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 bug10;
extern(C) int printf(char*, ...);

class C
{
    char[] msg;

    this()
    {
    }
    this(char[] msg)
    {
        this.msg = msg;
    }
}

void main()
{
    auto c = new C();
    c.msg = "world";
    auto b = new C("hello");
    printf("%.*s\n", b.msg.length, b.msg.ptr);
    printf("%.*s\n", c.msg.length, c.msg.ptr);
}