[llvm] [DA] Use ScalarEvolution::isKnownPredicate (PR #170919)

[Ryotaro Kasuga via llvm-commits]

================

----------------
kasuga-fj wrote:

Judging from this change, symbolicRDIV seems to be almost meaningless. If I understand correctly, we cannot even prove simple inequalities like `n <s n + 1`, as we cannot prove `n + 1` doesn't overflow.

https://github.com/llvm/llvm-project/pull/170919