I dunno that it is meant to be a full on replacement. Rust intends to use it as an alternative backend for debug builds that focuses on really fast build times with little if any optimizations.

It's not, but I'm also not intending to write a production grade language either.

Just FYI, there's an LLVM tutorial (for C++), but it's quite succinct, and you have to figure a lot of things out on your own: https://llvm.org/docs/tutorial/