The Unity build process uses a tool called the Unity linker to strip managed code. The Unity linker is a version of the IL Linker customized to work with Unity. Custom parts of the Unity linker specific to the Unity engine aren’t publicly available.
The Unity linker is responsible for both managed code stripping and part of the process of engine code stripping, which is a separate process available through the IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
See in Glossary scripting back end that removes unused engine code. For more information, refer to PlayerSettings.StripEngineCode
.
When you build a Unity project, the build process compiles your C# code to a .NET bytecode format called Common Intermediate Language (CIL). Unity packages this CIL bytecode into files called assemblies. The .NET framework libraries and any C# libraries in the plug-insA set of code created outside of Unity that creates functionality in Unity. There are two kinds of plug-ins you can use in Unity: Managed plug-ins (managed .NET assemblies created with tools like Visual Studio) and Native plug-ins (platform-specific native code libraries). More info
See in Glossary you use in your project are also pre-packaged as assemblies of CIL bytecode.
For the purpose of managed code stripping, assemblies are categorized as follows:
mscorlib.dll
and System.dll
, as well as .NET class library facade assemblies like netstandard.dll
.windows.winmd
assembly that’s part of the Universal Windows Platform SDK.UnityEngine.Core.dll
.Assembly-CSharp.dll
.In general, any assemblies in your project that don’t fall under one of these categories are not processed by the Unity linker and are excluded from the Player build .
During a build, the Unity linker processes all applicable types of assemblies and does the following:
At the High stripping level, the Unity linker edits method bodies to further reduce code size. The Unity linker only edits method bodies in the .NET Class Library assemblies.
The Unity linker can edit a method body in the following ways:
if
statement blocks that check System.Environment.OSVersion.Platform
and aren’t reachable for the currently targeted platform.const
value.void
return type.try-finally
blocks when the finally
block is empty. Removing empty calls can create empty finally
blocks. When that happens during method editing, the Unity linker removes the entire try-finally
block. One scenario where this can occur is when the compiler generates try-finally
blocks as part of foreach
loops in order to call Dispose
.Note: After editing method bodies, the source code of the assembly no longer matches the compiled code in the assembly, which can make debugging more difficult.
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