On 06/16/2016 06:40 PM, smaug wrote:
On 05/24/2016 08:33 AM, jww...@mozilla.com wrote:
For
RefPtr<T> GetFoo() {
RefPtr<T> foo;
// ...
}
should we:
1. return foo and expect RVO to kick in to eliminate additional AddRef/Release
2. return foo.forget()
3. return Move(foo)
Which one is preferred?
ps: I find gcc is able to apply RVO even with "-O0". Not sure if it is also
true for other compilers.
Can we somehow guarantee that RVO kicks in? It feels quite error prone to rely
on compiler optimization when dealing with
possibly slow Addref/Release calls.
https://en.wikipedia.org/wiki/Return_value_optimization#Compiler_support hints
that there are cases when RVO might not happen.
I've been told we can't guarantee RVO to kick in, which means, I think, that we
should assume we don't have RVO ever and need to
rely on other coding patterns which are guaranteed to optimize out extra
addref/release.
Currently having already_AddRefed as the return type is one such pattern.
What are the other options?
At least we can't start using RefPtr<T> as return type before we know it won't
be causing performance regressions.
So I would recommend using already_AddRefed for now.
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