[Bug libstdc++/70437] New: [6 Regression] Instantiation loop with pair and is_constructible

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70437

            Bug ID: 70437
           Summary: [6 Regression] Instantiation loop with pair and
                    is_constructible
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jason at gcc dot gnu.org
  Target Milestone: ---

Reduced from https://github.com/openscad/openscad/issues/1575

#include <utility>

template <class T> struct B;

template <class T> struct A
{
  A(A&&) = default;
  A(const B<T> &);
};

template <class T> struct B
{
  std::pair<A<T>,int> a;
  B(B&&) = default;
};

bool b = std::is_move_constructible<A<int> >::value;

This seems similar to bug 65760.