[Bug target/81863] [7 regression] -mword-relocations is unreliable

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81863

--- Comment #2 from Arnd Bergmann <arnd at linaro dot org> ---
This is a reduced test case that triggers with gcc-4.9 and higher (latest
tested is 7.1.1)

$ arm-linux-gnueabi-gcc-7.1.1 -mword-relocations -march=armv7-a -O2 -Wall -c
test-ww_mutex.c
$ objdump -dr test-ww_mutex.o | grep MOV
                        4c: R_ARM_MOVW_ABS_NC   c
                        50: R_ARM_MOVT_ABS      c

---
int a, d, f;
long b;
struct ww_class {
  int stamp;
} c;
struct stress {
  int locks;
  int nlocks;
};
void *e;
int atomic_add_return_relaxed(int *p1) {
  __builtin_prefetch(p1);
  return a;
}
void atomic_long_inc_return_relaxed(int *p1) {
  int *v = p1;
  atomic_add_return_relaxed(v);
}
void ww_acquire_init(struct ww_class *p1) {
  atomic_long_inc_return_relaxed(&p1->stamp);
}
void ww_mutex_lock();
int *get_random_order();
void stress_inorder_work() {
  struct stress *g = e;
  int h = g->nlocks;
  int *i = &g->locks, *j = get_random_order();
  do {
    int n;
    ww_acquire_init(&c);
  retry:
    for (n = 0; n < h; n++)
      ww_mutex_lock(i[j[n]]);
    f = n;
    if (d)
      goto retry;
  } while (b);
}