在 C++14 中关闭 RVO/NRVO 时，如何返回对象？

问：

我正在学习移动语义，所以我写了一个小程序，如下所示：

#include <iostream>

using namespace std;

int one_int = 123;

class A {
public:
    int *a;

    A(int *ptr) : a(ptr) {
        cout << "In A's constructor..." << endl;
    }

    A(const A &other) {
        cout << "In A's copy constructor..." << endl;
        a = other.a;
    }

    A(A &&other) noexcept {
        cout << "In A's move constructor..." << endl;
        a = other.a;
        other.a = nullptr;
    }

    ~A() {
        cout << "In A's destructor..." << endl;
    }
};

A make_obj() {
    cout << "In make_obj..." << endl;
    return A(&one_int);
}

A make_obj_by_move(A &&source) {
    cout << "In make_obj_by_move..." << endl;
    return A(static_cast<A&&>(source));
}

A make_obj_by_copy(A source) {
    cout << "In make_obj_by_copy..." << endl;
    return A(source);
}

int main() {
    A obj2 = make_obj_by_move(make_obj());
    cout << endl;
    A obj1 = make_obj_by_copy(make_obj());
    cout << endl;
    // to ensure that the information printed when obj1 and obj2 are destroyed is separated from the above ones
    obj1.a = nullptr;
    obj2.a = nullptr;
    return 0;
}

我通过编译器选项关闭了 clang 的 RVO/NRVO 并使用 .我得到了以下输出，非常令人困惑：-fno-elide-constructors-std=c++14

In make_obj...                                
In A's constructor...                   // make tmp obj
In A's move constructor...              // w/o RVO, need another construction to get return value?
In A's destructor...                    // destory the temp obj in make_obj scope?                
In make_obj_by_move...                
In A's move constructor...              // call the move constructor like expected? I guess by the position of "copy constructor" below
In A's move constructor...              // what happened here ???
In A's destructor...                    // destory which?            
In A's move constructor...              // w/o NRVO, need another construction to get obj1?
In A's destructor...                    // destory which?
In A's destructor...                    // destory which?

In make_obj...                            
In A's constructor...                   // make tmp obj
In A's move constructor...              // w/o RVO, need another construction to get return value?
In A's destructor...                    // destory the temp obj in make_obj scope?            
In A's move constructor...              // what happened here ???
In make_obj_by_copy...                
In A's copy constructor...              // call the copy constructor like expected
In A's move constructor...              // what happened here ???
In A's destructor...                    // destory which?            
In A's move constructor...              // w/o NRVO, need another construction to get obj2?
In A's destructor...                    // destory which?
In A's destructor...                    // destory which?
In A's destructor...                    // destory which?            

In A's destructor...                    // destory obj1/obj2
In A's destructor...                    // destory obj2/obj1

这里到底发生了什么？为什么会召唤许多意想不到的移动构造和破坏？我试图解释一些输出，但仍然有很多我不明白的输出行。你可以帮我吗？谢谢。