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

[RaoulGough@yahoo.co.uk]

>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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