> On Feb 3, 2023, at 2:49 AM, Richard Biener <rguent...@suse.de> wrote:
>
> On Thu, 2 Feb 2023, Qing Zhao wrote:
>
>>
>>
>>> On Feb 2, 2023, at 8:54 AM, Richard Biener <rguent...@suse.de> wrote:
>>>
>>> On Thu, 2 Feb 2023, Qing Zhao wrote:
>>>
>>>>
>>>>
>
> [...]
>
>>>>>>>> + return flexible_size_type_p (TREE_TYPE (last));
>>>>>>>
>>>>>>> For types with many members this can become quite slow (IIRC we had
>>>>>>> bugs about similar walks of all fields in types), and this function
>>>>>>> looks like it's invoked multiple times on the same type per TU.
>>>>>>>
>>>>>>> In principle the property is fixed at the time we lay out a record
>>>>>>> type, so we might want to compute it at that time and record the
>>>>>>> result.
>>>>>>
>>>>>> You mean in FE?
>>>>>
>>>>> Yes, either in the frontend or in the middle-ends layout_type.
>>>>>
>>>>>> Yes, that?s better and cleaner.
>>>>>>
>>>>>> I will add one more field in the TYPE structure to record this
>>>>>> information and check this field during middle end.
>>>>>>
>>>>>> I had the same thought in the beginning, but not sure whether adding a
>>>>>> new field in IR is necessary or not, other places in middle end might
>>>>>> not use this new field.
>>>>>
>>>>> It might be interesting to search for other code walking all fields of
>>>>> a type to determine this or similar info.
>>>>
>>>> There is one which is defined in tree.cc but only is referenced in
>>>> c/c-decl.cc:
>>>>
>>>> /* Determine whether TYPE is a structure with a flexible array member,
>>>> or a union containing such a structure (possibly recursively). */
>>>> flexible_array_type_p
>>>>
>>>> However, this routine is a little different than the one I tried to add:
>>>>
>>>> In the current routine ?flexible_array_type_p?, only one level nesting in
>>>> the structure is accepted, multiple nesting in structure is not permitted.
>>>>
>>>> So, my question is: shall we accept multiple nesting in structure? i.e.
>>>
>>> If we don't reject the testcase with an error, then yes.
>>
>> Gcc currently accepts the multiple nesting in structure without error.
>> So, we will continue to accept such extension as long as the flex array
>> is at the end of the structure. At the same time, for the case the flex
>> array is in the middle of the structure, issue additional warnings now
>> to discourage such usage, and deprecate this case in a future release.
>>
>> Does this sound reasonable?
>
> Please don't mix several issues - I think the flex array in the
> middle of a structure is separate and we shouldn't report that
> as flexible_array_type_p or flexible_size_type_p since the size
> of the containing structure is not variable.
Agreed on this.
My major question here is (for documentation change, sorry for mixing this
thread with the documentation change): do we need to document this case
together with the case in which struct with flex array is embedded into another
structure? (As a GCC extension?)
>
> For diagnostic purposes the intended use case is to treat
> a pointer to a structure that appears to have a fixed size
> but has (recursive) a member with a flexible array at the end
> as having variable size. Just the same as array_at_struct_end_p
> treats this for the case of accesses involving such a type.
Yes.
>
> For the middle position case that's not the case.
Yes.
Thanks.
Qing
>
> Richard.
>
>> Qing
>>>
>>>> struct A {
>>>> int n;
>>>> char data[];/* Content following header */
>>>> };
>>>>
>>>> struct B {
>>>> int m;
>>>> struct A a;
>>>> };
>>>>
>>>> struct C {
>>>> int q;
>>>> struct B b;
>>>> };
>>>>
>>>> Qing
>>>>>
>>>>>> thanks.
>>>>>>
>>>>>> Qing
>>>>>>
>>>>>>>
>>>>>>>> + return false;
>>>>>>>> + case UNION_TYPE:
>>>>>>>> + for (x = TYPE_FIELDS (type); x != NULL_TREE; x = DECL_CHAIN (x))
>>>>>>>> + {
>>>>>>>> + if (TREE_CODE (x) == FIELD_DECL
>>>>>>>> + && flexible_array_type_p (TREE_TYPE (x)))
>>>>>>>> + return true;
>>>>>>>> + }
>>>>>>>> + return false;
>>>>>>>> + default:
>>>>>>>> + return false;
>>>>>>>> + }
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> /* Compute __builtin_object_size for PTR, which is a ADDR_EXPR.
>>>>>>>> OBJECT_SIZE_TYPE is the second argument from __builtin_object_size.
>>>>>>>> If unknown, return size_unknown (object_size_type). */
>>>>>>>> @@ -633,45 +669,68 @@ addr_object_size (struct object_size_info *osi,
>>>>>>>> const_tree ptr,
>>>>>>>> v = NULL_TREE;
>>>>>>>> break;
>>>>>>>> case COMPONENT_REF:
>>>>>>>> - if (TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
>>>>>>>> + /* When the ref is not to an array, a record or a
>>>>>>>> union, it
>>>>>>>> + will not have flexible size, compute the object
>>>>>>>> size
>>>>>>>> + directly. */
>>>>>>>> + if ((TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
>>>>>>>> + && (TREE_CODE (TREE_TYPE (v)) != RECORD_TYPE)
>>>>>>>> + && (TREE_CODE (TREE_TYPE (v)) != UNION_TYPE))
>>>>>>>> {
>>>>>>>> v = NULL_TREE;
>>>>>>>> break;
>>>>>>>> }
>>>>>>>> - is_flexible_array_mem_ref =
>>>>>>>> array_ref_flexible_size_p (v);
>>>>>>>> - while (v != pt_var && TREE_CODE (v) ==
>>>>>>>> COMPONENT_REF)
>>>>>>>> - if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> - != UNION_TYPE
>>>>>>>> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> - != QUAL_UNION_TYPE)
>>>>>>>> - break;
>>>>>>>> - else
>>>>>>>> - v = TREE_OPERAND (v, 0);
>>>>>>>> - if (TREE_CODE (v) == COMPONENT_REF
>>>>>>>> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> - == RECORD_TYPE)
>>>>>>>> + /* if the record or union does not have flexible
>>>>>>>> size
>>>>>>>> + compute the object size directly. */
>>>>>>>> + if (TREE_CODE (TREE_TYPE (v)) == RECORD_TYPE
>>>>>>>> + || TREE_CODE (TREE_TYPE (v)) == UNION_TYPE)
>>>>>>>> {
>>>>>>>> - /* compute object size only if v is not a
>>>>>>>> - flexible array member. */
>>>>>>>> - if (!is_flexible_array_mem_ref)
>>>>>>>> + if (!flexible_size_type_p (TREE_TYPE (v)))
>>>>>>>> {
>>>>>>>> v = NULL_TREE;
>>>>>>>> break;
>>>>>>>> }
>>>>>>>> - v = TREE_OPERAND (v, 0);
>>>>>>>> + else
>>>>>>>> + v = TREE_OPERAND (v, 0);
>>>>>>>> }
>>>>>>>> - while (v != pt_var && TREE_CODE (v) ==
>>>>>>>> COMPONENT_REF)
>>>>>>>> - if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> - != UNION_TYPE
>>>>>>>> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> - != QUAL_UNION_TYPE)
>>>>>>>> - break;
>>>>>>>> - else
>>>>>>>> - v = TREE_OPERAND (v, 0);
>>>>>>>> - if (v != pt_var)
>>>>>>>> - v = NULL_TREE;
>>>>>>>> else
>>>>>>>> - v = pt_var;
>>>>>>>> + {
>>>>>>>> + /* Now the ref is to an array type. */
>>>>>>>> + is_flexible_array_mem_ref
>>>>>>>> + = array_ref_flexible_size_p (v);
>>>>>>>> + while (v != pt_var && TREE_CODE (v) ==
>>>>>>>> COMPONENT_REF)
>>>>>>>> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>>>>>>>> + != UNION_TYPE
>>>>>>>> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v,
>>>>>>>> 0)))
>>>>>>>> + != QUAL_UNION_TYPE)
>>>>>>>> + break;
>>>>>>>> + else
>>>>>>>> + v = TREE_OPERAND (v, 0);
>>>>>>>> + if (TREE_CODE (v) == COMPONENT_REF
>>>>>>>> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v,
>>>>>>>> 0)))
>>>>>>>> + == RECORD_TYPE)
>>>>>>>> + {
>>>>>>>> + /* compute object size only if v is not a
>>>>>>>> + flexible array member. */
>>>>>>>> + if (!is_flexible_array_mem_ref)
>>>>>>>> + {
>>>>>>>> + v = NULL_TREE;
>>>>>>>> + break;
>>>>>>>> + }
>>>>>>>> + v = TREE_OPERAND (v, 0);
>>>>>>>> + }
>>>>>>>> + while (v != pt_var && TREE_CODE (v) ==
>>>>>>>> COMPONENT_REF)
>>>>>>>> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v,
>>>>>>>> 0)))
>>>>>>>> + != UNION_TYPE
>>>>>>>> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v,
>>>>>>>> 0)))
>>>>>>>> + != QUAL_UNION_TYPE)
>>>>>>>> + break;
>>>>>>>> + else
>>>>>>>> + v = TREE_OPERAND (v, 0);
>>>>>>>> + if (v != pt_var)
>>>>>>>> + v = NULL_TREE;
>>>>>>>> + else
>>>>>>>> + v = pt_var;
>>>>>>>> + }
>>>>>>>> break;
>>>>>>>> default:
>>>>>>>> v = pt_var;
>>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Richard Biener <rguent...@suse.de>
>>>>>>> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461
>>>>>>> Nuernberg,
>>>>>>> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
>>>>>>> HRB 36809 (AG Nuernberg)
>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> Richard Biener <rguent...@suse.de>
>>>>> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
>>>>> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
>>>>> HRB 36809 (AG Nuernberg)
>>>>
>>>>
>>>
>>> --
>>> Richard Biener <rguent...@suse.de>
>>> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
>>> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
>>> HRB 36809 (AG Nuernberg)
>>
>>
>
> --
> Richard Biener <rguent...@suse.de>
> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> HRB 36809 (AG Nuernberg)
