https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87057
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Konstantin Kharlamov from comment #2)
> (In reply to Jonathan Wakely from comment #1)
> > That would require a lot of special-casing just for std::variant.
>
> Well, I think, in place of std::variant there could be any struct-wrapper;
If you have an example with a simple struct then please show it, maybe we can
improve that case. std::variant is hundreds of lines of complex
metaprogramming, not a struct-wrapper.
> > N.B. If you just write "return ret;" it will compile fine. In general
> > "return x;" is better than "return {x};" because it doesn't prevent NRVO.
>
> Thanks, I prefer the `{x}` to just `x` because in the latter I'm being
> explicit that the `x` is not the type I'm returning, but there's some other
> type that it's being wrapped to.
Which means you pessimize the code, because you force a copy, not an elidable
move.
> As far as such trivial optimizations concerned, I'd prefer to rely on the
> compiler figuring that out — in the end, that's why we don't write assembly,
> right? =)
If you write "return ret;" the compiler is allowed to move from the variable,
and is allowed to use the NVRO. It's not allowed to do that if you write
"return {ret};".
