[llvm] [InstCombine] Replace an integer comparison of a `phi` node with multiple `ucmp`/`scmp` operands and a constant with `phi` of individual comparisons of original intrinsic's arguments (PR #107769)

[Volodymyr Vasylkun via llvm-commits]

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Poseydon42 wrote:

The case you're proposing would still actually enable this optimization since we can still move the `icmp` into every incoming BB, and only one of the `scmp`s will not be removed due to it being used more than once (in this case the BB with `scmp` becomes what was previously `NonSimplifiedBB`). I think it's better to add a negative test where both `scmp`s are not one-use, since in that case the optimization wouldn't be trivially profitable.

https://github.com/llvm/llvm-project/pull/107769