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

[Heejin Ahn via llvm-commits]

https://github.com/aheejin commented:

Nice improvement!  I think we need to update the description on top of the pass file. (Especially the time complexity)

Below are mostly nits or comment suggestions.

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