Poor performance when `display-line-numbers` is set to `visual`

首先，在将 display-line-numbers 设置为 'visual 的情况下复现 php-mode 中的输入速度下降，然后检查经过性能分析的入口点 php-syntax-propertize-hash-line-comment、syntax-propertize 和 line-move。将其行为与 'relative 进行比较，并确认输入性能不再随缓冲区长度成比例地下降。

When using php-mode, if display-line-numbers is set to 'visual then the performance when typing is very poor. The problem gets worse proportionally to the number of buffer lines; in my case it becomes noticeable when the buffer gets to around 30 lines.

Here is a profile when set to 'visual: -

- command-execute                                                 291  88%
 - call-interactively                                             291  88%
  - funcall-interactively                                         291  88%
   - self-insert-command                                          273  82%
    - c-after-change                                              138  41%
     - c-trim-found-types                                         138  41%
      - c-beginning-of-current-token                              138  41%
       - skip-syntax-backward                                     138  41%
        - internal--syntax-propertize                             138  41%
         - syntax-propertize                                      138  41%
          - php-syntax-propertize-function                        138  41%
           - php-syntax-propertize-hash-line-comment                138  41%
            - move-beginning-of-line                              137  41%
             - line-move                                          137  41%
                line-move-1                                       137  41%
    - electric-pair-post-self-insert-function                     135  41%
     - electric-pair-syntax-info                                  135  41%
      - syntax-ppss                                               135  41%
       - parse-partial-sexp                                       135  41%
        - internal--syntax-propertize                             135  41%
         - syntax-propertize                                      135  41%
          - php-syntax-propertize-function                        135  41%
           - php-syntax-propertize-hash-line-comment                134  40%
            - move-beginning-of-line                              134  40%
             - line-move                                          134  40%
                line-move-1                                       134  40%
   + counsel-M-x                                                   18   5%

Here is a profile when set to 'relative: -

- command-execute                                                  75  70%
 - call-interactively                                              75  70%
  - funcall-interactively                                          75  70%
   - self-insert-command                                           55  51%
    - electric-pair-post-self-insert-function                      29  27%
     - electric-pair-syntax-info                                   29  27%
      - syntax-ppss                                                29  27%
       - parse-partial-sexp                                        29  27%
        - internal--syntax-propertize                              29  27%
         - syntax-propertize                                       29  27%
          - php-syntax-propertize-function                         29  27%
           - php-syntax-propertize-hash-line-comment                 29  27%
            - move-beginning-of-line                               29  27%
             - line-move                                           29  27%
              - line-move-1                                        29  27%
               - vertical-motion                                    4   3%
                - jit-lock-function                                 4   3%
                 - jit-lock-fontify-now                             4   3%
                  - jit-lock--run-functions                         4   3%
                   - run-hook-wrapped                               4   3%
                    - #<compiled 0x157529864965>                    4   3%
                     - font-lock-fontify-region                     4   3%
                      - c-font-lock-fontify-region                  4   3%
                       - font-lock-default-fontify-region                  3   2%
                        - font-lock-fontify-keywords-region                  2   1%
                         - #<compiled 0x1575295055fd>                  1   0%
                          - c-beginning-of-decl-1                   1   0%
                           - c-beginning-of-statement-1                  1   0%
                              c-beginning-of-macro                  1   0%
                       - c-before-context-fl-expand-region                  1   0%
                        - mapc                                      1   0%
                         - #<compiled 0x157529228b15>                  1   0%
                          - c-context-expand-fl-region                  1   0%
                           - c-fl-decl-end                          1   0%
                              c-backward-sws                        1   0%
    - c-after-change                                               26  24%
     - c-trim-found-types                                          26  24%
      - c-beginning-of-current-token                               26  24%
       - skip-syntax-backward                                      26  24%
        - internal--syntax-propertize                              26  24%
         - syntax-propertize                                       26  24%
          - php-syntax-propertize-function                         26  24%
           - php-syntax-propertize-hash-line-comment                 26  24%
            - move-beginning-of-line                               26  24%
             - line-move                                           26  24%
                line-move-1                                        25  23%
   + counsel-M-x                                                   19  17%
   + evil-normal-state                                              1   0%
+ ...                                                              30  28%
+ redisplay_internal (C function)                                   1   0%
+ timer-event-handler                                               1   0%

I am using GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, cairo version 1.17.3) of 2020-08-28