Re: [PATCH] ada-lang.c:coerce_unspec_val_to_type: Preserve laziness.

[Joel Brobecker <brobecker@adacore.com>]

Hi Pedro,

> ada-lang.c:coerce_unspec_val_to_type does:
> 
>       if (value_lazy (val)
> 	  || TYPE_LENGTH (type) > TYPE_LENGTH (value_type (val)))
> 	result = allocate_value_lazy (type);
>       else
> 	{
> 	  result = allocate_value (type);
> 	  memcpy (value_contents_raw (result), value_contents (val),
> 		  TYPE_LENGTH (type));
> 	}
>       set_value_component_location (result, val);
>       set_value_bitsize (result, value_bitsize (val));
>       set_value_bitpos (result, value_bitpos (val));
>       set_value_address (result, value_address (val));
>       set_value_optimized_out (result, value_optimized_out (val));
> 
> Notice that before value_optimized_out was made to auto-fetch lazy
> values, VAL would end up still lazy if it was lazy on entry.  It's not
> really a problem here if VAL is lazy, and VAL->optimized_out is 0,
> because RESULT is also left lazy.  IOW, this just wants to copy the
> VAL->optimized_out flag to RESULT->optimized_out, nothing else.
> 
> The patch adds the value_optimized_out_const function for that.
> 
> (I found this out by grepping for set_value_optimized_out and trying
> to convert the uses I found to instead allocate the value with
> allocate_optimized_out_value.)
> 
> Tested on x86_64 Fedora 17.

> gdb/
> 2013-07-04  Pedro Alves  <palves@redhat.com>
> 
> 	* ada-lang.c (coerce_unspec_val_to_type): Use
> 	value_optimized_out_const.
> 	* value.c (value_optimized_out_const): New function.
> 	* value.h (value_optimized_out_const): New declaration.

Thanks for the patch!

We can actually demonstrate a regression which your patch fixes.
Consider:

   type Small is range -64 .. 63;
   for Small'Size use 7;
   type Arr is array (1..10) of Small;
   pragma Pack (Arr);

   type Arr_Ptr is access Arr;

   An_Arr_Ptr : Arr_Ptr := new Arr'(10, 20, 30, 40, 50, 60, 62, 63,
                                    -23, 42);

Trying to print one element of An_Arr_Ptr yields:

    (gdb) p an_arr_ptr(3)
    Cannot access memory at address 0x0

I've updated one of the testcases that deals with array "pointers"
(we call them access types in Ada) to add this case:

    http://www.sourceware.org/ml/gdb-patches/2013-07/msg00254.html

Since your patch looks correct to me, you had answers to Andrew's
comments, this is a regression, you are away for a while and no one
else commented on your patch, I've taken the liberty of checking it
in.

> ---
>  gdb/ada-lang.c |    2 +-
>  gdb/value.c    |    6 ++++++
>  gdb/value.h    |    8 +++++++-
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index 8240fee..dc5f2b6 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -581,7 +581,7 @@ coerce_unspec_val_to_type (struct value *val, struct type *type)
>        set_value_bitsize (result, value_bitsize (val));
>        set_value_bitpos (result, value_bitpos (val));
>        set_value_address (result, value_address (val));
> -      set_value_optimized_out (result, value_optimized_out (val));
> +      set_value_optimized_out (result, value_optimized_out_const (val));
>        return result;
>      }
>  }
> diff --git a/gdb/value.c b/gdb/value.c
> index 353f62a..9e58199 100644
> --- a/gdb/value.c
> +++ b/gdb/value.c
> @@ -1062,6 +1062,12 @@ value_optimized_out (struct value *value)
>    return value->optimized_out;
>  }
>  
> +int
> +value_optimized_out_const (const struct value *value)
> +{
> +  return value->optimized_out;
> +}
> +
>  void
>  set_value_optimized_out (struct value *value, int val)
>  {
> diff --git a/gdb/value.h b/gdb/value.h
> index 8a66aa4..8d669ec 100644
> --- a/gdb/value.h
> +++ b/gdb/value.h
> @@ -319,10 +319,16 @@ extern int value_fetch_lazy (struct value *val);
>  extern int value_contents_equal (struct value *val1, struct value *val2);
>  
>  /* If nonzero, this is the value of a variable which does not actually
> -   exist in the program.  */
> +   exist in the program, at least partially.  If the value is lazy,
> +   this may fetch it now.  */
>  extern int value_optimized_out (struct value *value);
>  extern void set_value_optimized_out (struct value *value, int val);
>  
> +/* Like value_optimized_out, but don't fetch the value even if it is
> +   lazy.  Mainly useful for constructing other values using VALUE as
> +   template.  */
> +extern int value_optimized_out_const (const struct value *value);
> +
>  /* Like value_optimized_out, but return false if any bit in the object
>     is valid.  */
>  extern int value_entirely_optimized_out (const struct value *value);

-- 
Joel