[Bug c++/102691] New: rvalue reference overload in not preferred over lvalue reference

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102691

            Bug ID: 102691
           Summary: rvalue reference overload in not preferred over lvalue
                    reference
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This code is valid:
```
struct Foo {};
struct Bar {};

constexpr int Baz(const Foo&) { return 0; }
constexpr int Baz(Bar&&) { return 1; }

int main()
{
  static_assert( Baz({}) == 1 );
}
```
Here Baz(Bar&&) must be preferred according to [over.ics.rank]/(3.2), as Clang
does.

Unfortunately, GCC wrongly prints ambiguity error, demo:
https://gcc.godbolt.org/z/7Yq8hdcso

Related discussion: https://stackoverflow.com/q/62599846/7325599