[llvm] [WebAssembly] Replace Reachability with SCCs in Irreducible CFG Fixer (PR #179722)

[Petr Penzin via llvm-commits]

https://github.com/ppenzin commented:

Since this is a standalone implementation of Tarjan SCC algorithm, at a brief glance it seems to be OK, but more testing would be advisable.

`llvm/test/CodeGen/WebAssembly/irreducible-cfg.ll` seems to be fine as it seems to check which cases result in a `br_table` and which do not.

`llvm/test/CodeGen/WebAssembly/irreducible-cfg.mir` has a test with two entry points resulting in one dispatch block, I am not sure if or how it should be expanded for the new algorithm.

As an aside, did you get help from AI in writing this?

https://github.com/llvm/llvm-project/pull/179722