Documentation on debugging regexp performance

[Clément Pit--Claudel]

Hi emacs-devel,

I'm running into a surprising regular expressions issue. I have attached a file 
(~50k) in which (re-search-forward "   +[^:=]+ +:=?") seems to be extremely 
slow. (I killed it after 30 seconds). Truncating the file to its first 20 lines 
reduces the time for re-search-forward to about a second, which is still 
extremely slow. 

Are there good resources on how to rewrite regexps to make them Emacs-friendly? 
I didn't find such documentation, and I'm puzzled as to what could make the 
regexp above hard to re-search-forward for.

Cheers,
Clément.

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