Swiper is very slow on some files, but only when I have display-line-numbers 'visual

[alienbogart]

• GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.31) of 2018-08-16
• Swiper version 20180813.1625
• init.el

Swiper performs very well on Org files, opening in less than 2 seconds on my 3400 init.org, but it takes five seconds to show up on a .vim file with 216 lines, and on an i3 config file with 392 lines. If I switch to text-mode it is still slow, but it works well if I change it to fundamental-mode. I use this functions to set relative numbers:

(defun line-numbers ()
  (interactive)
(setq display-line-numbers 'visual)
(setq display-line-numbers-widen nil)
(setq display-line-numbers-current-absolute nil))

  (defun noct:relative ()
    (setq-local display-line-numbers 'visual))
  (defun noct:absolute ()
    (setq-local display-line-numbers t))
  (custom-set-faces '(line-number-current-line ((t :weight bold
                                                   :foreground "goldenrod"

And I have the following hooks to enable it:

(add-hook 'text-mode-hook 'line-numbers)
(add-hook 'prog-mode-hook 'line-numbers)

When I disable the line numbers Swiper responds much faster, but still a bit slower. I tried changing (setq display-line-numbers 'visual) to (setq display-line-numbers 'relative), and the performance does improve, but I on my init org file the numbers are so high that it's unpractical to navigate by line number (I'm an Evil user).

[abo-abo]

Please provide a sample file, .vim for instance.

[alienbogart]

Here you go.

[abo-abo]

I ran:

(benchmark-run 100
  (swiper--candidates))

on your init.vim file with relative line numbers. It took 0.2s for 100 runs, so that's 0.002s per run.
The issue is not reproducible on GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9).

[alienbogart]

Thank you! Do you have any suggestions on how could I proceed to further debug this problem?