What is AOT compilation?

AOT compilation (Ahead-Of-Time compilation) is the process of converting source code or bytecode of a program into machine code before the application runs.

Main features:

• Execution before launch: Compilation occurs once before execution, unlike JIT (Just-In-Time) compilation, which occurs during runtime.
• Creating an executable file: The result is an executable file specific to the target architecture and operating system.
• No compilation phase during runtime: This eliminates the overhead of compilation during the program's operation.

Advantages:

• Faster startup time: The program is ready to run immediately, without delays for JIT compilation.
• Optimization: The compiler can perform more aggressive optimizations based on the entire program, not just parts of it.
• Predictable performance: The absence of a JIT phase eliminates "warm-up" time and provides more stable response times.
• Reduced resource requirements during execution: No need to keep the JIT compiler in memory or run its processes.
• Smaller file size: In some cases, AOT-compiled programs can be smaller because they do not contain the JIT compiler and related metadata.

Disadvantages:

• Longer build time: The compilation process can take a significant amount of time.
• Lack of dynamic optimization: No ability to apply optimizations based on real-time execution and profiling.
• Creating platform-specific binaries: Each target platform requires a separate build.
• Larger binary size: Sometimes, AOT can lead to increased size due to including all necessary code and dependencies.

Examples of use:

• .NET Native
• OpenJDK (GraalVM Native Image)
• Go
• Rust
• Some JavaScript frameworks (e.g., Angular with AOT)

AOT compilation is often used in scenarios where startup time is critical, predictable performance is required, or deployment on resource-constrained devices is necessary.