[Bug c++/33573] New: over-optimization in 4.1.2

["dooglus at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Compiling the following code with -O2 or higher in g++ 4.1.2 produces incorrect
results.  The problem doesn't occur in version 4.2.1.

I compile like this:
  g++ -W -Wall -Werror        -O2 -fPIC -o gccbug gccbug.cpp

The last line of output should show the number 27, but it shows 0 when
optimizing  with -O2.

A tar archive containing the source file and a Makefile to build it is here:
http://dooglus.rincevent.net/random/gccbug.1190912601.tgz

Defining any of FIX0, FIX1 or FIX2 fixes the problem.

Here's the source file:

-----
#include <iostream>
#include <string>
#include <vector>

using namespace std;

struct Vector {
        float _x, _y;
        Vector(): _x(0), _y(0) {};
        float &m(const int &i) { return i?_y:_x; }
};

struct Node {
        vector<Node*> nl;
        Node() {nl.push_back(this);};
        string get_name() const {return "x";};
        vector<Node*> get_children() { return nl;};
};

int six() { return 6; }

Vector parse_vector(Node *element)
{
        Vector vect;
        Node *node = element->get_children()[0];
        if(node->get_name()=="x") { // true
#ifdef FIX0
                cout << "1. vect.m(0) <= 27" << endl;
#else
                printf("1. vect.m(0) <= 27\n");
#endif
                vect.m(0)=27;
#ifdef FIX1                      // printing the value stops the
over-optimization
                cout << "2. vect.m(0) == " << vect.m(0) << endl;
#endif
        } else if(six() == 6 && node->get_children().empty()) { // false
                exit(0);
                return Vector();
        }
#ifdef FIX2             // checking the value also stops the over optimization
        if (vect.m(0) + vect.m(1) == 24234.657) cout << "har" << endl;
#endif
        return vect;
}

int main() {
        cout << "3. vect.m(0) == " << parse_vector(new Node).m(0) << " <--
should be 27" << endl;
}
-----


-- 
           Summary: over-optimization in 4.1.2
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dooglus at gmail dot com
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33573