[llvm] [InstCombine] Turn Add into Or even when undef (PR #171556)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=42898499310b7b105db90701b579dc1cb8c23e8b&to=7a07247c5b6353fcec7305e9066d74bc178307a5&stat=instructions:u

https://github.com/llvm/llvm-project/pull/171556