bug#43631: 28.0.50; CC Mode multiline strings grinds performance to a halt

[Theodor Thornhill via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

> All the profiles posted there end prematurely, thus making it
> impossible to make independent conclusions regarding the possible
> culprits.  Would it be possible to post here a full profile,
> completely expanded, obtained after loading all the relevant *.el
> files as *.el (NOT *.elc!), so that the profile is detailed enough to
> show the relevant parts?  It would make the discussion much more
> focused.
>
> Bonus points for posting another profile, where the feature you think
> is the main culprit is disabled.
>
> TIA


Attached is two reports, one which is super slow, and one that is fast.

Recipe:
 - git clone https://github.com/unhammer/csharp-mode/
 - git checkout 164-repro
 - eval csharp-mode.el
 - open superslow.cs and write some text
 - rinse, repeat, but with
   
(c-lang-defconst c-multiline-string-start-char
  csharp ?@)

commented out.

One is unbearably slow, the other is super fast.

Hope this helps a little!

All the best,
Theodor Thornhill



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let save-excursion cond progn and while condition-case let] 2 [let and if save-restriction if progn if let c-beginning-of-macro progn unwind-protect let save-excursion cond progn and] 2 [cond progn and while condition-case let c-syntactic-re-search-forward and while progn and while progn if cond let*] 1 [and if let c-backward-sws c-determine-limit-get-base let* save-excursion c-determine-limit setq if let c-fl-decl-start or setq if c-change-expand-fl-region] 1 [let* c-pps-to-string-delim progn and while progn if cond let* progn unwind-protect let* c-before-change-check-unbalanced-strings funcall "#<lambda 0x8f29c4b23d484>" mapc] 1 [assq cdr looking-at if if while let* progn unwind-protect let* if c-after-change-mark-abnormal-strings funcall "#<lambda 0xb9ab7fa2473f23>" mapc save-excursion] 1 [let c-syntactic-re-search-forward and while progn and while progn if cond let* progn unwind-protect let* c-before-change-check-unbalanced-strings funcall] 1 [setq c-truncate-lit-pos-cache c-clear-syn-tab progn and while progn and while progn if cond let* progn unwind-protect let*] 1 [c-clear-syn-tab if progn while let* c-pps-to-string-delim progn and while progn if cond let* progn unwind-protect let*] 2 [char-before eq while progn while progn unwind-protect let progn if save-restriction if progn if let c-beginning-of-macro] 1 [c-syntactic-re-search-forward and while progn and while progn if cond let* progn unwind-protect let* c-before-change-check-unbalanced-strings funcall "#<lambda 0x8f29c4b23d484>"] 2 [setq c-truncate-lit-pos-cache c-invalidate-state-cache-1 if c-invalidate-state-cache cond while save-restriction let* progn unwind-protect let* c-parse-quotes-after-change funcall "#<lambda 0xb9ab7fa2473f23>" mapc] 1 [and while save-restriction let* progn unwind-protect let* c-parse-quotes-after-change funcall "#<lambda 0xb9ab7fa2473f23>" mapc save-excursion progn unwind-protect progn unwind-protect] 1 [not save-excursion cond while save-restriction let* progn 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