[Bug c++/105806] New: [concepts] template class specialization using concept issue

[josephcanedo at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105806

            Bug ID: 105806
           Summary: [concepts] template class specialization using concept
                    issue
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: josephcanedo at hotmail dot com
  Target Milestone: ---

We have a simple "trait" template class defining a static function holding a
static variable.

struct meta {};

template <typename T>
struct type_traits
{
  static meta& get_meta() {
    static meta m;
    return m;
  }
};

This is used in several .hpp files among several TUs, without any problems.

We are attempting to use concepts to make specialisations of these type_traits,
e.g.

class root_base {};

template <typename T>
concept root_type = std::is_base_of_v<root_base, T>;

template <typename>
struct type_traits;

template <root_type Root>
struct type_traits<Root>
{
  static meta& get_meta() {
    static meta m;
    return m;
  }
};

Using these compiles all fine, but we notice that for a given type_traits
instantiation with some type, we have several instances of get_meta() functions
symbols and hence several meta m variables, which we believe is not expected.

ie for given

class A: root_base {};

We have N type_traits<A>::get_meta() functions symbols (different addresses for
these functions).

This only occurs with -O1 or higher option. -O0 does not exhibit this behavior.