[llvm] Reland "[LoopVectorizer] Add support for chaining partial reductions #120272" (PR #124282)

[Sam Tebbs via llvm-commits]

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@@ -142,9 +142,9 @@ class VPRecipeBuilder {
   /// Returns null if no scaled reduction was found, otherwise a pair with a
   /// struct containing reduction information and the scaling factor between the
   /// number of elements in the input and output.
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SamTebbs33 wrote:

The comment will need updating too.

https://github.com/llvm/llvm-project/pull/124282