[llvm] [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if operands are identical (PR #115945)

[Akshay Deodhar via llvm-commits]

akshayrdeodhar wrote:

Thanks for the suggestions! Won't have internet access for 2 days, will address the comments on Monday. This does affect some real workloads, which is why I wanted to work around this in SCEV. 

https://github.com/llvm/llvm-project/pull/115945