gcc/testsuite/gcc.dg/auto-init-uninit-16.c

/* { dg-do compile } */
/* { dg-options "-O2 -Wuninitialized -ftrivial-auto-var-init=zero" } */
/* -ftrivial-auto-var-init will make the uninitialized warning for address
   taken auto var going away, FIXME later.  */

int foo, bar;

static
void decode_reloc(int reloc, int *is_alt)
{
  if (reloc >= 20)
      *is_alt = 1;
  else if (reloc >= 10)
      *is_alt = 0;
}

void testfunc()
{
  int alt_reloc;

  decode_reloc(foo, &alt_reloc);

  if (alt_reloc) /* { dg-warning "may be used uninitialized" "" { xfail *-*-* }  }  */
    bar = 42;
}