Re: [patch 10/10] debug-early merge: compiler proper

[Jason Merrill <jason@redhat.com>]

On 05/28/2015 02:53 PM, Aldy Hernandez wrote:
> On 05/27/2015 08:39 AM, Jason Merrill wrote:
>> On 05/20/2015 11:50 AM, Aldy Hernandez wrote:
>
>>> +  /* Fill in the size of variable-length fields in late dwarf.  */
>>> +  if (TREE_ASM_WRITTEN (type)
>>> +      && !early_dwarf_dumping)
>>> +    {
>>> +      tree member;
>>> +      for (member = TYPE_FIELDS (type); member; member = DECL_CHAIN
>>> (member))
>>> +    fill_variable_array_bounds (TREE_TYPE (member));
>>> +      return;
>>> +    }
>>
>> Why is this happening in late dwarf?  I'm concerned that front-end
>> information that is necessary to do this might be lost by that point.
>
> I thought only after the optimizations had run their course would we be
> guaranteed to have accurate bound information.  At least, that's what my
> experience showed.

Hmm, I'm don't know why optimizations would change the representation of 
the array type.

>>> +      /* Variable-length types may be incomplete even if
>>> +     TREE_ASM_WRITTEN.  For such types, fall through to
>>> +     gen_array_type_die() and possibly fill in
>>> +     DW_AT_{upper,lower}_bound attributes.  */
>>> +      if ((TREE_CODE (type) != ARRAY_TYPE
>>> +       && TREE_CODE (type) != RECORD_TYPE
>>> +       && TREE_CODE (type) != UNION_TYPE
>>> +       && TREE_CODE (type) != QUAL_UNION_TYPE)
>>> +      || (TYPE_SIZE (type)
>>> +          && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST))
>>
>> Similarly, why check for INTEGER_CST here?
>
> The INTEGER_CST check was supposed to mean "we have bound information
> already, no need to look further".
>
> I guess we could have a variable length bound that does not decay to a
> constant.

Right.  I would expect that to usually be the case with VLAs.

> Perhaps I could check the presence of a cached DIE with a
> type DIE containing a DW_TAG_subrange_type *and*
> DW_AT_{lower,upper}_bound ??.  Basically I just want to add bound
> information, if available and not already present.
>
> Suggestions?

I'm still not sure why we can't just emit bound info in early dwarf. 
Can you be more specific about the optimization thing?

Jason