It just surprises me, that it was not removed by linker...

This file type is recognized as .cpp source file, but unlike regular .cpp, which might be placed into the library first and eventually eliminated by linker, .icpp one is always linked as object file. This forces the file to be always linked. The rationale of this is that you can put module initialization code into .icpp that is linked into the executable even when code is not referenced from other files.