[Bug lto/61886] [4.8/4.9/4.10 Regression] LTO breaks fread with _FORTIFY_SOURCE=2

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61886

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.7.4
      Known to fail|                            |4.10.0, 4.8.3, 4.9.1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'm testing the patch, testcase:

/* { dg-lto-do link } */
/* { dg-lto-options { { -flto -O2 -Werror } } } */

typedef __SIZE_TYPE__ size_t;
typedef struct _IO_FILE FILE;

extern size_t __fread_chk_warn (void *__restrict __ptr, size_t __ptrlen, size_t
__size, size_t __n, FILE *__restrict __stream) __asm__ ("" "__fread_chk")     
__attribute__ ((__warn_unused_result__)) __attribute__((__warning__ ("fread
called with bigger size * nmemb than length " "of destination buffer")));

extern __inline __attribute__ ((__always_inline__)) __attribute__
((__gnu_inline__)) __attribute__ ((__artificial__)) __attribute__
((__warn_unused_result__))
size_t
fread (void *__restrict __ptr, size_t __size, size_t __n,
       FILE *__restrict __stream)
{
  if (__builtin_object_size (__ptr, 0) != (size_t) -1)
    {
      if (!__builtin_constant_p (__size)
          || !__builtin_constant_p (__n)
          || (__size | __n) >= (((size_t) 1) << (8 * sizeof (size_t) / 2)))
        return __fread_chk (__ptr, __builtin_object_size (__ptr, 0), __size,
__n, __stream);
      if (__size * __n > __builtin_object_size (__ptr, 0))
        return __fread_chk_warn (__ptr, __builtin_object_size (__ptr, 0),
__size, __n, __stream);
    }
}

volatile size_t nmemb;
FILE *fp;
int main ()
{
  char file_contents[4096];
  /* We shouldn't get this resolved to a call to __fread_chk_warn.  */
  return fread (file_contents, 1, nmemb, fp);
}