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

[Sam Tebbs via llvm-commits]

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@@ -2392,6 +2392,29 @@ struct VPFirstOrderRecurrencePHIRecipe : public VPHeaderPHIRecipe {
 #endif
 };
 
+// Possible variants of a reduction.
+
+// This reduction is ordered and in-loop.
+struct RdxOrdered {};
+// This reduction is in-loop.
+struct RdxInLoop {};
+// This reduction is unordered with the partial result scaled down by some
+// factor.
+struct RdxUnordered {
+  unsigned VFScaleFactor;
+};
+using ReductionStyle = std::variant<RdxOrdered, RdxInLoop, RdxUnordered>;
+
+static ReductionStyle getReductionStyle(bool InLoop, bool Ordered,
+                                        unsigned ScaleFactor) {
+  assert((!Ordered || InLoop) && "Ordered implies in-loop");
+  if (Ordered)
+    return RdxOrdered{};
+  if (InLoop)
+    return RdxInLoop{};
+  return RdxUnordered{/*VFScaleFactor=*/ScaleFactor};
+}
+
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SamTebbs33 wrote:

Done.

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