[llvm] [VPlan] Remove VPBlendRecipe and replace with select VPInstructions (PR #150369)

[Luke Lau via llvm-commits]

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lukel97 wrote:

I think it's because VPBlendRecipe was considered as generating vectors in `willGenerateVectors`, but now it's just a VPInstruction it returns false. It looks like nothing in this plan generates a vector anyway so it probably shouldn't be vectorized.

https://github.com/llvm/llvm-project/pull/150369