[Bug c++/88292] New: Static initialization problem with thread_local and templates

[tobias.bruell at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88292

            Bug ID: 88292
           Summary: Static initialization problem with thread_local and
                    templates
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tobias.bruell at gmail dot com
  Target Milestone: ---

I believe the following code should never print a null-pointer. Works as I
expect with clang. Also, there are various ways in which it can be made work in
gcc, including:
  * uncommenting the first commented line (and commenting the one before)
  * uncommenting the second commented line
  * removing the superfluous template parameter on context
  * removing all "thread_local" tokens

May be duplicate, but I submit it anyway, in case you might find it helpful as
an additional test.



#include <iostream>

template<typename T>
struct store_ptr
{
  static T *ptr () { return current_; }
  static thread_local T *current_;
};

template<typename T>
thread_local T * store_ptr<T>::current_ = []
{
  static thread_local T retval;
  return &retval;
} ();

template<typename T>
struct context
  : public store_ptr<context<T>>
{ 
  context () { } 

  context (T)
    : previous_ {store_ptr<context<T>>::current_}
//    : previous_ {store_ptr<context<T>>::ptr ()}
  {
    store_ptr<context<T>>::current_ = this;
  }

  ~context ()
  {
    store_ptr<context<T>>::current_ = this->previous_;
  } 

  context<T> *previous_ = nullptr;
};

int main ()
{
  //std::cout << context<int>::ptr () << '\n';

  { 
    context<int> ctx (1);

    std::cout << context<int>::ptr () << '\n';
  }

  std::cout << context<int>::ptr () << '\n';
}