bug#26051: 25.1; overlays may make emacs very slow

[ynyaaa]

Evaluating the form below in the *scratch* buffer,
it takes a few seconds to show the result.

(let ((n 65536))
  (save-excursion (dotimes (i n) (insert (format "%d\n" i))))
  (dotimes (i n) (make-overlay (point) (progn (forward-line) (point))))
  (message "Done."))

If I evaluate the form as below, it takes about 30 seconds.
  (1) switch to a newly created buffer
  (2) insert the code into the buffer
  (3) insert 2 line breaks after the last closing parenthesis
  (4) type C-x C-e

If I evaluate the form as below, it takes about 10 minutes.
  (1) switch to a newly created buffer
  (2) type M-: and input the code

In each case, the message "Done." is displayed in a few seconds.
But it takes a long time to display the buffer contents.



In GNU Emacs 25.1.1 (i686-w64-mingw32)
 of 2016-09-18 built on LAPHROAIG
Windowing system distributor 'Microsoft Corp.', version 6.0.6002
Configured using:
 'configure --host=i686-w64-mingw32 --without-dbus
 --without-compress-install CFLAGS=-static'

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

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Lisp Interaction

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
  line-number-mode: t
  transient-mark-mode: t

Recent messages:

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
cl-loaddefs pcase cl-lib mail-prsvr mail-utils time-date mule-util
japan-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table w32-win w32-vars
term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core 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 charscript case-table epa-hook jka-cmpr-hook help
simple abbrev 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
w32notify w32 multi-tty make-network-process emacs)

Memory information:
((conses 8 91638 4868)
 (symbols 32 19658 0)
 (miscs 32 50 119)
 (strings 16 15828 4143)
 (string-bytes 1 427112)
 (vectors 8 13127)
 (vector-slots 4 519096 5994)
 (floats 8 164 67)
 (intervals 28 213 16)
 (buffers 520 19))