C# Compiler optimization - Unused methods

Question

Does C# compiler (in VS2008 or VS2010) remove unused methods while compiling ?

I assume that it may have a problem deciding if public methods will ever be used, so I

Answer 1

No they won't be removed. It may give you warning for that but won't do it itself.

Answer 2

Just checked in reflector with a release build. The compiler doesn't remove the unused private methods.

There are ways to use a method without the compiler knowledge, like with reflection. So the compiler doesn't try to guess. It just leaves the methods there.

The only private methods the compiler removes are partial methods without implementation.

For the C# compiler optimizations, look here.

Answer 3

The compiler doesn't strip any method from the assembly, public or private. I could in fact cause weird issues with reflection, and prevent runtime calls to such methods.

There are a lot of frameworks (like the XAML parser) which enable you to call private methods without static bindings (think about OnClick="myFunction" in a XAML file) This markup will call the potentially private myFunction when the OnClick event is raised... But the compiler has no informations about such a behavior at compile time.

Dynamic code suffer from the same issue, IL generation too. And you can access private methods from any object when executing under full trust.

Answer 4

This optimization is effectively implemented at the JIT level, which is good because then it works for both public/private/whatever methods. If a method is never called (ignoring ngen, etc.), it never gets JITed. Now you might say that this is still a waste of space for metadata etc. but as others have pointed out, private isn't so private.