[llvm] [VPlan] Create header phis once, after constructing VPlan0 (NFC). (PR #168291)

[via llvm-commits]

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@@ -8357,6 +8265,9 @@ VPRecipeBuilder::tryToCreatePartialReduction(VPInstruction *Reduction,
        cast<VPReductionRecipe>(BinOpRecipe)->isPartialReduction()))
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ayalz wrote:

Unrelated: good to explain the purpose of `swap`; especially as it applies both when BinOp is defined by a ReductionPHI and when it's defined by a (Partial)Reduction recipe, and that the swap excludes `BinOpRecipe`.

https://github.com/llvm/llvm-project/pull/168291