[llvm] [VPlan] Use vputils helper in Blend::usesFirstLaneOnly (NFC) (PR #189697)

[Florian Hahn via llvm-commits]

https://github.com/fhahn approved this pull request.

LGTM with comment removed, thanks

> Confused, isn't the replaced code exactly the same as the code in vputils::onlyFirstLaneUsed, making this an NFC?

Ah yes, was thinking of another PR.

https://github.com/llvm/llvm-project/pull/189697