bug#63364: (man "gcc") very slow

[Tobias Bading]

With emacs-29 branch 7133784303 or master 31a66dc891:

1. emacs -Q

2. M-x man RET gcc RET

Emacs 29 and 30 both need almost 30 seconds to fully display this man page
on my machine (18714 lines, gcc-9, 2021-06-01). Emacs 26.3 needs about 2
seconds. (All tests done after “sudo cpupower frequency-set --max 3.5GHz”.)

According to “perf top -g”, rpl_re_search_2 and re_match_2_internal are
heavily involved.

---

In GNU Emacs 29.0.90 (build 3, x86_64-pc-linux-gnu, GTK+ Version
 3.24.20, cairo version 1.16.0) of 2023-05-08 built on omega
Repository revision: 71337843036d6a6b53aedcf898febd1b591b5f41
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.6 LTS

Configured using:
 'configure --with-modules --with-imagemagick --without-tree-sitter'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ
IMAGEMAGICK JPEG JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2
M17N_FLT MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LC_COLLATE: C.UTF-8
  value of $LC_MONETARY: de_DE.UTF-8
  value of $LC_NUMERIC: de_DE.UTF-8
  value of $LC_TIME: de_DE.UTF-8
  value of $LANG: C.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Man

Minor modes in effect:
  tooltip-mode: t
  global-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
  buffer-read-only: 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
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils tabify
cl-seq imenu man cl-loaddefs cl-lib ansi-color rmc iso-transl tooltip
cconv eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/x-win x-win term/common-win x-dnd 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 dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 330857 10339)
 (symbols 48 5616 0)
 (strings 32 14327 1855)
 (string-bytes 1 410345)
 (vectors 16 10104)
 (vector-slots 8 165652 21107)
 (floats 8 33 49)
 (intervals 56 158501 0)
 (buffers 976 11))