[llvm] [LoopVectorizer] Propagate underlying instruction to the cloned instances of VPPartialReductionRecipes (PR #123638)

[Florian Hahn via llvm-commits]

fhahn wrote:

IIUC this should only change VPlan printing or is the underlying instr used by other parts of the recipe? If it's the former, I guess to could be tested by check the printed VPlan during epilogue vectorization?

https://github.com/llvm/llvm-project/pull/123638