How does an ahead-of-time compiler improve performance?

An ahead-of-time (AOT) compiler improves performance by translating high-level code into machine code before execution.

An AOT compiler is a type of compiler that translates high-level programming languages into machine code prior to the program's execution. This is in contrast to just-in-time (JIT) compilers, which perform this translation during the program's execution. The primary advantage of AOT compilation is that it can significantly improve the performance of the resulting program.

The performance improvement comes from several factors. Firstly, because the translation is done ahead of time, the program can start executing immediately without the need for any compilation during runtime. This can lead to faster startup times, which can be particularly beneficial for large applications or systems that need to start quickly.

Secondly, AOT compilers can perform more extensive optimisations during the compilation process. Because they are not constrained by the need to compile code quickly during runtime, they can spend more time analysing the code and applying complex optimisation techniques. These optimisations can lead to more efficient machine code that executes faster and uses less memory.

Thirdly, AOT compilation can reduce the memory footprint of the program. JIT compilers need to keep both the original high-level code and the translated machine code in memory during execution. In contrast, AOT compilers only need to keep the machine code in memory, which can lead to significant memory savings.

However, it's worth noting that AOT compilation is not always the best choice. It can lead to longer build times, as the entire program needs to be compiled before it can be run. Additionally, some types of optimisations can only be done at runtime, based on the specific data and conditions that the program encounters. Therefore, the choice between AOT and JIT compilation often depends on the specific requirements and constraints of the project.