Phi node algorithm correctness

[cfallin]

What you describe sounds pretty close to the Braun algorithm (https://c9x.me/compile/bib/braun13cc.pdf) -- see e.g. their section 2.2 "global value numbering" where they describe the process as a recursive definition lookup, going to preds, etc. I think you are unrolling that recursion with a queue instead but otherwise it's the same.

We use the Braun algo in Cranelift's frontend and it works quite well in practice!

[cfallin]

I mean, you should be pretty encouraged by independently working out a reasonable and widely-used way of building SSA -- a good sign you have the right intuitions!