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

[Pedro Alves <palves@redhat.com>]

On 07/10/2013 01:44 AM, Joel Brobecker wrote:
> 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.

Thanks!

-- 
Pedro Alves