bug#22884: 25.0.92; C/l mode editing takes waaaayy too long

[Paul Eggert <eggert@cs.ucla.edu>]

On 05/13/2016 01:37 PM, Glenn Morris wrote:
> What about other C code, besides the Emacs sources?
> What if anyone ever wants to edit an older version of the Emacs sources?

Older versions of Emacs have smaller config.h files, which makes the 
problem significantly smaller. I just now visited a config.h file for 
Emacs 23.4, and the same “type ‘/ /’” benchmark took about two seconds 
on my six-year-old desktop (Fedora 23 x86-64, AMD Phenom II X4 910e). 
Although two seconds is pretty annoying, it's considerably better than 
the ten seconds I was seeing with emacs-25 before we worked around the 
problem there.

Although Non-Emacs sources may have the problem, I imagine it's 
reasonably rare.

> Your initial report said: "This sort of thing makes Emacs effectively
> unusable for editing [some C code]", which is, y'know, a pretty bad state.

Yes, it is indeed a bad state. However, the problematic situations are 
rare and cause slowdowns rather than crashes, so the case for making it 
a blocker is not as strong as it could be.