bug#18522: 24.4.50; mapcar is very slow

[Eli Zaretskii]

> From: Peter Münster <pmlists@free.fr>
> Cc: rudalics@gmx.at,  larsi@gnus.org,  18522@debbugs.gnu.org
> Date: Wed, 24 Feb 2016 19:00:07 +0100
> 
> perf report:
> 
>   33.17%  emacs         emacs                          [.] Fset_default
> 
> Uptime is only about 1 day now. Length of all_buffers is 207.
> 
> perf annotate:
> 
> --8<---------------cut here---------------start------------->8---
>        │     Fset_default():
>        │                    set it in the buffers that don't nominally have a 
> local value.  */
>        │                 if (idx > 0)
>        │                   {
>        │                     struct buffer *b;
>        │                     int i = 0;
>        │                     FOR_EACH_BUFFER (b)
>  15.68 │101:   mov    0x2d8(%rcx),%rcx
>  19.34 │       test   %rcx,%rcx
>   5.39 │     ↑ jne    f0
>        │                     {
>        │                       i++;
>        │                       if (!PER_BUFFER_VALUE_P (b, idx))
>        │                         set_per_buffer_value (b, offset, value);
>        │                     }
>        │                     fprintf(stderr, "XXXXX: %d\n", i);
>   0.07 │10d:   mov    stderr@@GLIBC_2.2.5,%rdi
>   2.49 │       mov    $0x5e90e5,%esi
>        │       xor    %eax,%eax
> --8<---------------cut here---------------end--------------->8---

What is that "f0" there?  Can you annotate it as well?  Otherwise,
this makes no sense to me: the part that takes most of the time is 2
simple instructions.  Sounds like we are looking at too small portion
of the code, so these are percents of a very small fraction of the
total running time.