An optimizing cispiler sounds really interesting. Something that applies all the optimizations that the compiler would do when translating your C to machine code but showing you the results in C. Of course not all optimizations are representable in C (calling conventions for instance) but many are.
There are several examples of this in the Java world, such as proguard. They're mostly centered around code obfuscation, but they do some useful optimizations as well.
