[Bug c++/51392] Wrong code with -Os when __attribute__((__const__)) function returns structure

[cyp561 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51392

--- Comment #4 from cyp561 at gmail dot com ---
Is there any case in which a function returning a structure may not elide the
return value copy to being passed by invisible reference?

If not, I think it is either a bug that the code fails, or a bug that the C++
frontend allows __attribute__((__const__)) on any function which returns a
structure.

It seems strange to me that __attribute__((__const__)) doesn't work in cases
where constexpr does work, since I thought constexpr is a now-standard version
of __attribute__((__const__)).