[llvm-branch-commits] [llvm] [SelectionDAG] Fix incorrect expansion of `CONVERT_TO_ARBITRARY_FP` (PR #221358)

[Matt Arsenault via llvm-branch-commits]

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@@ -9385,12 +9404,31 @@ SDValue TargetLowering::expandCONVERT_TO_ARBITRARY_FP(SDNode *Node,
   EVT FrexpExpScalarVT =
       getValueType(DAG.getDataLayout(), Type::getInt32Ty(*DAG.getContext()));
   EVT FrexpExpVT = SrcVT.changeElementType(*DAG.getContext(), FrexpExpScalarVT);
+  if (!FrexpExpVT.isVector() && !isTypeLegal(FrexpExpVT)) {
+    if (getTypeAction(*DAG.getContext(), FrexpExpScalarVT) !=
+        TypePromoteInteger) {
+      // We only know how to handle situations where the legal type is wider.
+      DAG.getContext()->emitError("CONVERT_TO_ARBITRARY_FP: the requested i32 "
+                                  "type for its legalization is not supported");
+      return SDValue();
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arsenm wrote:

Should return poison and ideally would test this case 

https://github.com/llvm/llvm-project/pull/221358