Hi, Richard,
Do you have more comments on my responds to your previous questions?
thanks.
Qing
> On Mar 10, 2023, at 8:48 AM, Qing Zhao via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>
>
>
>> On Mar 10, 2023, at 2:54 AM, Richard Biener <rguent...@suse.de> wrote:
>>
>> On Thu, 9 Mar 2023, Qing Zhao wrote:
>>
>>>
>>>
>>>> On Mar 9, 2023, at 7:20 AM, Richard Biener <rguent...@suse.de> wrote:
>>>>
>>>> On Fri, 24 Feb 2023, Qing Zhao wrote:
>>>>
>>>>> GCC extension accepts the case when a struct with a C99 flexible array
>>>>> member
>>>>> is embedded into another struct or union (possibly recursively).
>>>>> __builtin_object_size should treat such struct as flexible size.
>>>>>
>>>>> gcc/c/ChangeLog:
>>>>>
>>>>> PR tree-optimization/101832
>>>>> * c-decl.cc (finish_struct): Set TYPE_INCLUDE_FLEXARRAY for
>>>>> struct/union type.
>>>>
>>>> I can't really comment on the correctness of this part but since
>>>> only the C frontend will ever set this and you are using it from
>>>> addr_object_size which is also used for other C family languages
>>>> (at least), I wonder if you can really test
>>>>
>>>> + if (!TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (v)))
>>>>
>>>> there.
>>>
>>> You mean for C++ and also other C family languages (other than C), the
>>> above bit cannot be set?
>>> Yes, that’s true. The bit is only set for C. So is the bit
>>> DECL_NOT_FLEXARRAY, which is only set for C too.
>>> So, I am wondering whether the bit DECL_NOT_FLEXARRAY should be also set in
>>> middle end? Or we can set DECL_NOT_FLEXARRAY in C++ FE too? And then we can
>>> set TYPE_INCLUDE_FLEXARRAY also in C++ FE?
>>> What’s your suggestion?
>>>
>>> (I personally feel that DECL_NOT_FLEXARRAY and TYPE_INCLUDE_FLEXARRAY
>>> should be set in the same places).
>>
>> I was wondering if the above test errors on the conservative side
>> correctly - it will now, for all but C, cut off some thing where it
>> didn't before?
>
> As long as the default value of TYPE_INCLUDE_FLEXARRAY reflects the correct
> conservative behavior, then the testing should be correct, right?
>
> The default value of TYPE_INCLUDE_FLEXARRAY is 0, i.e, FALSE, means that the
> TYPE does not include a flex array by default, this is the correct behavior.
> Only when the TYPE does include a flexiarray, it will be set to TRUE. So, I
> think it’s correct.
>
> This is a different situation for DECL_NOT_FLEXARRAY, by default, the
> compiler will treat ALL trailing arrays as FMA, so in order to keep the
> correct conservative behavior, we should keep the default value for
> DECL_NOT_FLEXARRAY as it’s a FMA, i.e, DECL_NOT_FLEXARRAY being FALSE, by
> default. Only when the array is NOT a FMA, we set it to true.
>
> So, the default value for TYPE_INCLUDE_FLEXARRAY is correct.
>>
>>>>
>>>> Originally I was suggesting to set this flag in stor-layout.cc
>>>> which eventually all languages funnel their types through and
>>>> if there's language specific handling use a langhook (with the
>>>> default implementation preserving the status quo).
>>>
>>> If we decide to set the bits in stor-layout.cc, where is the best place to
>>> do it? I checked the star-layout.cc code, looks like “layout_type” might be
>>> the place where we can set these bits for RECORD_TYPE, UNION_TYPE?
>>
>> Yes, it would be layout_type.
>>
>>>>
>>>> Some more comments below ...
>>>>
>>>>> gcc/cp/ChangeLog:
>>>>>
>>>>> PR tree-optimization/101832
>>>>> * module.cc (trees_out::core_bools): Stream out new bit
>>>>> type_include_flexarray.
>>>>> (trees_in::core_bools): Stream in new bit type_include_flexarray.
>>>>>
>>>>> gcc/ChangeLog:
>>>>>
>>>>> PR tree-optimization/101832
>>>>> * print-tree.cc (print_node): Print new bit type_include_flexarray.
>>>>> * tree-core.h (struct tree_type_common): New bit
>>>>> type_include_flexarray.
>>>>> * tree-object-size.cc (addr_object_size): Handle structure/union type
>>>>> when it has flexible size.
>>>>> * tree-streamer-in.cc (unpack_ts_type_common_value_fields): Stream
>>>>> in new bit type_include_flexarray.
>>>>> * tree-streamer-out.cc (pack_ts_type_common_value_fields): Stream
>>>>> out new bit type_include_flexarray.
>>>>> * tree.h (TYPE_INCLUDE_FLEXARRAY): New macro
>>>>> TYPE_INCLUDE_FLEXARRAY.
>>>>>
>>>>> gcc/testsuite/ChangeLog:
>>>>>
>>>>> PR tree-optimization/101832
>>>>> * gcc.dg/builtin-object-size-pr101832.c: New test.
>>>>> ---
>>>>> gcc/c/c-decl.cc | 12 ++
>>>>> gcc/cp/module.cc | 2 +
>>>>> gcc/print-tree.cc | 5 +
>>>>> .../gcc.dg/builtin-object-size-pr101832.c | 134 ++++++++++++++++++
>>>>> gcc/tree-core.h | 4 +-
>>>>> gcc/tree-object-size.cc | 79 +++++++----
>>>>> gcc/tree-streamer-in.cc | 1 +
>>>>> gcc/tree-streamer-out.cc | 1 +
>>>>> gcc/tree.h | 6 +
>>>>> 9 files changed, 215 insertions(+), 29 deletions(-)
>>>>> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
>>>>>
>>>>> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
>>>>> index 08078eadeb8..f589a2f5192 100644
>>>>> --- a/gcc/c/c-decl.cc
>>>>> +++ b/gcc/c/c-decl.cc
>>>>> @@ -9284,6 +9284,18 @@ finish_struct (location_t loc, tree t, tree
>>>>> fieldlist, tree attributes,
>>>>> /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x. */
>>>>> DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field,
>>>>> x);
>>>>>
>>>>> + /* Set TYPE_INCLUDE_FLEXARRAY for the context of x, t
>>>>> + * when x is an array. */
>>>>> + if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
>>>>> + TYPE_INCLUDE_FLEXARRAY (t) = flexible_array_member_type_p (TREE_TYPE
>>>>> (x)) ;
>>>>> + /* Recursively set TYPE_INCLUDE_FLEXARRAY for the context of x, t
>>>>> + when x is the last field. */
>>>>> + else if ((TREE_CODE (TREE_TYPE (x)) == RECORD_TYPE
>>>>> + || TREE_CODE (TREE_TYPE (x)) == UNION_TYPE)
>>>>> + && TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (x))
>>>>> + && is_last_field)
>>>>> + TYPE_INCLUDE_FLEXARRAY (t) = true;
>>>>> +
>>>>> if (DECL_NAME (x)
>>>>> || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
>>>>> saw_named_field = true;
>>>>> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
>>>>> index ac2fe66b080..c750361b704 100644
>>>>> --- a/gcc/cp/module.cc
>>>>> +++ b/gcc/cp/module.cc
>>>>> @@ -5371,6 +5371,7 @@ trees_out::core_bools (tree t)
>>>>> WB (t->type_common.lang_flag_5);
>>>>> WB (t->type_common.lang_flag_6);
>>>>> WB (t->type_common.typeless_storage);
>>>>> + WB (t->type_common.type_include_flexarray);
>>>>> }
>>>>>
>>>>> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
>>>>> @@ -5551,6 +5552,7 @@ trees_in::core_bools (tree t)
>>>>> RB (t->type_common.lang_flag_5);
>>>>> RB (t->type_common.lang_flag_6);
>>>>> RB (t->type_common.typeless_storage);
>>>>> + RB (t->type_common.type_include_flexarray);
>>>>> }
>>>>>
>>>>> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
>>>>> diff --git a/gcc/print-tree.cc b/gcc/print-tree.cc
>>>>> index 1f3afcbbc86..efacdb7686f 100644
>>>>> --- a/gcc/print-tree.cc
>>>>> +++ b/gcc/print-tree.cc
>>>>> @@ -631,6 +631,11 @@ print_node (FILE *file, const char *prefix, tree
>>>>> node, int indent,
>>>>> && TYPE_CXX_ODR_P (node))
>>>>> fputs (" cxx-odr-p", file);
>>>>>
>>>>> + if ((code == RECORD_TYPE
>>>>> + || code == UNION_TYPE)
>>>>> + && TYPE_INCLUDE_FLEXARRAY (node))
>>>>> + fputs (" include-flexarray", file);
>>>>> +
>>>>> /* The transparent-union flag is used for different things in
>>>>> different nodes. */
>>>>> if ((code == UNION_TYPE || code == RECORD_TYPE)
>>>>> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
>>>>> b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
>>>>> new file mode 100644
>>>>> index 00000000000..60078e11634
>>>>> --- /dev/null
>>>>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
>>>>> @@ -0,0 +1,134 @@
>>>>> +/* PR 101832:
>>>>> + GCC extension accepts the case when a struct with a C99 flexible array
>>>>> + member is embedded into another struct (possibly recursively).
>>>>> + __builtin_object_size will treat such struct as flexible size.
>>>>> + However, when a structure with non-C99 flexible array member, i.e,
>>>>> trailing
>>>>> + [0], [1], or [4], is embedded into anther struct, the stucture will
>>>>> not
>>>>> + be treated as flexible size. */
>>>>> +/* { dg-do run } */
>>>>> +/* { dg-options "-O2" } */
>>>>> +
>>>>> +#include "builtin-object-size-common.h"
>>>>> +
>>>>> +#define expect(p, _v) do { \
>>>>> + size_t v = _v; \
>>>>> + if (p == v) \
>>>>> + __builtin_printf ("ok: %s == %zd\n", #p, p); \
>>>>> + else {\
>>>>> + __builtin_printf ("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
>>>>> + FAIL (); \
>>>>> + } \
>>>>> +} while (0);
>>>>> +
>>>>> +
>>>>> +struct A {
>>>>> + int n;
>>>>> + char data[];
>>>>> +};
>>>>> +
>>>>> +struct B {
>>>>> + int m;
>>>>> + struct A a;
>>>>> +};
>>>>> +
>>>>> +struct C {
>>>>> + int q;
>>>>> + struct B b;
>>>>> +};
>>>>> +
>>>>> +struct A0 {
>>>>> + int n;
>>>>> + char data[0];
>>>>> +};
>>>>> +
>>>>> +struct B0 {
>>>>> + int m;
>>>>> + struct A0 a;
>>>>> +};
>>>>> +
>>>>> +struct C0 {
>>>>> + int q;
>>>>> + struct B0 b;
>>>>> +};
>>>>> +
>>>>> +struct A1 {
>>>>> + int n;
>>>>> + char data[1];
>>>>> +};
>>>>> +
>>>>> +struct B1 {
>>>>> + int m;
>>>>> + struct A1 a;
>>>>> +};
>>>>> +
>>>>> +struct C1 {
>>>>> + int q;
>>>>> + struct B1 b;
>>>>> +};
>>>>> +
>>>>> +struct An {
>>>>> + int n;
>>>>> + char data[8];
>>>>> +};
>>>>> +
>>>>> +struct Bn {
>>>>> + int m;
>>>>> + struct An a;
>>>>> +};
>>>>> +
>>>>> +struct Cn {
>>>>> + int q;
>>>>> + struct Bn b;
>>>>> +};
>>>>> +
>>>>> +volatile void *magic1, *magic2;
>>>>> +
>>>>> +int main (int argc, char *argv[])
>>>>> +{
>>>>> + struct B *outer;
>>>>> + struct C *outest;
>>>>> +
>>>>> + /* Make sure optimization can't find some other object size. */
>>>>> + outer = (void *)magic1;
>>>>> + outest = (void *)magic2;
>>>>> +
>>>>> + expect (__builtin_object_size (&outer->a, 1), -1);
>>>>> + expect (__builtin_object_size (&outest->b, 1), -1);
>>>>> + expect (__builtin_object_size (&outest->b.a, 1), -1);
>>>>> +
>>>>> + struct B0 *outer0;
>>>>> + struct C0 *outest0;
>>>>> +
>>>>> + /* Make sure optimization can't find some other object size. */
>>>>> + outer0 = (void *)magic1;
>>>>> + outest0 = (void *)magic2;
>>>>> +
>>>>> + expect (__builtin_object_size (&outer0->a, 1), sizeof (outer0->a));
>>>>> + expect (__builtin_object_size (&outest0->b, 1), sizeof (outest0->b));
>>>>> + expect (__builtin_object_size (&outest0->b.a, 1), sizeof
>>>>> (outest0->b.a));
>>>>> +
>>>>> + struct B1 *outer1;
>>>>> + struct C1 *outest1;
>>>>> +
>>>>> + /* Make sure optimization can't find some other object size. */
>>>>> + outer1 = (void *)magic1;
>>>>> + outest1 = (void *)magic2;
>>>>> +
>>>>> + expect (__builtin_object_size (&outer1->a, 1), sizeof (outer1->a));
>>>>> + expect (__builtin_object_size (&outest1->b, 1), sizeof (outest1->b));
>>>>> + expect (__builtin_object_size (&outest1->b.a, 1), sizeof
>>>>> (outest1->b.a));
>>>>> +
>>>>> + struct Bn *outern;
>>>>> + struct Cn *outestn;
>>>>> +
>>>>> + /* Make sure optimization can't find some other object size. */
>>>>> + outern = (void *)magic1;
>>>>> + outestn = (void *)magic2;
>>>>> +
>>>>> + expect (__builtin_object_size (&outern->a, 1), sizeof (outern->a));
>>>>> + expect (__builtin_object_size (&outestn->b, 1), sizeof (outestn->b));
>>>>> + expect (__builtin_object_size (&outestn->b.a, 1), sizeof
>>>>> (outestn->b.a));
>>>>> +
>>>>> + DONE ();
>>>>> + return 0;
>>>>> +}
>>>>> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
>>>>> index acd8deea34e..705d5702b9c 100644
>>>>> --- a/gcc/tree-core.h
>>>>> +++ b/gcc/tree-core.h
>>>>> @@ -1718,7 +1718,9 @@ struct GTY(()) tree_type_common {
>>>>> unsigned empty_flag : 1;
>>>>> unsigned indivisible_p : 1;
>>>>> RECORD_OR_UNION_CHECK
>>>>
>>>> it looks like the bit could be eventually shared with
>>>> no_named_args_stdarg_p (but its accessor doesn't use
>>>> FUNC_OR_METHOD_CHECK)
>>> You mean to let “type_include_flexarray” share the same bit with
>>> “no_named_args_stdarg_p” in order to save 1-bit space in IR?
>>> Then change the
>>>
>>> /* True if this is a stdarg function with no named arguments (C2x
>>> (...) prototype, where arguments can be accessed with va_start and
>>> va_arg), as opposed to an unprototyped function. */
>>> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
>>> (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
>>>
>>> /* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
>>> at the last field recursively. */
>>> #define TYPE_INCLUDE_FLEXARRAY(NODE) \
>>> (TYPE_CHECK (NODE)->type_common.type_include_flexarray)
>>>
>>> To:
>>>
>>> union {
>>> unsigned no_named_args_stdarg_p : 1;
>>> /* TYPE_INCLUDE_FLEXARRAY flag for RECORD_TYPE and UNION_TYPE. */
>>> unsigned int type_include_flexarray : 1;
>>> } shared_bit;
>>> unsigned spare : 15;
>>>
>>> /* True if this is a stdarg function with no named arguments (C2x
>>> (...) prototype, where arguments can be accessed with va_start and
>>> va_arg), as opposed to an unprototyped function. */
>>> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
>>> (FUNC_OR_METHOD_CHECK (NODE)->type_common.shared_bit.no_named_args_stdarg_p)
>>>
>>> /* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
>>> at the last field recursively. */
>>> #define TYPE_INCLUDE_FLEXARRAY(NODE) \
>>> (RECORD_OR_UNION_CHECK(NODE)->type_common.shared_bit.type_include_flexarray)
>>
>> No, we're just overloading bits by using the same name for different
>> purposes. I don't think such a union would pack nicely. We overload
>> by documenting the uses, in the above cases the uses are separated
>> by the kind of the tree node, RECORD/UNION_TYPE vs. FUNCTION/METHOD_TYPE
>> and the accessor macros should be updated to use the appropriate
>> tree check macros covering that so we don't try to inspect the
>> "wrong bit”.
> Okay, I see. Then should I change the name of that bit to one that reflect
> two usages?
>>
>>>>
>>>>> alias_set_type alias_set;
>>>>> tree pointer_to;
>>>>> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
>>>>> index 9a936a91983..22b3c72ea6e 100644
>>>>> --- a/gcc/tree-object-size.cc
>>>>> +++ b/gcc/tree-object-size.cc
>>>>> @@ -633,45 +633,68 @@ 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 (TREE_CODE (TREE_TYPE (v)) == RECORD_TYPE
>>>>> + || TREE_CODE (TREE_TYPE (v)) == UNION_TYPE)
>>>>> + /* if the record or union does not include a flexible array
>>>>> + recursively, compute the object size directly. */
>>>>> {
>>>>> - /* compute object size only if v is not a
>>>>> - flexible array member. */
>>>>> - if (!is_flexible_array_mem_ref)
>>>>> + if (!TYPE_INCLUDE_FLEXARRAY (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;
>>>>> diff --git a/gcc/tree-streamer-in.cc b/gcc/tree-streamer-in.cc
>>>>> index d4dc30f048f..c19ede0631d 100644
>>>>> --- a/gcc/tree-streamer-in.cc
>>>>> +++ b/gcc/tree-streamer-in.cc
>>>>> @@ -390,6 +390,7 @@ unpack_ts_type_common_value_fields (struct bitpack_d
>>>>> *bp, tree expr)
>>>>> TYPE_TRANSPARENT_AGGR (expr) = (unsigned) bp_unpack_value (bp, 1);
>>>>> TYPE_FINAL_P (expr) = (unsigned) bp_unpack_value (bp, 1);
>>>>> TYPE_CXX_ODR_P (expr) = (unsigned) bp_unpack_value (bp, 1);
>>>>> + TYPE_INCLUDE_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1);
>>>>> }
>>>>> else if (TREE_CODE (expr) == ARRAY_TYPE)
>>>>> TYPE_NONALIASED_COMPONENT (expr) = (unsigned) bp_unpack_value (bp, 1);
>>>>> diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-out.cc
>>>>> index d107229da5c..73e4b4e547c 100644
>>>>> --- a/gcc/tree-streamer-out.cc
>>>>> +++ b/gcc/tree-streamer-out.cc
>>>>> @@ -357,6 +357,7 @@ pack_ts_type_common_value_fields (struct bitpack_d
>>>>> *bp, tree expr)
>>>>> bp_pack_value (bp, flag_wpa && TYPE_CANONICAL (expr)
>>>>> ? TYPE_CXX_ODR_P (TYPE_CANONICAL (expr))
>>>>> : TYPE_CXX_ODR_P (expr), 1);
>>>>> + bp_pack_value (bp, TYPE_INCLUDE_FLEXARRAY (expr), 1);
>>>>> }
>>>>> else if (TREE_CODE (expr) == ARRAY_TYPE)
>>>>> bp_pack_value (bp, TYPE_NONALIASED_COMPONENT (expr), 1);
>>>>> diff --git a/gcc/tree.h b/gcc/tree.h
>>>>> index 92ac0e6a214..ab1cdc3dc85 100644
>>>>> --- a/gcc/tree.h
>>>>> +++ b/gcc/tree.h
>>>>> @@ -778,6 +778,12 @@ extern void omp_clause_range_check_failed
>>>>> (const_tree, const char *, int,
>>>>> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
>>>>> (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
>>>>>
>>>>> +/* True if this RECORD_TYPE or UNION_TYPE includes a flexible array
>>>>> member
>>>>> + at the last field recursively. */
>>>>> +#define TYPE_INCLUDE_FLEXARRAY(NODE) \
>>>>> + (TYPE_CHECK (NODE)->type_common.type_include_flexarray)
>>>>
>>>> Please use RECORD_OR_UNION_CHECK.
>>> Okay.
>>>> The comment "at the last field"
>>>> doesn't seem to match implementation? (at least not obviously)
>>> The current implementation (in gcc/c/c-decl.cc) guarantees that it’s at the
>>> last field. (And recursively).
>>>> Given this is a generic header expanding on what a "flexible array member"
>>>> is to the middle-end here would be good. Especially the guarantees
>>>> made when the bit is _not_ set (we've evaded that with DECL_NOT_FLEXARRAY
>>>> vs. DECL_FLEXARRAY).
>>>
>>> The bit TYPE_INCLUDE_FLEXARRAY default is FALSE, i.e, not including a flex
>>> array by default.
>>> It’s only set to TRUE when the struct/union includes a flex array at the
>>> last field (and recursively). So, I think it should be correct.
>>> Let me know if I missed anything here.
>>
>> See above - I was looking at the use (but I'm not familiar with that
>> code), and wondered how the change affects uses from other frontends.
>
> Please see my explanation above, I think the default behavior from other FE
> should be kept correctly with this patch.
>
> thanks.
>
> Qing
>>
>> Richard.
