Winston: Revisiting iterative compilation for WCET minimization

International audienceStatic Worst-Case Execution Time (WCET) estimation techniques take as input the binary code of a program and output a conservative estimate of its execution time. While compilers, and iterative compilation, usually optimize for the average-case, previous work such as [7, 23] has shown that it is also possible to use existing optimization and iterative compilation techniques to lower the WCET estimates drastically. In this paper, we revisit the use of iterative compilation for WCET minimization and show that previous work can be improved both in terms of complexity and reduction of WCET estimates. In particular, we found that the use of long chains of compilation flags, from a few hundred to a few thousand, allows a significant reduction of WCET estimates, of 35% on average, and up to 70% on some benchmarks, compared to the best compilation level (-O0 ..-O3) applicable. These gains are significantly better than the reductions of WCET estimates obtained by [7], which, on the same benchmarks and experimental conditions, reduce the WCET estimates by 20% on average