GCC-MELT
a GCC compiler plugin and domain specific language ....
GCC-MELT is a high-level domain specific language to extend the GCC compiler. It provides several features (pattern-matching, first-class dynamically typed values, functional/applicative/object-oriented/reflective programming styles, Lisp-y syntax)
MELT can also be used to explore the internal representations used by GCC (Gimple, etc...)