NRVO not eliding copy for `std::string` with early exit

```cpp
#include

std::string f(int maxsize)
{
std::string ret;
for (int i = 0; ; ++i)
{
if (i > maxsize)
return "";
ret += ".";
}
return ret;
}
```

```
:12:12: warning: not eliding copy on return [-Wnrvo]
12 | return ret;
| ^
```
https://godbolt.org/z/fPfEGMh7E

Clearing `ret` and returning it addresses the warning but feels a bit awkward.

This also occurs without the loop but such a case can easily be mitigated without uglifying the code.

Start by reproducing the warning with the C++ example and Godbolt link, then trace the compiler's NRVO analysis and diagnostic for the early-exit case. The issue is addressed when the behavior is intentionally corrected or documented with a regression test covering this example.

Written by the indexing model from the issue text.