[llvm] Port `NVPTXTargetLowering::LowerCONCAT_VECTORS` to SelectionDAG (PR #120030)

[Matt Arsenault via llvm-commits]

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@@ -3371,7 +3393,11 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(ExpandInsertToVectorThroughStack(SDValue(Node, 0)));
     break;
   case ISD::CONCAT_VECTORS:
-    Results.push_back(ExpandVectorBuildThroughStack(Node));
+    if (!TLI.isOperationExpand(ISD::EXTRACT_VECTOR_ELT, Node->getOperand(0).getValueType())) {
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arsenm wrote:

Might need a guard against scalable vectors 

https://github.com/llvm/llvm-project/pull/120030