On 2011.07.17 at 18:54 +0200, Markus Trippelsdorf wrote: > On 2011.07.17 at 18:30 +0200, Richard Guenther wrote: > > On Sun, Jul 17, 2011 at 1:30 PM, Eric Botcazou <ebotca...@adacore.com> > > wrote: > > >> I have measured it at some point and IIRC it was about 10% slower > > >> (comparing C bootstrap with C++ in stag1 languages with C++ bootstrap, > > >> not sure if that included bootstrapping libstdc++ for the former). > > > > > > IMO acceptable now that the build time of libjava has been halved. > > > > Actually the penalty for using C++ was only 1.5%, that of bootstrapping C++ > > and > > libstdc++ was 15%. For reference: > > I've tested the difference today on an average 4 CPU machine with 8GB > RAM. This is the result of otherwise identical LTO+PGO builds: > > --enable-build-with-cxx make -j4 profiledbootstrap 3384.20s user 177.02s > system 291% cpu 20:23.12 total > <default> make -j4 profiledbootstrap 3011.03s user 144.30s > system 297% cpu 17:41.59 total > > That's a ~15% increase in build time.
And I guess that most of it comes from building libstdc++ to train the instrumented compiler. This doesn't happen in the default case AFAICS. -- Markus
