[llvm] [SDAG] Shrink (abd? (?ext x) (?ext y)) (PR #171865)

[Simon Pilgrim via llvm-commits]

================
@@ -5787,6 +5787,21 @@ SDValue DAGCombiner::visitABD(SDNode *N) {
       DAG.SignBitIsZero(N0) && DAG.SignBitIsZero(N1))
     return DAG.getNode(ISD::ABDU, DL, VT, N1, N0);
 
+  // fold (abds (?ext x), (?ext y)) -> (zext (abd? x, y))
----------------
RKSimon wrote:

```suggestion
  // fold (abd? (?ext x), (?ext y)) -> (zext (abd? x, y))
```

https://github.com/llvm/llvm-project/pull/171865