[llvm] [VPlan] Consistently use (Part, 0) for first lane scalar values (PR #80271)

[via llvm-commits]

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@@ -1779,6 +1788,7 @@ void VPFirstOrderRecurrencePHIRecipe::print(raw_ostream &O, const Twine &Indent,
 #endif
 
 void VPReductionPHIRecipe::execute(VPTransformState &State) {
+  // TODO: Store scalar value for in-loop reductions as {Part, 0}.
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ayalz wrote:

TODO done?

https://github.com/llvm/llvm-project/pull/80271