[llvm] [VPlan] Add visited set for onlyFirstLaneUsed() (PR #228438)

[Nikita Popov via llvm-commits]

nikic wrote:

I'm not sure I understand your suggestion. Do you want to change onlyFirstLaneUsed() to directly handle the recursive cases so that the visited set stays local to that function (and I guess it could also be non-recursive via worklist)? Though then we'd have to be careful that it handles all the recursive cases, which may get out of sync with the usesFirstLaneOnly() implementations.

Probably I misunderstood what you have in mind.

https://github.com/llvm/llvm-project/pull/228438