The author striked out the part about CedarDB not being available -- which is true -- but Umbra is available as a docker container[1] for some time now. The "Umbra paper" linked also contains an artifact[2] with a copy of Umbra as well as some instructions on how to control the back-ends used etc. (Cranelift is not available as an option in the docker versions however)

I kind of disagree with the assumption that baseline compilers are easy to build (depending on your definition of baseline). A back-end like DirectEmit is not easy to write and even harder to verify. If you have a back-end written for your own IR you will likely have to write tests in that IR and it will probably be quite hard to simply port over codegen (or run-) tests from other compilers. Especially in the context of databases it is not very reassuring if you have a back-end that may explode the second you start to generate code slightly differently. We're working on making this a bit more commoditized but in our opinion you will always need to do some work since having another IR (with defined semantics someone could write a code generator for you) for a back-end is very expensive. In Umbra, translating Umbra-IR to LLVM-IR takes more time than compiling to machine code with DirectEmit.

Also, if it is easy to write them, I would expect to see more people write them.

Copy-and-patch was also tried in the context of MLIR[3] but the exec-time results were not that convincing and I have been told that it is unlikely for register allocation to work sufficiently well to make a difference.

[1]: https://hub.docker.com/r/umbradb/umbra

[2]: https://zenodo.org/records/10357363

[3]: https://home.cit.tum.de/~engelke/pubs/2403-cc.pdf