[Bug c++/63657] New: [4.9 regression] -Wunused-variable: warning supressed by virtual dtor fn

[petschy at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63657

            Bug ID: 63657
           Summary: [4.9 regression] -Wunused-variable: warning supressed
                    by virtual dtor fn
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: petschy at gmail dot com

The under code has two unused variables, which are references to classes. We
should have two warnings, however 4.9.1 and 5.0 trunk gives just one. 4.7.2 and
4.8.3 are ok. The second warning is supressed by the virtual dtor in Bar. Only
the dtor does the trick, if I comment it out or instead I define a plain
virtual fn, the warning appears.

g++-4.8 -Wunused-variable -c 20141022-unused_warn.cpp 
20141022-unused_warn.cpp: In function ‘void foo()’:
20141022-unused_warn.cpp:7:7: warning: unused variable ‘f’ [-Wunused-variable]
  Foo& f = getfoo();
       ^
20141022-unused_warn.cpp: In function ‘void bar()’:
20141022-unused_warn.cpp:18:7: warning: unused variable ‘b’ [-Wunused-variable]
  Bar& b = getbar();
       ^


g++-5.0.0 -Wunused-variable -c 20141022-unused_warn.cpp 
20141022-unused_warn.cpp: In function ‘void foo()’:
20141022-unused_warn.cpp:7:7: warning: unused variable ‘f’ [-Wunused-variable]
  Foo& f = getfoo();
       ^

----8<----8<----8<----
class Foo 
{
};
Foo& getfoo();
void foo()
{
        Foo& f = getfoo();
}

class Bar
{
        virtual ~Bar() {}
};
Bar& getbar();
void bar()
{
        Bar& b = getbar();
}