bug#4558: forw_comment slowdown since 22.3

[Dan Nicolaescu]

$ cd emacs/src

$ cat emacs.c emacs.c emacs.c emacs.c emacs.c > /tmp/emacs.c

$ emacs /tmp/emacs.c
C-x h
M-;
C-x C-s
C-x C-c

$ cat /tmp/t.el
(defun myfwd ()
  (interactive)
  (dotimes (n 1)
    (while (forward-comment 1))
    (while (forward-comment -1)))
  (save-buffers-kill-emacs))
;; increase N if your machine is much faster

Now do:

emacs -Q -l /tmp/t.el /tmp/emacs.c -f myfwd

with both CVS HEAD and 22.3.

The gprof results with 22.3:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 81.40      4.90     4.90  5200163     0.00     0.00  forw_comment
 12.62      5.66     0.76      642     0.00     0.01  scan_sexps_forward
  0.83      5.71     0.05    34941     0.00     0.00  back_comment
  0.66      5.75     0.04  1282235     0.00     0.00  char_quoted
  0.66      5.79     0.04    13498     0.00     0.00  re_search_2
  0.66      5.83     0.04    10738     0.00     0.00  mark_object
  0.33      5.85     0.02    54716     0.00     0.00  read1
  0.33      5.87     0.02    38404     0.00     0.00  Feval
  0.33      5.89     0.02    38012     0.00     0.00  Fbyte_code
  0.17      5.90     0.01   183599     0.00     0.00  specbind
  0.17      5.91     0.01    99154     0.00     0.00  find_interval
  0.17      5.92     0.01    61433     0.00     0.00  get_keymap
  0.17      5.93     0.01    37912     0.00     0.00  funcall_lambda
  0.17      5.94     0.01    23239     0.00     0.00  oblookup
  0.17      5.95     0.01    18737     0.00     0.00  scan_newline
  0.17      5.96     0.01    12410     0.00     0.00  get_keyelt
  0.17      5.97     0.01      664     0.00     0.00  append_glyph
  0.17      5.98     0.01      515     0.00     0.00  re_compile_pattern
  0.17      5.99     0.01        7     0.00     0.00  detect_coding_mask
  0.17      6.00     0.01        3     0.00     0.00  decode_eol


and with CVS HEAD:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 84.45      6.30     6.30  5200163     0.00     0.00  forw_comment
  9.12      6.98     0.68      642     0.00     0.01  scan_sexps_forward
  1.47      7.09     0.11    34941     0.00     0.00  back_comment
  1.21      7.18     0.09  1747491     0.00     0.00  mark_object
  0.40      7.21     0.03  1282235     0.00     0.00  char_quoted
  0.40      7.24     0.03    50653     0.00     0.00  re_search_2
  0.27      7.26     0.02   768825     0.00     0.00  readchar
  0.27      7.28     0.02   738707     0.00     0.00  Faref
  0.27      7.30     0.02    25406     0.00     0.00  re_compile_pattern
  0.27      7.32     0.02    12264     0.00     0.00  mem_insert
  0.13      7.33     0.01   890859     0.00     0.00  mark_vectorlike
  0.13      7.34     0.01   739728     0.00     0.00  readbyte_from_file
  0.13      7.35     0.01   104164     0.00     0.00  
balance_possible_root_interval
  0.13      7.36     0.01    64037     0.00     0.00  re_match_2_internal
  0.13      7.37     0.01    34284     0.00     0.00  update_syntax_table
  0.13      7.38     0.01    25395     0.00     0.00  re_compile_fastmap
  0.13      7.39     0.01    21718     0.00     0.00  oblookup
  0.13      7.40     0.01    21080     0.00     0.00  multibyte_chars_in_text
  0.13      7.41     0.01     1170     0.00     0.00  str_as_unibyte
  0.13      7.42     0.01      529     0.00     0.00  mark_char_table
  0.13      7.43     0.01       10     0.00     0.01  Fgarbage_collect
  0.13      7.44     0.01       10     0.00     0.00  free_glyph_matrix
  0.13      7.45     0.01        3     0.00     0.01  Fparse_partial_sexp
  0.07      7.46     0.01   158439     0.00     0.00  
multibyte_char_to_unibyte_safe
  0.07      7.46     0.01                             multibyte_char_to_unibyte
  0.00      7.46     0.00   727705     0.00     0.00  char_table_translate
  0.00      7.46     0.00   205798     0.00     0.00  Fcdr

The same number of calls to forw_comment take longer with CVS HEAD.