[llvm] [SimplifyCFG] Add optimization for switches of powers of two (PR #70977)

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DianQK wrote:

> I added all your suggestions and also wrote a test with both positive and negative cases. But what should I do with a failed test in the pipeline? Thanks.

Possibly you could change `i32 64, label %bb5` to `i32 128, label %bb5`. But I'm not sure that's okay.



https://github.com/llvm/llvm-project/pull/70977