r212125 - MS ABI: Reference MSVC RTTI from the VFTable
David Majnemer
david.majnemer at gmail.com
Tue Jul 1 13:30:32 PDT 2014
Author: majnemer
Date: Tue Jul 1 15:30:31 2014
New Revision: 212125
URL: http://llvm.org/viewvc/llvm-project?rev=212125&view=rev
Log:
MS ABI: Reference MSVC RTTI from the VFTable
The pointer for a class's RTTI data comes right before the VFTable but
has no name. To be properly compatible with this, we do the following:
* Create a single GlobalVariable which holds the contents of the VFTable
_and_ the pointer to the RTTI data.
* Create a GlobalAlias, with appropriate linkage/visibility, that points
just after the RTTI data pointer. This ensures that the VFTable
symbol will always refer to VFTable data.
* Create a Comdat with a "Largest" SelectionKind and stick the private
GlobalVariable in it. By transitivity, the GlobalAlias will be a
member of the Comdat group. Using "Largest" ensures that foreign
definitions without an RTTI data pointer will _not_ be chosen in the
final linked image.
Whether or not we emit RTTI data depends on several things:
* The -fno-rtti flag implies that we should never not emit a pointer to
RTTI data before the VFTable.
* __declspec(dllimport) brings in the VFTable from a remote DLL. Use an
available_externally GlobalVariable to provide a local definition of
the VFTable. This means that we won't have any available_externally
definitions of things like complete object locators. This is
acceptable because they are never directly referenced.
To my knowledge, this completes the implementation of MSVC RTTI code
generation.
Further semantic work should be done to properly support /GR-.
Modified:
cfe/trunk/lib/AST/VTableBuilder.cpp
cfe/trunk/lib/CodeGen/CGVTables.cpp
cfe/trunk/lib/CodeGen/CGVTables.h
cfe/trunk/lib/CodeGen/CodeGenModule.h
cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp
cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp
cfe/trunk/lib/CodeGen/MicrosoftRTTI.cpp
cfe/trunk/test/CodeGenCXX/dllexport.cpp
Modified: cfe/trunk/lib/AST/VTableBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/VTableBuilder.cpp?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/AST/VTableBuilder.cpp (original)
+++ cfe/trunk/lib/AST/VTableBuilder.cpp Tue Jul 1 15:30:31 2014
@@ -2574,6 +2574,12 @@ public:
MostDerivedClassLayout(Context.getASTRecordLayout(MostDerivedClass)),
WhichVFPtr(*Which),
Overriders(MostDerivedClass, CharUnits(), MostDerivedClass) {
+ // Only include the RTTI component if we know that we will provide a
+ // definition of the vftable.
+ if (Context.getLangOpts().RTTI &&
+ !MostDerivedClass->hasAttr<DLLImportAttr>())
+ Components.push_back(VTableComponent::MakeRTTI(MostDerivedClass));
+
LayoutVFTable();
if (Context.getLangOpts().DumpVTableLayouts)
@@ -2915,7 +2921,8 @@ void VFTableBuilder::AddMethods(BaseSubo
// it requires return adjustment. Insert the method info for this method.
unsigned VBIndex =
LastVBase ? VTables.getVBTableIndex(MostDerivedClass, LastVBase) : 0;
- MethodInfo MI(VBIndex, Components.size());
+ MethodInfo MI(VBIndex, Context.getLangOpts().RTTI ? Components.size() - 1
+ : Components.size());
assert(!MethodInfoMap.count(MD) &&
"Should not have method info for this method yet!");
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;
Modified: cfe/trunk/lib/CodeGen/CGVTables.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGVTables.h?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGVTables.h (original)
+++ cfe/trunk/lib/CodeGen/CGVTables.h Tue Jul 1 15:30:31 2014
@@ -61,11 +61,10 @@ public:
/// decl.
/// \param Components - The vtable components; this is really an array of
/// VTableComponents.
- llvm::Constant *CreateVTableInitializer(const CXXRecordDecl *RD,
- const VTableComponent *Components,
- unsigned NumComponents,
- const VTableLayout::VTableThunkTy *VTableThunks,
- unsigned NumVTableThunks);
+ llvm::Constant *CreateVTableInitializer(
+ const CXXRecordDecl *RD, const VTableComponent *Components,
+ unsigned NumComponents, const VTableLayout::VTableThunkTy *VTableThunks,
+ unsigned NumVTableThunks, llvm::Constant *RTTI);
CodeGenVTables(CodeGenModule &CGM);
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.h?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.h (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.h Tue Jul 1 15:30:31 2014
@@ -750,8 +750,8 @@ public:
/// \brief Gets or a creats a Microsoft TypeDescriptor.
llvm::Constant *getMSTypeDescriptor(QualType Ty);
/// \brief Gets or a creats a Microsoft CompleteObjectLocator.
- llvm::GlobalVariable *getMSCompleteObjectLocator(const CXXRecordDecl *RD,
- const VPtrInfo *Info);
+ llvm::Constant *getMSCompleteObjectLocator(const CXXRecordDecl *RD,
+ const VPtrInfo *Info);
/// Gets the address of a block which requires no captures.
llvm::Constant *GetAddrOfGlobalBlock(const BlockExpr *BE, const char *);
Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp (original)
+++ cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Tue Jul 1 15:30:31 2014
@@ -1182,11 +1182,13 @@ void ItaniumCXXABI::emitVTableDefinition
ItaniumVTableContext &VTContext = CGM.getItaniumVTableContext();
const VTableLayout &VTLayout = VTContext.getVTableLayout(RD);
llvm::GlobalVariable::LinkageTypes Linkage = CGM.getVTableLinkage(RD);
+ llvm::Constant *RTTI =
+ CGM.GetAddrOfRTTIDescriptor(CGM.getContext().getTagDeclType(RD));
// Create and set the initializer.
llvm::Constant *Init = CGVT.CreateVTableInitializer(
RD, VTLayout.vtable_component_begin(), VTLayout.getNumVTableComponents(),
- VTLayout.vtable_thunk_begin(), VTLayout.getNumVTableThunks());
+ VTLayout.vtable_thunk_begin(), VTLayout.getNumVTableThunks(), RTTI);
VTable->setInitializer(Init);
// Set the correct linkage.
Modified: cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp (original)
+++ cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp Tue Jul 1 15:30:31 2014
@@ -403,9 +403,11 @@ public:
private:
typedef std::pair<const CXXRecordDecl *, CharUnits> VFTableIdTy;
- typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalVariable *> VFTablesMapTy;
+ typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalVariable *> VTablesMapTy;
+ typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalValue *> VFTablesMapTy;
/// \brief All the vftables that have been referenced.
VFTablesMapTy VFTablesMap;
+ VTablesMapTy VTablesMap;
/// \brief This set holds the record decls we've deferred vtable emission for.
llvm::SmallPtrSet<const CXXRecordDecl *, 4> DeferredVFTables;
@@ -1051,26 +1053,22 @@ void MicrosoftCXXABI::emitVTableDefiniti
const CXXRecordDecl *RD) {
MicrosoftVTableContext &VFTContext = CGM.getMicrosoftVTableContext();
VPtrInfoVector VFPtrs = VFTContext.getVFPtrOffsets(RD);
- llvm::GlobalVariable::LinkageTypes Linkage = CGM.getVTableLinkage(RD);
for (VPtrInfo *Info : VFPtrs) {
llvm::GlobalVariable *VTable = getAddrOfVTable(RD, Info->FullOffsetInMDC);
if (VTable->hasInitializer())
continue;
- if (getContext().getLangOpts().RTTI)
- CGM.getMSCompleteObjectLocator(RD, Info);
+
+ llvm::Constant *RTTI = CGM.getMSCompleteObjectLocator(RD, Info);
const VTableLayout &VTLayout =
VFTContext.getVFTableLayout(RD, Info->FullOffsetInMDC);
llvm::Constant *Init = CGVT.CreateVTableInitializer(
RD, VTLayout.vtable_component_begin(),
VTLayout.getNumVTableComponents(), VTLayout.vtable_thunk_begin(),
- VTLayout.getNumVTableThunks());
- VTable->setInitializer(Init);
-
- VTable->setLinkage(Linkage);
+ VTLayout.getNumVTableThunks(), RTTI);
- CGM.setGlobalVisibility(VTable, RD);
+ VTable->setInitializer(Init);
}
}
@@ -1079,8 +1077,9 @@ llvm::Value *MicrosoftCXXABI::getVTableA
const CXXRecordDecl *NearestVBase, bool &NeedsVirtualOffset) {
NeedsVirtualOffset = (NearestVBase != nullptr);
- llvm::Value *VTableAddressPoint =
- getAddrOfVTable(VTableClass, Base.getBaseOffset());
+ (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
+ VFTableIdTy ID(VTableClass, Base.getBaseOffset());
+ llvm::GlobalValue *VTableAddressPoint = VFTablesMap[ID];
if (!VTableAddressPoint) {
assert(Base.getBase()->getNumVBases() &&
!CGM.getContext().getASTRecordLayout(Base.getBase()).hasOwnVFPtr());
@@ -1097,9 +1096,11 @@ static void mangleVFTableName(MicrosoftM
llvm::Constant *MicrosoftCXXABI::getVTableAddressPointForConstExpr(
BaseSubobject Base, const CXXRecordDecl *VTableClass) {
- llvm::Constant *VTable = getAddrOfVTable(VTableClass, Base.getBaseOffset());
- assert(VTable && "Couldn't find a vftable for the given base?");
- return VTable;
+ (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
+ VFTableIdTy ID(VTableClass, Base.getBaseOffset());
+ llvm::GlobalValue *VFTable = VFTablesMap[ID];
+ assert(VFTable && "Couldn't find a vftable for the given base?");
+ return VFTable;
}
llvm::GlobalVariable *MicrosoftCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
@@ -1108,9 +1109,9 @@ llvm::GlobalVariable *MicrosoftCXXABI::g
// shouldn't be used in the given record type. We want to cache this result in
// VFTablesMap, thus a simple zero check is not sufficient.
VFTableIdTy ID(RD, VPtrOffset);
- VFTablesMapTy::iterator I;
+ VTablesMapTy::iterator I;
bool Inserted;
- std::tie(I, Inserted) = VFTablesMap.insert(std::make_pair(ID, nullptr));
+ std::tie(I, Inserted) = VTablesMap.insert(std::make_pair(ID, nullptr));
if (!Inserted)
return I->second;
@@ -1140,21 +1141,73 @@ llvm::GlobalVariable *MicrosoftCXXABI::g
for (size_t J = 0, F = VFPtrs.size(); J != F; ++J) {
if (VFPtrs[J]->FullOffsetInMDC != VPtrOffset)
continue;
+ SmallString<256> VFTableName;
+ mangleVFTableName(getMangleContext(), RD, VFPtrs[J], VFTableName);
+ StringRef VTableName = VFTableName;
- llvm::ArrayType *ArrayType = llvm::ArrayType::get(
- CGM.Int8PtrTy,
+ uint64_t NumVTableSlots =
VTContext.getVFTableLayout(RD, VFPtrs[J]->FullOffsetInMDC)
- .getNumVTableComponents());
+ .getNumVTableComponents();
+ llvm::GlobalValue::LinkageTypes VTableLinkage =
+ llvm::GlobalValue::ExternalLinkage;
+ llvm::ArrayType *VTableType =
+ llvm::ArrayType::get(CGM.Int8PtrTy, NumVTableSlots);
+ if (getContext().getLangOpts().RTTI) {
+ VTableLinkage = llvm::GlobalValue::PrivateLinkage;
+ VTableName = "";
+ }
- SmallString<256> Name;
- mangleVFTableName(getMangleContext(), RD, VFPtrs[J], Name);
- VTable = CGM.CreateOrReplaceCXXRuntimeVariable(
- Name.str(), ArrayType, llvm::GlobalValue::ExternalLinkage);
- VTable->setUnnamedAddr(true);
- if (RD->hasAttr<DLLImportAttr>())
- VTable->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
- else if (RD->hasAttr<DLLExportAttr>())
- VTable->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
+ VTable = CGM.getModule().getNamedGlobal(VFTableName);
+ if (!VTable) {
+ llvm::GlobalValue *VFTable = VTable = new llvm::GlobalVariable(
+ CGM.getModule(), VTableType, /*isConstant=*/true, VTableLinkage,
+ /*Initializer=*/nullptr, VTableName);
+ VTable->setUnnamedAddr(true);
+ if (getContext().getLangOpts().RTTI && !RD->hasAttr<DLLImportAttr>()) {
+ llvm::Value *GEPIndices[] = {llvm::ConstantInt::get(CGM.IntTy, 0),
+ llvm::ConstantInt::get(CGM.IntTy, 1)};
+ llvm::Constant *VTableGEP =
+ llvm::ConstantExpr::getInBoundsGetElementPtr(VTable, GEPIndices);
+ VFTable = llvm::GlobalAlias::create(
+ cast<llvm::SequentialType>(VTableGEP->getType())->getElementType(),
+ /*AddressSpace=*/0, llvm::GlobalValue::ExternalLinkage,
+ VFTableName.str(), VTableGEP, &CGM.getModule());
+ } else {
+ VTable->setName(VFTableName.str());
+ }
+
+ VFTable->setUnnamedAddr(true);
+ if (RD->hasAttr<DLLImportAttr>())
+ VFTable->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
+ else if (RD->hasAttr<DLLExportAttr>())
+ VFTable->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
+
+ llvm::GlobalValue::LinkageTypes VFTableLinkage = CGM.getVTableLinkage(RD);
+ if (VFTable != VTable) {
+ if (llvm::GlobalValue::isAvailableExternallyLinkage(VFTableLinkage)) {
+ // AvailableExternally implies that we grabbed the data from another
+ // executable. No need to stick the alias in a Comdat.
+ } else if (llvm::GlobalValue::isLocalLinkage(VFTableLinkage)) {
+ // If it's local, it means that the virtual function table can't be
+ // referenced in another translation unit. No need to stick the alias
+ // in a Comdat.
+ } else if (llvm::GlobalValue::isWeakODRLinkage(VFTableLinkage) ||
+ llvm::GlobalValue::isLinkOnceODRLinkage(VFTableLinkage)) {
+ // The alias is going to be dropped into a Comdat, no need to make it
+ // weak.
+ VFTableLinkage = llvm::GlobalValue::ExternalLinkage;
+ llvm::Comdat *C =
+ CGM.getModule().getOrInsertComdat(VFTable->getName());
+ C->setSelectionKind(llvm::Comdat::Largest);
+ VTable->setComdat(C);
+ } else {
+ llvm_unreachable("unexpected linkage for vftable!");
+ }
+ }
+ VFTable->setLinkage(VFTableLinkage);
+ CGM.setGlobalVisibility(VFTable, RD);
+ VFTablesMap[ID] = VFTable;
+ }
break;
}
Modified: cfe/trunk/lib/CodeGen/MicrosoftRTTI.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/MicrosoftRTTI.cpp?rev=212125&r1=212124&r2=212125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/MicrosoftRTTI.cpp (original)
+++ cfe/trunk/lib/CodeGen/MicrosoftRTTI.cpp Tue Jul 1 15:30:31 2014
@@ -505,8 +505,10 @@ llvm::Constant *CodeGenModule::getMSType
Int8PtrTy);
}
-llvm::GlobalVariable *
+llvm::Constant *
CodeGenModule::getMSCompleteObjectLocator(const CXXRecordDecl *RD,
const VPtrInfo *Info) {
+ if (!getLangOpts().RTTI)
+ return llvm::Constant::getNullValue(Int8PtrTy);
return MSRTTIBuilder(*this, RD).getCompleteObjectLocator(Info);
}
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 {};
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