[llvm] [InstCombine] Do not simplify lshr/shl arg if it is part of fshl rotate pattern. (PR #73441)

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goldsteinn wrote:

> > I would expect to see test difference in the commit adding the new restriction.
> 
> I didn't get what you meant by this. Should I have code changes and test in the same commit?

Yes, otherwise the commit with the impl will not be passing (and it makes review more difficult as its hard to see the proper side affects of a change).

https://github.com/llvm/llvm-project/pull/73441