times, and we explain why modelling it is not straightforward. We feel that pure static analysis might not allow safe WCET computation, due to the fact that speculative execution prevents the decoupling between the high-level (path) analysis and the low-level (timing) analysis.