[Bug c++/67906] New: Missing warning about std::move without effect

[Bug c++/67906] New: Missing warning about std::move without effect

[virkony at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67906

            Bug ID: 67906
           Summary: Missing warning about std::move without effect
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: virkony at gmail dot com
  Target Milestone: ---

It would be nice to have something like -Wno-effect which will issue warnings
on usage of std::move for objects that cannot be moved.

See also http://stackoverflow.com/q/28595117/230744

I assume that it may require introducing differentiation between
explicit-rvalue (through std::move()/cast) and implicit-rvalue.

This may save from errors like:

```
const Frame& x = stack.top();
Value y = std::move(x.value); // x.value - non-mutable
```

Though there might be a false-positives in template functions or when developer
expects that in future function will have move overload for that argument.

[Bug c++/67906] Missing warning about std::move without effect

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67906

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #11 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I'm going to add a testcase that ensures that we don't warn for

struct X {
  X() { }
  X(const X&) { }
  X(const X&&) { }
};

const X x;
const X y = std::move(x);

but otherwise I don't see any useful extension to our std::move warnings.