Hello,
The wip-rtl-cps branch has been rebased again (on top of wip-rtl). It now includes support for toplevel references and sets, thanks mostly to Andy's work on supporting them in RTL. (Although you shouldn't kick that part of it too hard just yet; I think I know where it will break.) Other highlights include using the top-level variable support to evaluate "(+ 3 4)" correctly.
Overall, I think it's coming along well. The parts of Tree-IL that are left to implement are local mutable variables (should be easy after toplevel ones), module references and sets (very similar to top-level ones), closures, and the dynamic environment stuff. Local mutable variables are my next project, and then I think closures.
One question I've had is, can we assume that the variables in the (guile) module are immutable? I think the current compiler does this. Otherwise there's no correct way to inline primitive procedures like + unless we have a way to invalidate our compiled code and recompile it (which I would like to have anyway, but that's a different story).
Best,
Noah