diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -4035,7 +4035,25 @@
     LC = RTLIB::MULO_I64;
   else if (VT == MVT::i128)
     LC = RTLIB::MULO_I128;
-  assert(LC != RTLIB::UNKNOWN_LIBCALL && "Unsupported XMULO!");
+
+  if (LC == RTLIB::UNKNOWN_LIBCALL || !TLI.getLibcallName(LC)) {
+    // FIXME: This is not an optimal expansion, but better than crashing.
+    EVT WideVT =
+        EVT::getIntegerVT(*DAG.getContext(), VT.getScalarSizeInBits() * 2);
+    SDValue LHS = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, N->getOperand(0));
+    SDValue RHS = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, N->getOperand(1));
+    SDValue Mul = DAG.getNode(ISD::MUL, dl, WideVT, LHS, RHS);
+    SDValue MulLo, MulHi;
+    SplitInteger(Mul, MulLo, MulHi);
+    SDValue SRA =
+        DAG.getNode(ISD::SRA, dl, VT, MulLo,
+                    DAG.getConstant(VT.getScalarSizeInBits() - 1, dl, VT));
+    SDValue Overflow =
+        DAG.getSetCC(dl, N->getValueType(1), MulHi, SRA, ISD::SETNE);
+    SplitInteger(MulLo, Lo, Hi);
+    ReplaceValueWith(SDValue(N, 1), Overflow);
+    return;
+  }
 
   SDValue Temp = DAG.CreateStackTemporary(PtrVT);
   // Temporary for the overflow value, default it to zero.