[llvm] [llvm] Adding scalarization of `llvm.vector.insert` (PR #71614)

[Matt Arsenault via llvm-commits]

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@@ -766,6 +769,22 @@ SDValue DAGTypeLegalizer::ScalarizeVecOp_BITCAST(SDNode *N) {
                      N->getValueType(0), Elt);
 }
 
+/// If the value to subvector is a vector that needs to be scalarized, it must
+/// be <1 x ty>. Return the element instead.
+SDValue DAGTypeLegalizer::ScalarizeVecOp_INSERT_SUBVECTOR(SDNode *N,
+                                                          unsigned OpNo) {
+  // If the destination vector is unary, we can just return the source vector
+  auto Src = GetScalarizedVector(N->getOperand(1));
+  if (OpNo == 0) {
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arsenm wrote:

Result types are always legalized first and need to update the first operand along with them. You could try just asserting OpNo == 1

https://github.com/llvm/llvm-project/pull/71614