[llvm] [X86] Handle BSF/BSR "zero-input pass through" behaviour (PR #123623)

[Shengchen Kan via llvm-commits]

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@@ -5220,42 +5220,42 @@ inline static bool isDefConvertible(const MachineInstr &MI, bool &NoSignFlag,
 }
 
 /// Check whether the use can be converted to remove a comparison against zero.
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KanRobert wrote:

Could we have a comment for the returned pair?

https://github.com/llvm/llvm-project/pull/123623