[llvm] [SimplifyCFG] Look at all uses when checking phi incoming for UB (PR #200164)

[Nikita Popov via llvm-commits]

nikic wrote:

@igogo-x86 See https://github.com/llvm/llvm-project/pull/98802. It originally had the code you propose here and then changed it.

You may want to try whether the compile-time issue with the cmGeneratorExpressionLexer test case still reproduces (it's not part of the llvm-opt-benchmark-nightly test set, only the old llvm-opt-benchmark one).

The behavior is going to be dependent on the use list order in any case, as we don't check all uses.

https://github.com/llvm/llvm-project/pull/200164