On 2017.05.15 at 15:07 +0200, Mason wrote: > On 15/05/2017 14:01, Markus Trippelsdorf wrote: > > > On 2017.05.15 at 12:11 +0200, Matthias Kretz wrote: > > > >> I'm looking for help on improving the compile times of my unit tests. Compile > >> times of >60s per TU is making my life hard. > >> Alternatively, if you can tell me there's nothing I can do, then I can accept > >> my fate and stop worrying about compile time optimizations. > >> > >> Picking one example from my ~500 unit test TUs: > >> You can see the source at https://github.com/VcDevel/Vc/blob/ > >> c807aa0c841950e50ec7d370c9c22d6038c7e068/tests/loadstore.cpp > >> > >> Note that TEST_TYPES (line 109) produces 91 instantiations of the > >> `load_store<VU>` function template from an outer product of two type lists. > >> (I'd actually like to make the type list larger by a factor of 13, but that > >> just blows the compiler up.) > >> > >> Attached is the output of -ftime-report. I must say I was surprised to see > >> "phase opt and generate" with 62.5s and 95% of the total time, as well as 84% > >> of the memory usage. Though, OTOH, the resulting binary is 4.4MiB large with > >> about 3/4 of it being the .text section. > >> > >> If you have any ideas what I could do (other than "test less"), I'd like to > >> try it. > > > > Enabling Link Time Optimization may help: -flto=<some number, e.g. the > > number of cores you have> > > I'm confused. Are you suggesting that requesting /more/ optimizations > might reduce compile+link time? Yes. For huge compilation units (like the template heavy example above) -flto=<number of 'cores'> reduces compile+link time, because it causes the backend to run in parallel. -- Markus
