Re: [PATCH 1/2] Handle component_ref to a structre/union field including flexible array member [PR101832]

[Richard Biener <rguenther@suse.de>]

On Thu, 2 Feb 2023, Qing Zhao wrote:

> 
> 
> > On Feb 2, 2023, at 3:07 AM, Richard Biener <rguenther@suse.de> wrote:
> > 
> > On Wed, 1 Feb 2023, Qing Zhao wrote:
> > 
> >> 
> >> 
> >>> On Feb 1, 2023, at 6:41 AM, Richard Biener <rguenther@suse.de> wrote:
> >>> 
> >>> On Tue, 31 Jan 2023, Qing Zhao wrote:
> >>> 
> >>>> GCC extension accepts the case when a struct with a flexible array member
> >>>> is embedded into another struct (possibly recursively).
> >>>> __builtin_object_size should treat such struct as flexible size per
> >>>> -fstrict-flex-arrays.
> >>>> 
> >>>> 	PR tree-optimization/101832
> >>>> 
> >>>> gcc/ChangeLog:
> >>>> 
> >>>> 	PR tree-optimization/101832
> >>>> 	* tree-object-size.cc (flexible_size_type_p): New function.
> >>>> 	(addr_object_size): Handle structure/union type when it has
> >>>> 	flexible size.
> >>>> 
> >>>> gcc/testsuite/ChangeLog:
> >>>> 
> >>>> 	PR tree-optimization/101832
> >>>> 	* gcc.dg/builtin-object-size-pr101832-2.c: New test.
> >>>> 	* gcc.dg/builtin-object-size-pr101832-3.c: New test.
> >>>> 	* gcc.dg/builtin-object-size-pr101832-4.c: New test.
> >>>> 	* gcc.dg/builtin-object-size-pr101832.c: New test.
> >>>> ---
> >>>> .../gcc.dg/builtin-object-size-pr101832-2.c   | 135 ++++++++++++++++++
> >>>> .../gcc.dg/builtin-object-size-pr101832-3.c   | 135 ++++++++++++++++++
> >>>> .../gcc.dg/builtin-object-size-pr101832-4.c   | 135 ++++++++++++++++++
> >>>> .../gcc.dg/builtin-object-size-pr101832.c     | 119 +++++++++++++++
> >>>> gcc/tree-object-size.cc                       | 115 +++++++++++----
> >>>> 5 files changed, 611 insertions(+), 28 deletions(-)
> >>>> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832-2.c
> >>>> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832-3.c
> >>>> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832-4.c
> >>>> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >>>> 
> >>>> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-2.c b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-2.c
> >>>> new file mode 100644
> >>>> index 00000000000..f38babc5415
> >>>> --- /dev/null
> >>>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-2.c
> >>>> @@ -0,0 +1,135 @@
> >>>> +/* PR 101832: 
> >>>> +   GCC extension accepts the case when a struct with a flexible array member
> >>>> +   is embedded into another struct (possibly recursively).
> >>>> +   __builtin_object_size will treat such struct as flexible size per
> >>>> +   -fstrict-flex-arrays.  */ 
> >>>> +/* { dg-do run } */
> >>>> +/* { dg-options "-O2 -fstrict-flex-arrays=1" } */
> >>>> +
> >>>> +#include <stdio.h>
> >>>> +
> >>>> +unsigned n_fails = 0;
> >>>> +
> >>>> +#define expect(p, _v) do { \
> >>>> +  size_t v = _v; \
> >>>> +  if (p == v) \
> >>>> +    printf("ok:  %s == %zd\n", #p, p); \
> >>>> +  else {\
> >>>> +    printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> >>>> +    n_fails++; \
> >>>> +  } \
> >>>> +} while (0);
> >>>> +
> >>>> +struct A {
> >>>> +  int n;
> >>>> +  char data[];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B {
> >>>> +  int m;
> >>>> +  struct A a;
> >>>> +};
> >>>> +
> >>>> +struct C {
> >>>> +  int q;
> >>>> +  struct B b;
> >>>> +};
> >>>> +
> >>>> +struct A0 {
> >>>> +  int n;
> >>>> +  char data[0];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B0 {
> >>>> +  int m;
> >>>> +  struct A0 a;
> >>>> +};
> >>>> +
> >>>> +struct C0 {
> >>>> +  int q;
> >>>> +  struct B0 b;
> >>>> +};
> >>>> +
> >>>> +struct A1 {
> >>>> +  int n;
> >>>> +  char data[1];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B1 {
> >>>> +  int m;
> >>>> +  struct A1 a;
> >>>> +};
> >>>> +
> >>>> +struct C1 {
> >>>> +  int q;
> >>>> +  struct B1 b;
> >>>> +};
> >>>> +
> >>>> +struct An {
> >>>> +  int n;
> >>>> +  char data[8];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +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), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b.a, 1), -1);
> >>>> +
> >>>> +    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), -1);
> >>>> +    expect(__builtin_object_size(&outest1->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest1->b.a, 1), -1);
> >>>> +
> >>>> +    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));
> >>>> +
> >>>> +    if (n_fails > 0)
> >>>> +      __builtin_abort ();
> >>>> +
> >>>> +    return 0;
> >>>> +}
> >>>> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-3.c b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-3.c
> >>>> new file mode 100644
> >>>> index 00000000000..aaae99b8d67
> >>>> --- /dev/null
> >>>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-3.c
> >>>> @@ -0,0 +1,135 @@
> >>>> +/* PR 101832: 
> >>>> +   GCC extension accepts the case when a struct with a flexible array member
> >>>> +   is embedded into another struct (possibly recursively).
> >>>> +   __builtin_object_size will treat such struct as flexible size per
> >>>> +   -fstrict-flex-arrays.  */
> >>>> +/* { dg-do run } */
> >>>> +/* { dg-options "-O2 -fstrict-flex-arrays=2" } */
> >>>> +
> >>>> +#include <stdio.h>
> >>>> +
> >>>> +unsigned n_fails = 0;
> >>>> +
> >>>> +#define expect(p, _v) do { \
> >>>> +  size_t v = _v; \
> >>>> +  if (p == v) \
> >>>> +    printf("ok:  %s == %zd\n", #p, p); \
> >>>> +  else {\
> >>>> +    printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> >>>> +    n_fails++; \
> >>>> +  } \
> >>>> +} while (0);
> >>>> +
> >>>> +struct A {
> >>>> +  int n;
> >>>> +  char data[];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B {
> >>>> +  int m;
> >>>> +  struct A a;
> >>>> +};
> >>>> +
> >>>> +struct C {
> >>>> +  int q;
> >>>> +  struct B b;
> >>>> +};
> >>>> +
> >>>> +struct A0 {
> >>>> +  int n;
> >>>> +  char data[0];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B0 {
> >>>> +  int m;
> >>>> +  struct A0 a;
> >>>> +};
> >>>> +
> >>>> +struct C0 {
> >>>> +  int q;
> >>>> +  struct B0 b;
> >>>> +};
> >>>> +
> >>>> +struct A1 {
> >>>> +  int n;
> >>>> +  char data[1];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B1 {
> >>>> +  int m;
> >>>> +  struct A1 a;
> >>>> +};
> >>>> +
> >>>> +struct C1 {
> >>>> +  int q;
> >>>> +  struct B1 b;
> >>>> +};
> >>>> +
> >>>> +struct An {
> >>>> +  int n;
> >>>> +  char data[8];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +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), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b.a, 1), -1);
> >>>> +
> >>>> +    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));
> >>>> +
> >>>> +    if (n_fails > 0)
> >>>> +      __builtin_abort ();
> >>>> +
> >>>> +    return 0;
> >>>> +}
> >>>> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-4.c b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-4.c
> >>>> new file mode 100644
> >>>> index 00000000000..424264e2acd
> >>>> --- /dev/null
> >>>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832-4.c
> >>>> @@ -0,0 +1,135 @@
> >>>> +/* PR 101832: 
> >>>> +   GCC extension accepts the case when a struct with a flexible array member
> >>>> +   is embedded into another struct (possibly recursively).
> >>>> +   __builtin_object_size will treat such struct as flexible size per
> >>>> +   -fstrict-flex-arrays.  */
> >>>> +/* { dg-do run } */
> >>>> +/* { dg-options "-O2 -fstrict-flex-arrays=3" } */
> >>>> +
> >>>> +#include <stdio.h>
> >>>> +
> >>>> +unsigned n_fails = 0;
> >>>> +
> >>>> +#define expect(p, _v) do { \
> >>>> +  size_t v = _v; \
> >>>> +  if (p == v) \
> >>>> +    printf("ok:  %s == %zd\n", #p, p); \
> >>>> +  else {\
> >>>> +    printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> >>>> +    n_fails++; \
> >>>> +  } \
> >>>> +} while (0);
> >>>> +
> >>>> +struct A {
> >>>> +  int n;
> >>>> +  char data[];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B {
> >>>> +  int m;
> >>>> +  struct A a;
> >>>> +};
> >>>> +
> >>>> +struct C {
> >>>> +  int q;
> >>>> +  struct B b;
> >>>> +};
> >>>> +
> >>>> +struct A0 {
> >>>> +  int n;
> >>>> +  char data[0];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B0 {
> >>>> +  int m;
> >>>> +  struct A0 a;
> >>>> +};
> >>>> +
> >>>> +struct C0 {
> >>>> +  int q;
> >>>> +  struct B0 b;
> >>>> +};
> >>>> +
> >>>> +struct A1 {
> >>>> +  int n;
> >>>> +  char data[1];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B1 {
> >>>> +  int m;
> >>>> +  struct A1 a;
> >>>> +};
> >>>> +
> >>>> +struct C1 {
> >>>> +  int q;
> >>>> +  struct B1 b;
> >>>> +};
> >>>> +
> >>>> +struct An {
> >>>> +  int n;
> >>>> +  char data[8];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +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));
> >>>> +
> >>>> +    if (n_fails > 0)
> >>>> +      __builtin_abort ();
> >>>> +
> >>>> +    return 0;
> >>>> +}
> >>>> 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..8ed6980edf0
> >>>> --- /dev/null
> >>>> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >>>> @@ -0,0 +1,119 @@
> >>>> +/* PR 101832: 
> >>>> +   GCC extension accepts the case when a struct with a flexible array member
> >>>> +   is embedded into another struct (possibly recursively).
> >>>> +   __builtin_object_size will treat such struct as flexible size per
> >>>> +   -fstrict-flex-arrays.  */
> >>>> +/* { dg-do run } */
> >>>> +/* { dg-options "-O2" } */
> >>>> +
> >>>> +#include <stdio.h>
> >>>> +
> >>>> +unsigned n_fails = 0;
> >>>> +
> >>>> +#define expect(p, _v) do { \
> >>>> +  size_t v = _v; \
> >>>> +  if (p == v) \
> >>>> +    printf("ok:  %s == %zd\n", #p, p); \
> >>>> +  else {\
> >>>> +    printf("WAT: %s == %zd (expected %zd)\n", #p, p, v); \
> >>>> +    n_fails++; \
> >>>> +  } \
> >>>> +} while (0);
> >>>> +
> >>>> +struct A {
> >>>> +  int n;
> >>>> +  char data[];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B {
> >>>> +  int m;
> >>>> +  struct A a;
> >>>> +};
> >>>> +
> >>>> +struct C {
> >>>> +  int q;
> >>>> +  struct B b;
> >>>> +};
> >>>> +
> >>>> +struct A0 {
> >>>> +  int n;
> >>>> +  char data[0];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B0 {
> >>>> +  int m;
> >>>> +  struct A0 a;
> >>>> +};
> >>>> +
> >>>> +struct C0 {
> >>>> +  int q;
> >>>> +  struct B0 b;
> >>>> +};
> >>>> +
> >>>> +struct A1 {
> >>>> +  int n;
> >>>> +  char data[1];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +struct B1 {
> >>>> +  int m;
> >>>> +  struct A1 a;
> >>>> +};
> >>>> +
> >>>> +struct C1 {
> >>>> +  int q;
> >>>> +  struct B1 b;
> >>>> +};
> >>>> +
> >>>> +struct An {
> >>>> +  int n;
> >>>> +  char data[8];/* Content following header */
> >>>> +};
> >>>> +
> >>>> +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 = (void *)magic1;
> >>>> +    struct C *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 = (void *)magic1;
> >>>> +    struct C0 *outest0 = (void *)magic2;
> >>>> +
> >>>> +    expect(__builtin_object_size(&outer0->a, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest0->b.a, 1), -1);
> >>>> +
> >>>> +    struct B1 *outer1 = (void *)magic1;
> >>>> +    struct C1 *outest1 = (void *)magic2;
> >>>> +
> >>>> +    expect(__builtin_object_size(&outer1->a, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest1->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outest1->b.a, 1), -1);
> >>>> +
> >>>> +    struct Bn *outern = (void *)magic1;
> >>>> +    struct Cn *outestn = (void *)magic2;
> >>>> +
> >>>> +    expect(__builtin_object_size(&outern->a, 1), -1);
> >>>> +    expect(__builtin_object_size(&outestn->b, 1), -1);
> >>>> +    expect(__builtin_object_size(&outestn->b.a, 1), -1);
> >>>> +
> >>>> +    if (n_fails > 0)
> >>>> +      __builtin_abort ();
> >>>> +
> >>>> +    return 0;
> >>>> +}
> >>>> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
> >>>> index 9a936a91983..56b78ca2a8c 100644
> >>>> --- a/gcc/tree-object-size.cc
> >>>> +++ b/gcc/tree-object-size.cc
> >>>> @@ -500,6 +500,42 @@ decl_init_size (tree decl, bool min)
> >>>>  return size;
> >>>> }
> >>>> 
> >>>> +/* Determine whether TYPE is a structure with a flexible array member
> >>>> +   per -fstrict-flex-array or a union containing such a structure
> >>>> +   (possibly recursively).  */
> >>>> +static bool
> >>>> +flexible_size_type_p (const_tree type)
> >>>> +{
> >>>> +  tree x = NULL_TREE;
> >>>> +  tree last = NULL_TREE;
> >>>> +  switch (TREE_CODE (type))
> >>>> +    {
> >>>> +    case RECORD_TYPE:
> >>>> +      for (x = TYPE_FIELDS (type); x != NULL_TREE; x = DECL_CHAIN (x))
> >>>> +	if (TREE_CODE (x) == FIELD_DECL)
> >>>> +	  last = x;
> >>>> +      if (last == NULL_TREE)
> >>>> +	return false;
> >>>> +      if (TREE_CODE (TREE_TYPE (last)) == ARRAY_TYPE
> >>>> +	  && !DECL_NOT_FLEXARRAY (last))
> >>>> +	return true;
> >>>> +      else if (TREE_CODE (TREE_TYPE (last)) == RECORD_TYPE
> >>>> +	       || TREE_CODE (TREE_TYPE (last)) == UNION_TYPE)
> >>>> +	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.

> 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 <rguenther@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 <rguenther@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 <rguenther@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)