[llvm] [VPlan] Use DomTreeUpdater to automatically update DT for vector loop. (PR #92525)

[via llvm-commits]

https://github.com/ayalz commented:

Nice cleanup!

Worth separating into two NFC's: one simplifying how legacy updates its DT, and another which teaches native to start update its DT?

Worth noting that parts of DT external to VPlan's scope are still updated directly (i.e., skeletal parts).

https://github.com/llvm/llvm-project/pull/92525