I've recently read how `std::move` can speed up code by just moving the values instead of copying them. So I made a test program to compare the speed using `std::vector`.

The code:

```
#include <iostream>
#include <vector>
#include <stdint.h>

#ifdef WIN32
#include <Windows.h>
#else
#include <sys/time.h>
#include <ctime>
#endif
#undef max

// Returns the amount of milliseconds elapsed since the UNIX epoch. Works on both
// windows and linux.

uint64_t GetTimeMs64()
{
#ifdef _WIN32
    // Windows
    FILETIME ft;
    LARGE_INTEGER li;

    // Get the amount of 100 nano seconds intervals elapsed since January 1, 1601 (UTC) and copy it
    // to a LARGE_INTEGER structure.
    GetSystemTimeAsFileTime(&ft);
    li.LowPart = ft.dwLowDateTime;
    li.HighPart = ft.dwHighDateTime;

    uint64_t ret = li.QuadPart;
    ret -= 116444736000000000LL; // Convert from file time to UNIX epoch time.
    ret /= 10000; // From 100 nano seconds (10^-7) to 1 millisecond (10^-3) intervals

    return ret;
#else
    // Linux
    struct timeval tv;

    gettimeofday(&tv, NULL);

    uint64 ret = tv.tv_usec;
    // Convert from micro seconds (10^-6) to milliseconds (10^-3)
    ret /= 1000;

    // Adds the seconds (10^0) after converting them to milliseconds (10^-3)
    ret += (tv.tv_sec * 1000);

    return ret;
#endif
}

static std::vector<std::string> GetVec1()
{
    std::vector<std::string> o(100000, "abcd");
    bool tr = true;
    if (tr)
        return std::move(o);
    return std::move(std::vector<std::string>(100000, "abcd"));
}

static std::vector<std::string> GetVec2()
{
    std::vector<std::string> o(100000, "abcd");
    bool tr = true;
    if (tr)
        return o;
    return std::vector<std::string>(100000, "abcd");
}

int main()
{
    uint64_t timer;
    std::vector<std::string> vec;

    timer = GetTimeMs64();
    for (int i = 0; i < 1000; ++i)
        vec = GetVec1();
    std::cout << GetTimeMs64() - timer << " timer 1(std::move)" << std::endl;
    timer = GetTimeMs64();
    for (int i = 0; i < 1000; ++i)
        vec = GetVec2();
    std::cout << GetTimeMs64() - timer << " timer 2(no move)" << std::endl;
    std::cin.get();
    return 0;
}

```

I got the following results:

**Release (x86) /O2. `tr = true`**

> 
> 4376 timer 1(std::move)
> 
> 
> 4191 timer 2(no move)
> 
> 
> 

**Release (x86) /O2. `tr = false`**

> 
> 7311 timer 1(std::move)
> 
> 
> 7301 timer 2(no move)
> 
> 
> 

The results between the 2 timers are really close and don't really differ that much. I already assumed this is because of **Return value optimization (RVO)** which means that my returns by value are already moved by the compiler without me knowing, right?

So then I ran new tests without any optimizations to make sure I was right.
The results:

**Release (x86) /Od. `tr = true`**

> 
> 40860 timer 1(std::move)
> 
> 
> 40863 timer 2(no move)
> 
> 
> 

**Release (x86) /Od. `tr = false`**

> 
> 83567 timer 1(std::move)
> 
> 
> 82075 timer 2(no move)
> 
> 
> 

Now even though the difference between /O2 and /Od is really significant, the difference between no move or `std::move` (and even between `tr` being `true` or `false`) is minimal.

Does this mean that even though optimizations are disabled, the compiler is allowed to apply `RVO` or is `std::move` not as fast as I thought I'd be?