[Bug c++/43522] New: 4.4 regression: Attempts to instantiate unnecessary code

[georgeh at rentec dot com]

Code:
---------------
template <bool x> struct tester;
template <> struct tester<true> { enum { value = 1 }; };

template <class T>
struct allow_double_instantiations {
  static const bool value = false;
};

template <int Power>
class FixedPoint {
  static const bool allow_double_instantiations = false;

  typedef FixedPoint<Power> Self;

public:
  FixedPoint(): mValue(0) {}

  //Default copy c'tor, assignment op valid & useful.

  Self &operator=(double const &d) {
    mValue = sizeof(tester<Self::allow_double_instantiations>);
    return *this;
  }

  int mValue;
};

void foo(FixedPoint<4> &);

int main() {
  FixedPoint<4> x;
  foo(x);
  return 0;
}

template <>
FixedPoint<4> &FixedPoint<4>::operator=(double const &d) {
  mValue = int(d);
  return *this;
}

void foo(FixedPoint<4> &t) {
  t = 13.5;
}
-------------

gcc 4.3.2 and earlier versions compile this without complaint; 4.4.3 dies with 
test_fixedpoint.C: In member function `FixedPoint<Power>&
FixedPoint<Power>::operator=(const double&)':
test_fixedpoint.C:21: error: invalid application of `sizeof' to incomplete type
`tester<false>'

By my reading of the standard, the invalid definition of operator= should not
be attempted to be instantiated until line 43, where the valid template
specialization has been seen, and previous versions of g++ agree with me. Note
that in the original code, line 21 was a BOOST_STATIC_ASSERT and produced the
same result.


-- 
           Summary: 4.4 regression: Attempts to instantiate unnecessary code
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: georgeh at rentec dot com
GCC target triplet: i686-suse-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43522