r241102 - CodeGen: Assign an appropriate comdat to thunks.

[Peter Collingbourne]

This looks more like r241103. David is working on a fix.

On Tue, Jun 30, 2015 at 01:10:13PM -0700, Nico Weber wrote:
> It looks like this breaks building base.dll in the Chromium project:
> http://code.google.com/p/chromium/issues/detail?id=505916
> 
> On Tue, Jun 30, 2015 at 12:07 PM, Peter Collingbourne <peter at pcc.me.uk>
> wrote:
> 
> > Author: pcc
> > Date: Tue Jun 30 14:07:26 2015
> > New Revision: 241102
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=241102&view=rev
> > Log:
> > CodeGen: Assign an appropriate comdat to thunks.
> >
> > Previously we were not assigning a comdat to thunks in the Microsoft ABI,
> > which would have required us to emit these functions outside of a comdat.
> > (Due to an inconsistency in how we were emitting objects, we were getting
> > this
> > right most of the time, but only when compiling with function sections.)
> > This
> > code generator change causes us to create a comdat for each thunk.
> >
> > Differential Revision: http://reviews.llvm.org/D10829
> >
> > Modified:
> >     cfe/trunk/lib/CodeGen/CGVTables.cpp
> >     cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp
> >
> > Modified: cfe/trunk/lib/CodeGen/CGVTables.cpp
> > URL:
> > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGVTables.cpp?rev=241102&r1=241101&r2=241102&view=diff
> >
> > ==============================================================================
> > --- cfe/trunk/lib/CodeGen/CGVTables.cpp (original)
> > +++ cfe/trunk/lib/CodeGen/CGVTables.cpp Tue Jun 30 14:07:26 2015
> > @@ -378,9 +378,6 @@ void CodeGenFunction::GenerateThunk(llvm
> >    // Set the right linkage.
> >    CGM.setFunctionLinkage(GD, Fn);
> >
> > -  if (CGM.supportsCOMDAT() && Fn->isWeakForLinker())
> > -    Fn->setComdat(CGM.getModule().getOrInsertComdat(Fn->getName()));
> > -
> >    // Set the right visibility.
> >    const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
> >    setThunkVisibility(CGM, MD, Thunk, Fn);
> > @@ -450,17 +447,18 @@ void CodeGenVTables::emitThunk(GlobalDec
> >      // expensive/sucky at the moment, so don't generate the thunk unless
> >      // we have to.
> >      // FIXME: Do something better here; GenerateVarArgsThunk is extremely
> > ugly.
> > -    if (!UseAvailableExternallyLinkage) {
> > -      CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD,
> > Thunk);
> > -      CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
> > -                                      !Thunk.Return.isEmpty());
> > -    }
> > +    if (UseAvailableExternallyLinkage)
> > +      return;
> > +    CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
> >    } else {
> >      // Normal thunk body generation.
> >      CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
> > -    CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
> > -                                    !Thunk.Return.isEmpty());
> >    }
> > +
> > +  CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
> > +                                  !Thunk.Return.isEmpty());
> > +  if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
> > +
> > ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
> >  }
> >
> >  void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
> >
> > Modified: cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp
> > URL:
> > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp?rev=241102&r1=241101&r2=241102&view=diff
> >
> > ==============================================================================
> > --- cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp (original)
> > +++ cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp Tue Jun 30 14:07:26
> > 2015
> > @@ -91,7 +91,7 @@ struct E : D {
> >
> >  E::E() {}  // Emits vftable and forces thunk generation.
> >
> > -// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.C* @"\01?goo at E
> > @@QAEPAUB@@XZ"
> > +// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.C* @"\01?goo at E
> > @@QAEPAUB@@XZ"{{.*}} comdat
> >  // CODEGEN:   call x86_thiscallcc %struct.C* @"\01?goo at E@@UAEPAUC@@XZ"
> >  // CODEGEN:   getelementptr inbounds i8, i8* {{.*}}, i32 4
> >  // CODEGEN: ret
> > @@ -124,7 +124,7 @@ struct I : D {
> >
> >  I::I() {}  // Emits vftable and forces thunk generation.
> >
> > -// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.{{[BF]}}*
> > @"\01?goo at I@@QAEPAUB@@XZ"
> > +// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.{{[BF]}}*
> > @"\01?goo at I@@QAEPAUB@@XZ"{{.*}} comdat
> >  // CODEGEN: %[[ORIG_RET:.*]] = call x86_thiscallcc %struct.F* @"\01?goo at I
> > @@UAEPAUF@@XZ"
> >  // CODEGEN: %[[ORIG_RET_i8:.*]] = bitcast %struct.F* %[[ORIG_RET]] to i8*
> >  // CODEGEN: %[[VBPTR_i8:.*]] = getelementptr inbounds i8, i8*
> > %[[ORIG_RET_i8]], i32 4
> >
> >
> > _______________________________________________
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> > cfe-commits at cs.uiuc.edu
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> >

-- 
Peter