gcc optimization constant propagation

[charfi asma <charfiasma at yahoo dot fr>]

Hi every one,

I have a question about gcc optimization, I hope I am writing to the right list

I compiled a simple c++ program using gcc 4.0.1

#include <iostream>

using namespace std;

intc;

calss Calcul

{

public: void affich()

{

cout << "hello world" << endl;

}

public void inc (int& c)

{

switch (c)

{

case 1 : c=c+1; break;

case 2 : c=c+2; break;

case 3 : c=c+3; break;

default : c=c+0;

}

};


int main()

{

Calcul ca;

c=3;

ca.affich();

ca.inc(c);

cout << "the value of c is" << c << endl;

return 0;

}

 

I am interested in cpp optimisation (constant propagation)

normally, if I compile it using  g++ test.cpp -O3 -fdump-tree-all, the c variable will be considered as constant (ca.inc(c); will be replaced only by c = 6; )

This kind of optimization is well done if I declare c just before ca.inc(c)): compiling the code bellow, the ca.inc(c) is replaced by c=6; (in the test1.dom1 file)

 

int main()

{

Calcul ca;

ca.affich();

c=3;

ca.inc(c);

cout << "the value of c is" << c << endl;

return 0;

}

 

Why in the fist code, c is not considered as a constant (in spite that affich() does not change c) 

 Thank you very much

 

Asma