[llvm] [WebAssembly] Reapply "[WebAssembly] Incorporate SCCs into WebAssemblyFixIrreducibleControlFlow" (#181755) (PR #184441)

[Heejin Ahn via llvm-commits]

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aheejin wrote:

What if there are a cluster of unreachable blocks? They will have non-empty preds and succs.

Also, would it be possible that those unreachable blocks to form an irreducible CFG? Then CFGStackify will try to linearize it and fail.

https://github.com/llvm/llvm-project/pull/184441