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Groups > comp.lang.c++ > #9820
| From | Lynn McGuire <lmc@winsim.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: does virtualizing all methods slow C++ down ? |
| Date | 2011-09-06 14:13 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <j45rf0$d9e$1@dont-email.me> (permalink) |
| References | <j45hvi$6at$1@dont-email.me> <87ipp5zjb2.fsf@dpt-info.u-strasbg.fr> |
On 9/6/2011 12:12 PM, Alain Ketterlin wrote:
> Lynn McGuire<lmc@winsim.com> writes:
>
>> Does virtualizing all methods slow C++ down ? We
>> virtualize all methods as a matter of course since
>> we use groups of objects all over the place.
>
> Not sure I understand what you mean, but yes, virtualizing all
> (non-really-virtual) methods will slow things down, in cases where the
> compiler cannot statically decide the class where the method is defined.
> In the worst case:
>
> - all calls through a reference or pointer will be indirect calls
> - all other calls will be direct calls.
>
> The branch predictor may help here, but you still pay some price. In
> your example:
>
>> virtual GenGroup * clone () { return new GenGroup ( * this); }
>
> the compiler would normally (probably) inline any call to this method in
> the non-virtual case. With virtual, all calls to this method through a
> ref/pointer will be translated into an indirect call.
>
> (I know, cloning usually requires dynamic binding, I used this example
> because it was the only method potentially inlinable.)
>
> C++11 provides the "final" qualifier, which may help here. Whether it is
> taken into account depends on your compiler.
>
> -- Alain.
Thanks, I had not thought about the direct calls just
directly binding to the proper method. I'll bet that
there are few direct calls in our code though as we
have many children classes.
ObjPtr -> DataGroup -> GenGroup
ObjPtr -> DataGroup -> NodeGroup -> StreamGroup
are a couple of example lineages.
Lynn
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does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-06 11:31 -0500
Re: does virtualizing all methods slow C++ down ? Christopher <cpisz@austin.rr.com> - 2011-09-06 10:00 -0700
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-06 14:09 -0500
Re: does virtualizing all methods slow C++ down ? Christopher <cpisz@austin.rr.com> - 2011-09-06 12:35 -0700
Re: does virtualizing all methods slow C++ down ? "Kevin P. Fleming" <news@kpfleming.us> - 2011-09-06 16:41 -0500
Re: does virtualizing all methods slow C++ down ? "Balog Pal" <pasa@lib.hu> - 2011-09-11 12:02 +0200
Re: does virtualizing all methods slow C++ down ? "Thomas J. Gritzan" <phygon_antispam@gmx.de> - 2011-09-07 02:42 +0200
Re: does virtualizing all methods slow C++ down ? Noah Roberts <roberts.noah@gmail.com> - 2011-09-07 07:39 -0700
Re: does virtualizing all methods slow C++ down ? Richard Damon <news.x.richarddamon@xoxy.net> - 2011-09-07 11:46 -0400
Re: does virtualizing all methods slow C++ down ? Nobody <nobody@nowhere.com> - 2011-09-07 01:45 +0100
Re: does virtualizing all methods slow C++ down ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-09-06 19:12 +0200
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-06 14:13 -0500
Re: does virtualizing all methods slow C++ down ? jacob navia <jacob@spamsink.net> - 2011-09-06 21:57 +0200
Re: does virtualizing all methods slow C++ down ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-09-06 22:40 +0200
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-06 16:13 -0500
Re: does virtualizing all methods slow C++ down ? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-07 08:01 +0000
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-14 12:08 -0500
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-14 14:04 -0500
Re: does virtualizing all methods slow C++ down ? Lynn McGuire <lmc@winsim.com> - 2011-09-06 16:11 -0500
Re: does virtualizing all methods slow C++ down ? Paavo Helde <myfirstname@osa.pri.ee> - 2011-09-07 11:44 -0500
Re: does virtualizing all methods slow C++ down ? Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-07 14:11 -0700
Re: does virtualizing all methods slow C++ down ? Paavo Helde <myfirstname@osa.pri.ee> - 2011-09-08 01:26 -0500
Re: does virtualizing all methods slow C++ down ? Nobody <nobody@nowhere.com> - 2011-09-08 07:37 +0100
Re: does virtualizing all methods slow C++ down ? zindorsky <nephi.allred@gmail.com> - 2011-09-09 10:20 -0700
Re: does virtualizing all methods slow C++ down ? "Kevin P. Fleming" <news@kpfleming.us> - 2011-09-10 11:48 -0400
Re: does virtualizing all methods slow C++ down ? Nobody <nobody@nowhere.com> - 2011-09-10 17:58 +0100
Re: does virtualizing all methods slow C++ down ? Juha Nieminen <nospam@thanks.invalid> - 2011-09-07 06:19 +0000
Re: does virtualizing all methods slow C++ down ? Goran <goran.pusic@gmail.com> - 2011-09-06 23:52 -0700
Re: does virtualizing all methods slow C++ down ? Juha Nieminen <nospam@thanks.invalid> - 2011-09-07 07:57 +0000
Re: does virtualizing all methods slow C++ down ? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-07 10:39 +0000
Re: does virtualizing all methods slow C++ down ? Goran <goran.pusic@gmail.com> - 2011-09-07 04:30 -0700
Re: does virtualizing all methods slow C++ down ? Juha Nieminen <nospam@thanks.invalid> - 2011-09-07 13:04 +0000
Re: does virtualizing all methods slow C++ down ? Goran <goran.pusic@gmail.com> - 2011-09-07 06:18 -0700
Re: does virtualizing all methods slow C++ down ? ld <laurent.deniau@gmail.com> - 2011-09-08 05:34 -0700
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