FIP analysis does not handle boxing of value types correctly

[anfelor]

In Koka 3.1.2, the following program is accepted:

fip fun test( b : bool ) : maybe<(int, int)>
  if b then Just((1, 2)) else Nothing

but it is compiled to the following code:

kk_std_core_types__maybe kk_test7_test(bool b, kk_context_t* _ctx) { /* (b : bool) -> maybe<(int, int)> */ 
  if (b) {
    kk_box_t _x_x6;
    kk_std_core_types__tuple2 _x_x7 = kk_std_core_types__new_Tuple2(kk_integer_box(kk_integer_from_small(1), _ctx), kk_integer_box(kk_integer_from_small(2), _ctx), _ctx); /*(1038, 1039)*/
    _x_x6 = kk_std_core_types__tuple2_box(_x_x7, _ctx); /*1027*/
    return kk_std_core_types__new_Just(_x_x6, _ctx);
  }
  {
    return kk_std_core_types__new_Nothing(_ctx);
  }
}

Since the tuple in the Just constructor is boxed, this example allocates and is in fact not fip.