LLVM: Creating a CallInst with a null pointer operand

Question

I'm trying to use the LLVM C++ bindings to write a pass which generates the following IR

%1 = call i64 @time(i64* null) #3

@time here is the C standard library time() function.

Here's the code I've written

void Pass::Insert(BasicBlock *bb, Type *timety, Module *m) {
  Type *timetype[1];
  timetype[0] = timety;
  ArrayRef<Type *> timeTypeAref(timetype, 1);
  Value *args[1];
  args[0] = ConstantInt::get(timety, 0, false);
  ArrayRef<Value *> argsRef(args, 1);
  FunctionType *signature = FunctionType::get(timety, false);
  Function *timeFunc =
      Function::Create(signature, Function::ExternalLinkage, "time", m);
  IRBuilder<> Builder(&*(bb->getFirstInsertionPt()));
  AllocaInst *a1 = Builder.CreateAlloca(timety, nullptr, Twine("a1"));
  CallInst *c1 = Builder.CreateCall(timeFunc, args, Twine("time"));
}

This compiles, but results in the following error when run

Incorrect number of arguments passed to called function!
  %time = call i64 @time(i64 0)

As I understand this, I need to pass an int64 pointer which deferences to nullptr, but I'm unable to figure out how to do that.

Answer 1

LLVM provides a ConstantPointerNull class which does exactly what I want - it returns a null pointer of the required type.

All that needs to be changed is the line beginning with args[0] = ... to args[0] = ConstantPointerNull::get(PointerType::get(timety, 0));.