[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Florian Hahn via llvm-commits]

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@@ -1962,6 +1970,35 @@ class VPReductionPHIRecipe : public VPHeaderPHIRecipe {
   bool isInLoop() const { return IsInLoop; }
 };
 
+class VPPartialReductionRecipe : public VPRecipeWithIRFlags {
+  unsigned Opcode;
+  unsigned Scale;
+
+public:
+  template <typename IterT>
+  VPPartialReductionRecipe(Instruction &I, iterator_range<IterT> Operands,
+                           unsigned Scale)
+      : VPRecipeWithIRFlags(VPDef::VPPartialReductionSC, Operands, I),
+        Opcode(I.getOpcode()), Scale(Scale) {}
+  ~VPPartialReductionRecipe() override = default;
+  VPPartialReductionRecipe *clone() override {
+    auto *R =
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fhahn wrote:

This is only used for epilogue vectorization, should be unreachable if not supported/tested yet

https://github.com/llvm/llvm-project/pull/92418