[llvm] [DAGCombiner] Expose CSE for shifts of logic operations (PR #213091)

[Justin Fargnoli via llvm-commits]

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justinfargnoli wrote:

Let's move this into `rebuild` and add a comment explaining that this will be CSEd. (`getNode()` does the CSE for us.)

https://github.com/llvm/llvm-project/pull/213091