> On Nov 25, 2024, at 16:46, Martin Uecker <uec...@tugraz.at> wrote:
>
>
> Hi Qing,
>
> Am Montag, dem 25.11.2024 um 17:40 +0000 schrieb Qing Zhao:
>> Hi, Martin,
>>
>> I didn’t go through all the details of your patch.
>>
>> But I have one question:
>>
>> Did you consider the effect of the option -fstrict-flex-array
>> (https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/C-Dialect-Options.html#index-fstrict-flex-arrays)
>> on how gcc treats the zero size trailing array, 1-element trailing array as
>> flexible array member in the patch?
>
> I used the function which was already there which
> does not take this into account. For the new version
> of the patch this should not matter anymore.
Why it’s not matter anymore?
For the following testing case:
struct S{int x,y[1];}*a;
int main(void){
struct S{int x,y[];};
}
With your latest patch, the two structures are considered as compatible with
-g;
However, if we add -fstrict-flex-array=2 or -fstrict-flex-array=3, the
trailing array y[1] is NOT treated
as FAM anymore, as a result, these two structure are NOT compatible too.
Do I miss anything obvious?
Thanks.
Qing
>
> Martin
>
>
>>
>> thanks.
>>
>> Qing
>>> On Nov 23, 2024, at 14:45, Martin Uecker <uec...@tugraz.at> wrote:
>>>
>>>
>>> This patch tries fixes the errors we have because of
>>> flexible array members. I am bit unsure about the exception
>>> for the mode.
>>>
>>> Bootstrapped and regression tested on x86_64.
>>>
>>>
>>>
>>> Fix type compatibility for types with flexible array member
>>> [PR113688,PR114014,PR117724]
>>>
>>> verify_type checks the compatibility of TYPE_CANONICAL using
>>> gimple_canonical_types_compatible_p. But it is stricter than what the
>>> C standard requires and therefor inconsistent with how TYPE_CANONICAL is
>>> set
>>> in the C FE. Here, the logic is changed to ignore array size when one of
>>> the
>>> types is a flexible array member. To not get errors because of
>>> inconsistent
>>> number of members, zero-sized arrays are not ignored anymore when checking
>>> fields of a struct (which is stricter than what was done before).
>>> Finally, a exception is added that allows the TYPE_MODE of a type with
>>> flexible array member to differ from another compatible type.
>>>
>>> PR c/113688
>>> PR c/114014
>>> PR c/117724
>>>
>>> gcc/ChangeLog:
>>> * tree.cc (gimple_canonical_types_compatible_p): Revise
>>> logic for types with FAM.
>>> (verify_type): Add exception for mode for types with FAM.
>>>
>>> gcc/testsuite/ChangeLog:
>>> * gcc.dg/pr113688.c: New test.
>>> * gcc.dg/pr114014.c: New test.
>>> * gcc.dg/pr117724.c: New test.
>>>
>>> diff --git a/gcc/testsuite/gcc.dg/pr113688.c
>>> b/gcc/testsuite/gcc.dg/pr113688.c
>>> new file mode 100644
>>> index 00000000000..8dee8c86f1b
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/pr113688.c
>>> @@ -0,0 +1,8 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-g" } */
>>> +
>>> +struct S{int x,y[1];}*a;
>>> +int main(void){
>>> + struct S{int x,y[];};
>>> +}
>>> +
>>> diff --git a/gcc/testsuite/gcc.dg/pr114014.c
>>> b/gcc/testsuite/gcc.dg/pr114014.c
>>> new file mode 100644
>>> index 00000000000..ab783f4f85d
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/pr114014.c
>>> @@ -0,0 +1,14 @@
>>> +/* PR c/114014
>>> + * { dg-do compile }
>>> + * { dg-options "-std=c23 -g" } */
>>> +
>>> +struct r {
>>> + int a;
>>> + char b[];
>>> +};
>>> +struct r {
>>> + int a;
>>> + char b[0];
>>> +}; /* { dg-error "redefinition" } */
>>> +
>>> +
>>> diff --git a/gcc/testsuite/gcc.dg/pr117724.c
>>> b/gcc/testsuite/gcc.dg/pr117724.c
>>> new file mode 100644
>>> index 00000000000..d631daeb644
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/pr117724.c
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-g" } */
>>> +
>>> +struct {
>>> + unsigned long len;
>>> + unsigned long size;
>>> + char data[];
>>> +}; /* { dg-warning "unnamed struct" } */
>>> +struct {
>>> + struct {
>>> + unsigned long len;
>>> + unsigned long size;
>>> + char data[6];
>>> + };
>>> +}; /* { dg-warning "unnamed struct" } */
>>> +
>>> diff --git a/gcc/tree.cc b/gcc/tree.cc
>>> index 1da06c7d4e9..dbf6b180496 100644
>>> --- a/gcc/tree.cc
>>> +++ b/gcc/tree.cc
>>> @@ -13900,8 +13900,11 @@ gimple_canonical_types_compatible_p (const_tree
>>> t1, const_tree t2,
>>> || TREE_CODE (t1) == NULLPTR_TYPE)
>>> return true;
>>>
>>> - /* Can't be the same type if they have different mode. */
>>> - if (TYPE_MODE (t1) != TYPE_MODE (t2))
>>> + /* Can't be compatible types if they have different mode. We allow
>>> + mismatching modes for types with flexible array member. */
>>> + if (!flexible_array_type_p (t1)
>>> + && !flexible_array_type_p (t2)
>>> + && (TYPE_MODE (t1) != TYPE_MODE (t2)))
>>> return false;
>>>
>>> /* Non-aggregate types can be handled cheaply. */
>>> @@ -13952,7 +13955,7 @@ gimple_canonical_types_compatible_p (const_tree t1,
>>> const_tree t2,
>>> {
>>> case ARRAY_TYPE:
>>> /* Array types are the same if the element types are the same and
>>> - the number of elements are the same. */
>>> + minimum and maximum index are the same. */
>>> if (!gimple_canonical_types_compatible_p (TREE_TYPE (t1), TREE_TYPE
>>> (t2),
>>> trust_type_canonical)
>>> || TYPE_STRING_FLAG (t1) != TYPE_STRING_FLAG (t2)
>>> @@ -14046,23 +14049,35 @@ gimple_canonical_types_compatible_p (const_tree
>>> t1, const_tree t2,
>>> f1 || f2;
>>> f1 = TREE_CHAIN (f1), f2 = TREE_CHAIN (f2))
>>> {
>>> - /* Skip non-fields and zero-sized fields. */
>>> - while (f1 && (TREE_CODE (f1) != FIELD_DECL
>>> - || (DECL_SIZE (f1)
>>> - && integer_zerop (DECL_SIZE (f1)))))
>>> + /* Skip non-fields. */
>>> + while (f1 && (TREE_CODE (f1) != FIELD_DECL))
>>> f1 = TREE_CHAIN (f1);
>>> - while (f2 && (TREE_CODE (f2) != FIELD_DECL
>>> - || (DECL_SIZE (f2)
>>> - && integer_zerop (DECL_SIZE (f2)))))
>>> + while (f2 && (TREE_CODE (f2) != FIELD_DECL))
>>> f2 = TREE_CHAIN (f2);
>>> if (!f1 || !f2)
>>> break;
>>> +
>>> + tree t1 = TREE_TYPE (f1);
>>> + tree t2 = TREE_TYPE (f2);
>>> +
>>> + /* Special case for flexible array members. */
>>> + if (TREE_CHAIN (f1) == NULL_TREE
>>> + && TREE_CHAIN (f2) == NULL_TREE
>>> + && TREE_CODE (t1) == ARRAY_TYPE
>>> + && TREE_CODE (t2) == ARRAY_TYPE
>>> + && (!DECL_NOT_FLEXARRAY (f1)
>>> + || !DECL_NOT_FLEXARRAY (f2))
>>> + && TYPE_REVERSE_STORAGE_ORDER (t1) == TYPE_REVERSE_STORAGE_ORDER (t2)
>>> + && TYPE_NONALIASED_COMPONENT (t1) == TYPE_NONALIASED_COMPONENT (t2)
>>> + && gimple_canonical_types_compatible_p
>>> + (TREE_TYPE (t1), TREE_TYPE (t2),
>>> + trust_type_canonical))
>>> + ;
>>> /* The fields must have the same name, offset and type. */
>>> - if (DECL_NONADDRESSABLE_P (f1) != DECL_NONADDRESSABLE_P (f2)
>>> + else if (DECL_NONADDRESSABLE_P (f1) != DECL_NONADDRESSABLE_P (f2)
>>>>> !gimple_compare_field_offset (f1, f2)
>>>>> !gimple_canonical_types_compatible_p
>>> - (TREE_TYPE (f1), TREE_TYPE (f2),
>>> - trust_type_canonical))
>>> + (t1, t2, trust_type_canonical))
>>> return false;
>>> }
>>>
>>> @@ -14206,6 +14221,9 @@ verify_type (const_tree t)
>>> }
>>>
>>> if (COMPLETE_TYPE_P (t) && TYPE_CANONICAL (t)
>>> + /* We allow a mismatch for flexible array members. */
>>> + && !flexible_array_type_p (t)
>>> + && !flexible_array_type_p (TYPE_CANONICAL (t))
>>> && TYPE_MODE (t) != TYPE_MODE (TYPE_CANONICAL (t)))
>>> {
>>> error ("%<TYPE_MODE%> of %<TYPE_CANONICAL%> is not compatible");
>>>
>>>
>>
>
