[llvm] [LV] Bundle sub reductions into VPExpressionRecipe (PR #147255)

[Sander de Smalen via llvm-commits]

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@@ -1649,12 +1649,12 @@ class TargetTransformInfo {
       TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput) const;
 
   /// Calculate the cost of an extended reduction pattern, similar to
-  /// getArithmeticReductionCost of an Add reduction with multiply and optional
-  /// extensions. This is the cost of as:
-  /// ResTy vecreduce.add(mul (A, B)).
-  /// ResTy vecreduce.add(mul(ext(Ty A), ext(Ty B)).
+  /// getArithmeticReductionCost of an Add/Sub reduction with multiply and
+  /// optional extensions. This is the cost of as:
+  /// ResTy vecreduce.add/sub(mul (A, B)).
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sdesmalen-arm wrote:

nit:
```suggestion
  /// ResTy vecreduce.add/sub(mul(A, B)).
```

https://github.com/llvm/llvm-project/pull/147255