[llvm] [SCEV] Handle backedge-count logic for std::reverse like loops (PR #92560)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I was experimenting with the Alive2 proof a bit, and ran into the following which seems a bit worrying: https://alive2.llvm.org/ce/z/gabymq .  (See https://github.com/AliveToolkit/alive2/issues/727 for discussion of the unrolling options.)

https://github.com/llvm/llvm-project/pull/92560