[clang-tools-extra] [llvm] [clang] [InstCombine] Convert or concat to fshl if opposite or concat exists (PR #68502)

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goldsteinn wrote:

For my money this was merged prematurely. There are still outstanding concerns about whether this transform is desirable, as well there is an outstanding comment about the implementation itself.
I'm fairly agnostic about this code getting in, but I think it should be reverted until some degree of consensus is reached.
It's painful to have comments/a PR languish without replies, but don't think the answer is to just push.

https://github.com/llvm/llvm-project/pull/68502