To build a project with IL2CPP, you need to have the backend installed in your Unity installation. For more information, see Debugging C# code in Unity. IL2CPP supports the debugging of managed code in the same way as the Mono scripting backend. For more information, see How IL2CPP works and the blog series An introduction to IL2CPP internals. IL2CPP can improve performance across a variety of platforms, but the need to include machine code in built applications increases both the build time and the size of the final built application. For more information, see Scripting restrictions. When a platform can support both backends, Mono is the default. Other platforms support AOT and IL2CPP, but don’t allow JIT compilation, and so can’t support the Mono backend. Some platforms don’t support AOT compilation Ahead of Time (AOT) compilation is an iOS optimization method for optimizing the size of the built iOS player More info See in Glossary, so the IL2CPP backend doesn’t work on every platform. Enabling runtime checks using IL2CppSetOption.The Mono backend compiles code at runtime, with a technique called just-in-time compilation (JIT).

This type of compilation, in which Unity compiles code specifically for a target platform when it builds the native binary, is called ahead-of-time (AOT) compilation. The IL2CPP backend converts MSIL (Microsoft Intermediate Language) code (for example, C# code in scripts) into C++ code, then uses the C++ code to create a native binary file (for example. IL2CPP provides better support for applications across a wider range of platforms. More info See in Glossary is an alternative to the Mono backend. Universal Windows Platform, however, supports only two. Unity supports three different scripting backends depending on target platform: Mono.

The IL2CPP (Intermediate Language To C++) scripting backend A framework that powers scripting in Unity.

Il2cpp source code