[llvm] [polly] [SCEV] Introduce SDiv expressions (PR #216862)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> If you're interested, you can take a look at https://github.com/llvm/llvm-project/pull/212816 for the stride speculation on the LAA side, and https://github.com/llvm/llvm-project/pull/216760 for digging out the stride for strided accesses on the VPlan side.

For the motivation, I think it would be more effective to provide a concrete example of a case where an `SDiv` SCEV expression is needed. Ideally this would be part of the description.

This would be clearer than providing links to the patches; AFAICT they only show what we can currently handle, with a bit of extra work to dig out the stride.

https://github.com/llvm/llvm-project/pull/216862