[llvm] [InstCombine] Fold (X << Y) / (X << Z) -> (1 << Y) / (1 << Z) (PR #68863)

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XChy wrote:

Thanks for your review. Here is a more direct fold. [Alive2](https://alive2.llvm.org/ce/z/iDt-wU).

https://github.com/llvm/llvm-project/pull/68863