C++ performance of global variables

Question

For clarification: I know how evil globals are and when not to use them :)

• Is there any performance penalty when accessing/setting a global variable vs. a loca

Answer 1

The answer is tied to the overall structure of the program.

For example, I just disassembled this, and in both cases the looping variable was moved into a register, after which there was no difference:

int n = 9;
int main()
{
    for (n = 0; n < 10; ++n)
        printf("%d", n);

    for (int r = 0; r < 10; ++r)
        printf("%d", r);

    return 0;
}

Just to be sure, I did similar things with classes and again saw no difference. But if the global is in a different compilation unit that might change.