[AsmWriter] Don't crash when printing a null operand bundle.

llvm/lib/IR/AsmWriter.cpp

for (unsigned i = 0, e = Call->getNumOperandBundles(); i != e; ++i) {
 
     bool FirstInput = true;
     auto WriterCtx = getContext();
     for (const auto &Input : BU.Inputs) {
       if (!FirstInput)
         Out << ", ";
       FirstInput = false;
 
+      if (Input == nullptr)
+        Out << "<null operand bundle!>";
+      else {
         TypePrinter.print(Input->getType(), Out);
         Out << " ";
         WriteAsOperandInternal(Out, Input, WriterCtx);
       }
+    }
 
     Out << ')';
   }
 
   Out << " ]";
 }
 
 void AssemblyWriter::printModule(const Module *M) {

llvm/unittests/IR/AsmWriterTest.cpp

TEST(AsmWriterTest, PrintAddrspaceWithNullOperand) {
   Call->dropAllReferences();
 
   std::string S;
   raw_string_ostream OS(S);
   Call->print(OS);
   std::size_t r = OS.str().find("<cannot get addrspace!>");
   EXPECT_TRUE(r != std::string::npos);
 }
+
+TEST(AsmWriterTest, PrintNullOperandBundle) {
+  LLVMContext C;
+  Type *Int32Ty = Type::getInt32Ty(C);
+  FunctionType *FnTy = FunctionType::get(Int32Ty, Int32Ty, /*isVarArg=*/false);
+  Value *Callee = Constant::getNullValue(FnTy->getPointerTo());
+  Value *Args[] = {ConstantInt::get(Int32Ty, 42)};
+  std::unique_ptr<BasicBlock> NormalDest(BasicBlock::Create(C));
+  std::unique_ptr<BasicBlock> UnwindDest(BasicBlock::Create(C));
+  OperandBundleDef Bundle("bundle", UndefValue::get(Int32Ty));
+  std::unique_ptr<InvokeInst> Invoke(
+      InvokeInst::Create(FnTy, Callee, NormalDest.get(), UnwindDest.get(), Args,
+                         Bundle, "result"));
+  // Makes the operand bundle null.
+  Invoke->dropAllReferences();
+  Invoke->setNormalDest(NormalDest.get());
+  Invoke->setUnwindDest(UnwindDest.get());
+
+  std::string S;
+  raw_string_ostream OS(S);
+  Invoke->print(OS);
+  EXPECT_TRUE(OS.str().find("<null operand bundle!>") != std::string::npos);
+}
 }