[llvm] [AArch64] Fold uaddv(a) to a if the all lanes except the 0th are zeros (PR #159086)

[David Green via llvm-commits]

================
@@ -18995,6 +18995,16 @@ static SDValue performUADDVCombine(SDNode *N, SelectionDAG &DAG) {
     else if (SDValue R = performUADDVZextCombine(A, DAG))
       return R;
   }
+
+  // uaddv(A) --> A if all lanes of A are known to be zeros except the 0th lane.
+  MVT VT = N->getSimpleValueType(0);
+  MVT OpVT = A.getSimpleValueType();
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davemgreen wrote:

Are VT and OpVT always the same type for a AArch64ISD::UADDV? I believe they are, but they are not the most strictly defined opcodes we have, and the bitcast might be wrong otherwise. Can you add an assert for it?

https://github.com/llvm/llvm-project/pull/159086