[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
----------------
fhahn wrote:

nit: 
```suggestion
  /// after the loop body.
```

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