Oh man, block-argument-SSA makes so much more sense to me than Φ-SSA. That alone is going to change my life. Thank you, Max!

A lot of this process is the same as graph-coloring register allocation on SSA, of which I found an extensive explanation in Appel's textbook. I think it's maybe time for me to go back to it and do the exercises so I really understand it. The book unfortunately predates the linear allocator age.

The link to https://brrt-to-the-future.blogspot.com/2019/03/reverse-line..., which is a learner's introduction to the LuaJIT reverse linear scan allocator, also seems valuable.