[llvm] [LAA] Rewrite findForkedPointer (NFC) (PR #140298)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Gentle ping. I think findForkedSCEVs can be made significantly more powerful, and I think that LAA will be able to permit a lot more cases for vectorization as a consequence. This patch is a prerequisite for that work.

https://github.com/llvm/llvm-project/pull/140298