A few years back I was working on a WAM to LLVM compiler as a way to learn LLVM. Never fully finished my implementation, but this book really was an amazing reference. I particularly enjoyed the way the "tutorial style" that built up starting from a very simple language and explaining the design choices being made while extending the language to eventually become Prolog.

I don't know where the code is now, maybe I should make a point of digging it up and fixing it up to work with a recent versions of LLVM.