On May 29, 2015 8:42:50 PM GMT+02:00, Aldy Hernandez <al...@redhat.com> wrote:
>On 05/28/2015 04:35 PM, Jason Merrill wrote:
>> 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?
>
>Ok, I see what I was trying to do, albeit incorrectly. Imagine this:
>
>unsigned int i=555;
>
>int main()
>{
> unsigned int array[i];
> ...
>}
>
>For the VLA, I'd like to check if we have an array type with a missing
>DW_AT_{upper,lower}_bound late in the game, and fill it in.
>
>During early dwarf we only have an uninitialized gimple register
>representing the bound, and loc_list_from_tree() cannot find the RTL
>with the final bound location. Thus, we end up with a missing bound,
>which I propose to fill in late dwarf.
>
>Obviously I was doing some nonsense with TYPE_SIZE != INTEGER_CST, when
>
>in reality I should probably check that TREE_CODE (type) == ARRAY_TYPE
>and that we are missing the bound late (by looking for DW_AT_*_bound in
>
>the cached DIE).
>
>Is this acceptable, or where you thinking of some other scheme?
ISTR I had to mark the gimple reg used for the bound as non-DECL_IGNORED for
the LTO stuff.
Richard.
>Thanks.
>Aldy
