Is there a possibility (most likely by using gcc / g++ itself?) to determine which code lines of all files included by a single compilation are actually used?
I use much third-party includes and would like to strip them to the actually used code to speed up compilation.
Maybe g++ can output this by some combination of it's many options?
The best advice I can offer is to break apart huge include files into smaller pieces. This allows developers to include only the files they need to resolve symbols.
My favorite example is
windows.h. The mega include file declares the entire Windows API, whether you need them or not. If you only want the APIs for processing files, you get the APIs for dialg boxes as well.Some shops like the monster include files because they only have to include the one file in their sources. One draw back is that every source file now depends on mega include file. If I change one of the include files, the entire system will be rebuilt instead of a few modules that depend on the header file that I changed.
In my projects, only a couple of files are compiled at a time; usually less than 5. This makes the average turnaround time (modify then build) very fast. The entire system is rebuilt overnight by a server or by developers. There is no need to rebuild source files that have not changed.
So split up your modules, so you are not rebuilding your system every time.