Incorrect unused statement warnings

[David Mazieres <dm at reeducation-labor dot lcs dot mit dot edu>]

I'm using:
  Reading specs from /usr/local/egcs/lib/gcc-lib/i386-netbsd/egcs-2.91.40/specs
  gcc version egcs-2.91.40 19980614 (gcc2 ss-980502 experimental)

EGCS generates incorrect "statement with no effect" warnings when
initializing variables from default constructors.  The easiest way to
see this is to compile a simple program using STL.  The following
program:

  #include <hash_map>
  
  hash_map<int, char *> hm;
  
Results in these warnings.
  
% c++ -c -O2 -Wall h.C
/usr/local/egcs/include/g++/stl_hashtable.h: In method `hashtable<pair<const int,char *>,int,hash<int>,select1st<pair<const int,char *> >,equal_to<int>,__default_alloc_template<false,0> >::hashtable<pair<const int,char *>, int, hash<int>, select1st<pair<const int,char *> >, equal_to<int>, alloc>(unsigned int, const struct hash<int> &, const struct equal_to<int> &)':
/usr/local/egcs/include/g++/stl_hash_map.h:78:   instantiated from `hash_map<int,char *,hash<int>,equal_to<int>,__default_alloc_template<false,0> >::hash_map<int, char *, hash<int>, equal_to<int>, alloc>()'
h.C:3:   instantiated from here
/usr/local/egcs/include/g++/stl_hashtable.h:220: warning: statement with no effect


These warnings are incorrect, because in general there is no way to
get rid of such statements.  The following simpler, self-contained
example illustrates the problem:

  struct bar {
    int operator() (int);
  };
  
  template<class F>
  class c1 {
    c1 ();
    F f;
  public:
    c1 (const F &ff) : f (ff) {};
  };
  
  template<class T>
  class c2 : public c1<T> {
  public:
    c2 () : c1 (T ()) {}
  };
  
  c2<bar> xxx;

This legitimate program cannot be made to compile without warnings.
EGCS reports:

h.C: In method `c1<bar>::c1<bar>(const struct bar &)':
h.C:16:   instantiated from `c2<bar>::c2<bar>()'
h.C:19:   instantiated from here
h.C:10: warning: statement with no effect

But how else can one feed a default T to c1's constructor?

Thanks,
David