Approximation of the worst-case execution time using structural analysis

Abstract

We present a technique to approximate the worst-case execution time that combines structural analysis with a loop-bounding algorithm based on local induction variable analysis. Structural analysis is an attractive foundation for several reasons: it delivers better bounds on the number of executions for each basic block than previous approaches, its complexity is well understood, and it allows the compiler to easily work on Java bytecode without requiring access to the original program source. There are two major steps. We first compute (min, max) bounds on the number of iterations for each loop. Then we use precise structural information to propagate these bounds to the whole control-flow graph and compute a bound for each basic block. Such a fine-grained result eases the identification of infeasible paths and improves the approximation of the worst-case execution time of a function or method. This analysis was successfully implemented in an ahead-of-time Java bytecode to native compiler and produces input for a worst-case execution time estimator. We describe the effectiveness in reducing the worst-case execution time for a number of programs from small kernels and soft-real-time applications.