bug#37652: 26.3; performance drops massively when on some elisp manual pages

["Chris Hecker" <checker@d6.com>]

--text follows this line--

Recipe:
1. start emacs -Q for 26.3
2. hit C-h i to get to the info directory
3. m elisp
4. m buffer contents
5. page around in the file for a few seconds, emacs starts crawling and
using an entire cpu


In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
  of 2019-08-29 built on CIRROCUMULUS
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Composing main Info directory...done
Mark saved where search started [2 times]
next-line: End of buffer
Mark set
scroll-up-command: End of buffer [2 times]
scroll-down-command: Beginning of buffer
scroll-up-command: End of buffer
scroll-down-command: Beginning of buffer
C-; is undefined
user-error: No menu in this node
Configured using:
  'configure --without-dbus --host=x86_64-w64-mingw32
  --without-compress-install 'CFLAGS=-O2 -static -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS THREADS LCMS2

Important settings:
   value of $LANG: ENU
   locale-coding-system: cp1252

Major mode: Info

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-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
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   buffer-read-only: t
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils misearch multi-isearch info
easymenu elec-pair time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic 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 charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 131855 8983)
  (symbols 48 20922 1)
  (miscs 40 61 246)
  (strings 32 35842 1141)
  (string-bytes 1 886864)
  (vectors 16 15187)
  (vector-slots 8 507148 10310)
  (floats 8 55 100)
  (intervals 56 5549 1121)
  (buffers 992 12))