[cmake-developers] dependency scanning speed

[Alexander Neundorf]

Hi,

today I compiled unity (khtml ported to WebKit ported back to KDE) on a 
Pentium 4 1.8 GHz, 512 MB RAM notebook.

Dependency scanning takes approx. 30 seconds for the WebCore subdir there.
At http://www.neundorf.net/cmake/unity you can find the cmake files for this 
directory. As you can see they are BIG. build.make is 2 MB, depend.make is 10 
MB.
Any ideas how the scanning could be made faster ?
includecache.C and includecache.CXX cache the #includes, so only the files 
which have really changed are scanned again. Then the dependencies for all 
files are calculated again.
I see two things (but I didn't measure):
-save/load the cache files faster: is there a way to write/read a map more 
faster ?
-cache which files are checked during the dependency checking. 
Then when checking the next time, at first check which of these files have 
changed. Then for each file, load which files it depends on, and only 
calculate the dependencies new if if any of the depend files have changed.
I'm not sure the logic is right and how much it could gain.

What do you think ?

Bye
Alex
-- 
Work: alexander.neundorf AT jenoptik.com - http://www.jenoptik-los.de
Home: neundorf AT kde.org                - http://www.kde.org
      alex AT neundorf.net               - http://www.neundorf.net