[llvm] [VPlan] Preserve DT (and SCEV) in VPlan-native path (PR #93287)

[via llvm-commits]

https://github.com/ayalz approved this pull request.

Thanks for splitting, ship it, with a minor nit. Comment of @tschuett about VPSCEV can be addressed independently.

https://github.com/llvm/llvm-project/pull/93287