This is not a perfect solution yet. I have identified two problems:
1) The heuristic used at `mark_to_reset_fields` is too weak.
Suppose we have
```
let ...
_x := prod.mk field_1 0
in some _x
```
The current implementation will mark `field_1` to be reset since it
occurs in a non tail call `prod.mk field_1 0`. However, we can
assume `prod.mk field_1 0` is part of the return value.
2) The current semantics of the reset instruction may produce
unnecessary memory allocation. Consider the following example
```
let _x_1 := x.1,
_x_2 := x.2,
_x_3 := _reset.2 x
in @bool.cases_on y
(_cnstr.0.0)
(let _x_4 := f _x_2,
in _updt.2 _x_3 _x_4)
```
The memory cell `_x_3` is only used in the second branch of
the `bool.cases_on`. So, if `y` is `ff`, and `x` is a shared
object, we will allocate memory at `_reset.2 x` for nothing.
d98a1d1da3