Re: Shrinking the C core

[Ihor Radchenko]

"Alfred M. Szmidt" <ams@gnu.org> writes:

> Please keep the CC intact, not everyone subscribed.
>
>    > It should be quite obvious why SBCL is faster than the Emacs
>    > Lisp VM (or even native). Just look at this call to (car
>    > "foo"), and compare what happens in Emacs.
>    >
>    > * (disassemble 'foo)
>    > ; disassembly for FOO
>    > ; Size: 166 bytes. Origin: #x225D873F                         ; FOO
>> ...
>    Okay?
>
> I guess that you do not understand the above?  Or what?  Do you know
> and understand what happens in Emacs when a similar call is done?  It
> is far more than "166 bytes".

It would be helpful if you show us what happens in Elisp with a similar
call. Especially after native compilation.

I am asking genuinely because `car' (1) has dedicated opt code and thus
should be one of the best-optimized function calls on Elisp side; (2)
Fcar is nothing but

/* Take the car or cdr of something whose type is not known.  */
INLINE Lisp_Object
CAR (Lisp_Object c)
{
  if (CONSP (c))
    return XCAR (c); // <- XCONS (c)->u.s.car
  if (!NILP (c))
    wrong_type_argument (Qlistp, c);
  return Qnil;
}

So, it is a very simple example that can actually explain the basic
differences between Elisp and CL. It would be nice if you (considering
your low-level understanding) can provide us with an analysis of what is
different between Elisp and CL implementations of such a simple
function.

> This has literally nothing to do with the difference between static
> typing, and dynamic typing.  The author, and you, have it completeley
> backwards ...

I am sorry, because it was my message that started the confusion.
I was mostly referring to separation between Elisp
interpreted/byte/native code and C subrs. AFAIU, static analysis info
cannot be passed between these two parts of Emacs runtime: subr cannot
know in advance what Lisp_Object type it is working on, even if static
analysis of the caller Elisp code has such information (e.g. from GCC
JIT compiler).

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>