GNU bug report logs - #69385
30.0.50; Long lines with bidi text slow down Emacs

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#69385: closed (30.0.50; Long lines with bidi text slow down
 Emacs)
Date: Thu, 21 Mar 2024 08:31:02 +0000

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Your message dated Thu, 21 Mar 2024 10:29:12 +0200
with message-id <86jzlw2dk7.fsf <at> gnu.org>
and subject line Re: bug#69385: 30.0.50; Long lines with bidi text slow down Emacs
has caused the debbugs.gnu.org bug report #69385,
regarding 30.0.50; Long lines with bidi text slow down Emacs
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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69385: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=69385
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From: Stephen Berman <stephen.berman <at> gmx.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; Long lines with bidi text slow down Emacs
Date: Sun, 25 Feb 2024 17:23:11 +0100

Displaying a buffer that contains a long line with bidirectional text
greatly slows down Emacs.  A simple reproduction is to copy the the
Arabic example from etc/HELLO (`C-h h'), yank it into a buffer
(fundamental-mode suffices), add " Hello ", and then create a single
line consisting of a large number of copies of these strings; on my
machine 500 copies clearly shows the slowdown, and with 800 copies it is
much worse.

There is no slowdown with a line of the same length consisting only of
RTL or only of LTR text, nor with the above test line when
bidi-display-reordering is set to nil in the buffer (but then, of
course, the Arabic is not displayed correctly).  It seems that the long
line optimizations added to Emacs 29 do not work with bidirectional
text.

(FTR, I encountered this issue with a program of mine that generates
Emacs Lisp files containing such long lines with bidirectional text.
These files are not intended for display but I was examining one and
experienced the slowdown.)


In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.18.0) of 2024-02-20 built on strobelfs2
Repository revision: d9afa1f30fdf9d00b447fea0a8343397333e172f
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101009
System Description: Linux From Scratch r12.0-112

Configured using:
 'configure -C --with-xwidgets 'CFLAGS=-Og -g3'
 PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM XWIDGETS GTK3 ZLIB

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Stephen Berman <stephen.berman <at> gmx.net>
Cc: 69385-done <at> debbugs.gnu.org
Subject: Re: bug#69385: 30.0.50; Long lines with bidi text slow down Emacs
Date: Thu, 21 Mar 2024 10:29:12 +0200

> From: Stephen Berman <stephen.berman <at> gmx.net>
> Cc: 69385 <at> debbugs.gnu.org
> Date: Thu, 07 Mar 2024 12:12:51 +0100
> 
> > So I will wait for you to report any problems, and if no problems are
> > seen, will install in a week or so.
> 
> I haven't yet run into any issues concerning your patch

No further comments, so I assume the patch is indeed safe, and I have
now installed it on the master branch.

I'm therefore closing this bug.  Thanks for testing the patch.

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