[llvm] [AArch64] Convert UADDV(add(zext, zext)) into UADDLV(concat). (PR #78301)

[David Sherwood via llvm-commits]

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@@ -16528,6 +16531,34 @@ static SDValue performUADDVAddCombine(SDValue A, SelectionDAG &DAG) {
     return DAG.getNode(Opcode, SDLoc(A), VT, Ext0.getOperand(0));
   };
 
+  // We can convert a UADDV(add(zext(64-bit source), zext(64-bit source))) into
+  // UADDLV(concat), where the concat represents the 64-bit zext sources.
+  auto DetectZextConcat = [&](SDValue A, SelectionDAG &DAG) {
+    // Look for add(zext(64-bit source), zext(64-bit source)), returning
+    // UADDLV(concat(zext, zext)) if found.
+    if (A.getOpcode() != ISD::ADD)
+      return SDValue();
+    EVT VT = A.getValueType();
+    if (VT != MVT::v4i32)
+      return SDValue();
+    SDValue Op0 = A.getOperand(0);
+    SDValue Op1 = A.getOperand(1);
+    if (Op0.getOpcode() != ISD::ZERO_EXTEND)
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david-arm wrote:

This might explain some of the odd regressions in the existing tests perhaps?

https://github.com/llvm/llvm-project/pull/78301