diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -2334,6 +2334,7 @@
   InstructionCost getArithmeticReductionCost(unsigned Opcode, VectorType *Ty,
                                              std::optional<FastMathFlags> FMF,
                                              TTI::TargetCostKind CostKind) {
+    assert(Ty && "Unknown reduction vector type");
     if (TTI::requiresOrderedReduction(FMF))
       return getOrderedReductionCost(Opcode, Ty, CostKind);
     return getTreeReductionCost(Opcode, Ty, CostKind);