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)

interface Iin
{
    void[] read(size_t n);
}

interface Iout
{
    size_t write(void[] d);
}

class C : Iin
{
    void[] read(size_t n)
    {
        return null;
    }

    size_t write(void[] d)
    {
        return 0;
    }
}

void main()
{
    scope c = new C;
}