Slow compilation with many files

Zed perrose@kth.se
Tue Apr 15 04:17:00 GMT 2008


I've tried to make my c++ source files small in my current project. Compiling
my approx. 20 files takes very long time. I created a new source file that
just includes all my original ones with #include statements, and compiled
it. This method was much quicker. Compiling all files included in one takes
approx. double the time compared to that of compiling just one of the small
source files. So If I make a change to some header that is included by many
of the source files, the last described method that includes the files to
one is much faster. 

It seems there is a lot of compilation time overhead if the code is compiled
in many small parts - this is without taking linking into account. Is there
any settings or some trick that can reduce this overhead, except my ugly
inclusion method?

This is the command executed per source file, created by autoconf:

g++ -DHAVE_CONFIG_H -I. -I.. -DPACKAGE_LOCALE_DIR=\""/usr/local//locale"\"
-DPACKAGE_SRC_DIR=\""."\" -DPACKAGE_DATA_DIR=\""/usr/local/share"\"
-I/usr/include/opencv   -pthread -I/usr/include/glib-2.0
-I/usr/lib/glib-2.0/include   -I/usr/include/gtk-2.0
-I/usr/lib/gtk-2.0/include -I/usr/include/atk-1.0 -I/usr/include/cairo
-I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include
-I/usr/include/freetype2 -I/usr/include/libpng12 -I/usr/include/pixman-1  
-I/usr/local/include/ltilib -D_GNU_SOURCE -fpic -D_DEBUG    -g -O2 -MT
pick-vertex-manipulator.o -MD -MP -MF .deps/pick-vertex-manipulator.Tpo -c
-o pick-vertex-manipulator.o pick-vertex-manipulator.cpp

Which is essentially after removing unimportant stuff:

g++ -DHAVE_CONFIG_H -D_GNU_SOURCE -fpic -D_DEBUG -g -O2 -MT
pick-vertex-manipulator.o -MD -MP -MF .deps/pick-vertex-manipulator.Tpo -c
-o pick-vertex-manipulator.o pick-vertex-manipulator.cpp

Thank you!
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