Slow compilation with many files

[Brian Dessent]

Zed wrote:

> 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.

This is essentially what the -combine switch does, except that switch
only supports C.

> 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?

Yes, there's the startup/cleanup overhead of the compiler itself, plus
the overhead of parsing all the various headers 20 times instead of
once.  You can try using a precompiled header to reduce the cost of the
latter, see
<http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html>.  Note that
this isn't something you can just switch on, you have to think a little
bit about how to implement it, but the manual gives some good
suggestions about how to do that.

Brian