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 mini.nested13;

extern(C) int printf(char*, ...);

void main()
{
    int var = 2;

    void exec(void delegate() dg)
    {
        printf("var = %d\n", var);
        dg();
    }

    void foo()
    {
        printf("var = %d\n", var);
        assert(var == 5);
    }

    void bar()
    {
        printf("var = %d\n", var);
        var += 3;
        exec(&foo);
    }

    printf("var = %d\n", var);
    exec(&bar);

    return 0;
}