bug#35316: 26.2; Emacs lags in c++-mode buffer when editing with iedit-mode on

[Zhang Haijun]

iedit.el(https://github.com/victorhge/iedit) is a multiple-cursors like 
package. It can setup more than one virtual cursors at different positions in 
the buffer. When you edit in the buffer, it clones changes at the main cursor 
to all other virtual cursors.

The problem is that: Emacs lags too much when editing in c++-mode with 
iedit-mode on.
Profiler shows that cpu are most used by c-after-change.

The related issue: https://github.com/victorhge/iedit/issues/83



In GNU Emacs 26.2 (build 1, x86_64-apple-darwin17.7.0, NS appkit-1561.60 
Version 10.13.6 (Build 17G6030))
 of 2019-04-13 built on jundeMac
Windowing system distributor 'Apple', version 10.3.1561
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules --disable-acl
 --without-makeinfo 'CC=cc ' CFLAGS=-O2
 PKG_CONFIG_PATH=/Users/jun/source/build-emacs-master/brew/lib/pkgconfig:'

Configured features:
JPEG NOTIFY GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS
LCMS2

Important settings:
  value of $LANG: zh_CN.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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

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 easymenu 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 elec-pair time-date
china-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/ns-win ns-win ucs-normalize mule-util
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 kqueue cocoa ns lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 205104 12763)
 (symbols 48 20136 0)
 (miscs 40 373 202)
 (strings 32 28953 1768)
 (string-bytes 1 764912)
 (vectors 16 35914)
 (vector-slots 8 784151 7972)
 (floats 8 48 311)
 (intervals 56 224 0)
 (buffers 992 11))