Also is there any work to multi-thread the Rust compiler on a more fine-grained level like the recent GCC work? I know you allude to that potentially that would make the instruction counts potentially less reliable so wondering if that's something being explored.

Finally, while I have you, I'm wondering if there's been any exploration of the idea of keeping track of information across builds so that incremental compilation is faster (i.e. only bother recompiling/relinking the parts of the code impacted by a code change). I've always thought that should almost completely eliminate compilation/linking times (at least for debug builds where full utmost optimization is less important).