r212125 - MS ABI: Reference MSVC RTTI from the VFTable

[David Majnemer]

On Tue, Jul 1, 2014 at 2:20 PM, Reid Kleckner <rnk at google.com> wrote:

> On Tue, Jul 1, 2014 at 1:30 PM, David Majnemer <david.majnemer at gmail.com>
> wrote:
>>
>> Modified: cfe/trunk/lib/CodeGen/CGVTables.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGVTables.cpp?rev=212125&r1=212124&r2=212125&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/CodeGen/CGVTables.cpp (original)
>> +++ cfe/trunk/lib/CodeGen/CGVTables.cpp Tue Jul  1 15:30:31 2014
>> @@ -431,12 +431,10 @@ void CodeGenVTables::EmitThunks(GlobalDe
>>      emitThunk(GD, (*ThunkInfoVector)[I], /*ForVTable=*/false);
>>  }
>>
>> -llvm::Constant *
>> -CodeGenVTables::CreateVTableInitializer(const CXXRecordDecl *RD,
>> -                                        const VTableComponent
>> *Components,
>> -                                        unsigned NumComponents,
>> -                                const VTableLayout::VTableThunkTy
>> *VTableThunks,
>> -                                        unsigned NumVTableThunks) {
>> +llvm::Constant *CodeGenVTables::CreateVTableInitializer(
>> +    const CXXRecordDecl *RD, const VTableComponent *Components,
>> +    unsigned NumComponents, const VTableLayout::VTableThunkTy
>> *VTableThunks,
>> +    unsigned NumVTableThunks, llvm::Constant *RTTI) {
>>    SmallVector<llvm::Constant *, 64> Inits;
>>
>>    llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
>> @@ -444,9 +442,6 @@ CodeGenVTables::CreateVTableInitializer(
>>    llvm::Type *PtrDiffTy =
>>      CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
>>
>> -  QualType ClassType = CGM.getContext().getTagDeclType(RD);
>> -  llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(ClassType);
>> -
>>    unsigned NextVTableThunkIndex = 0;
>>
>>    llvm::Constant *PureVirtualFn = nullptr, *DeletedVirtualFn = nullptr;
>> @@ -594,13 +589,14 @@ CodeGenVTables::GenerateConstructionVTab
>>    // V-tables are always unnamed_addr.
>>    VTable->setUnnamedAddr(true);
>>
>> +  llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
>> +      CGM.getContext().getTagDeclType(Base.getBase()));
>> +
>>    // Create and set the initializer.
>> -  llvm::Constant *Init =
>> -    CreateVTableInitializer(Base.getBase(),
>> -                            VTLayout->vtable_component_begin(),
>> -                            VTLayout->getNumVTableComponents(),
>> -                            VTLayout->vtable_thunk_begin(),
>> -                            VTLayout->getNumVTableThunks());
>> +  llvm::Constant *Init = CreateVTableInitializer(
>> +      Base.getBase(), VTLayout->vtable_component_begin(),
>> +      VTLayout->getNumVTableComponents(), VTLayout->vtable_thunk_begin(),
>> +      VTLayout->getNumVTableThunks(), RTTI);
>>    VTable->setInitializer(Init);
>>
>>    return VTable;
>>
>
> Why hoist this out to callers?
>

Because there is substantial difference between RTTI in vtables for MSVC
and GCC.  MSVC complete object locators need to know which vftable they are
pairing with.


>
>
>> Modified: cfe/trunk/test/CodeGenCXX/dllexport.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/dllexport.cpp?rev=212125&r1=212124&r2=212125&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/CodeGenCXX/dllexport.cpp (original)
>> +++ cfe/trunk/test/CodeGenCXX/dllexport.cpp Tue Jul  1 15:30:31 2014
>> @@ -24,6 +24,9 @@ struct External { int v; };
>>  #define INSTVAR(var) template int var;
>>  #define INST(func) template void func();
>>
>> +// The vftable for struct W is comdat largest because we have RTTI.
>> +// M32-DAG: $"\01??_7W@@6B@" = comdat largest
>> +
>>
>>
>>  //===----------------------------------------------------------------------===//
>>  // Globals
>> @@ -518,7 +521,8 @@ struct __declspec(dllexport) W { virtual
>>  // Copy ctor:
>>  // M32-DAG: define weak_odr dllexport x86_thiscallcc %struct.W*
>> @"\01??0W@@QAE at ABU0@@Z"
>>  // vftable:
>> -// M32-DAG: @"\01??_7W@@6B@" = weak_odr dllexport unnamed_addr constant
>> [1 x i8*] [i8* bitcast (void (%struct.W*)* @"\01?foo at W@@UAEXXZ" to i8*)]
>> +// M32-DAG: [[W_VTABLE:@.*]] = private unnamed_addr constant [2 x i8*]
>> [i8* bitcast (%MSRTTICompleteObjectLocator* @"\01??_R4W@@6B@" to i8*),
>> i8* bitcast (void (%struct.W*)* @"\01?foo at W@@UAEXXZ" to i8*)], comdat
>> $"\01??_7W@@6B@"
>> +// M32-DAG: @"\01??_7W@@6B@" = dllexport unnamed_addr alias
>> getelementptr inbounds ([2 x i8*]* [[W_VTABLE]], i32 0, i32 1), comdat
>> $"\01??_7W@@6B@"
>>  // G32-DAG: @_ZTV1W = weak_odr dllexport unnamed_addr constant [3 x i8*]
>> [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1W to i8*), i8* bitcast (void
>> (%struct.W*)* @_ZN1W3fooEv to i8*)]
>>
>>  struct __declspec(dllexport) X : public virtual W {};
>>
>
> This seems like not enough tests, did you forget to add a file?
>

Yep, good catch! r212139.
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