[Mingw-users] optimizing away "dummy" inline functions?

[Christopher S. <cl...@se...>]

If a c++ class is declared using __declspec(dllexport/dllimport) and it 
contains a function that is basically unused, should gcc still create an 
entry in the import library for that function?  A small test case if 
available at http://www.seawood.org/mingw/class.zip .

#ifdef _IMPL_COM
#define NS_COM __declspec(dllexport)
#else
#define NS_COM __declspec(dllimport)
#endif

class NS_COM cls_Class {
     public:
         cls_Class() { mStr = 0; };
         cls_Class(const char* in);
         ~cls_Class();
         virtual const char* get() const;
         void DoNothing() { }
     protected:
         virtual int length() const;
     private:
         char *mStr;
};

Whenever the dll is compiled, cls_Class::DoNothing() does not show up in 
either the dll or the import library.  This happens regardless of 
whatever optimization level is passed to the compiler.  If I make 
DoNothing() virtual (as get() is), then it shows up.  I would have 
expected it to show up if I added NS_COM to the function declaration but 
it doesn't.  Using -fkeep-inline-functions prevents the function from 
being dropped but causes other problems for me when building Mozilla.

I ran across this problem while trying to getting gcc 3.3.1RC1 to 
compile Mozilla, http://bugzilla.mozilla.org/show_bug.cgi?id=217009 . 
When I stopped linking xpcom using -Wl,--export-all-symbols to avoid the 
auto-import problem, the test programs failed to compile because of some 
missing symbols from the xpcom import library.  Afaict, the classes 
themselves were properly decorated with NS_COM (though some of their 
base classes weren't) but the functions still would not show up in the 
import library.  In some cases, adding an explicit NS_COM to the 
function did help.  I'm not completely sure how those test programs are 
referencing those functions as lxr shows them to be otherwise unused 
(which is why I figure that gcc is dropping them).

Is this normal behavior or just some dllimport/dllexport quirk that I'm 
unaware of?

- cls