I am looking for a library for doing custom static code analysis on CIL code. READ: I have no interest in a tool that already does static analysis like those shown here.
For custom analysis with Java Bytecodes, I have used ASM and I like the features it offers and the good documentation. A quick google search for "CIL static analysis library" doesn't yield anything that seems to provide the features of ASM.
Mono.Cecil is the best library for CIL analysis available. It is free, open-source, complete, lightweight, robust and fast. In addition to reading CIL, it can also write CIL. It also supports PDB files.
Many static analysis tools rely on Cecil for years.