[llvm] [SelectionDAG] Merge consecutive loads feeding as shuffle operands (PR #207303)

[Simon Pilgrim via llvm-commits]

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@@ -27001,6 +27007,125 @@ static SDValue combineConcatVectorOfShuffleAndItsOperands(
   return DAG.getVectorShuffle(VT, dl, ShufOps[0], ShufOps[1], Mask);
 }
 
+// concat(shuffle(mask0, loadA, loadB), shuffle(mask1, loadA, loadB))
+// -> shuffle(concat(mask0, mask1), loadAB, poison)
+// only if loadA and loadB can be proven consecutive.
+static SDValue combineConcatVectorOfShuffles(SDNode *N, SelectionDAG &DAG,
+                                             const TargetLowering &TLI,
+                                             bool LegalTypes) {
+  // Check if concat has only two operands
+  if (N->getNumOperands() != 2)
+    return SDValue();
+
+  // Check if both operands are shuffle
+  if (N->getOperand(0).getOpcode() != ISD::VECTOR_SHUFFLE ||
+      N->getOperand(1).getOpcode() != ISD::VECTOR_SHUFFLE)
+    return SDValue();
+
+  // Check if both shuffles have both of its operands as loads and they are same
+  // respectively.
+  auto *L00 = dyn_cast<LoadSDNode>(N->getOperand(0).getOperand(0));
+  auto *L01 = dyn_cast<LoadSDNode>(N->getOperand(0).getOperand(1));
+  auto *L10 = dyn_cast<LoadSDNode>(N->getOperand(1).getOperand(0));
+  auto *L11 = dyn_cast<LoadSDNode>(N->getOperand(1).getOperand(1));
+  if (!L00 || !L01 || !L10 || !L11)
+    return SDValue();
+  if (L00 != L10 || L01 != L11)
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RKSimon wrote:

Just use sd_match for all of this

https://github.com/llvm/llvm-project/pull/207303