On Tue, 4 Aug 2015, Jonathan Wakely wrote:
> On 4 August 2015 at 16:00, Nikolay Vorobyov wrote:
> > Is this a gcc's bug?
>
> I believe this is due to how symbol resolution works in DLLs on
> Windows, where each DLL has its own copy of the static variable. I
> don't know how to make it work as required by the C++ standard.
One way would be to eliminate the inline definition of getInstance() in the
header file, and move it into inst.cpp.
If you inspect generated files with 'nm -C', you'll see that both libinst.dll
and liba.dll have a definition for StaticObject<int>::getInstance()::t.
Jonathan, I think there might be a GCC bug here, but not what Nikolay
originally meant. With -std=c++11, 'extern template' should prevent the
compiler from instantiating methods of StaticObject, but it doesn't happen.
Here's a minimal example:
template<int V>
struct S {
static int bar()
{
return V;
}
};
extern template struct S<42>;
int foo()
{
return S<42>::bar();
}
Compile with g++ -std=c++11 -S -o- -Os and observe that 'foo' is optimized to
'return 42', although 'bar' should not have been instantiated. If you don't
have a template class and make 'bar' itself a template function, GCC does not
optimize 'foo', as expected. WDYT?
Thanks.
Alexander
