http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53316
--- Comment #10 from David Stone <david at doublewise dot net> 2012-05-16 15:57:13 UTC --- I did some research to see how often each optimization level is actually used. Looking solely at the most followed C and C++ repositories on github, I collected the following data: C: Linux kernel: 2 s redis: 2 0 vim: 2 6 0 (6 and 0 for commented out options that are selectively enabled for testing) git: 2 s 0 (s for debugging, 0 for code coverage tests) PHP: 0 2 s openFrameworks: s memcached: no defaults found (somewhat thorough check, autotools) libfreenect: 2 xbmc: 2 mruby: 3 (even for debugging!) wax: no defaults found (rake) beanstalkd: use the default 0 (implicit, Make) ccv: 1 (but they preceed it with CC = clang, so it's not really relevant for us) yajl-ruby: no defaults found (rake) libgit2: 2 0 iProxy: seems to be XCode only http-parser: 0 3 nginx_http_push_module: no build scripts, so no defaults C++: hiphop-php: 0 3 s MongoDB: 0 3 Doom GPL: 0 1 3 (0 and 1 are both used with debugging) PhantomJS: no defaults found (qmake) MaNGOS: Does not appear to set (thorough check, CMake) Scribe: 3 0 TrinityCore: Does not appear to set any optimization level, but does turn on some 'f' flags specifically (CMake) bitcoin: 2 firesheep: 0 Mosh: 2 farbrausch/fr_public: Written for Visual Studio twitter/MySQL: 0 3 Cinder: (uses XCode 3.2 on Mac, Visual C++ on Windows) therubyracer: no defaults found (rake) wkhtmltopdf: no defaults found (qmake) v8: 0 3 2 (the 2 seems to be always added after the 3, so I don't know if the 3 is actually ever used) depthjs: no defaults found (CMake) node-canvas: 3 libzmq: 0 HandlerSocket: 3 I think it's interesting to note that -O1 only appears a single time, and that is in the Doom 3 source. -O0 and -O1 are both used for debugging, with -O3 used for release. -O0 shows up 16 times for sure (plus possibly some implicit -O0), -O2 shows up 11 times, -O3 shows up 10 times (although I believe it is overwritten with -O2 in one of them), and -Os shows up 5 times. -Os is used 4 times in C code compared to just once in C++. However, -O3 is used 8 times in C++, compared to only twice in C. In general, C projects seem to prefer -O2, while C++ projects seem to prefer -O3. I could not find a default optimization setting for 11 out of 34 projects (+ 4 that definitely do not use gcc). Of those 11 projects: * 1 has no build scripts at all (and thus the default is just whatever the compiler default is, therefore -O0) * 2 use qmake, which I believe can be called with something like -release, which gets -O3, but defaults to -O0 (I'm not sure on this, I don't use qmake) * 3 use rake, which may set its own defaults (I don't know). I couldn't find a single default for projects using rake. * 3 use CMake, which may set its own defaults (I don't know) * 1 uses a plain Makefile, and I believe I checked everything and could not find any defaults (so I counted it as -O0) * 1 uses the auto-tools, and I checked pretty thoroughly and I could not find any default settings, but there is a slight chance I may have missed it so I didn't count it as -O0
