Assignment vs if not equal to then assign... Swift being the language I care most about

I have some code that will get ran every so often. As far as performance goes, is there any difference between the following to satements, and if so, which one is faster?

num = 4

vs

if num != 4 {
    num = 4
}

I understand the difference is probably minimal, but I have had this question run through my mind on occasion. Also I would be interested in the closely related questions to this that might use a Bool or String instead of an Int.