Stallman on GCC, LLVM, and copyleft

I'm curious. Has anyone *ever* produced a truly pluggable compiler? I doubt it. I doubt it's even possible: sure, the horrible implicit dependencies GCC is rife with are mostly a function of age, but the fundamental problem that a compiler's job is to manipulate a giant data structure, that *everything* manipulates that data structure, that all the things that do the manipulation care about properties of that data structure before they touch it and thus are exposed to precisely what everything that ran before them did, and that enhancements that span more than one such component necessarily change the giant data structure in ways that almost everything must adapt to... these problems seem to me to be fundamental.

You can impose useful properties that everything expects (being in SSA form, for instance) but that doesn't mean that you can dictate *all* properties. So the problem of adding or reordering compiler passes, particularly passes that change the program rather than just emitting warnings or spying on the compiler's state, remains an intractable bugger.