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