[llvm] [LV] Add support for absolute difference partial reductions (PR #188043)

[Sander de Smalen via llvm-commits]

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@@ -6216,6 +6242,33 @@ matchExtendedReductionOperand(VPWidenRecipe *UpdateR, VPValue *Op,
   assert(is_contained(UpdateR->operands(), Op) &&
          "Op should be operand of UpdateR");
 
+  // Try matching an absolute difference operand of the form:
+  // `abs(sub(ext(A), ext(B)))`. We can rewrite these to
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sdesmalen-arm wrote:

```suggestion
  // `abs(sub(ext(A), ext(B)))`, which is later transformed into
```

https://github.com/llvm/llvm-project/pull/188043