Re: [PATCH] Fix casting in-memory values of primitive types to const reference

[Hannes Domani <ssbssa@yahoo.de>]

 Am Mittwoch, 20. März 2024 um 18:05:48 MEZ hat Tom Tromey <tom@tromey.com> Folgendes geschrieben:

> >>>>> "Hannes" == Hannes Domani <ssbssa@yahoo.de> writes:
>
> Hannes> It's currently not possible to cast an in-memory value of a primitive
> Hannes> type to const reference:
>
> Thank you for the patch.
>
> I think it is ok.  However I suspect there may be other bugs here.
>
> Approved-By: Tom Tromey <tom@tromey.com>

Pushed, thanks.


> Hannes> Fixed by ignoring const/volatile/restrict qualifications in
> Hannes> value_cast when comparing cast type to original type, so the new
> Hannes> value will point to the same location as the original value:
>
> Hannes> -  if (types_deeply_equal (arg2->type (), type))
> Hannes> +  if (types_deeply_equal (make_unqualified_type (arg2->type ()),
> Hannes> +              make_unqualified_type (type)))
>
> This code seems slightly weird in that it isn't calling check_typedef.
> So, I wonder what happens if typedefs are involved, for example if you
> did:
>
> typedef const int ci;
>
> (gdb) print (ci&) Q.id

This happens:

(gdb) p (ci&) Q.id
$1 = (const int &) @0x3cfb8c: 42

Because check_typedef is called when the reference is removed:
```
  /* Check if we are casting struct reference to struct reference.  */
  if (TYPE_IS_REFERENCE (check_typedef (type)))
    {
      /* We dereference type; then we recurse and finally
     we generate value of the given reference.  Nothing wrong with
     that.  */
      struct type *t1 = check_typedef (type);
      struct type *dereftype = check_typedef (t1->target_type ());
      struct value *val = value_cast (dereftype, arg2);

      return value_ref (val, t1->code ());
    }
```


Hannes