test program:

struct S { int x; };
int test1(int x)
{
	// compile error because it's static (but currently this segfaults when compiling)
	// using a local variable assigned to x, it gives "Error: non-constant expression `y = x`"
	struct S *b = &(struct S){x};
	return 0;
}
int test2(int x)
{
	struct S *s = &(struct S){0};
	s->x = x;
	if (x != 0)
	{
		test2(0);
		// detect if it's static instead of automatic
		// the recursive call shouldn't have affected this copy
		if (s->x != x) return 2;
	}
	return 0;
}
int test3(void)
{
	// detect if it's GC instead of static or automatic
	// this is true in CTFE
	void *prev;
	for (int i = 0; i < 2; i++)
	{
		void *curr = &(struct S){0}; // should have the same address on both loop iterations
		if (i == 0)
			prev = curr;
		else
			if (curr != prev) return 3;
	}
	return 0;
}
_Static_assert(test1(1) == 0, "1");
_Static_assert(test2(1) == 0, "2");
_Static_assert(test3() == 0, "3"); // fails
int main()
{
	int rv;
	if (rv = test1(1)) return rv; // function fails to compile
	if (rv = test2(1)) return rv; // fails
	if (rv = test3()) return rv;
	return 0;
}

"&(struct S){0}" here should work like taking the address of a local variable

outside CTFE, it works like a static variable, in CTFE it's allocated using GC (which is also wrong)