slowness of Cpp::EnvironmentFile::merge

[Milian Wolff]

Milian Wolff, 21.12.2010:
> Milian Wolff, 21.12.2010:
> > Hey all, esp. David:
> > 
> > According to this:
> > https://userpage.physik.fu-berlin.de/~milianw/callgrind.out.4728.bz2
> > 
> > the Cpp::EnvironmentFile::merge is responsible for 13.4% of the time
> > spent parsing a part of boost (duchainify --force-update-recursive
> > boost_1_45_0/libs/serialization/performance/xml/string256_test.cpp). Is
> > this sane? I'll redo the callgrind in RelWithDebInfo soon but I hope we
> > could improve that even now.
> > 
> > What I don't quite get are the lines like these:
> >   d_func_dynamic()->m_strings = (d_func()->m_strings + (file.d_func()-
> > >
> > >m_strings - d_func()->m_definedMacroNames)) - d_func()-
> > >m_unDefinedMacroNames;
> > 
> > Won't that lead to duplicated entries? Essentially that is:
> > 
> > A = (A + (A - B)) - C
> > 
> >   = 2 A - B - C
> > 
> > so all items in A not contained in B and C will show up twice (or the Set
> > is indeed a Set and prevents that internally). Still, this should be
> > faster and more clear, no?:
> > 
> > A -= B;
> > A -= C;
> 
> this doesn't hold though:
> 
>   ReferenceCountedStringSet strings2 = (d_func()->m_strings +
> (file.d_func()-
> 
> >m_strings - d_func()->m_definedMacroNames)) - d_func()-
> >m_unDefinedMacroNames;
> 
>   d_func_dynamic()->m_strings -= d_func()->m_definedMacroNames;
>   d_func_dynamic()->m_strings -= d_func()->m_unDefinedMacroNames;
>   Q_ASSERT(strings2  == d_func_dynamic()->m_strings);
> 
> I wonder why - is the set not a set after all? I.e. can it contain
> duplicates?

Ah, there is a file.d_func() in the original, of course it's not the same 
then!

Bye
-- 
Milian Wolff
mail at milianw.de
http://milianw.de
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