How much communication is there between the Julia compiler team and the LLVM team? I don't get the impression LLVM has been very sensitive to Julia's needs so far.
Quite a bit: several of the Julia compiler team are LLVM maintainers and contributors. LLVM has started to track compile time, so that's gotten a bit better with recent releases. Making noise about compile time was mainly to get the LLVM project to start paying attention to compile time, which they now have, so mission accomplished — as long as they stop completely allowing latency to degenerate, it's ok. LLVM is never going to be fast at compiling code (and if we used something else that was as good at producing fast code, it would almost certainly also be slow), so avoiding putting LLVM in the fast path is always going to be necessary to make more latency improvements.
That's great to hear. I found some info about it which looks promising.