bug#32175: Terrible performance of c++-mode refontifying

[Stefan Kangas]

Hi Alan,

This bug was reported in July 2018 but got no followup.

Perhaps you could take a look?

Best regards,
Stefan Kangas

Konstantin Kharlamov <hi-angel@yandex.ru> writes:

> Sometimes for working with C++ code I start experiencing lags for typing
> the text, like, 1-second delay between pressing the key and the actual
> text appearing. This does not happen at the beginning of the work, but
> rather after Emacs have been running for a while.
>
> It seems to be a per-buffer issue. E.g. right now I
> have the problem in one c++mode buffer, but not in another.
>
> This problem have definitely existed for 2 years (maybe more). I
> didn't report it because I thought it's my computer slow. I attached
> profiling result at the end, and I remember that some years ago traces
> of low performance have also been leading to functions about
> refontifying.
>
> Emacs version: GNU Emacs 27.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version
> 3.22.30) of 2018-07-06
> (It's 12 days old build from git, commit 3bbd4ffc68b)
>
> FWIW it's built with -flto -march=native options, i.e. I have as much
> optimization as possible.
>
> Profiling below is done by pressing <SPACE> key, then waiting for
> symbol to appear; and repeating this for ≈10 times.
>
> - redisplay_internal (C function)                                6900  69%
>  - jit-lock-function                                             6887  69%
>   - jit-lock-fontify-now                                         6887  69%
>    - jit-lock--run-functions                                     6873  69%
>     - run-hook-wrapped                                           6873  69%
>      - #<compiled 0x289f6f5>                                     6873  69%
>       - font-lock-fontify-region                                 6873  69%
>        - c-font-lock-fontify-region                              6866  69%
>         - font-lock-default-fontify-region                       6514  65%
>          - font-lock-fontify-keywords-region                     6447  65%
>           - c-font-lock-declarations                             5059  51%
>            - c-find-decl-spots                                   5012  50%
>             - c-bs-at-toplevel-p                                 2972  29%
>              - c-brace-stack-at                                  2937  29%
>               - c-update-brace-stack                             2831  28%
>                - c-syntactic-re-search-forward                   1263  12%
>                 + c-beginning-of-macro                            548   5%
>                   #<compiled 0x14ed36d>                             6   0%
>                - c-forward-<>-arglist                            1220  12%
>                 - c-forward-<>-arglist-recur                     1041  10%
>                  + c-syntactic-re-search-forward                  285   2%
>                  + c-forward-<>-arglist-recur                     245   2%
>                  + c-backward-token-2                             125   1%
>                    c-forward-sws                                   52   0%
>                  + c-backward-sws                                  12   0%
>                  c-beginning-of-current-token                      48   0%
>                  match-string-no-properties                         6   0%
>             + #<compiled 0x1503add>                              1823  18%
>             + c-beginning-of-macro                                 40   0%
>               c-backward-sws                                        8   0%
>               c-forward-sws                                         6   0%
>               #<compiled 0x14ed6cd>                                 4   0%
>             + c-backward-token-2                                    3   0%
>           + c-font-lock-enclosing-decls                           240   2%
>           + #<compiled 0x150a5d1>                                 203   2%
>           + c-font-lock-<>-arglists                               183   1%
>           + c-font-lock-cut-off-declarators                       176   1%
>           + color-identifiers:colorize                            140   1%
>           + c-font-lock-raw-strings                                45   0%
>           + c-font-lock-invalid-single-quotes                      37   0%
>           + c-font-lock-enum-tail                                  34   0%
>             #<compiled 0x150a4f1>                                  31   0%
>             #<compiled 0x150a1cd>                                  29   0%
>           + c-font-lock-complex-decl-prepare                       25   0%
>             #<compiled 0x150a495>                                  24   0%
>             #<compiled 0x150a57d>                                  22   0%
>           + c-font-lock-c++-lambda-captures                        18   0%
>             #<compiled 0x150a555>                                   9   0%
>             #<compiled 0x150a535>                                   3   0%
>             eval                                                    3   0%
>             c-font-lock-enum-body                                   3   0%
>          + font-lock-fontify-syntactically-region                  40   0%
>         + c-before-context-fl-expand-region                       348   3%
>  + eval                                                             9   0%
>  + mode-line-default-help-echo                                      4   0%
> - ...                                                            1411  14%
>    Automatic GC                                                  1411  14%
> + command-execute                                                1252  12%
> + flycheck-handle-signal                                          301   3%
> + timer-event-handler                                              32   0%
> + evil-repeat-post-hook                                             5   0%
>   global-highlight-symbol-mode-check-buffers                        5   0%
>   evil--jump-hook                                                   1   0%