Simple test to see how 'noexcept' improves performance of that code

noexcept_move.cpp

// noexcept
// $ g++ -Wall -pedantic -std=c++1y -O3 -march=native -DNOEXCEPT="noexcept" noexcept_move.cpp && ./a.out
// cap.: 10000000
// 28 ms

// no noexcept
// $ g++ -Wall -pedantic -std=c++1y -O3 -march=native -DNOEXCEPT="" noexcept_move.cpp && ./a.out
// cap.: 10000000
// 251 ms

#include <chrono>
#include <iostream>
#include <string>
#include <vector>

using namespace std;
using namespace std::chrono;

class X
{
private:
    string s;

public:
    X() : s(100, 'a') {}
    X(const X &x) = default;
    X (X &&x) NOEXCEPT : s(move(x.s)) {}
};

int main()
{
    vector<X> v(10000000);

    cout << "cap.: " << v.capacity() << endl;

    auto t0 = high_resolution_clock::now();

    v.emplace_back();

    auto t1 = high_resolution_clock::now();
    auto d = duration_cast<milliseconds>(t1 - t0);
    cout << d.count() << " ms\n";

    return 0;
}