How to improve Visual C++ compilation times?
I am compiling 2 C++ projects in a buildbot, on each commit. Both are around 1000 files, one is 100 kloc, the other 170 kloc. Compilation times are very different from gcc (4.4) to Visual C++ (2008).
Visual C++ compilations for one project take in the 20 minutes. They cannot take advantage of the multiple cores because a project depend on the other. In the end, a full compilation of both projects in Debug and Release, in 32 and 64 bits takes more than 2 1/2 hours.
gcc compilations for one project take in the 4 minutes. It can be parallelized on the 4 cores and takes around 1 min 10 secs. All 8 builds for 4 versions (Debug/Release, 32/64 bits) of the 2 projects are compiled in less than 10 minutes.
What is happening with Visual C++ compilation times? They are basically 5 times slower.
What is the average time that can be expected to compile a C++ kloc? Mine are 7 s/kloc with vc++ and 1.4 s/kloc with gcc.
Can anything be done to speed-up compilation times on Visual C++?
Answer
One thing that slows down the VC++ compiler is if you have a header file that initializes concrete instances of non-trival const value types. You may see this happen with constants of type std::string or GUIDs. It affects both compilation and link time.
For a single dll, this caused a 10x slowdown. It helps if you put them in a precompiled header file, or, just declare them in a header and initialize them in a cpp file.
Do take a look into the virus scanner, and be sure to experiment with precompiled headers, without it you won't see VC++ at its best.
Oh yeah, and make sure the %TMP% folder is on the same partition as where your build is written to, as VC++ makes temp files and moves them later.