[llvm] [AArch64] Remove EXT instr before UZP when extracting elements from vector (PR #91328)

[David Green via llvm-commits]

================
@@ -21448,6 +21448,29 @@ static SDValue performUzpCombine(SDNode *N, SelectionDAG &DAG,
   SDValue Op1 = N->getOperand(1);
   EVT ResVT = N->getValueType(0);
 
+  // uzp(extract_lo(x), extract_hi(x)) -> extract_lo(uzp x, x)
+  if (Op0.getOpcode() == ISD::EXTRACT_SUBVECTOR &&
+      Op1.getOpcode() == ISD::EXTRACT_SUBVECTOR &&
+      Op0.getOperand(0) == Op1.getOperand(0)) {
+
+    SDValue SourceVec = Op0.getOperand(0);
+    uint64_t ExtIdx0 = Op0.getConstantOperandVal(1);
+    uint64_t ExtIdx1 = Op1.getConstantOperandVal(1);
+    uint64_t NumElements = SourceVec.getValueType().getVectorMinNumElements();
+    if (ExtIdx0 == 0 && ExtIdx1 == NumElements / 2) {
+      EVT OpVT = Op0.getOperand(1).getValueType();
+      EVT WidenedResVT = ResVT.getDoubleNumVectorElementsVT(*DAG.getContext());
+      SDValue uzp2 =
+          DAG.getNode(N->getOpcode(), DL, WidenedResVT, SourceVec, SourceVec);
+      return DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, ResVT, uzp2,
+                         DAG.getConstant(0, DL, OpVT));
+    }
+  }
+
+  // following optimization only work with uzp1
----------------
davemgreen wrote:

-> The following optimizations only work with uzp1

https://github.com/llvm/llvm-project/pull/91328