Modern Llvm-Based Compiler Autotuning for Wcet Optimization

The problem of compiler optimization selection and ordering, known in the literature as compiler autotuning, has been tackled many times for average-case execution time reduction. Optimizing the WCET is becoming a prominent problem for modern hard real-time systems, where the difficulties in accurate WCET estimation hinder the full exploitation of computing platform capabilities. In this article, we propose a novel methodology and a tool based on LLVM for iterative WCET-driven compiler autotuning, which is the first strategy to operate at function-level granularity and to consider not only the selection of optimization passes, but also their ordering. Our findings show that standard optimization levels$\mathrm{O} 0, \mathrm{O} 1, \mathrm{O} 2$, and O 3 are suboptimal when targeting the WCET, and that a per-function selection and ordering of the transformations is necessary. Experimental results show that our approach outperforms the standard optimizations and opens up new directions for future research.