[Bug c++/63364] New: GCC optimizer causing memory corruption

[contact at ncomputers dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63364

            Bug ID: 63364
           Summary: GCC optimizer causing memory corruption
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: contact at ncomputers dot org

http://ncomputers.org/content/code.php?src=findings/gcc%20optimizer%20memory%20corruption.cpp

We found that probably some optimization flags of the GCC compiler are causing
memory corruption after the reading of a variable's content through a pointer
to a class or a struct.

We've tested and confirmed this bug with these compiler's versions: 4.7.2 and
4.8.2

#include<iostream>
using namespace std;

struct A{
    unsigned int const v;
    A():v(10){}
    void test_A();
};

struct B{
    A const*const&a;
    B(A const*const&aa):a(aa){}
    void test_B(){
        unsigned int it=0;
        cout<<"Value of constant a->v: "<<a->v<<endl;
        do{
            cout<<it<<',';
        }while(++it<a->v);
        cout<<endl<<"Value of constant a->v: "<<a->v<<endl;
        //cout<<endl<<"Value of constant a->v:"<<' '<<a->v<<endl;

        /*
         * GNU Compiler with -O2 or -O3 flag
         * Value of constant a->v changes to zero
         *
         * If this result was shown:
         *
         * Value of constant a->v: 10
         * 0,
         * Value of constant a->v: 0
         *
         * Now comment the previous "cout" line and uncomment the next "cout"
line.
         * Note that this is the only difference between both lines:
         * <<' '
         *
         * The right result should be shown:
         *
         * Value of constant a->v: 10
         * 0,1,2,3,4,5,6,7,8,9,
         * Value of constant a->v: 10
         */
    }
};

void A::test_A(){
    B*b=new B(this);
    b->test_B();
    delete b;
}

int main(){
    A*a=new A();
    a->test_A();
    delete a;
    return 0;
};