[llvm] [VPlan] Add BranchOnMultiCond, use for early exit plans. (PR #172750)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> > Should the BranchOnTwoConds abstraction be introduced first as an NFC patch - with an expansion that keeps the current early exit from the vector loop folded into the latch, minimizing test diff and potential disruption, followed by a patch that optimizes the expansion by early-exiting from the vector loop (possibly followed by placing it even earlier), providing the significant performance gains outlined?

Should be done in the latest version, thanks!

https://github.com/llvm/llvm-project/pull/172750