Re: slow output in *compilation* buffer

[Stefan Monnier <monnier@iro.umontreal.ca>]

>   %   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

- not sure why it's GCing that much, but it sounds like something that
  can be improved.
- the re_* part of the profile is hard to improve with a quick fix,
  I think: it just represents regexp-searching every one of the regexps
  in compilation-error-regexp-alist in turn.  Of course, there is a way
  to do that (a lot) faster, by compiling all those regexps into a DFA.
- why does the gprof data only seem to account for a bit less than 10s
  when you say it takes 25s to complete?
- It seems that they the calls to the interval code come from
  compilation-error-properties, but that function should only be called
  for regexps that do match, which shouldn't be that many.  Can you look
  at the text to see if there really are that many matches?  BTW, we
  should probably be able to make compile.el a bit lazier (i.e. the
  font-lock-phase part of the code should do a bit less work by moving
  it to the next-error-phase code).

Another thing: the compilation code currently uses font-lock-keywords,
but it should probably be changed to use font-lock-syntactic-keywords
instead (which should make it unnecessary to disable jit-lock).

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

compile.el does its work via font-lock, so I do expect most/all of the
time to be spent there.


        Stefan