[Bug c++/66476] New: Erroneous initializer_list lifetime extension from temporary initializer_list

["ed at catmur dot co.uk" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66476

            Bug ID: 66476
           Summary: Erroneous initializer_list lifetime extension from
                    temporary initializer_list
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at catmur dot co.uk
  Target Milestone: ---

#include <stdio.h>
#include <initializer_list>
struct S { S(int) { puts("S(int)"); } ~S() { puts("~S()"); } };
int main() {
  std::initializer_list<S> ss({42});  // note extra parentheses
  puts("main");
}

Expected output (clang 3.7, MSVC 18.00.21005.1):
S(int)
~S()
main

Observed output (gcc 5.1.0):
S(int)
main
~S()

The same behaviour is observed when the temporary initializer_list is made
explicit:
  std::initializer_list<S> ss = std::initializer_list<S>{42};


Again, gcc lifetime-extends the backing array; MSVC and clang do not.