[Bug tree-optimization/92765] [10 Regression] Wrong code caused by folding of -Wstring-compare since r276773

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92765

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Testcase showing wrong-code with the __builtin_strcmp_eq stuff (assuming the
testcase is considered valid):
/* { dg-do run { target mmap } } */
/* { dg-options "-O2" } */

#include <stdlib.h>
#include <sys/mman.h>
#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif
#ifndef MAP_ANON
#define MAP_ANON 0
#endif
#ifndef MAP_FAILED
#define MAP_FAILED ((void *)-1)
#endif

union U { struct T { char a[2]; char b[4094]; } c; struct S { char d[4]; int e;
} f; };

__attribute__((noipa)) void
bar (char *p)
{
  asm volatile ("" : : "g" (p) : "memory");
}

__attribute__((noipa)) int
foo (union U *p)
{
  bar ((char *) &p->c.b);
  return __builtin_strcmp (&p->f.d[2], "abcdefghijk") == 0;
}

int
main ()
{
  char *p = mmap (NULL, 131072, PROT_READ | PROT_WRITE,
                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (p == MAP_FAILED)
    return 0;
  if (munmap (p + 65536, 65536) < 0)
    return 0;
  union U *u;
  u = (union U *) (p + 65536 - sizeof (u->f));
  __builtin_memcpy (u->f.d, "abc", 4);
  u->f.e = 1;
  if (foo (u) != 0)
    __builtin_abort ();
  return 0;
}