[llvm] Reland "[LoopVectorizer] Add support for partial reductions" (PR #120721)

[Sam Tebbs via llvm-commits]

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@@ -3367,6 +3427,8 @@ void VPFirstOrderRecurrencePHIRecipe::print(raw_ostream &O, const Twine &Indent,
 void VPReductionPHIRecipe::execute(VPTransformState &State) {
   auto &Builder = State.Builder;
 
+  auto VF = State.VF.divideCoefficientBy(VFScaleFactor);
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SamTebbs33 wrote:

This line wasn't changed, but the second commit is the only difference to the landed diff. The first commit and the landed one would have the same commit ID but I squashed all of the fixup commits from the old branch first.

A comment is a great idea, done!

https://github.com/llvm/llvm-project/pull/120721