llvm-gcc-4.2/gcc/testsuite/gcc.c-torture/execute/mayalias-2.c

struct S { short x; };
typedef struct S __attribute__((__may_alias__)) test;

int f() {
  int a=10;
  test *p=(test *)&a;
  p->x = 1;
  return a;
}

int main() {
  if (f() == 10)
    __builtin_abort();
  return 0;
}