[llvm] [LoopFusion] Fix false-positive dependency blocking fusion of idempot… (PR #206401)

[Ehsan Amiri via llvm-commits]

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amehsan wrote:

There is not enough information here to prove `%a` and `%b` do not alias each other. The caller may pass the same pointer as the first and second argument of the function. 

https://github.com/llvm/llvm-project/pull/206401