Compiling OOP Features
Swati Jaiswal
Department of Computer Science and Engineering,
Visvesvaraya National Institute of Technology, Nagpur
Slides borrowed from Uday Khedker
Department of Computer Science and Engineering,
Indian Institute of Technology, Bombay
July 2021
Part 1
Compiling OOP Features
ACM Summer School on Compilers: Compiling OOP Features
Outline
• Internal representation of a class
• Translating virtual function calls
• Proposed optimization
• Translating function template and class template
Uday Khedker
1/23
ACM Summer School on Compilers: Compiling OOP Features
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
a.f1(5);
b.f1(10);
Uday Khedker
Data Memory
Code Memory
2/23
ACM Summer School on Compilers: Compiling OOP Features
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
Data Memory
Code Memory
2/23
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
ThereA is*no
int A::f2(struct
const this, int i)
between the
{ return distinction
i+1;}
public and private data
in memory
int main()
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Every function with
n parameters
Object
a
is converted to a function of n + 1
x parameter
y
zwith the first parameter
being the addressObject
of thebobject
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
12
y
x
y
z
Object a
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
2/23
Internal Representation of a Class
class A
{
private:
int x;
int f2(int i)
{ return i+1;}
public:
int y,z;
void f1(int i)
{ x = f2(i)*2;}
};
A a;
A b;
a.f1(5);
b.f1(10);
Uday Khedker
x
y
z
Object a
x
22
y
z
Object b
Data Memory
Code Memory
void A::f1(struct A * const this , int i)
{ this-> x = A::f2(this, i)*2;}
int A::f2(struct A * const this, int i)
{ return i+1;}
int main()
{ struct A a,b;
A::f1 ( &a , 5); A::f1 ( &b , 10);
}
ACM Summer School on Compilers: Compiling OOP Features
Padding Data and Computing Sizeof an Object
class White
{ public:
int w1;
char w2;
int w3;
char w4;
};
White w;
Uday Khedker
0
4
8
12
w1
w2
w3
w4
size: 16 bytes
3/23
ACM Summer School on Compilers: Compiling OOP Features
Padding Data and Computing Sizeof an Object
class White
{ public:
int w1;
char w2;
char w4;
int w3;
};
White w;
Uday Khedker
0
4
8
12
w1
w2
w4
size: 12 bytes
w3
4/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
5/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
w=b
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
w=b
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
x
p
w1
b1
b2
p1
p2
w=b
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
w=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
w=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
w=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
x
b=p
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue b;
Pink p;
Uday Khedker
w
b
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b=w
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
w
int w1;
w1
};
class Blue : public White
b
w1
{ public:
b1
int b1;
b2
int b2;
};
p
class Pink : public Blue
w1
{ public:
b1
int p1;
b2
Error!!
int p2;
Base
class
does
not
include
everything
in
the
Derived
class.
p1
};
However,
base
class
is
contained
in
the
Derived
class.
p2
White w;
Blue b;
Pink p;
b=w
Uday Khedker
6/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
p
w1
b1
b2
p1
p2
w = &b
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
p
w1
b1
b2
p1
p2
w = &b
w
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
x
p
w1
b1
b2
p1
p2
w = &b
w
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
p
w1
b1
b2
p1
p2
w = &p
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
p
w1
b1
b2
p1
p2
w = &p
w
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White *w;
Blue b;
Pink p;
Uday Khedker
w1
b
w1
b1
b2
p
w1
b1
b2
p1
p2
w = &p
w
7/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue *b;
Pink p;
Uday Khedker
w
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b = &p
8/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue *b;
Pink p;
Uday Khedker
w
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b = &p
b
8/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue *b;
Pink p;
Uday Khedker
w
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
x
b = &p
b
8/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
int w1;
};
class Blue : public White
{ public:
int b1;
int b2;
};
class Pink : public Blue
{ public:
int p1;
int p2;
};
White w;
Blue *b;
Pink p;
Uday Khedker
w
w1
w1
b1
b2
p
w1
b1
b2
p1
p2
b = &w
8/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Data: Object Slicing
class White
{ public:
w
int w1;
w1
};
class Blue : public White
w1
{ public:
b1
int b1;
b2
int b2;
};
p
class Pink : public Blue
w1
{ public:
b1
int p1;
b2
Error!!
int p2;
Base
class
does
not
include
everything
in
the
Derived
class.
p1
};
However,
base
class
is
contained
in
the
Derived
class.
p2
White w;
Blue *b;
Pink p;
b = &w
Uday Khedker
8/23
ACM Summer School on Compilers: Compiling OOP Features
Representing Inheritance of Functions
• Non-virtual functions are inherited much like data members
However, there is a single class-hierachy-wide copy of the code and the
address of the object is the first parameter
• Virtual functions create interesting possibilities based on the object to
which a pointer points to
A pointer to a base class object may point to an object of any derived
class in the class hierarchy
Uday Khedker
9/23
ACM Summer School on Compilers: Compiling OOP Features
An Example with Virtual Functions
class A
{ public:
virtual void f() {cout << "\tA:f" << endl;}
virtual void f(string i) {cout << "\tA:f." << i << endl;}
virtual void g() {cout << "\tA:g" << endl;}
};
class B : public A
{ public:
virtual void g() {cout << "\tB:g" << endl;}
void f() {cout << "\tB:f" << endl;}
};
class C : public B
{ public:
void f() {cout<< "\tC:f" << endl;}
};
Uday Khedker
10/23
ACM Summer School on Compilers: Compiling OOP Features
An Example with Virtual Functions
class A
{ public:
virtual void f() {cout << "\tA:f" << endl;}
virtual void f(string i) {cout << "\tA:f." << i << endl;}
virtual void g() {cout << "\tA:g" << endl;}
};
class B : public A
{ public:
virtual void g() {cout << "\tB:g" << endl;}
void f() {cout << "\tB:f" << endl;}
};
class C : public B
{ public:
void f() {cout<< "\tC:f" << endl;}
};
Uday Khedker
10/23
ACM Summer School on Compilers: Compiling OOP Features
An Example with Virtual Functions
class A
{ public:
virtual void f() {cout << "\tA:f" << endl;}
virtual void f(string i) {cout << "\tA:f." << i << endl;}
virtual void g() {cout << "\tA:g" << endl;}
};
class B : public A
{ public:
virtual void g() {cout << "\tB:g" << endl;}
void f() {cout << "\tB:f" << endl;}
};
class C : public B
{ public:
void f() {cout<< "\tC:f" << endl;}
};
Uday Khedker
10/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
A a; B b; C c;
Output
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classA
A:f
A:g
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classA
A:f
A:g
A:f.classB
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classA
A:f
A:g
A:f.classB
B:f
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classB
B:f
B:g
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classB
B:f
B:g
p = &c;
p->f("classC");
p->f();
p->g();
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classB
B:f
B:g
p = &c;
p->f("classC");
p->f();
p->g();
A:f.classC
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classB
B:f
B:g
p = &c;
p->f("classC");
p->f();
p->g();
A:f.classC
C:f
11/23
ACM Summer School on Compilers: Compiling OOP Features
Examining the Behaviour of Virtual Functions (1)
Class Declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Calls
Output
A a; B b; C c;
p = &a;
p->f("classA");
p->f();
p->g();
A:f.classA
A:f
A:g
p = &b;
p->f("classB");
p->f();
p->g();
A:f.classB
B:f
B:g
p = &c;
p->f("classC");
p->f();
p->g();
A:f.classC
C:f
B:g
11/23
ACM Summer School on Compilers: Compiling OOP Features
12/23
Examining the Behaviour of Virtual Functions (2)
Class declarations
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
Output with
virtual functions
A:f.classA
A:f
A:g
A:f.classB
B:f
B:g
A:f.classC
C:f
B:g
Output with no
virtual functions
A:f.classA
A:f
A:g
A:f.classB
A:f
A:g
A:f.classC
A:f
A:g
ACM Summer School on Compilers: Compiling OOP Features
13/23
Virtual Function Resolution
• Partially static and partially dynamic activity
• At compile time, a compiler creates a virtual function table for each class
• At run time, a pointer may point to an object of any derived class
• Compiler generates code to pick up the appropriate function by indexing
into the virtual table to each class
(the exact virtual table depends on the pointee object)
Uday Khedker
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
In general, at
compile time we do
C *r;
not
know the class of
the pointee of p
r = ...
r->f();
v A::g()
v g()
v A::f()
v B::f()
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
In general, at
compile time we do
C *r;
not
know the class of
the pointee of p
r = ...
r->f();
v A::g()
v g()
v A::f()
v B::f()
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
In general, at
compile time we do
C *r;
not
know the class of
the pointee of p
r = ...
r->f();
v A::g()
v g()
v A::f()
v B::f()
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
v f()
v f(i)
v g()
A *p;
p = ...
p->f();
×
B *q;
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
v A::f()
A
f()
v A::f(i)
Compiler can
v A::g()
g()
rule
this out vstatically
by looking up the
declaration of q
v A::f()
v B::f() f()
B
v A::f(i)
C
v A::g()
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
v f()
v f(i)
v g()
A *p;
p = ...
p->f();
v A::f()
B *q;
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
×
A
f()
v A::f(i)
v A::g()
B
v g()
Compiler can
rulev this
out v B::f()
A::f()
statically
v A::f(i)
v A::g()
v B::g()
f()
C
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
v f()
v f(i)
v g()
A *p;
p = ...
p->f();
v A::f()
B *q;
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
×
×
A
f()
v A::f(i)
v A::g()
B
v g()
Compiler can
rule out
these toov B::f()
v A::f()
statically
v A::f(i)
v A::g()
v B::g()
f()
C
14/23
ACM Summer School on Compilers: Compiling OOP Features
Virtual Function Resolution Requires Dynamic Information
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
v A::f(i)
q = ...
q->f();
v A::g()
v g()
v A::f()
v B::f()
C *r;
r = ...
r->f();
Uday Khedker
B
v A::f(i)
v A::g()
f()
C
v B::g()
14/23
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
q = ...
q->f();
v A::f(i)
v A::g()
v g()
C *r;
r = ...
r->f();
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
B *q;
q = ...
q->f();
In general, at
compile
time we do
C *r;
know the class of
r not
= ...
the pointee of p
r->f();
f()
v A::f(i)
B
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
A
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
q = ...
q->f();
v A::f(i)
v A::g()
v g()
C *r;
r = ...
r->f();
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
×
B *q;
q = ...
q->f();
Even if the
pointee is an object
class B, p->f() must
Cof *r;
rbe=A::f()
... because p is
a pointer to
r->f();
class A
Uday Khedker
v A::f()
A
f()
v A::f(i)
B
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
B *q;
q = ...
q->f();
Even if the
pointee is an object
class B, p->f() must
Cof *r;
rbe=A::f()
... because p is
a pointer to
r->f();
class A
Uday Khedker
A
f()
v A::f(i)
B
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
A *p;
p = ...
p->f();
v f()
v f(i)
v g()
v A::f()
A
f()
B *q;
q = ...
q->f();
v A::f(i)
v A::g()
v g()
C *r;
r = ...
r->f();
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
15/23
Non-Virtual Functions Do Not Require Dynamic Information
Non-virtual function = a function which is not virtual in any class in a hierarchy
v f()
v f(i)
v g()
A *p;
p = ...
p->f();
v A::f()
B *q;
q = ...
q->f();
f()
v A::f(i)
×
q is a
C *r; pointer to an
r = ... object of
r->f(); class B
B
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
A
f()
C
v B::g()
ACM Summer School on Compilers: Compiling OOP Features
16/23
A Summary of Function Call Resolution
• Resolution of virtual functions depends on the class of the pointee object
⇒ Needs dynamic information
• Resolution of non-virtual functions depends on the class of the pointer
⇒ Compile time information is sufficient
• In either case, a pointee cannot belong to a “higher” class in the hierarchy
(“higher” class = a class from which the class of the pointer is derived)
Uday Khedker
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (1)
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
17/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (1)
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
• Consider a pointer to an
object of class A
• This pointer could point to
an object of class A, B, or C
17/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (1)
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
A
v f()
v f(i)
v g()
17/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (1)
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
A
v f()
v f(i)
v g()
v A::f()
B
f()
v A::f(i)
v A::g()
v g()
17/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (1)
class A
{ public:
virtual void f()
virtual void f(string i)
virtual void g()
};
class B : public A
{ public:
virtual void g()
void f()
};
class C : public B
{ public:
void f()
};
Uday Khedker
A
v f()
v f(i)
v g()
v A::f()
B
C
f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
v B::g()
f()
17/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
v A::f()
f()
B::f()
B
C
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
v A::f()
f()
B::f()
B
C
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
v A::f()
f()
B::f()
B
C
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
A::f() is
overridden by
B::f()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
A::f(i) is
inherited
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
A::g() is
overridden by
B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
××
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
Both A::f() and
B::f() are overridden
by C::f()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
××
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
A::f(i) is
inherited
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
××
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
B::g()
f()
C::f()
v B::g()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
×
×
××
×
v A::f()
B
C
f()
B::f()
v A::f(i)
v A::g()
v g()
v A::f()
v B::f()
v A::f(i)
v A::g()
Uday Khedker
v B::g()
B::g()
f()
C::f()
A::g() is
overridden by
B::g() which is
inherited
18/23
ACM Summer School on Compilers: Compiling OOP Features
Constructing Virtual Function Table (2)
A::f()
A
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B
B::f()
v A::f(i)
v g()
B::g()
f()
C
v A::f(i)
v B::g()
Uday Khedker
C::f()
18/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
At runtime,
two dereferences
q->f();
are sufficient
to get the callee
function
(or one
followed
C dereference,
*r;
by addition of an offset decided
by therfunction
= ... prototype, and
then the
second dereference)
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
At runtime,
two dereferences
q->f();
are sufficient
to get the callee
function
(or one
followed
C dereference,
*r;
by addition of an offset decided
by therfunction
= ... prototype, and
then the
second dereference)
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
At runtime,
two dereferences
q->f();
are sufficient
to get the callee
function
(or one
followed
C dereference,
*r;
by addition of an offset decided
by therfunction
= ... prototype, and
then the
second dereference)
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
B *q;
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
q = ...
q->f();
C *r;
r = ...
r->f();
Uday Khedker
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
Using the Constructed Virtual Function Table
A::f()
A *p;
p = ...
p->f();
This is possible because the
B *q;
size of the virtual function
table is made same for all
q = ...
classes in the hierarchy
q->f();
(there can be only one
function with a given name
and permutation
of types of
C *r;
the arguments)
r = ...
r->f();
Uday Khedker
v f()
v f(i)
v g()
A::f(i)
A::g()
f()
B::f()
v A::f(i)
v g()
B::g()
f()
v A::f(i)
v B::g()
C::f()
19/23
ACM Summer School on Compilers: Compiling OOP Features
20/23
A Summary of Virtual Function Implementation
• Compile time activity
◮
◮
◮
Uday Khedker
Collect all virtual functions across a class hierarchy
Ignore non-virtual functions
Analyse the class hierarchy to locate the appropriate function with a
given permutation of argument types
ACM Summer School on Compilers: Compiling OOP Features
20/23
A Summary of Virtual Function Implementation
• Compile time activity
◮
◮
◮
Collect all virtual functions across a class hierarchy
Ignore non-virtual functions
Analyse the class hierarchy to locate the appropriate function with a
given permutation of argument types
• Execution time activity
◮
◮
◮
Uday Khedker
Dereference object pointer to access the virtual function table
Add offset to the base of the table to access the function pointer
Dereference the function pointer to make the call
ACM Summer School on Compilers: Compiling OOP Features
Optimizing Virtual Function Calls
Source Code
Translated Code
A a; B b; C c;
A a; B b; C c;
p = &a;
p->f("AA");
p->f();
p->g();
p = &a;
(*((p-> vptr)[1]))(&a, "AA");
(*((p-> vptr)[0]))(&a);
(*((p-> vptr)[2]))(&a);
p = &b;
p->f("BB");
p->f();
p->g();
p = &b;
(*((p-> vptr)[1]))(&b,"BB");
(*((p-> vptr)[0]))(&b);
(*((p-> vptr)[2]))(&b);
p = &c;
p->f("CC");
p->f();
p->g();
p = &c;
(*((p-> vptr)[1]))(&c,"CC");
(*((p-> vptr)[0]))(&c);
(*((p-> vptr)[2]))(&c);
Uday Khedker
Optimized Code
21/23
ACM Summer School on Compilers: Compiling OOP Features
Optimizing Virtual Function Calls
Source Code
A a; B b; C c;
Translated Code
Optimized Code
A a; B b; C c;
p = &a;
p = &a;
"AA");
p->f("AA"); • Each
(*((p->
functionvptr)[1]))(&a,
call involves a pointer
indirection
vptr)[0]))(&a);
(*((p->
p->f();
and an array indirection
(*((p->
vptr)[2]))(&a);
p->g();
Runtime
overheads
• No pfunction
= &b; call can be resolved at link time
p = &b;
p->f("BB"); Call(*((p->
graph is vptr)[1]))(&b,"BB");
not known and hence
(*((p->
vptr)[0]))(&b);
p->f();
interprocedural
optimizations are prohibited
(*((p-> vptr)[2]))(&b);
p->g();
p = &c;
p->f("CC");
p->f();
p->g();
Uday Khedker
p = &c;
(*((p-> vptr)[1]))(&c,"CC");
(*((p-> vptr)[0]))(&c);
(*((p-> vptr)[2]))(&c);
21/23
ACM Summer School on Compilers: Compiling OOP Features
Optimizing Virtual Function Calls
Source Code
Translated Code
Optimized Code
A a; B b; C c;
A a; B b; C c;
A a; B b; C c;
p = &a;
p->f("AA");
p->f();
p->g();
p = &a;
(*((p-> vptr)[1]))(&a, "AA");
(*((p-> vptr)[0]))(&a);
(*((p-> vptr)[2]))(&a);
p = &a;
A::f(&a, "AA");
A::f(&a);
A::g(&a);
p = &b;
p->f("BB");
p->f();
p->g();
p = &b;
(*((p-> vptr)[1]))(&b,"BB");
(*((p-> vptr)[0]))(&b);
(*((p-> vptr)[2]))(&b);
p = &b;
A::f(&b,"BB");
B::f(&b);
B::g(&b);
p = &c;
p->f("CC");
p->f();
p->g();
p = &c;
(*((p-> vptr)[1]))(&c,"CC");
(*((p-> vptr)[0]))(&c);
(*((p-> vptr)[2]))(&c);
p = &c;
A::f(&b,"CC");
C::f(&c);
B::g(&c);
Uday Khedker
21/23
ACM Summer School on Compilers: Compiling OOP Features
Translating Function Template
template <typename T>
T myMax(T x, T y)
{
return (x > y)? x: y;
}
Uday Khedker
int main()
{
cout << myMax<int>(3, 7);
cout << myMax<double>(3.0, 7.0);
cout << myMax<char>(’g’, ’e’);
}
22/23
ACM Summer School on Compilers: Compiling OOP Features
Translating Function Template
template <typename T>
T myMax(T x, T y)
{
return (x > y)? x: y;
}
int main()
{
cout << myMax<int>(3, 7);
cout << myMax<double>(3.0, 7.0);
cout << myMax<char>(’g’, ’e’);
}
T myMax(T, T) [with T = int] ( int x, int y) {. . .}
T myMax(T, T) [with T = double] ( double x, double y) {. . .}
T myMax(T, T) [with T = char] ( char x, char y) {. . .}
int main ()
{
D.22263 = myMax<int> (3, 7);
D.22265 = myMax<double> (3.0e+0, 7.0e+0);
D.22267 = myMax<char> (103, 101);
}
Uday Khedker
22/23
ACM Summer School on Compilers: Compiling OOP Features
Translating Function Template
template <typename T>
T myMax(T x, T y)
{
return (x > y)? x: y;
}
int main()
{
cout << myMax<int>(3, 7);
cout << myMax<double>(3.0, 7.0);
cout << myMax<char>(’g’, ’e’);
}
T myMax(T, T) [with T = int] ( int x, int y) {. . .}
T myMax(T, T) [with T = double] ( double x, double y) {. . .}
T myMax(T, T) [with T = char] ( char x, char y) {. . .}
int main ()
{
D.22263 = myMax<int> (3, 7);
D.22265 = myMax<double> (3.0e+0, 7.0e+0);
D.22267 = myMax<char> (103, 101);
}
Uday Khedker
22/23
ACM Summer School on Compilers: Compiling OOP Features
Translating Function Template
template <typename T>
T myMax(T x, T y)
{
return (x > y)? x: y;
}
int main()
{
cout << myMax<int>(3, 7);
cout << myMax<double>(3.0, 7.0);
cout << myMax<char>(’g’, ’e’);
}
T myMax(T, T) [with T = int] ( int x, int y) {. . .}
T myMax(T, T) [with T = double] ( double x, double y) {. . .}
T myMax(T, T) [with T = char] ( char x, char y) {. . .}
int main ()
{
D.22263 = myMax<int> (3, 7);
D.22265 = myMax<double> (3.0e+0, 7.0e+0);
D.22267 = myMax<char> (103, 101);
}
Uday Khedker
22/23
ACM Summer School on Compilers: Compiling OOP Features
23/23
Translating Class Template
template <typename T>
class Array {
private:
T *ptr;
int size;
public:
Array(T arr[], int s);
void print();
};
template <typename T>
Array<T>::Array(T arr[], int s) {
ptr = new T[s];
size = s;
for(int i = 0; i < size; i++)
ptr[i] = arr[i];
}
template <typename T>
void Array<T>::print() {
int main() {
for (int i = 0; i < size; i++)
int arr[5] = {1, 2, 3, 4, 5};
cout<<" "<<*(ptr + i);
Array<int> a1(arr, 5);
cout<<endl;
a1.print();
}
}
Uday Khedker
ACM Summer School on Compilers: Compiling OOP Features
23/23
Translating Class Template
template <typename T>
class Array {
private:
T *ptr;
int size;
public:
Array(T arr[], int s);
void print();
};
template <typename T>
Array<T>::Array(T arr[], int s) {
ptr = new T[s];
size = s;
for(int i = 0; i < size; i++)
ptr[i] = arr[i];
}
template <typename T>
void Array<T>::print() {
int main() {
for (int i = 0; i < size; i++)
int arr[5] = {1, 2, 3, 4, 5};
cout<<" "<<*(ptr + i);
Array<int> a1(arr, 5);
cout<<endl;
a1.print();
}
}
Array<T>::Array(T*, int) [with T = int] (struct Array * const
this, int * arr, int s) {. . .}
void Array<T>::print() [with T = int] (struct Array * const this)
{. . .}
Uday Khedker
ACM Summer School on Compilers: Compiling OOP Features
23/23
Translating Class Template
template <typename T>
class Array {
private:
T *ptr;
int size;
public:
Array(T arr[], int s);
void print();
};
template <typename T>
Array<T>::Array(T arr[], int s) {
ptr = new T[s];
size = s;
for(int i = 0; i < size; i++)
ptr[i] = arr[i];
}
template <typename T>
void Array<T>::print() {
int main() {
for (int i = 0; i < size; i++)
int arr[5] = {1, 2, 3, 4, 5};
cout<<" "<<*(ptr + i);
Array<int> a1(arr, 5);
cout<<endl;
a1.print();
}
}
Array<T>::Array(T*, int) [with T = int] (struct Array * const
this, int * arr, int s) {. . .}
void Array<T>::print() [with T = int] (struct Array * const this)
{. . .}
Uday Khedker
ACM Summer School on Compilers: Compiling OOP Features
23/23
Translating Class Template
template <typename T>
class Array {
private:
T *ptr;
int size;
public:
Array(T arr[], int s);
void print();
};
template <typename T>
Array<T>::Array(T arr[], int s) {
ptr = new T[s];
size = s;
for(int i = 0; i < size; i++)
ptr[i] = arr[i];
}
template <typename T>
void Array<T>::print() {
int main() {
for (int i = 0; i < size; i++)
int arr[5] = {1, 2, 3, 4, 5};
cout<<" "<<*(ptr + i);
Array<int> a1(arr, 5);
cout<<endl;
a1.print();
}
}
Array<T>::Array(T*, int) [with T = int] (struct Array * const
this, int * arr, int s) {. . .}
void Array<T>::print() [with T = int] (struct Array * const this)
{. . .}
Uday Khedker