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

[Sander de Smalen via llvm-commits]

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@@ -6030,6 +6030,31 @@ optimizeExtendsForPartialReduction(VPSingleDefRecipe *BinOp,
     return BinOp;
   }
 
+  // reduce.add(abs(sub(ext(A), ext(B))))
+  // -> reduce.add(ext(absolute-difference(A, B)))
+  VPValue *X, *Y;
+  if (match(BinOp,
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sdesmalen-arm wrote:

nit: more an observation that `BinOp` is not a binary operator if it is `Intrinsic::abs`. Maybe you can rename this in an NFC follow up for something.

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