>>norir+fQ8
This is operating on IR, not on lines of code. Figuring out where the operation came from is extremely difficult because you have to propagate all of that info back and forth across the passes, and it may end up being split "across" syntactic elements. If your language has any form of metaprogramming or code reuse (i.e. all of them), that operation may also be necessary at some use sites and not at others, among other issues.