[Bug objc/48109] New: Objective-C class defs/refs are lost under LTO on Darwin for ABI0/1

["iains at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48109

           Summary: Objective-C class defs/refs are lost under LTO on
                    Darwin for ABI0/1
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: objc
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: iains@gcc.gnu.org
              Host: *-apple-darwin*
            Target: *-apple-darwin*
             Build: *-apple-darwin*


This is a FE bug that manifests only on Darwin/NeXT (m32) under LTO.

(originally reported as part of PR48094)

e.g.

-L/sw/src/fink.build/gcc46-4.6.0-1000/darwin_objdir/x86_64-apple-darwin10.7.0/i386/libobjc/.libs
  -lobjc     -m32 -o objc-dg-lto-trivial-1-21    (timeout = 300)
ld: warning: section __OBJC/__image_info has unexpectedly large size 16 in
/var/tmp//ccMlEsXS.lto.o^M
Undefined symbols for architecture i386:^M
  ".objc_class_name_myRootObject", referenced from:^M
      pointer-to-literal-objc-class-name in ccMlEsXS.lto.o^M
      pointer-to-literal-objc-class-name in ccMlEsXS.lto.o^M
ld: symbol(s) not found for architecture i386^M

---

The reason is an anachronism in using target macros to emit efficient
representations of class presence and requirement
(ASM_DECLARE_CLASS_REFERENCE/ASM_DECLARE_UNRESOLVED_REFERENCE).

.. because of this, there are no real vars representing the
presence/requirement for the classes and, when LTO is engaged, the information
is lost.

The separate external defs/refs are required because the class metadata
structures are all local to a given TU.  The refs meet the linkage
requirements.

For the m64 ABI-2 this is not longer an issue, since class metadata definitions
are now external and thus visible without additional action.