Re: Does binding to const-reference outperform copy-initialization from returned value?
"Niels Dekker - no return address" <invalid@this.is.invalid> wrote in
message news:%23vhBe7w2JHA.1432@TK2MSFTNGP02.phx.gbl
But I guess there might be another performance related difference
between the two cases, when the type has a virtual function:
const Foo& constReference = GetFoo();
const Foo constValue = GetFoo();
constReference.VirtualFunc();
constValue.VirtualFunc();
When calling the virtual function on the reference, I guess it will
use the VTable, while it won't do so on the copy-initialized value.
Not necessarily. It is clear that constReference can only be bound to an
instance of Foo here, and not any derived class. Optimizer could figure
this out and generate a direct (non-virtual) call. I don't know if it's
smart enough though, and I'm too lazy to test.
Or would VC++ skip the VTable for the reference? I'm not sure how to
test this (unless by digging into the assembler output).
Yes, looking at assembly appears to be the only way.
--
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Igor Tandetnik
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