[llvm] [SCEV] Add non-poison/non-zero checks on denominators (PR #117152)

[Nikita Popov via llvm-commits]

nikic wrote:

> Do we need an AllowRefinement argument for SCEV constructors and disallow refinement in these rewriters?

Assuming this special case isn't particularly important, can we get away with just checking that the SCEV doesn't contain UB / poison?

https://github.com/llvm/llvm-project/pull/117152