[llvm] [VPlan] Don't fold UDiv in replicate regions. (PR #175460)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Hm, I'd have never guessed: why are VPInstructions not supported in VPReplicateRegions? I understand that this is probably a design flaw, but I'm interested in some design history?


Replicate regions are a bit of a legacy construct which are coupled with replicate (and scalar-iv-steps) recipes since the initial VPlan introduction. Lots of things changed since then, but not yet the handling of replicate regions. Down the line, the plan is to explicitly dissolve replicate regions as well (https://github.com/llvm/llvm-project/pull/170212), eventually completely removing the implicit VPTransformState::Lane. After that, it should be possible to support VPInstructions in replicate regions as well

https://github.com/llvm/llvm-project/pull/175460