Results for Windows XP with CPPFLAGS='-DGLYPH_DEBUG=1' CFLAGS='-O0 -g3'
--enable-checking=yes --enable-check-lisp-object-type=yes:


Unmodified xdisp.c from trunk:

24.3 1007 scrolls, total time = 105.60900020599365s.
24.4 1007 scrolls, total time = 73.21900010108948s.
25.0 1007 scrolls, total time = 318.5629997253418s.


xdisp.c from trunk with odd apostrophes eradicated:

24.3 1007 scrolls, total time = 100.1240005493164s.
24.4 1007 scrolls, total time = 60.13900017738342s.
25.0 1007 scrolls, total time = 197.95300006866455s.


I can't test with older versions since those don't have
`scroll-down-command' here.

So while it might be worthwhile to do such an optimization, here the
great differenece is the 3-to-5-fold increase of execution time from
24.4 to 25.0 for which I don't have an explanation.  The cc-mode used is
always the one bundled with the respective Emacs version.

martin



BTW, if you want to quickly visualize constructs like

(defconst odd-apostrophes
   "/\\*\\([^*']\\|\\*+[^*'/]\\)*\\(\\**'\\([^*']\\|\\*+[^*'/]\\)*\\**'\\([^*']\\|\\*+[^*'/]\\)*\\)*\\**\\('\\)\\([^*']\\|\\*+[^*'/]\\)*\\*+/"
)

without adding comments like

   ;;     1                        2       3                             4                                5      6

you can use the regexp-lock.el package I attached here ;-)