[llvm] [RISCV][WIP] Optimize sum of absolute differences pattern. (PR #82722)

[Craig Topper via llvm-commits]

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@@ -13176,6 +13176,61 @@ static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG,
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false, Subtarget);
 }
 
+// Look for (abs (sub (zext X), (zext Y))).
+// Rewrite as (zext (sub (zext (max X, Y), (min X, Y)))) if the user is an add
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topperc wrote:

> Is lowering (abs (sub X, Y)) to (sub (umax x, y), (umin x, y)) worthwhile doing on its own, ignoring pulling through the zexts for now?

I'm not sure that's valid.

https://github.com/llvm/llvm-project/pull/82722