Taking vector size() out of loop condition to optimize

Question

fibs is a std::vector. Using g++, I was advised to take fibs.size() out of the loop, to save computing it each time (because the vector could change)

int sum = 0;
for(int i = 0; i < fibs.size(); ++i){
    if(fibs[i] % 2 == 0){
        sum += fibs[i];
    }
}

Surely there is some dataflow analysis in the compiler that would tell us that fibs won't change size. Is there? Or should I set some other variable to be fibs.size() and use that in the loop condition?

Answer 1

The compiler will likely determine that it won't change. Even if it did, size() for vectors is an O(1) operation.