Speed of accessing a pointer

I'm rewriting all of the data structures I learned in school as an exercise to reinforce my understanding of the fundamentals of computer science, but I'm attempting to optimize my naïve implementations that I created when I was younger.

This lead me to a question:

I have these few lines from my linked list implementation where temp is used in both variations...

Node<T> *temp = head;

if(temp == nullptr) {
    ...
}

... // temp used here

My linked list also has an attribute long listSize, so the above line is analog to

if(!listSize) {
   ...
}

... // temp used here, too.

This is obvious. What is less obvious (to me) is which of these would be faster for the computer.

From what (little) I understand about pointers, any operation with them is fairly expensive, which leads me to believe that the former might be less optimal than the latter; however, I'm not entirely sure.

Can anyone help clear up this nuance for me?

Thanks, erip