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

[Sushant Gokhale via llvm-commits]

================
@@ -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)
+    return SDValue();
+
+  // Check if all the loads are simple.
+  if (!L00->isSimple() || !L01->isSimple())
+    return SDValue();
+
+  // Check if the loads have the same chain.
+  if (L00->getChain() != L01->getChain())
----------------
sushgokh wrote:

changed.

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