[Bug tree-optimization/49079] [4.6/4.7 Regression] Bogus constant folding

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49079

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.20 13:28:05
     Ever Confirmed|0                           |1

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-20 13:28:05 UTC ---
Because the array length is of size 1 and get_ref_base_and_extent returns an
exact match in that case.  We have to account for trailing flexible arrays.

Testcase:

extern void abort (void);

struct Ustr
{
  unsigned char data[1];
};

static unsigned int
ustr_xi__embed_val_get(const unsigned char *data)
{
  return (unsigned int)data[0];
}

int __attribute__((noinline)) zero(void) { return 0; }

static unsigned int
ustr_len(const struct Ustr *s1)
{
  return ustr_xi__embed_val_get(s1->data + 1 + zero());
}

int
main()
{
  if (ustr_len (((struct Ustr *) "\x01" "\x0002" "s2")) != 2)
    abort ();

  return 0;
}