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

[Florian Hahn via llvm-commits]

================
@@ -22,6 +22,25 @@ class LoopVectorizationLegality;
 class LoopVectorizationCostModel;
 class TargetLibraryInfo;
 struct HistogramInfo;
+class TargetTransformInfo;
+
+/// A chain of instructions that form a partial reduction.
+/// Designed to match: reduction_bin_op (bin_op (extend (A), (extend (B))),
+/// accumulator)
+struct PartialReductionChain {
+  /// The top-level binary operation that forms the reduction to a scalar
+  /// after the loop body
+  Instruction *Reduction;
+  /// The extension of each of the inner binary operation's operands
+  Instruction *ExtendA;
+  Instruction *ExtendB;
+
+  Instruction *BinOp;
+
+  /// The scaling factor between the size of the reduction type and the
+  /// (possibly extended) inputs
----------------
fhahn wrote:

nit: 
```suggestion
  /// (possibly extended) inputs.
```

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