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

[via llvm-commits]

goldsteinn wrote:

> I have squashed the changes and test into one commit. @goldsteinn

Thats not really ideal either... Then its difficult to review the test changes.
Typically the way we do it is two seperate commits i.e

commit 1: Tests (w/ checks before the implementation)
commit 2: Implementation (re update test checks)

That way in commit 2 we can see what actual changes the implementation is causing.

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