查看编译器生成的默认函数？ [英] view the default functions generated by a compiler?

问题描述

有没有什么方法来查看由编译器（例如VC ++ 2008）生成的默认函数（例如，默认的复制构造函数，默认赋值运算符），这个类不定义它们？

Is there any way to view the default functions ( e.g., default copy constructor, default assignment operator ) generated by a compiler such as VC++2008 for a class which does not define them?

推荐答案

使用 clang 编译器，您可以通过传递 -ast-dump 参数来查看它们。 Clang仍处于开发阶段，但您可以使用它来处理这些事情：

With the clang compiler, you can see them by passing the -ast-dump argument. Clang is still in development stage, but you can already use it for these things:

[js@HOST2 cpp]$ cat main1.cpp
struct A { };
[js@HOST2 cpp]$ clang++ -cc1 -ast-dump main1.cpp
typedef char *__builtin_va_list;
struct A {
public:
    struct A;
    inline A();
    inline A(struct A const &);
    inline struct A &operator=(struct A const &);
    inline void ~A();
};
[js@HOST2 cpp]$

我希望这是您要求的。让我们改变代码，再看看。

I hope that's what you asked for. Let's change the code and look again.

[js@HOST2 cpp]$ cat main1.cpp
struct M { M(M&); };
struct A { M m; };
[js@HOST2 cpp]$ clang++ -cc1 -ast-dump main1.cpp
typedef char *__builtin_va_list;
struct M {
public:
    struct M;
    M(struct M &);
    inline struct M &operator=(struct M const &);
    inline void ~M();
};
struct A {
public:
    struct A;
    struct M m;
    inline A();
    inline A(struct A &);
    inline struct A &operator=(struct A const &);
    inline void ~A();
};
[js@HOST2 cpp]$

注意如何隐式声明拷贝构造函数 A 现在有一个非const引用参数，因为它的一个成员也有（成员 m ）， c $ c> M 没有声明默认构造函数。

Notice how the implicitly declared copy constructor of A now has a non-const reference parameter, because one of its members has too (member m), and that M has no default constructor declared.

为了获得生成的代码，可以让它发出虚拟机中间语言。让我们来看看生成的代码：

For getting the generated code, you can let it emit virtual machine intermediate language. Let's look on the generated code for this:

struct A { virtual void f(); int a; };
A f() { A a; a = A(); return a; } // using def-ctor, assignment and copy-ctor

[js@HOST2 cpp]$ clang++ -cc1 -O1 -emit-llvm -o - main1.cpp | c++filt
[ snippet ]
define linkonce_odr void @A::A()(%struct.A* nocapture %this) nounwind align 2 {
entry:
  %0 = getelementptr inbounds %struct.A* %this, i32 0, i32 0 ; <i8***> [#uses=1]
  store i8** getelementptr inbounds ([3 x i8*]* @vtable for A, i32 0, i32 2), i8*** %0
  ret void
}

define linkonce_odr %struct.A* @A::operator=(A const&)(%struct.A* %this, 
  %struct.A* nocapture) nounwind align 2 {
entry:
  %tmp = getelementptr inbounds %struct.A* %this, i32 0, i32 1 ; <i32*> [#uses=1]
  %tmp2 = getelementptr inbounds %struct.A* %0, i32 0, i32 1 ; <i32*> [#uses=1]
  %tmp3 = load i32* %tmp2                         ; <i32> [#uses=1]
  store i32 %tmp3, i32* %tmp
  ret %struct.A* %this
}

define linkonce_odr void @A::A(A const&)(%struct.A* nocapture %this, %struct.A* nocapture) 
  nounwind align 2 {
entry:
  %tmp = getelementptr inbounds %struct.A* %this, i32 0, i32 1 ; <i32*> [#uses=1]
  %tmp2 = getelementptr inbounds %struct.A* %0, i32 0, i32 1 ; <i32*> [#uses=1]
  %tmp3 = load i32* %tmp2                         ; <i32> [#uses=1]
  store i32 %tmp3, i32* %tmp
  %1 = getelementptr inbounds %struct.A* %this, i32 0, i32 0 ; <i8***> [#uses=1]
  store i8** getelementptr inbounds ([3 x i8*]* @vtable for A, i32 0, i32 2), i8*** %1
  ret void
}

现在，我不明白中间语言=http://llvm.org> llvm.org ）。但您可以使用llvm编译器将所有代码转换为C：

Now, i don't understand that intermediate language (which is defined at llvm.org). But you can translate all that code into C using the llvm compiler:

[js@HOST2 cpp]$ clang++ -cc1 -O1 -emit-llvm -o - main1.cpp | llc -march=c -o - | c++filt
[snippet]
void A::A()(struct l_struct.A *llvm_cbe_this) {
  *((&llvm_cbe_this->field0)) = ((&_ZTV1A.array[((signed int )2u)]));
  return;
}


struct l_struct.A *A::operator=(A const&)(struct l_struct.A *llvm_cbe_this, struct l_struct.A
  *llvm_cbe_tmp__1) {
  unsigned int llvm_cbe_tmp3;

  llvm_cbe_tmp3 = *((&llvm_cbe_tmp__1->field1));
  *((&llvm_cbe_this->field1)) = llvm_cbe_tmp3;
  return llvm_cbe_this;
}


void A::A(A const&)(struct l_struct.A *llvm_cbe_this, struct l_struct.A *llvm_cbe_tmp__2) {
  unsigned int llvm_cbe_tmp3;

  llvm_cbe_tmp3 = *((&llvm_cbe_tmp__2->field1));
  *((&llvm_cbe_this->field1)) = llvm_cbe_tmp3;
  *((&llvm_cbe_this->field0)) = ((&_ZTV1A.array[((signed int )2u)]));
  return;
}

Tada！注意它如何在复制构造函数和默认构造函数中设置虚表指针。希望这可以帮助。

Tada! Notice how it sets the virtual table pointer in the copy constructor and default constructor. Hope this helps.

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