Re: Does binding to const-reference outperform copy-initialization from returned value?

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Fri, 22 May 2009 09:27:26 -0400
Message-ID:
<ONLJQEu2JHA.6004@TK2MSFTNGP02.phx.gbl>
"Niels Dekker - no return address" <invalid@this.is.invalid> wrote in
message news:%23JQggvs2JHA.1196@TK2MSFTNGP03.phx.gbl

When using VC++ 2008 SP1, is there any possible performance difference
between binding a temporary object (rvalue) returned by a function to
a const-reference, and using the temporary object to copy-initialize
a local (const) variable? For example:

 // Forward declarations:
 class Foo;
 Foo GetFoo(void);

 const Foo& constReference = GetFoo();
 const Foo constValue = GetFoo();


In principle, the compiler is allowed to call Foo's copy-constructor one
more time in the second case, compared to the first. However, it is
highly likely the compiler would optimize this extra call away in a
release build. I can't think of any situation where it would be unable
to, off the top of my head.
--
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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