Ahead-of-time Compilation of FastR Functions Using Static Analysis

The FastR project delivers high peak-performance through the use of JIT-compilation, but cannot currently provide this performance for methods on first call. This especially affects startup-performance and performance of applications that only call functions once, possibly with large inputs (i.e. data processing). This project presents an approach and the necessary patterns for implementing an AOT-compilation facility within FastR, enabling compilation of call targets just before being first called. The AOT-compilation produces code that has profiling and specialization information tailored to the expected function argument values for the first call, without needing to execute the function in full. The performance results show a clear and unambiguous performance gain for first-call performance of AOT-compiled functions (up to 4x faster, excluding compilation time). Due to constant compilation time there is the potential for overall startup performance improvement for long-running functions even when compilation time is included. While the static analysis itself imposes almost no overhead, compilation times are up to 1.4x higher than with regularly compiled code, due to the inherent imprecision of the current analysis. Although peak performance is reduced, AOT-compilation can be the solution where faster first-call performance, the possibility of offloading/remote execution, and more performance predictability are important.