Re: c++/6771: no code emitted for locally unused class with dllexport attribute

Re: c++/6771: no code emitted for locally unused class with dllexport attribute

[Raoul Gough]

The following reply was made to PR c++/6771; it has been noted by GNATS.

From: "Raoul Gough" <raoulgough@clara.co.uk>
To: <gcc-gnats@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<RaoulGough@yahoo.co.uk>
Cc:  
Subject: Re: c++/6771: no code emitted for locally unused class with dllexport attribute
Date: Tue, 19 Nov 2002 13:05:19 -0000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database
 =gcc&pr=6771
 
 This bug was already fixed in the mingw/cygwin branch. Building with,
 for example, cygwin-mingw-gcc-3_2-branch (or 3_1 AFAIK) makes the
 problem disappear. I guess the bug should be moved to the "closed"
 state or equivalent.
 
 Regards,
 Raoul Gough.
 

Re: c++/6771: no code emitted for locally unused class with dllexport attribute

[Giovanni Bajo]

The following reply was made to PR c++/6771; it has been noted by GNATS.

From: "Giovanni Bajo" <giovannibajo@libero.it>
To: <gcc-gnats@gcc.gnu.org>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<RaoulGough@yahoo.co.uk>
Cc:  
Subject: Re: c++/6771: no code emitted for locally unused class with dllexport attribute
Date: Thu, 1 May 2003 18:53:23 +0200

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6771
 
 I think it's again the usual regression in winnt.c (see pr/7910). The
 problem appears to be fixed with 3.2 and a recent 3.3 CVS, but it causes an
 ICE with 3.4 CVS 20030430. So I keep this as 3.4 ice-on-legal, in case it's
 a slightly different issue.
 
 Giovanni Bajo
 

Re: c++/6771: no code emitted for locally unused class with dllexport attribute

[Raoul Gough]

The following reply was made to PR c++/6771; it has been noted by GNATS.

From: "Raoul Gough" <RaoulGough@yahoo.co.uk>
To: <gcc-gnats@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>
Cc:  
Subject: Re: c++/6771: no code emitted for locally unused class with dllexport attribute
Date: Fri, 24 May 2002 13:45:30 +0100

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&p
 r=6771
 
 I have some more information regarding this dllexport problem (and
 a quick and dirty fix for my system). I hope this is the right way to
 submit additional information...
 
 I've determined that the problematic member function (foofunction) is
 having comdat_flag set (I believe erroneously) in decl2.c via the
 import_export_decl function (called from finish_file in the first
 deferred_fns loop). According the the comments in tree.h, comdat_flag
 should be set for entities "guaranteed to be generated by any
 translation unit that needs them, and therefore need not be put out
 anywhere where they are not needed", which is clearly not the case
 here (member function of a class with attribute dllexport). So I just
 hacked the comdat_linkage function as follows, and the problem went
 away :-)
 
 /cygdrive/d/gcc/CVS/gcc/gcc/cp $ diff decl2.c~ decl2.c
 2183c2183
 <   if (DECL_LANG_SPECIFIC (decl))
 ---
 >   if (DECL_LANG_SPECIFIC (decl) && !i386_pe_dllexport_p (decl))
 
 (diff with decl2.c CVS:1.520.2.5)
 
 This generates an "implicit declaration" warning, and is only suitable
 for systems that use config/i386/winnt.c. I'm sure this is not the
 right way to fix it, because comdat_linkage should probably never get
 called on a dllexport'd member function - maybe a better fix would be
 to clear DECL_DECLARED_INLINE_P at some stage?
 
 I'm willing to spend some more time on this (and possibly any other
 open bugs within my abilities), but would need a bit of advice on
 producing a legitimate fix.
 
 Regards,
 Raoul Gough.
 
 
 PS: I've upgraded via CVS to gcc_latest_snapshot (gcc_ss_20020521) and
 the problem is unchanged. Also, setting the -fno-default-inline flag
 fixes the problem for the export case, but crashes the compiler for
 the import case:
 
 /cygdrive/f/Users/Raoul/cxx $ /usr/local/bin/g++ -c
 dllexport.cc -fno-default-inline -save-temps
 dllexport.cc: In member function `void bar::barfunction()':
 dllexport.cc:26: Internal compiler error in rest_of_compilation, at
 toplev.c:
    3478
 Please submit a full bug report,
 with preprocessed source if appropriate.
 See <URL:http://www.gnu.org/software/gcc/bugs.html> for instructions.
 
 This would otherwise be a temporary work-around for the original problem.
 
 
 
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c++/6771: no code emitted for locally unused class with dllexport attribute

[RaoulGough]

>Number:         6771
>Category:       c++
>Synopsis:       no code emitted for locally unused class with dllexport attribute
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 22 10:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Raoul Gough
>Release:        3.0.4
>Organization:
>Environment:
Cygwin
>Description:
*locally* unused class with __attribute__(dllexport) does not emit any code. This is a problem because the corresponding __attribute__(dllimport) in the client module would leave unresolved externals during linking.

e.g.

namespace
{
  int blah = 0;
};

struct __attribute__((dllexport)) foo
{
  void foofunction () { ++blah; }
};

generates *no code* for foo::foofunction, but a client module with the corresponding __attribute__(dllimport) would require the code. e.g.:

struct __attribute__((dllimport)) bar
{
  void barfunction () { };
};

void __attribute__((dllexport)) blahblah ()
{
  bar b;
  b.barfunction ();
}

Leaves an unresolved external bar::barfunction. My guess is that barfunction was not inlined because it is dllimport, whereas foofunction was not generated because it is erroneously expected to be inlined. gcc 2.95.3-5 (cygwin special) used to emit the required code.
>How-To-Repeat:
Don't try to link the attached code - it's cut down too far. Compile the example code with -save-temps and inspect the .s file for the absence of foofunction, and requirement for external barfunction.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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