C++ 编译器可以内联函数指针吗？

Question

假设我有一个函数 functionProxy，它接受一个泛型参数 function 并调用它的 operator():

template< typename Function > void functionProxy( Function function ) {
    function();
}

---

传递给它的对象可能是:

• 仿函数:

  struct Functor {
      void operator()() const {
          std::cout << "functor!" << std::endl;
      }
  };
  

• 一个函数:

  void function( ) {
      std::cout << "function!" << std::endl;
  }
  

• 一个 (C++0x) lambda 函数:

  [](){ std::cout << "lambda!" << std::endl; }
  

---

int main( )
{
    functionProxy( Functor() );
    functionProxy( function );
    functionProxy( [](){ std::cout << "lambda!" << std::endl; } );
    return 0;
}

---

在上述所有情况下，编译器能否将 function 内联到 functionProxy 中？

Answer 1

当然。

它知道function的值和它传给它的值是一样的，知道函数的定义，所以直接替换定义inline，直接调用函数。

我想不出编译器不会内联单行函数调用的情况，它只是用函数调用替换函数调用，没有可能的损失。

---

鉴于此代码:

#include <iostream>

template <typename Function>
void functionProxy(Function function)
{
    function();
}

struct Functor
{
    void operator()() const
    {
        std::cout << "functor!" << std::endl;
    }
};

void function()
{
    std::cout << "function!" << std::endl;
}

//#define MANUALLY_INLINE

#ifdef MANUALLY_INLINE
void test()
{
    Functor()();

    function();

    [](){ std::cout << "lambda!" << std::endl; }();
}
#else
void test()
{
    functionProxy(Functor());

    functionProxy(function);

    functionProxy([](){ std::cout << "lambda!" << std::endl; });
}
#endif

int main()
{
    test();
}

定义 MANUALLY_INLINE 后，我们得到:

test:
00401000  mov         eax,dword ptr [__imp_std::endl (402044h)]  
00401005  mov         ecx,dword ptr [__imp_std::cout (402058h)]  
0040100B  push        eax  
0040100C  push        offset string "functor!" (402114h)  
00401011  push        ecx  
00401012  call        std::operator<<<std::char_traits<char> > (401110h)  
00401017  add         esp,8  
0040101A  mov         ecx,eax  
0040101C  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401022  mov         edx,dword ptr [__imp_std::endl (402044h)]  
00401028  mov         eax,dword ptr [__imp_std::cout (402058h)]  
0040102D  push        edx  
0040102E  push        offset string "function!" (402120h)  
00401033  push        eax  
00401034  call        std::operator<<<std::char_traits<char> > (401110h)  
00401039  add         esp,8  
0040103C  mov         ecx,eax  
0040103E  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401044  mov         ecx,dword ptr [__imp_std::endl (402044h)]  
0040104A  mov         edx,dword ptr [__imp_std::cout (402058h)]  
00401050  push        ecx  
00401051  push        offset string "lambda!" (40212Ch)  
00401056  push        edx  
00401057  call        std::operator<<<std::char_traits<char> > (401110h)  
0040105C  add         esp,8  
0040105F  mov         ecx,eax  
00401061  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401067  ret  

没有，这个:

test:
00401000  mov         eax,dword ptr [__imp_std::endl (402044h)]  
00401005  mov         ecx,dword ptr [__imp_std::cout (402058h)]  
0040100B  push        eax  
0040100C  push        offset string "functor!" (402114h)  
00401011  push        ecx  
00401012  call        std::operator<<<std::char_traits<char> > (401110h)  
00401017  add         esp,8  
0040101A  mov         ecx,eax  
0040101C  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401022  mov         edx,dword ptr [__imp_std::endl (402044h)]  
00401028  mov         eax,dword ptr [__imp_std::cout (402058h)]  
0040102D  push        edx  
0040102E  push        offset string "function!" (402120h)  
00401033  push        eax  
00401034  call        std::operator<<<std::char_traits<char> > (401110h)  
00401039  add         esp,8  
0040103C  mov         ecx,eax  
0040103E  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401044  mov         ecx,dword ptr [__imp_std::endl (402044h)]  
0040104A  mov         edx,dword ptr [__imp_std::cout (402058h)]  
00401050  push        ecx  
00401051  push        offset string "lambda!" (40212Ch)  
00401056  push        edx  
00401057  call        std::operator<<<std::char_traits<char> > (401110h)  
0040105C  add         esp,8  
0040105F  mov         ecx,eax  
00401061  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]  
00401067  ret

同样的。 (与 MSVC 2010 一起编译， Vanilla 版本。)