Implement first D-specific optimization pass: -simplify-drtcalls. It uses the machinery of the standard -simplify-libcalls pass, but optimizes calls to the D runtime instead of calls to C libraries. At the moment, these optimizations are implemented by this pass: - Avoid the runtime call for `arr.length = newlen` if it can determine that the new length isn't longer than the old one. - Ditto for `cast(T[]) arr` if it will clearly always succeed. (e.g. if the length of the original array is zero, or if the old element size is a multiple of the new element size)

module tuple1;

template Tuple(T...) {
    alias T Tuple;
}

struct S
{
    int i;
    long l;
}

void main()
{
    S s = S(Tuple!(1,2L));
    assert(s.i == 1);
    assert(s.l == 2);
}