If you want a simple modern compiler backend intended for production-readiness, consider Cranelift [1]. It's largely written by Dan Gohman, who is a longtime LLVM contributor (and a colleague of mine). It does a lot of the things LLVM's backend passes do, but it's cleaner and better factored, with the benefit of a decade of hindsight [2]. Cranelift should be great for teaching purposes.

[1]: https://github.com/CraneStation/cranelift

[2]: https://cranelift.readthedocs.io/en/latest/compare-llvm.html