slow output in *compilation* buffer

[Dan Nicolaescu]

Running a compilation job the produces a lot of text output with M-x
compile is much slower than running it in a shell.

For example

With emacs/lisp as the current directory, doing
M-x compile RET grep -nH -e emacs *.el */*.el RET
takes 25 seconds 
The output is 4500 lines

Running the same command in an xterm takes 1.5 seconds!


gprof data:

  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 31.19      2.72     2.72 52618323     0.00     0.00  lookup_char_property
 20.30      4.49     1.77 51726150     0.00     0.00  previous_interval
 12.16      5.55     1.06 208889310     0.00     0.00  Fcdr
  5.85      6.06     0.51 52444384     0.00     0.00  Fassq
  5.39      6.53     0.47     4573     0.00     0.00  
Fprevious_single_property_change
  2.64      6.76     0.23  8860105     0.00     0.00  mark_object
  2.52      6.98     0.22    10621     0.00     0.00  Fsetcar
  2.29      7.18     0.20 52618300     0.00     0.00  textget
  1.83      7.34     0.16    59828     0.00     0.00  re_search_2
  1.72      7.49     0.15   305181     0.00     0.00  re_match_2_internal
  1.03      7.58     0.09    82087     0.00     0.00  Fbyte_code
  0.80      7.65     0.07     9094     0.00     0.00  adjust_for_invis_intang
  0.80      7.72     0.07   581767     0.00     0.00  find_interval
  0.69      7.78     0.06   295253     0.00     0.00  next_interval
  0.69      7.84     0.06       21     0.00     0.02  Fgarbage_collect
  0.57      7.89     0.05    23886     0.00     0.00  mark_vectorlike

Observations:
- there's a lot of garbage collection going on
- Fprevious_single_property_change is probably mostly called from
  compilation-error-properties

Doing 
M-x (setq compilation-error-regexp-alist nil) RET
then
M-x compile RET grep -nH -e emacs *.el */*.el RET
takes 3 seconds.

So it seems that fontification (and things related to it) are very very 
expensive.

Can someone familiar with the code in question take a look and figure
out how to optimize this?

Thanks

        --dan