AoT

Ahead-of-Time compilation (AOT) is a method of transforming source code into native machine code before a program is executed. In contrast to interpreters or Just-In-Time (JIT) compilers, AOT produces a standalone native binary that can run directly on the target platform. The technique is used to optimize performance characteristics by shifting work from runtime to build time.

AOT typically involves a separate build or installation step during which the compiler analyzes the program and generates optimized machine code for the target architecture. This reduces or eliminates the need for runtime code generation, leading to faster startup times, more predictable performance, and often lower memory usage by avoiding JIT caches and runtime compilation.

Common applications include mobile and embedded environments, where startup latency is critical. Android’s runtime environment uses AOT compilation as part of ART. Web development frameworks such as Angular employ AoT to precompile templates into efficient code at build time. In broader ecosystems, languages and platforms offer native AOT options, such as GraalVM’s Native Image and .NET’s Native AOT, which generate standalone executables from managed code.

Benefits of AOT include improved startup speed, reduced runtime CPU usage, and a potentially smaller runtime footprint. Drawbacks include longer build times, larger binary sizes, the need for platform-specific binaries, and reduced flexibility for dynamic features or late binding. Debugging can also be more complex since issues may appear in the generated native code rather than in the original source.