[Bug c++/120822] bad warn -Wredundant-move on return std::move

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120822

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
They're both redundant. In both cases the return operand is treated as an
rvalue.

For fb() the std::move defeats copy elision, so actually pessimizes the code.

For fa() it's just redundant, because b will be treated as an rvalue and so the
return value will be move constructed from static_cast<A&&>(b) automatically,
without a std::move.