bug#4222: calls to char_table_ref slow down 23.1 (vs 22.3)

[Dan Nicolaescu <dann@ics.uci.edu>]

Take src/config.h run C-x r t on it to insert a space in front of each
line.

Then build both emacs-23.1 and 22.3 with profiling enabled (-O2 -g -pg).
Then run:

emacs -Q -nw config.h
M-: (indent-region (point-min)(point-max)) RET
C-x C-c

The 22.3 gprof results:

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  ms/call  ms/call  name    
 41.29      7.13     7.13  4653244     0.00     0.00  forw_comment
 16.10      9.91     2.78    32473     0.09     0.31  scan_sexps_forward
  9.09     11.48     1.57    15132     0.10     0.15  re_search_2
  5.62     12.45     0.97    17286     0.06     0.15  scan_lists
  5.59     13.41     0.96 33462255     0.00     0.00  lookup_char_property
  3.36     13.99     0.58 18478958     0.00     0.00  next_interval
  2.14     14.37     0.37   129733     0.00     0.00  mark_object
  1.80     14.68     0.31   137020     0.00     0.00  skip_chars
  1.74     14.97     0.30 14459993     0.00     0.00  previous_interval
  1.62     15.26     0.28 57446793     0.00     0.00  Fcdr
  1.36     15.49     0.23  2156082     0.00     0.00  update_syntax_table
  1.27     15.71     0.22  3315615     0.00     0.00  re_match_2_internal
  1.19     15.91     0.20 23687203     0.00     0.00  Fassq
  0.87     16.07     0.15    13478     0.01     0.06  Fprevious_single_property_change
  0.75     16.20     0.13 33462255     0.00     0.00  textget
  0.75     16.32     0.13   228439     0.00     0.00  Fbyte_code
  0.52     16.41     0.09  1978403     0.00     0.00  update_interval
  0.46     16.50     0.08  1101056     0.00     0.00  find_interval
  0.29     16.55     0.05  3613429     0.00     0.00  buf_bytepos_to_charpos
  0.26     16.59     0.04 10137050     0.00     0.00  Fcar
  0.26     16.64     0.04  1154883     0.00     0.00  balance_an_interval
  0.23     16.68     0.04   579275     0.00     0.00  unbind_to



The 23.1 gprof results:

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 29.60      7.03     7.03 406111658     0.00     0.00  char_table_ref
 26.72     13.37     6.34  4653244     0.00     0.00  forw_comment
 11.80     16.17     2.80    32121     0.00     0.00  scan_sexps_forward
  5.98     17.59     1.42    23271     0.00     0.00  re_search_2
  5.27     18.84     1.25    17289     0.00     0.00  scan_lists
  4.13     19.82     0.98 33439981     0.00     0.00  lookup_char_property
  1.94     20.28     0.46 18488739     0.00     0.00  next_interval
  1.73     20.69     0.41 10038210     0.00     0.00  mark_object
  1.26     20.99     0.30  2156799     0.00     0.00  update_syntax_table
  1.20     21.27     0.29                             sub_char_table_ref
  1.10     21.53     0.26 14455134     0.00     0.00  previous_interval
  0.88     21.74     0.21 57391428     0.00     0.00  Fcdr
  0.88     21.95     0.21  3318263     0.00     0.00  re_match_2_internal
  0.72     22.12     0.17 23671456     0.00     0.00  Fassq
  0.67     22.28     0.16   196373     0.00     0.00  Fbyte_code
  0.59     22.42     0.14    13478     0.00     0.00  Fprevious_single_property_change
  0.51     22.54     0.12       38     0.00     0.02  Fgarbage_collect
  0.38     22.63     0.09 33439981     0.00     0.00  textget
  0.38     22.72     0.09 10115583     0.00     0.00  Fcar
[snip]

-----------------------------------------------
                0.05    0.22     612/32121       back_comment [28]
                2.75   11.33   31509/32121       Fparse_partial_sexp [6]
[5]     60.5    2.80   11.55   32121         scan_sexps_forward [5]
                5.17    3.76 3796695/4653244     forw_comment [7]
                1.62    0.00 93379139/406111658     char_table_ref [8]
                0.15    0.86 1092890/2156799     update_syntax_table [11]
                0.00    0.00    5096/10115583     Fcar [46]
                0.00    0.00    6552/57391428     Fcdr [33]
                0.00    0.00     147/952550      Fcons [105]

It can be seen that 23.1 is quite a bit slower, and that it has a lot of
extra calls to char_table_ref.  

Is there some easy way to reduce the number of those calls?