[llvm] [SimplifyCFG] Avoid scanning functions multiple times in `removeUnreachableBlocks` (PR #213416)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto commented:

Agree that computing reachability should be a graph-level problem, though it looks like past attempts to consolidate the two (DFS traversal vs scanning the whole function body) didn't work out (https://discourse.llvm.org/t/rfc-consolidate-remove-unreachable-blocks-functions), as the latter is seemingly more aggressive. Would be great to revisit this.

https://github.com/llvm/llvm-project/pull/213416