[Bug c++/71442] New: [5/6/7 Regression] r232569 breaks -Wunused-*

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71442

            Bug ID: 71442
           Summary: [5/6/7 Regression] r232569 breaks -Wunused-*
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

// { dg-do compile { target c++11 } }
// { dg-options "-Wunused-variable" }

struct C
{
  template<typename... Ts>
  int operator()(Ts &&...)
  {
    return sizeof...(Ts);
  }
};

int
main ()
{
  C {} (1, 1L, 1LL, 1.0);
  char a;               // { dg-warning "unused variable" }
  short b;              // { dg-warning "unused variable" }
  int c;                // { dg-warning "unused variable" }
  long d;               // { dg-warning "unused variable" }
  long long e;          // { dg-warning "unused variable" }
  float f;              // { dg-warning "unused variable" }
  double g;             // { dg-warning "unused variable" }
}

FAILs to diagnose c, d, e and g vars as unused, starting with r323569, because
it marks not just decls as TREE_USED, but also types, and when e.g. int type is
TREE_USED, then all vars/parameters with that type are also considered
TREE_USED.