[llvm] [LV] Make partial-reduction naming consistent (NFC) (PR #222377)

[Sander de Smalen via llvm-commits]

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@@ -4947,12 +4947,12 @@ struct ExtendedReductionOperand {
   ReductionExtend ExtendA, ExtendB;
 };
 
-/// A chain of recipes that form a partial reduction. Matches either
+/// A collection of recipes that form a partial reduction. Matches either
 ///   reduction_bin_op (extended op, accumulator), or
 ///   reduction_bin_op (accumulator, extended op).
 /// The possible forms of the "extended op" are listed in
 /// matchExtendedReductionOperand.
-struct VPPartialReductionChain {
+struct VPPartialReduction {
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sdesmalen-arm wrote:

I personally would favour '`PartialReductionDescriptor`' as it merely describes the elements used to form a partial reduction operation later. It doesn't link to any other `VPPartialReduction` objects, so from that perspective the object itself doesn't directly describe that it's part of a chain either, only the wider context that uses it (i.e. `createPartialReductions`) knows that, so I think it's fine to omit it from the name.

I also believe we can drop the `VP` because it's just an internal utility struct in this file (it's not related to anything in VPlan).

https://github.com/llvm/llvm-project/pull/222377