[llvm] [DAG] narrowExtractedVectorBinOp - ensure we limit late node creation to LegalOperations only (PR #72130)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Sorry this was my first attempt at a patch series and I screwed it up - converting to draft until I've fixed it up

https://github.com/llvm/llvm-project/pull/72130