[llvm] [InstCombine] Canonicalize Bit Testing by Shifting to Bit 0 (PR #101838)

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mskamp wrote:

Good point. I think we could adapt the transformation in [InstCombineCasts.cpp:988](https://github.com/llvm/llvm-project/blob/b024fd267b813149f7bd5ba88731673b9a29258d/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp#L988) to also support smaller bit widths (and insert a trunc in this case).

https://github.com/llvm/llvm-project/pull/101838