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)

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

void main()
{
    int i = func();
    printf("%d\n", i);
    assert(i == 42);
}

int func()
{
    version (D_InlineAsm_X86)
    {
        asm
        {
            naked;
            mov EAX, 42;
            ret;
        }
    }
    else version(D_InlineAsm_X86_64)
    {
        asm
        {
            naked;
            movq RAX, 42;
            ret;
        }
    }
}