bug#44983: Truncate long lines of grep output

[Juri Linkov]

>> Perhaps (setq truncate-lines t) could help in that case?
>
> Not necessarily, because the truncated parts are still in the buffer,
> and the display code which is slow in that case basically moves
> through the buffer one character at a time in many cases.  Only some
> specific scenarios (read: a small number of commands) can jump to the
> next physical line disregarding the truncated parts.

It's very strange that after adding the text property 'display "[…]"
on a very long line, motion commands are still very slow in that buffer.

Could you help to understand why hiding long regions
doesn't help to improve performance?