[llvm] [VPlan] Impl VPlan-based pattern match for ExtendedRed and MulAccRed (NFCI) (PR #113903)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Thanks for the update, some  initial suggestions inline.

Would be good if we could avoid any references to IR operands, and possibly unify both recipes (and avoid duplication with the existing reduction recipe)

https://github.com/llvm/llvm-project/pull/113903