Clang has a plugin system. Compiler extension can be created by making a shared library and loading it via the "-fplugin". This allows for custom warnings and static analyzers.

In the past, Lustre has used custom compiler plugins in the past - although they haven't been maintained in a while: https://wiki.whamcloud.com/pages/viewpage.action?pageId=18645101

I've developed a plugin which detects functions which ought to be static. Since Clang has an easier time reasoning about static functions, the plugin has the side effect of finding some cases of dead code. This ticket tracks implementing build system support for that plugin (and potential future/past plugins).