bug#28795: 25.2; UTF-8 language environment causes extreme sluggishness

[Mark Laws <mdl@60hz.org>]

M-x set-language-environment UTF-8
M-: (insert #x2207)

Then hold down C-o until you have a bunch of empty lines, and start moving
around the buffer with the usual movement keys.  You will notice it is very,
very slow.  Then delete the character from the buffer, and notice how things are
fast again.

The issue doesn't seem to happen in the Linux console version of Emacs (even
with UTF-8 set).  It also does not happen in the Windows (NT) GUI version if the
language environment is set to something other than UTF-8.

I can reproduce this 100% of the time under emacs -Q with the instructions given above.



In GNU Emacs 25.2.1 (x86_64-w64-mingw32)
 of 2017-04-30 built on HAYAI
Repository revision: d8cf7c798722e58aa4ebb9ecfcaa6724f905e18e
Windowing system distributor 'Microsoft Corp.', version 10.0.14393
Configured using:
 'configure --host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32
 --build=x86_64-w64-mingw32 --prefix=/c/Users/mdl/local/emacs --without-dbus
 --without-gconf --without-gsettings --with-modules --with-file-notification=w32
 CFLAGS=-O2 CPPFLAGS=-I/mingw64/include LDFLAGS=-L/mingw64/lib'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES W32_IME

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

Major mode: Emacs-Lisp

Minor modes in effect:
  company-quickhelp-mode: t
  company-quickhelp-local-mode: t
  elisp-slime-nav-mode: t
  rainbow-mode: t
  flycheck-pos-tip-mode: t
  company-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  diff-auto-refine-mode: t
  desktop-save-mode: t
  eldoc-in-minibuffer-mode: t
  global-form-feed-mode: t
  form-feed-mode: t
  global-whitespace-cleanup-mode: t
  whitespace-cleanup-mode: t
  whitespace-mode: t
  global-undo-tree-mode: t
  undo-tree-mode: t
  show-paren-mode: t
  global-hl-line-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  auto-fill-function: do-auto-fill
  transient-mark-mode: t

Recent messages:
Wrote c:/Users/mdl/AppData/Roaming/.emacs.d/elisp/mdl-loaddefs.el
Loading c:/Users/mdl/AppData/Roaming/.emacs.d/elisp/mdl-loaddefs.el (source)...done
Please type y, n, or !: y
Error while checking syntax automatically: (irony-server-error "irony-server version mismatch: type ‘M-x irony-install-server’ to reinstall")
Please type y, n, or !: y
Error while checking syntax automatically: (irony-server-error "irony-server is broken! Invalid version syntax: ‘1.1.0’")
Please type y, n, or !: y
Error while checking syntax automatically: (irony-server-error "irony-server is broken! Invalid version syntax: ‘1.1.0’")
Wrote c:/Users/mdl/AppData/Roaming/.emacs.d/.emacs.desktop.lock
Desktop: 3 frames, 46 buffers restored.

Load-path shadows:
c:/Users/mdl/AppData/Roaming/.emacs.d/elpa/seq-2.20/seq hides c:/Users/mdl/local/emacs/share/emacs/25.2/lisp/emacs-lisp/seq

Features:
(shadow sort mail-extr warnings emacsbug sendmail bat-mode make-mode
irony-cdb-libclang irony-cdb-json pp goto-addr view matlab derived tempo
pandoc-mode pandoc-mode-utils hydra lv vc-git irony-eldoc
irony-cdb-clang-complete irony-cdb modern-cpp-font-lock cc-mode cc-fonts
cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs
markdown-mode thingatpt noutline outline jka-compr company-quickhelp
fsharp-mode-font fsharp-mode-indent info-look fsharp-mode
fsharp-mode-indent-smie inf-fsharp-mode fsharp-doc flycheck-fsharp
fsharp-mode-completion fsharp-mode-util tramp tramp-compat tramp-loaddefs
trampver ucs-normalize stupid-indent-mode clean-aindent-mode wolfram-mode smie
autoinsert elisp-slime-nav rainbow-mode company-oddmuse company-keywords
company-etags etags xref project company-gtags company-dabbrev-code
company-dabbrev company-files company-capf company-cmake company-xcode
company-clang company-semantic company-eclim company-css company-nxml
company-bbdb company-irony company-template irony-completion irony-snippet
flycheck-irony flycheck-pos-tip pos-tip flycheck find-func irony-diagnostics
irony irony-iotask color company proof-site proof-autoloads pg-vars
magit-obsolete magit-blame magit-stash magit-bisect magit-remote magit-commit
magit-sequence magit-notes magit-worktree magit-branch magit-files magit-refs
magit-status magit magit-repos magit-apply magit-wip magit-log magit-diff
smerge-mode magit-core magit-autorevert autorevert filenotify magit-process
magit-margin magit-mode magit-git magit-section magit-popup git-commit
magit-utils crm log-edit message format-spec rfc822 mml mml-sec epg mm-decode
mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mailabbrev
mail-utils gmm-utils mailheader pcvs-util add-log with-editor async-bytecomp
async shell pcomplete p4 ps-print ps-def lpr diff-mode dired compile comint
ansi-color ring server revive desktop frameset eldoc-eval form-feed easy-mmode
whitespace-cleanup-mode whitespace ido undo-tree diff paren hl-line vlf-setup
visual-regexp-steroids advice visual-regexp dim mdl-utils mdl-loaddefs autoload
lisp-mnt tex-site edmacro kmacro gh-common gh-profile url-parse auth-source
gnus-util mm-util help-fns mail-prsvr password-cache url-vars rx s marshal
eieio-compat ht json map dash eieio eieio-core cl-seq cl-macs cl finder-inf info
package epg-config seq byte-opt gv bytecomp byte-compile cl-extra help-mode
easymenu cconv cl-loaddefs cl-lib subr-x pcase time-date mule-util japan-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 ls-lisp w32-ime 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 16 546773 36422)
 (symbols 56 44493 0)
 (miscs 48 281 814)
 (strings 32 125737 19777)
 (string-bytes 1 3681556)
 (vectors 16 68989)
 (vector-slots 8 1133465 9793)
 (floats 8 1100 285)
 (intervals 56 2889 0)
 (buffers 976 70))