C++ STL: The third parameter of sort(), why the functor is faster than inline function?

Question

inline bool mycmp(int i, int j) {
    return (i < j);
}

class mycmp2 {
public:
    bool operator()(int i, int j) {
        return (i < j);
    }
};

above is my example. I want know why the functor one is faster than the inline funcion!

//test example:
#include <iostream>
#include <vector>
#include <algorithm>
#include <ctime>
struct CompareFunctor {
    bool operator()(int a, int b) const {
        return a < b;
    }
};

inline bool compareFunction(int a, int b) {
    return a < b;
}

int main() {
    std::vector<int> nums(10000000);
    std::generate(nums.begin(), nums.end(), std::rand);

    {
        std::vector<int> numsObj = nums;
        clock_t start = clock();
        std::sort(numsObj.begin(), numsObj.end(), CompareFunctor());
        clock_t end = clock();
        double duration = (double)(end - start) / CLOCKS_PER_SEC;
        std::cout << "use functor：" << duration << " second" << std::endl;
    }

    {
        std::vector<int> numsFunc = nums;
        clock_t start = clock();
        std::sort(numsFunc.begin(), numsFunc.end(), compareFunction);
        clock_t end = clock();
        double duration = (double)(end - start) / CLOCKS_PER_SEC;
        std::cout << "use inline function：" << duration << " second" << std::endl;
    }

    return 0;
}

Translation: "The above is the code I used for testing, and the result shows that the functor is faster. I would like to know why. It seems that the functor is also an inline function at the underlying level. Is there any optimization performed by the compiler?"