void f(ref int i, ref string str, ref int[int] aa){
    i = 2;
    str ~= "hello";
    aa[1] = 2;
    assert(aa[1] == 2);
}

static assert({
    int[int] aa;
    int i;
    string str;
    f(i, str, aa);
    assert(i == 2);// OK
    assert(str == "hello");// OK
    assert(aa[1] == 2);// Error: cannot index null array aa
}());

The above code doesn't be compiled by the dmd v2.056 DEBUG built from github after the commit 42fea4c1f2.
This means that ref argument of AA doesn't work well in CTFE.