Deciding the array size to be used when differentiating VisitCallExpr

[sudo-panda]

This issue references the PR #237

We need to decide the size temporary array that is build for a CallExpr. For example, when the below function is differentiated:

void f(double *a, double *out) {
  g(a, out);
}

The grad function is:

f_grad(double *a, double *_d_a, double *out) {
    double *_t0;
    double *_t1;
    _t0 = a;
    _t1 = out;
    g(_t0, _t1);
    {
        double _grad0[10] = {};           // This is the array in consideration
        g_grad(_t0, _grad0, _t1);
        double *_r0 = _grad0;
        _d_a = _r0;
        double *_r1;
    }
}

The required size of _grad0 cannot be calculated before differentiating the g function so we need to decide between:

• Allowing users to set a size by using a macro or an argument
• Calculating the diff function and determining the size required before declaring the grad array (will take more computation)

[PetroZarytskyi]

This was fixed at some point. The gradient generated on the current master is:

void f_grad(double *a, double *out, clad::array_ref<double> _d_a, clad::array_ref<double> _d_out) {
    g(a, out);
    g_pullback(a, out, _d_a, _d_out);
}

We don't create _grad/_r variables for pointer arguments anymore.
If somebody believes this is not the case, please reopen the issue.