Incorrect results for comma expressions in forward mode AD

[vaithak]

Minimal example

double f(double x) {
   // returns (x+1)^2
   return (++x , x * x);
}

Theoretically expected derivative: 2*(x+1)

Generated code results in calculation of 2*x (i.e ++x is missing before returning the derivative):

double f_darg0(double x) {
    double _d_x = 1;
    return (_d_x * x + x * _d_x);
}

Similar, is the case with a slightly modified code for the same function:

double f(double x) {
   // returns (x+1)^2
   double temp = (++x , x * x);
   return temp;
}

Generated code again results in calculation of 2*x (this time ++x is misplaced)

double f_darg0(double x) {
    double _d_x = 1;
    double _d_temp = (_d_x * x + x * _d_x);
    double temp = (++x , x * x);
    return _d_temp;
}