[Bug c/51971] unclear/unverified restrictions on attribute((const|pure))

[davidfromonline at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51971

--- Comment #5 from David Stone <davidfromonline at gmail dot com> ---
After compiling this code

```
struct s {
        s();
};

s::s() {}

s g() {
        return s();
}
```

with `-O3 -Wsuggest-attribute=pure -Wsuggest-attribute=const`

I get the output

```
<source>: In function 's g()':
<source>:7:3: warning: function might be candidate for attribute 'const'
[-Wsuggest-attribute=const]
    7 | s g() {
      |   ^
Compiler returned: 0
```