[llvm] [InstCombine] Remove dead phi web (PR #108876)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

LGTM. This seems like a reasonable extension, the number of visited phi nodes is still limited to a small number. Compile-time impact looks ok: https://llvm-compile-time-tracker.com/compare.php?from=223e2efa5e886502a9467b7ef700ebce9b7886e8&to=55a38338a2ebeef31ad8da34d965763f522e5799&stat=instructions:u

https://github.com/llvm/llvm-project/pull/108876