[llvm] [SDAG] fix miss opt: shl nuw + zext adds unnecessary masking (PR #172046)

[via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 3
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actinks wrote:

done, pr #172127

https://github.com/llvm/llvm-project/pull/172046