Say I have something like this, which one executes faster?

Code:
if(m_submitmode)m_submitmode=false;
OR

Code:
m_submitmode=false;
This is assuming m_submitmode will not always be true, but I want it to be false at that point. Is it faster to just assign it false, or should I be checking first? Now if it is true, the first statement will be slower as it has to do two things, but if it's already false, will the first one be faster?

This is extremely small time we are talking about and wont really make a difference on a small or even medium scale but it's one of those things that is fairly easy to do so may as well pick the faster route.