Institute of Embedded Systems

Note: hfalk, ESD, WCC

Abstract: Embedded software spends most of its execution time in loops. To allow a precise static WCET analysis, each loop iteration should, in theory, be represented by an individual calling context. However, due to the enormous analysis times of real-world applications, this approach is not feasible and requires a reduction of the analysis complexity by limiting the number of considered contexts. This restricted timing analysis results in imprecise WCET estimates. In particular, data-dependent loops with iteration counts depending on function parameters cannot be precisely analyzed. In order to reduce the number of contexts that must be implicitly considered, causing an increase in analysis time, we apply the standard compiler optimization procedure cloning which improves the program's predictability by making loops explicit and thus allowing a precise annotation of loop bounds. The result is a tight WCET estimation within a reduced analysis time. Our results indicate that reductions of the WCET between 12% and 95% were achieved for real-world benchmarks. In contrast, the reduction of the simulated program execution time remained marginal with only 3%. As will be also shown, this optimization only produces a small overhead for the WCET analysis.