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Re: PATCH RFA: Build stages 2 and 3 with C++
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 <firstname.lastname@example.org> 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.