bug#65250: 30.0.50; "C-h f" is much slower on the master branch

[Eli Zaretskii]

To reproduce:

  emacs -Q
  C-h f dictionary-search RET

(almost any other function will do, I think).

This takes a whopping 6.6 sec of CPU on master, vs 2.4 sec on the
emacs-29 branch.  These are both unoptimized builds, but even so,
6.6 seconds of CPU time for looking up a doc string of a function
is too much, I think.

The patch below fixes the problem in a build without
native-compilation, but won't help in a build with native-compilation.
I wonder why comp-function-type-spec is so expensive?



In GNU Emacs 30.0.50 (build 417, i686-pc-mingw32) of 2023-08-12 built on
 HOME-C4E4A596F7
Repository revision: d3dae88e6cc8118c875957ba0347be9599014b34
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
System Description: Microsoft Windows XP Service Pack 3 (v5.1.0.2600)

Configured using:
 'configure -C --prefix=/d/usr --with-wide-int
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -gdwarf-4 -g3''

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NOTIFY
W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel dos-w32
ls-lisp disp-table term/w32-win w32-win w32-vars term/common-win
touch-screen tool-bar dnd fontset image regexp-opt fringe tabulated-list
replace newcomment text-mode lisp-mode prog-mode register page tab-bar
menu-bar rfn-eshadow isearch easymenu timer select scroll-bar mouse
jit-lock font-lock syntax font-core term/tty-colors frame minibuffer
nadvice seq simple cl-generic indonesian philippine cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite emoji-zwj charscript charprop
case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp
files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads w32notify w32 lcms2 multi-tty move-toolbar make-network-process
emacs)

Memory information:
((conses 16 42844 17019) (symbols 48 6336 0) (strings 16 16702 3269)
 (string-bytes 1 401689) (vectors 16 9351)
 (vector-slots 8 147820 16098) (floats 8 23 25) (intervals 40 276 95)
 (buffers 896 10))

Here's the patch I promised:

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index fc8f431..bedc5a9 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -715,7 +715,8 @@ help-fns--signature
           (unless (and (symbolp function)
                        (get function 'reader-construct))
             (insert high-usage "\n")
-            (when-let* ((res (comp-function-type-spec function))
+            (when-let* ((res (and (native-comp-available-p)
+                                  (comp-function-type-spec function)))
                         (type-spec (car res))
                         (kind (cdr res)))
               (insert (format