[llvm] [ConstraintElim] Try to get induction step/start/flags from IR (NFC-ish) (PR #209284)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> LGTM, assuming we are fine trading potential precision on flags on AddRecs that SCEV might have previously inferred for compile-time improvement (tracker's data seem unavailable right now?).

That's a fair point, I could not find any end-to-end regressions, but was able to construct cases where we fail to remove checks with -O3 due to not checking SCEV (added a new test file for those cases ``llvm/test/Transforms/ConstraintElimination/induction-nowrap-from-scev-not-ir.ll`); the number of those cases is quite small in practice, so I updated the code to fall back on SCEV monotonicity check



https://github.com/llvm/llvm-project/pull/209284