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

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> Can you confirm you're stilling seeing the miscompile after https://github.com/llvm/llvm-project/pull/176064? I'm not sure exactly what that would have done on a non-asserts build.

Ah yeah, patching that one in fixes the problem.

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