[llvm] [ConstraintElim] Bound non-increasing header IVs by start value. (PR #217921)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw commented:

> it will never exceed the start value and we can add PN s>=
StartValue.

PN s<= StartValue


https://github.com/llvm/llvm-project/pull/217921