How IL2CPP works

Upon starting a build using IL2CPP, Unity automatically performs the following steps:

1. Compiles Unity Scripting API code to regular .NET DLLs (managed assemblies).

2. Applies managed bytecode stripping. This step significantly reduces the size of a built game.

3. Converts all managed assemblies to standard C++ code.

4. Compiles the generated C++ code and the runtime part of IL2CPP with a native platform compiler.

5. Links the code into either an executable file or a DLL, depending on the platform you are targeting.

IL2CPP provides a few useful options which you can control by attributes in your scripts. See documentation on Platform-dependent compilation for further information.