[Bug c++/66944] New: static thread_local member in class template may cause compilation to fail

[Bug c++/66944] New: static thread_local member in class template may cause compilation to fail

[zhykzhykzhyk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66944

            Bug ID: 66944
           Summary: static thread_local member in class template may cause
                    compilation to fail
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhykzhykzhyk at gmail dot com
  Target Milestone: ---

Affect Versions: 4.9.3, 5.1.0, 5.2.0

Expected behavior:
  compiles correctly (like clang does)

Compiler output:
bug.cc:14:34: error: redefinition of 'bool __tls_guard'
 thread_local std::vector<void *> A<T>::v;
                                  ^
bug.cc:14:34: note: 'bool __tls_guard' previously declared here
bug.cc:14: confused by earlier errors, bailing out

== code ==
struct Heavy { Heavy(){} };

template <typename T>
struct A {
  virtual void foo() { v; }
  static thread_local Heavy v;
};

template <typename T>
thread_local Heavy A<T>::v;

struct E {};
struct F {};

int main() {
  A<E> foo;
  A<F> bar;
  bar.v;
}
==========