Fast and Compact: Reducing Size of AOT-Compiled Java Code without Sacrificing Performance

GraalVM Native Image is a technology that compiles Java applications to native executables ahead of time (AOT). Due to highly aggressive optimizations, it is possible to reach a peak performance similar to that of a regular Java application executed on a Java Virtual Machine (JVM) and its Just-in-Time (JIT) compiler. The advantage of Native Image is much faster start-up when compared to the JVM and the JIT compiler. However, binary files resulting from Native Image tend to be quite large.
In this work, we present an approach to shrink the executables produced by Native Image while maintaining high peak performance: Instead of compiling everything to machine code, we exclude rarely or never executed methods and keep them as bytecode instead. When called, these methods can be run with a lightweight interpreter. If an interpreted method turns out to cause high overhead, its execution continues in native mode by simulating a JIT compiler. For the DaCapo benchmark suite, we are able to reduce the sizes of Native Image executables by up to 36.9% without significantly reducing peak performance or increasing start-up times.