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List:       gcc-bugs
Subject:    [Bug c++/21306] New: [4.0 Regression] Another way to generate "inline function A::~A() used but neve
From:       "prw at ceiriog1 dot demon dot co dot uk" <gcc-bugzilla () gcc ! gnu ! org>
Date:       2005-04-30 20:59:52
Message-ID: 20050430205946.21306.prw () ceiriog1 ! demon ! co ! uk
[Download RAW message or body]

The attached test case leads to this error:

[prw@ceiriog1 Orfeo]$ g++ main.ii
../../Orfeo/A.h:3: warning: inline function A::~A() used but never defined
/tmp/cc2W2kUK.o(.gnu.linkonce.t._ZN1BI1AED1Ev[B<A>::~B()]+0xf): In function
`B<A>::~B()':
: undefined reference to `A::~A()'
collect2: ld returned 1 exit status

This is a very simplified model of a bug which I have found when using
the STL vector template, which explicitly invokes a destructor via
p->~T().  The problem is that class A does not define an explicit
destructor, but the class B<A> needs it.

This is a regression since 3.4.2 (or at least the Fedora Core version
gcc-3.4.2-6.fc3).  Running that on the same code, no destructor call
~A() is generated in ~B().  Presumably the compiler deduces that the
template class T(=A) has no nontrivial destructor in this case and so
optimizes out the call t->~T();

[Presumably an empty stub could be generated, but where?  In the
present example it is not generated since the filename for the #pragma
implementation (main.cc) does not match that for the #pragma interface
(A.h).  You might add an implementation file A.cc with a #pragma
implementation, but this does not help unless it contains an explicit
reference to ~A.  Otherwise it doesn't know that any such destructor
is needed.  The destructor would have to be generated at the point of
use, even though this may lead to some duplication between modules,
since there seems to be no way of deducing the "correct" place to put
it.]

-- 
           Summary: [4.0 Regression] Another way to generate "inline
                    function ‘A::~A()’ used but never defined" errors
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: prw at ceiriog1 dot demon dot co dot uk
                CC: gcc-bugs at gcc dot gnu dot org,prw at ceiriog1 dot
                    demon dot co dot uk
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21306
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