bug#30849: 27.0.50; CC-mode: very slow when parsing big C array initializer

[David Welch]

Run 'emacs -Q bar.c' (this file is attached)
Goto a line inside the initializer e.g. 'M-x goto-line RET 9522'
emacs will hang for ~50 seconds on a 100% cpu on a Intel i7 @ 3.40GHz.

This bug seems to be introduced by

commit d3090a3a3e22c4b0f4e0e833942f5942eb392c51 (HEAD, refs/bisect/bad)
Author: Alan Mackenzie <acm@muc.de>
Date:   Fri Feb 2 20:46:35 2018 +0000

    CC Mode: Fix an enum intro being parsed as defun-block-intro
    
    * lisp/progmodes/cc-engine.el (c-inside-bracelist-p): Return a bufpos rather
    than t for the enum case.
    (c-add-stmt-syntax, c-guess-continued-construct): Replace
    c-looking-at-or-maybe-in-bracelist by c-inside-bracelist-p, since the former
    does not recognize enum brace lists, but the latter does.
    
    * lisp/progmodes/cc-fonts.el (c-get-fontification-context): Replace
    c-looking-at-or-maybe-in-bracelist by c-inside-bracelist-p.

I generated a profile and 95% of time is spent in c-inside-bracelist-p
called from c-get-fontification-context.


In GNU Emacs 27.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.25)
 of 2018-03-17 built on lgw01-amd64-055
Windowing system distributor 'The X.Org Foundation', version 11.0.11803000
System Description: Ubuntu 17.10

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 --disable-silent-rules '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=-snapshot --with-modules=yes --with-x=yes
 --with-x-toolkit=gtk3 --with-xwidgets=yes 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-snapshot-lB2ym1/emacs-snapshot-94474=. 
-fstack-protector-strong
 -Wformat -Werror=format-security' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES THREADS XWIDGETS LIBSYSTEMD LCMS2

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

Major mode: C/*l

Minor modes in effect:
  diff-auto-refine-mode: t
  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
  abbrev-mode: t

Load-path shadows:
/usr/share/emacs/site-lisp/llvm-4.0/tablegen-mode hides 
/usr/share/emacs/site-lisp/llvm-5.0/tablegen-mode
/usr/share/emacs/site-lisp/llvm-4.0/emacs hides 
/usr/share/emacs/site-lisp/llvm-5.0/emacs
/usr/share/emacs/site-lisp/llvm-4.0/llvm-mode hides 
/usr/share/emacs/site-lisp/llvm-5.0/llvm-mode
/usr/share/emacs/site-lisp/rst hides /usr/share/emacs/27.0.50/lisp/textmodes/rst
/usr/share/emacs/site-lisp/dictionaries-common/flyspell hides 
/usr/share/emacs/27.0.50/lisp/textmodes/flyspell
/usr/share/emacs/site-lisp/dictionaries-common/ispell hides 
/usr/share/emacs/27.0.50/lisp/textmodes/ispell

Features:
(shadow sort mail-extr emacsbug message rmc puny 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 vc-git diff-mode easy-mmode map
seq byte-opt gv bytecomp byte-compile cconv cc-mode cc-fonts easymenu
cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs
cl-loaddefs cl-lib elec-pair time-date mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type 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 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 dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting xwidget-internal move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 119309 10422)
 (symbols 48 22894 1)
 (miscs 40 83 136)
 (strings 32 35675 2207)
 (string-bytes 1 1073774)
 (vectors 16 18053)
 (vector-slots 8 536564 11124)
 (floats 8 57 70)
 (intervals 56 417 1)
 (buffers 992 13))

bar.c.gz
Description: bar.c.gz

bar-slow.profile.gz
Description: bar-slow.profile.gz

bar-fast.profile.gz
Description: bar-fast.profile.gz