[llvm] [LV] Introduce m_One and improve (0|1)-match (NFC) (PR #157419)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> Oh it looks like VPlanPatternMatch's int_pred_ty doesn't allow poison. If we want this to truly mirror LLVM IR's m_One then we should probably add a template argument to int_pred_ty to allow poison

I don't think it's necessary to mirror so faithfully.

https://github.com/llvm/llvm-project/pull/157419