[AsmWriter] Don't crash when printing addrspace and the operand is null

[vporpo]

Summary

This helps print instructions with detached operands in the debugger.

[aeubanks]

matches other error handling code in AsmWriter, lg

[arsenm]

llvm/lib/IR/AsmWriter.cpp

4019–4022

Drive by comment but this behavior is super annoying, it should just always print non-0 like everywhere else

[vporpo]

Rebase

llvm/lib/IR/AsmWriter.cpp

void AssemblyWriter::printInfoComment(const Value &V) {
 
   if (AnnotationWriter)
     AnnotationWriter->printInfoComment(V, Out);
 }
 
 static void maybePrintCallAddrSpace(const Value *Operand, const Instruction *I,
                                     raw_ostream &Out) {
   // We print the address space of the call if it is non-zero.
+  if (Operand == nullptr) {
+    Out << " <cannot get addrspace!>";
+    return;
+  }
   unsigned CallAddrSpace = Operand->getType()->getPointerAddressSpace();
   bool PrintAddrSpace = CallAddrSpace != 0;
   if (!PrintAddrSpace) {
     const Module *Mod = getModuleFromVal(I);
     // We also print it if it is zero but not equal to the program address space
     // or if we can't find a valid Module* to make it possible to parse
     // the resulting file even without a datalayout string.
     if (!Mod || Mod->getDataLayout().getProgramAddressSpace() != 0)
       PrintAddrSpace = true;
   }
   if (PrintAddrSpace)
     Out << " addrspace(" << CallAddrSpace << ")";
 }
 
 // This member is called for each Instruction in a function..
 void AssemblyWriter::printInstruction(const Instruction &I) {

llvm/unittests/IR/AsmWriterTest.cpp

TEST(AsmWriterTest, DumpDIExpression) {
   DIExpression *Expr = DIExpression::get(Ctx, Ops);
   std::string S;
   raw_string_ostream OS(S);
   Expr->print(OS);
   EXPECT_EQ("!DIExpression(DW_OP_constu, 4, DW_OP_minus, DW_OP_deref)",
             OS.str());
 }
 
+TEST(AsmWriterTest, PrintAddrspaceWithNullOperand) {
+  LLVMContext Ctx;
+  std::unique_ptr<Module> M;
+  SmallVector<Type *, 3> FArgTypes;
+  FArgTypes.push_back(Type::getInt64Ty(Ctx));
+  FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx), FArgTypes, false);
+  Function *F = Function::Create(FTy, Function::ExternalLinkage, "", M.get());
+  Argument *Arg0 = F->getArg(0);
+  Value *Args[] = {Arg0};
+  std::unique_ptr<CallInst> Call(CallInst::Create(F, Args));
+  // This will make Call's operand null.
+  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);
+}
 }