bug#56682: Fix the long lines font locking related slowdowns

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

>>> Or when you have a slower CPU, with moderately large files.
>> I doubt there are any CPUs in wide use that are even 5x slower than mine.
> Have a look at e.g. https://www.cpubenchmark.net/singleThread.html , you'll
> see that many CPUs in wide use are 5x slower, or more than 5x slower, than
> your CPU.

Which one of those CPUs that are 5x slower than the top performer do you
consider as being "in wide use"?

AFAICT the highest score there is 4400.  So 5x slower would mean a score
below 880.  My 2006-vintage Thinkpad T60 is just below at 848.  But my
T61 (released in 2007, tho I bought it refurbished in 2012) is already
rated at 1K.

Admittedly, these were top-of-the-line machines when they were released,
and are hence faster than many machine released later (e.g. netbooks),
but still: I have seen *very* few people recently using machines slower
than my T61.

I don't know what machine Dmitry is using, but based on that
"cpubenchmark" data I'd indeed be very surprised if "there are any CPUs
in wide use that are even 5x slower than" his.


        Stefan