traverse CFG in Clang

could anybody tell me how to traverse CFG in Clang towards c/cpp source code?

Currently I am able to find out all the assignment declaration , do a source to source transformation to insert certain code I want.

I want to find out all the basic control block, using source 2 source transformation to insert certain code.

I think class clang::CFG could help but actually I have no idea how to use it…

What I am referring now are these tutorials

Thanks !

Shuai