[Bug c++/47347] New: "pragma GCC diagnostic ignored" has no effect sometimes

["gcc at dpinol dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47347

           Summary: "pragma GCC diagnostic ignored" has no effect
                    sometimes
           Product: gcc
           Version: 4.5.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gcc@dpinol.com


The code below produces warning "warning: unused parameter âaâ
[-Wunused-parameter]" were it shouldn't, since this diagnostic should be
ignored.
If we remove the final line, the warning does not appear, but I understand that
a pragma should not affect previous lines.

#pragma GCC diagnostic ignored "-Wunused-parameter"

#include <vector>

template <class ContainerAllocator>
struct KeyValue
{
public:
  virtual ~KeyValue()
  {
  }

  virtual void serialize(int a) const
  {
  }
};

void f()
{
  std::vector< KeyValue<int >  >  values;
}
#pragma GCC diagnostic warning "-Wunused-parameter"