[llvm] [VPlan] Support tailfolded loops in multi-use-reductions (PR #214455)

[Philipp Rados via llvm-commits]

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prados-oc wrote:

Yes I simplified the tests in general. I realized they are  almost the same to the ones in `llvm/test/Transforms/LoopVectorize/select-smin-last-index.ll`. However I think this duplication should be fine as the new tests in `llvm/test/Transforms/LoopVectorize/RISCV/tail-folding-reduction.ll` check RISCV specific IR.

https://github.com/llvm/llvm-project/pull/214455