Information is based on Unity version 2018.2:
Quoting the Unity manual on IL2CPP:
IL2CPP (Intermediate Language To C++) is a Unity-developed scripting backend which you can use as an alternative to Mono when building projects for various platforms. IL2CPP (An ahead-of-time (AOT) compiler) supports debugging of managed code in the same way as the Mono scripting backend.
When building a project using IL2CPP, Unity converts IL code from scripts and assemblies to C++, before creating a native binary file (.exe, apk, .xap, for example) for your chosen platform. Some of the uses for IL2CPP include increasing the performance, security, and platform compatibility of your Unity projects.
Quoting the Unity tutorial on IL2CPP & Mono:
Each Scripting Backend has benefits and drawbacks that should influence your decision on which is the right choice for your situation:
IL2CPP:
- Code generation is heavily improved compared to Mono.
- Debugging Script code in C++ from top to bottom is possible.
- You can enable Engine code stripping to reduce code size.
- Build times are longer than with Mono.
- Only supports Ahead of Time (AOT) compilation.
Mono:
- Faster build times than IL2CPP.
- Supports more managed libraries due to Just In Time compilation (JIT).
- Supports runtime code execution.
- Must ship managed assemblies (.dll files that mono- or .net produce).
Important Points:
- The default Target Architecture in the Android Player Settings are armv7 and x86 with the IL2CPP and Mono Scripting Backend.
Mono is not supported on UWP (Universal Windows Platform) or iOS 11 and above. The default Architecture in the iOS Player Settings are armv7 and arm64 with the IL2CPP Scripting Backend.
UWP build only support IL2CPP and .NET, The .NET scripting backend (Deprecated ) uses Microsoft’s .NET to power scripting.
