Re: [Emacs-diffs] emacs-24 r117502: Always use matched specpdl entry to record call arguments (Bug#18473).

Re: [Emacs-diffs] emacs-24 r117502: Always use matched specpdl entry to record call arguments (Bug#18473).

[Stefan Monnier]

> -void
> +ptrdiff_t
>  record_in_backtrace (Lisp_Object function, Lisp_Object *args, ptrdiff_t nargs)
>  {
> +  ptrdiff_t count = SPECPDL_INDEX ();
> +
>    eassert (nargs >= UNEVALLED);
>    specpdl_ptr-> bt.kind = SPECPDL_BACKTRACE;
>    specpdl_ptr-> bt.debug_on_exit = false;
> @@ -2049,6 +2045,8 @@
>    specpdl_ptr-> bt.args = args;
>    specpdl_ptr-> bt.nargs = nargs;
>    grow_specpdl ();
> +
> +  return count;
>  }

This will slow down every single function call.  Not by much, but
they're already pretty slow, so we should work hard not to make it worse.

In this respect, your previous patch (which used backtrace_top instead
of keeping a `count') was better since it only affected *some*
function calls.


        Stefan

Re: [Emacs-diffs] emacs-24 r117502: Always use matched specpdl entry to record call arguments (Bug#18473).

[Dmitry Antipov]

On 09/16/2014 06:13 PM, Stefan Monnier wrote:

> This will slow down every single function call.  Not by much, but
> they're already pretty slow, so we should work hard not to make it worse.

IMO if we really care about speed in eval_sub, we should redesign this first:

   2111    if (SUBRP (fun))
   2112      {
   2113        Lisp_Object numargs;
   2114        Lisp_Object argvals[8];
   2115        Lisp_Object args_left;
   2116        register int i, maxargs;
   2117
   2118        args_left = original_args;
   2119        numargs = Flength (args_left);     <-- bad

Generic Flength is too slow due to monster if...else:

    121    if (STRINGP (sequence))
    122      XSETFASTINT (val, SCHARS (sequence));
    123    else if (VECTORP (sequence))
    124      XSETFASTINT (val, ASIZE (sequence));
    125    else if (CHAR_TABLE_P (sequence))
    126      XSETFASTINT (val, MAX_CHAR);
    127    else if (BOOL_VECTOR_P (sequence))
    128      XSETFASTINT (val, bool_vector_size (sequence));
    129    else if (COMPILEDP (sequence))
    130      XSETFASTINT (val, ASIZE (sequence) & PSEUDOVECTOR_SIZE_MASK);
    131    else if (CONSP (sequence))

and we know that args_left is always a list.

Dmitry

Re: [Emacs-diffs] emacs-24 r117502: Always use matched specpdl entry to record call arguments (Bug#18473).

[Stefan Monnier]

> IMO if we really care about speed in eval_sub,

I don't (it should only impact non-compiled code).  But I do care about
Ffuncall which also calls record_in_backtrace.


        Stefan