[llvm] [VPlan] Move predication to VPlanTransform (NFC) (WIP). (PR #128420)

[Florian Hahn via llvm-commits]

fhahn wrote:

Still WIP, but early-exits are now handled properly as well, by retaining exit branches during initial construction.

This needs to be split up, which I'll start once https://github.com/llvm/llvm-project/pull/129402 lands

https://github.com/llvm/llvm-project/pull/128420