Re: [PATCH] Remove ada_value_slice

[Andrew Burgess <aburgess@redhat.com>]

Tom Tromey <tromey@adacore.com> writes:

> ada_value_slice and ada_value_slice_from_ptr are nearly identical.
> From what I can tell, the former can be removed without any problem.

I tried running the testsuite adding a print out at the call site where
ada_value_slice used to be called.  I ran gdb.ada/*.exp and
gdb.dwarf2/*.exp and didn't see the call site being hit once.  Which is
not great.

I looked at the history of these two functions, and they are both added
in commit 0b5d8877912034b2af0c548afbb794e4dcd07fbd, so clearly at one
point there was an expectation that these would do different things.  If
they do the same now, then I wonder if that's intentional, or a mistake
because one code path was never used?

However, I'm curious about some of the differences between these two
functions ....

> -
> -  return value_cast (slice_type,
> -		     value_slice (array, low, *high_pos - *low_pos + 1));

In ada_value_slice_from_ptr  the final return is:

  base = value_as_address (array_ptr) + (*low_pos - *base_low_pos) * stride;
  return value_at_lazy (slice_type, base);

The value_as_address call, for an array, will end up calling
coerce_array, which is:

  struct value *
  coerce_array (struct value *arg)
  {
    struct type *type;
  
    arg = coerce_ref (arg);
    type = check_typedef (arg->type ());
  
    switch (type->code ())
      {
      case TYPE_CODE_ARRAY:
        if (!type->is_vector () && current_language->c_style_arrays_p ())
  	arg = value_coerce_array (arg);
        break;
      case TYPE_CODE_FUNC:
        arg = value_coerce_function (arg);
        break;
      }
    return arg;
  }

Notice that for TYPE_CODE_ARRAY we only actually do anything when
c_style_arrays_p() is true, which it isn't for Ada.  So we're not going
to convert the array into a pointer, which means (I think) that the
value_at_lazy isn't going to do what you want.  I suspect this is why
there are two, very similar functions.

What are your thoughts?

Thanks,
Andrew