[Bug c++/84221] New: spurious -Wmaybe-uninitialized warning on a variable of a template type declared unused

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84221

            Bug ID: 84221
           Summary: spurious -Wmaybe-uninitialized warning on a variable
                    of a template type declared unused
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

As Jason points out in
https://gcc.gnu.org/ml/gcc-patches/2018-02/msg00197.html, issuing
-Wunused-variable for definition of the local 'a' in the test case below is a
false positive:

$ cat y.C && gcc -O2 -S -Wall -Wextra y.C
template <class T> struct [[gnu::unused]] A { };
template <> struct A<int> { };

void f (void)
{
  A<int> a;   // shouldn't warn
}              
y.C: In function ‘void f()’:
y.C:6:10: warning: unused variable ‘a’ [-Wunused-variable]
   A<int> a;   // shouldn't warn
          ^