[llvm] [LV] Use VPReductionRecipe for partial reductions (PR #147513)

[Graham Hunter via llvm-commits]

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@@ -2370,6 +2370,23 @@ struct VPFirstOrderRecurrencePHIRecipe : public VPHeaderPHIRecipe {
 #endif
 };
 
+// Possible variants of a reduction.
+
+// This reduction is ordered and in-loop.
+struct RdxOrderedInLoop {};
+// This reduction is in-loop.
+struct RdxInLoop {};
+// This reduction isn't partial, ordered or in-loop.
+struct RdxNormal {};
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huntergr-arm wrote:

`ComputeReductionResult` should be the final node in the middle block for a normal reduction (or more specialized recipes for AnyOf or Find'X' reductions). But there needs to be a header phi and an update operation inside the loop as well, we just don't reduce across lanes within the vector body.

https://github.com/llvm/llvm-project/pull/147513