bug#26079: 26.0.50; Performance regression in delete-trailing-whitespace

[Sho Takemori <stakemorii@gmail.com>]

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Dear developers,

delete-trailing-whitespace in Emacs 26 for large files is very slow.

For example, it took about 1.6s for this file (
https://raw.githubusercontent.com/stakemori/e8theta_degree3/master/results/wt18_17_5/wt18_17_5.org
).
But in Emacs 25, it took about 0.003s.
A similar code to the following is used in delete-trailing-whitespace. And
it is slow for large files.

(save-excursion
    (let ((end-marker nil))
      (goto-char (point-min))
      (with-syntax-table (make-syntax-table (syntax-table))
        (modify-syntax-entry ?\f "_")
        (modify-syntax-entry ?\n "_")
        (re-search-forward "\\s-+$" end-marker t))))

Best regards,
Sho Takemori

In GNU Emacs 26.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2017-03-13 built on 500-270jp
Repository revision: cf670b49a7704d63575863f832426d32bf6a8c3c
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description: Ubuntu 16.04.2 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
delete-backward-char: Text is read-only
(1.6173726940000002 0 0.0)
Quit
Configured using:
 'configure --with-sound=no --with-modules'

Configured features:
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ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LC_MONETARY: ja_JP.UTF-8
  value of $LC_NUMERIC: ja_JP.UTF-8
  value of $LC_TIME: ja_JP.UTF-8
  value of $LANG: ja_JP.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Org

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  tool-bar-mode: t
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  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

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Memory information:
((conses 16 275028 6205)
 (symbols 48 28629 1)
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