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//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This contains code dealing with C++ code generation of virtual tables.
#include "CGCXXABI.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/CodeGen/ConstantInitBuilder.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/RecordLayout.h"
#include "clang/CodeGen/CGFunctionInfo.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "llvm/Support/Format.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include <algorithm>
#include <cstdio>
using namespace clang;
using namespace CodeGen;
CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
: CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
llvm::Constant *CodeGenModule::GetAddrOfThunk(GlobalDecl GD,
const ThunkInfo &Thunk) {
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
// Compute the mangled name.
SmallString<256> Name;
llvm::raw_svector_ostream Out(Name);
if (const CXXDestructorDecl* DD = dyn_cast<CXXDestructorDecl>(MD))
getCXXABI().getMangleContext().mangleCXXDtorThunk(DD, GD.getDtorType(),
Thunk.This, Out);
getCXXABI().getMangleContext().mangleThunk(MD, Thunk, Out);
llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
/*DontDefer=*/true, /*IsThunk=*/true);
static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
const ThunkInfo &Thunk, llvm::Function *Fn) {
CGM.setGlobalVisibility(Fn, MD);
static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
llvm::Function *ThunkFn, bool ForVTable,
GlobalDecl GD) {
CGM.setFunctionLinkage(GD, ThunkFn);
CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
// Set the right visibility.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
setThunkVisibility(CGM, MD, Thunk, ThunkFn);
if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
#ifndef NDEBUG
static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
const ABIArgInfo &infoR, CanQualType typeR) {
return (infoL.getKind() == infoR.getKind() &&
(typeL == typeR ||
(isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
(isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
QualType ResultType, RValue RV,
const ThunkInfo &Thunk) {
// Emit the return adjustment.
bool NullCheckValue = !ResultType->isReferenceType();
llvm::BasicBlock *AdjustNull = nullptr;
llvm::BasicBlock *AdjustNotNull = nullptr;
llvm::BasicBlock *AdjustEnd = nullptr;
llvm::Value *ReturnValue = RV.getScalarVal();
if (NullCheckValue) {
AdjustNull = CGF.createBasicBlock("adjust.null");
AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
AdjustEnd = CGF.createBasicBlock("adjust.end");
llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF,
Address(ReturnValue, ClassAlign),
if (NullCheckValue) {
llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
PHI->addIncoming(ReturnValue, AdjustNotNull);
ReturnValue = PHI;
return RValue::get(ReturnValue);
// This function does roughly the same thing as GenerateThunk, but in a
// very different way, so that va_start and va_end work correctly.
// FIXME: This function assumes "this" is the first non-sret LLVM argument of
// a function, and that there is an alloca built in the entry block
// for all accesses to "this".
// FIXME: This function assumes there is only one "ret" statement per function.
// FIXME: Cloning isn't correct in the presence of indirect goto!
// FIXME: This implementation of thunks bloats codesize by duplicating the
// function definition. There are alternatives:
// 1. Add some sort of stub support to LLVM for cases where we can
// do a this adjustment, then a sibcall.
// 2. We could transform the definition to take a va_list instead of an
// actual variable argument list, then have the thunks (including a
// no-op thunk for the regular definition) call va_start/va_end.
// There's a bit of per-call overhead for this solution, but it's
// better for codesize if the definition is long.
llvm::Function *
CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
const CGFunctionInfo &FnInfo,
GlobalDecl GD, const ThunkInfo &Thunk) {
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
QualType ResultType = FPT->getReturnType();
// Get the original function
llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
llvm::Function *BaseFn = cast<llvm::Function>(Callee);
// Clone to thunk.
llvm::ValueToValueMapTy VMap;
llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
Fn = NewFn;
// "Initialize" CGF (minimally).
CurFn = Fn;
// Get the "this" value
llvm::Function::arg_iterator AI = Fn->arg_begin();
if (CGM.ReturnTypeUsesSRet(FnInfo))
// Find the first store of "this", which will be to the alloca associated
// with "this".
Address ThisPtr(&*AI, CGM.getClassPointerAlignment(MD->getParent()));
llvm::BasicBlock *EntryBB = &Fn->front();
llvm::BasicBlock::iterator ThisStore =
std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
return isa<llvm::StoreInst>(I) &&
I.getOperand(0) == ThisPtr.getPointer();
assert(ThisStore != EntryBB->end() &&
"Store of this should be in entry block?");
// Adjust "this", if necessary.
llvm::Value *AdjustedThisPtr =
CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
ThisStore->setOperand(0, AdjustedThisPtr);
if (!Thunk.Return.isEmpty()) {
// Fix up the returned value, if necessary.
for (llvm::BasicBlock &BB : *Fn) {
llvm::Instruction *T = BB.getTerminator();
if (isa<llvm::ReturnInst>(T)) {
RValue RV = RValue::get(T->getOperand(0));
RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
return Fn;
void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
const CGFunctionInfo &FnInfo) {
assert(!CurGD.getDecl() && "CurGD was already set!");
CurGD = GD;
CurFuncIsThunk = true;
// Build FunctionArgs.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
QualType ThisType = MD->getThisType(getContext());
const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
QualType ResultType = CGM.getCXXABI().HasThisReturn(GD)
? ThisType
: CGM.getCXXABI().hasMostDerivedReturn(GD)
? CGM.getContext().VoidPtrTy
: FPT->getReturnType();
FunctionArgList FunctionArgs;
// Create the implicit 'this' parameter declaration.
CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
// Add the rest of the parameters.
FunctionArgs.append(MD->param_begin(), MD->param_end());
if (isa<CXXDestructorDecl>(MD))
CGM.getCXXABI().addImplicitStructorParams(*this, ResultType, FunctionArgs);
// Start defining the function.
auto NL = ApplyDebugLocation::CreateEmpty(*this);
StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
// Create a scope with an artificial location for the body of this function.
auto AL = ApplyDebugLocation::CreateArtificial(*this);
// Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
CXXThisValue = CXXABIThisValue;
CurCodeDecl = MD;
CurFuncDecl = MD;
void CodeGenFunction::FinishThunk() {
// Clear these to restore the invariants expected by
// StartFunction/FinishFunction.
CurCodeDecl = nullptr;
CurFuncDecl = nullptr;
void CodeGenFunction::EmitCallAndReturnForThunk(llvm::Constant *CalleePtr,
const ThunkInfo *Thunk) {
assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
"Please use a new CGF for this thunk");
const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
// Adjust the 'this' pointer if necessary
llvm::Value *AdjustedThisPtr =
Thunk ? CGM.getCXXABI().performThisAdjustment(
*this, LoadCXXThisAddress(), Thunk->This)
: LoadCXXThis();
if (CurFnInfo->usesInAlloca()) {
// We don't handle return adjusting thunks, because they require us to call
// the copy constructor. For now, fall through and pretend the return
// adjustment was empty so we don't crash.
if (Thunk && !Thunk->Return.isEmpty()) {
MD, "non-trivial argument copy for return-adjusting thunk");
EmitMustTailThunk(MD, AdjustedThisPtr, CalleePtr);
// Start building CallArgs.
CallArgList CallArgs;
QualType ThisType = MD->getThisType(getContext());
CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
if (isa<CXXDestructorDecl>(MD))
CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
// Add the rest of the arguments.
for (const ParmVarDecl *PD : MD->parameters())
EmitDelegateCallArg(CallArgs, PD, SourceLocation());
const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
#ifndef NDEBUG
const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1, MD));
assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
// Determine whether we have a return value slot to use.
QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
? ThisType
: CGM.getCXXABI().hasMostDerivedReturn(CurGD)
? CGM.getContext().VoidPtrTy
: FPT->getReturnType();
ReturnValueSlot Slot;
if (!ResultType->isVoidType() &&
CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
// Now emit our call.
llvm::Instruction *CallOrInvoke;
CGCallee Callee = CGCallee::forDirect(CalleePtr, MD);
RValue RV = EmitCall(*CurFnInfo, Callee, Slot, CallArgs, &CallOrInvoke);
// Consider return adjustment if we have ThunkInfo.
if (Thunk && !Thunk->Return.isEmpty())
RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
// Emit return.
if (!ResultType->isVoidType() && Slot.isNull())
CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
// Disable the final ARC autorelease.
AutoreleaseResult = false;
void CodeGenFunction::EmitMustTailThunk(const CXXMethodDecl *MD,
llvm::Value *AdjustedThisPtr,
llvm::Value *CalleePtr) {
// Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
// to translate AST arguments into LLVM IR arguments. For thunks, we know
// that the caller prototype more or less matches the callee prototype with
// the exception of 'this'.
SmallVector<llvm::Value *, 8> Args;
for (llvm::Argument &A : CurFn->args())
// Set the adjusted 'this' pointer.
const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
if (ThisAI.isDirect()) {
const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
llvm::Type *ThisType = Args[ThisArgNo]->getType();
if (ThisType != AdjustedThisPtr->getType())
AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
Args[ThisArgNo] = AdjustedThisPtr;
} else {
assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
llvm::Type *ThisType = ThisAddr.getElementType();
if (ThisType != AdjustedThisPtr->getType())
AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
Builder.CreateStore(AdjustedThisPtr, ThisAddr);
// Emit the musttail call manually. Even if the prologue pushed cleanups, we
// don't actually want to run them.
llvm::CallInst *Call = Builder.CreateCall(CalleePtr, Args);
// Apply the standard set of call attributes.
unsigned CallingConv;
CodeGen::AttributeListType AttributeList;
*CurFnInfo, MD, AttributeList,
CallingConv, /*AttrOnCallSite=*/true);
llvm::AttributeSet Attrs =
llvm::AttributeSet::get(getLLVMContext(), AttributeList);
if (Call->getType()->isVoidTy())
// Finish the function to maintain CodeGenFunction invariants.
// FIXME: Don't emit unreachable code.
void CodeGenFunction::generateThunk(llvm::Function *Fn,
const CGFunctionInfo &FnInfo,
GlobalDecl GD, const ThunkInfo &Thunk) {
StartThunk(Fn, GD, FnInfo);
// Create a scope with an artificial location for the body of this function.
auto AL = ApplyDebugLocation::CreateArtificial(*this);
// Get our callee.
llvm::Type *Ty =
llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
// Make the call and return the result.
EmitCallAndReturnForThunk(Callee, &Thunk);
void CodeGenVTables::emitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
bool ForVTable) {
const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
// FIXME: re-use FnInfo in this computation.
llvm::Constant *C = CGM.GetAddrOfThunk(GD, Thunk);
llvm::GlobalValue *Entry;
// Strip off a bitcast if we got one back.
if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(C)) {
assert(CE->getOpcode() == llvm::Instruction::BitCast);
Entry = cast<llvm::GlobalValue>(CE->getOperand(0));
} else {
Entry = cast<llvm::GlobalValue>(C);
// There's already a declaration with the same name, check if it has the same
// type or if we need to replace it.
if (Entry->getType()->getElementType() !=
CGM.getTypes().GetFunctionTypeForVTable(GD)) {
llvm::GlobalValue *OldThunkFn = Entry;
// If the types mismatch then we have to rewrite the definition.
assert(OldThunkFn->isDeclaration() &&
"Shouldn't replace non-declaration");
// Remove the name from the old thunk function and get a new thunk.
Entry = cast<llvm::GlobalValue>(CGM.GetAddrOfThunk(GD, Thunk));
// If needed, replace the old thunk with a bitcast.
if (!OldThunkFn->use_empty()) {
llvm::Constant *NewPtrForOldDecl =
llvm::ConstantExpr::getBitCast(Entry, OldThunkFn->getType());
// Remove the old thunk.
llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
if (!ThunkFn->isDeclaration()) {
if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
// There is already a thunk emitted for this function, do nothing.
setThunkProperties(CGM, Thunk, ThunkFn, ForVTable, GD);
CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
if (ThunkFn->isVarArg()) {
// Varargs thunks are special; we can't just generate a call because
// we can't copy the varargs. Our implementation is rather
// 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)
ThunkFn =
CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
} else {
// Normal thunk body generation.
CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, Thunk);
setThunkProperties(CGM, Thunk, ThunkFn, ForVTable, GD);
void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
const ThunkInfo &Thunk) {
// If the ABI has key functions, only the TU with the key function should emit
// the thunk. However, we can allow inlining of thunks if we emit them with
// available_externally linkage together with vtables when optimizations are
// enabled.
if (CGM.getTarget().getCXXABI().hasKeyFunctions() &&
// We can't emit thunks for member functions with incomplete types.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
if (!CGM.getTypes().isFuncTypeConvertible(
emitThunk(GD, Thunk, /*ForVTable=*/true);
void CodeGenVTables::EmitThunks(GlobalDecl GD)
const CXXMethodDecl *MD =
// We don't need to generate thunks for the base destructor.
if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
if (!ThunkInfoVector)
for (const ThunkInfo& Thunk : *ThunkInfoVector)
emitThunk(GD, Thunk, /*ForVTable=*/false);
void CodeGenVTables::addVTableComponent(
ConstantArrayBuilder &builder, const VTableLayout &layout,
unsigned idx, llvm::Constant *rtti, unsigned &nextVTableThunkIndex) {
auto &component = layout.vtable_components()[idx];
auto addOffsetConstant = [&](CharUnits offset) {
llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
switch (component.getKind()) {
case VTableComponent::CK_VCallOffset:
return addOffsetConstant(component.getVCallOffset());
case VTableComponent::CK_VBaseOffset:
return addOffsetConstant(component.getVBaseOffset());
case VTableComponent::CK_OffsetToTop:
return addOffsetConstant(component.getOffsetToTop());
case VTableComponent::CK_RTTI:
return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
case VTableComponent::CK_FunctionPointer:
case VTableComponent::CK_CompleteDtorPointer:
case VTableComponent::CK_DeletingDtorPointer: {
GlobalDecl GD;
// Get the right global decl.
switch (component.getKind()) {
llvm_unreachable("Unexpected vtable component kind");
case VTableComponent::CK_FunctionPointer:
GD = component.getFunctionDecl();
case VTableComponent::CK_CompleteDtorPointer:
GD = GlobalDecl(component.getDestructorDecl(), Dtor_Complete);
case VTableComponent::CK_DeletingDtorPointer:
GD = GlobalDecl(component.getDestructorDecl(), Dtor_Deleting);
if (CGM.getLangOpts().CUDA) {
// Emit NULL for methods we can't codegen on this
// side. Otherwise we'd end up with vtable with unresolved
// references.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
// OK on device side: functions w/ __device__ attribute
// OK on host side: anything except __device__-only functions.
bool CanEmitMethod =
? MD->hasAttr<CUDADeviceAttr>()
: (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
if (!CanEmitMethod)
return builder.addNullPointer(CGM.Int8PtrTy);
// Method is acceptable, continue processing as usual.
auto getSpecialVirtualFn = [&](StringRef name) {
llvm::FunctionType *fnTy =
llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
llvm::Constant *fn = CGM.CreateRuntimeFunction(fnTy, name);
if (auto f = dyn_cast<llvm::Function>(fn))
return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
llvm::Constant *fnPtr;
// Pure virtual member functions.
if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
if (!PureVirtualFn)
PureVirtualFn =
fnPtr = PureVirtualFn;
// Deleted virtual member functions.
} else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
if (!DeletedVirtualFn)
DeletedVirtualFn =
fnPtr = DeletedVirtualFn;
// Thunks.
} else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
layout.vtable_thunks()[nextVTableThunkIndex].first == idx) {
auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
maybeEmitThunkForVTable(GD, thunkInfo);
fnPtr = CGM.GetAddrOfThunk(GD, thunkInfo);
// Otherwise we can use the method definition directly.
} else {
llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
fnPtr = llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy);
case VTableComponent::CK_UnusedFunctionPointer:
return builder.addNullPointer(CGM.Int8PtrTy);
llvm_unreachable("Unexpected vtable component kind");
llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
SmallVector<llvm::Type *, 4> tys;
for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
tys.push_back(llvm::ArrayType::get(CGM.Int8PtrTy, layout.getVTableSize(i)));
return llvm::StructType::get(CGM.getLLVMContext(), tys);
void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
const VTableLayout &layout,
llvm::Constant *rtti) {
unsigned nextVTableThunkIndex = 0;
for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
auto vtableElem = builder.beginArray(CGM.Int8PtrTy);
size_t thisIndex = layout.getVTableOffset(i);
size_t nextIndex = thisIndex + layout.getVTableSize(i);
for (unsigned i = thisIndex; i != nextIndex; ++i) {
addVTableComponent(vtableElem, layout, i, rtti, nextVTableThunkIndex);
llvm::GlobalVariable *
CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
const BaseSubobject &Base,
bool BaseIsVirtual,
llvm::GlobalVariable::LinkageTypes Linkage,
VTableAddressPointsMapTy& AddressPoints) {
if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
std::unique_ptr<VTableLayout> VTLayout(
Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
// Add the address points.
AddressPoints = VTLayout->getAddressPoints();
// Get the mangled construction vtable name.
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
.mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
Base.getBase(), Out);
StringRef Name = OutName.str();
llvm::Type *VTType = getVTableType(*VTLayout);
// Construction vtable symbols are not part of the Itanium ABI, so we cannot
// guarantee that they actually will be available externally. Instead, when
// emitting an available_externally VTT, we provide references to an internal
// linkage construction vtable. The ABI only requires complete-object vtables
// to be the same for all instances of a type, not construction vtables.
if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
Linkage = llvm::GlobalVariable::InternalLinkage;
// Create the variable that will hold the construction vtable.
llvm::GlobalVariable *VTable =
CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage);
CGM.setGlobalVisibility(VTable, RD);
// V-tables are always unnamed_addr.
llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
// Create and set the initializer.
ConstantInitBuilder builder(CGM);
auto components = builder.beginStruct();
createVTableInitializer(components, *VTLayout, RTTI);
CGM.EmitVTableTypeMetadata(VTable, *VTLayout.get());
return VTable;
static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
const CXXRecordDecl *RD) {
return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
/// Compute the required linkage of the vtable for the given class.
/// Note that we only call this at the end of the translation unit.
CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
if (!RD->isExternallyVisible())
return llvm::GlobalVariable::InternalLinkage;
// We're at the end of the translation unit, so the current key
// function is fully correct.
const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
// If this class has a key function, use that to determine the
// linkage of the vtable.
const FunctionDecl *def = nullptr;
if (keyFunction->hasBody(def))
keyFunction = cast<CXXMethodDecl>(def);
switch (keyFunction->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
assert((def || CodeGenOpts.OptimizationLevel > 0) &&
"Shouldn't query vtable linkage without key function or "
if (!def && CodeGenOpts.OptimizationLevel > 0)
return llvm::GlobalVariable::AvailableExternallyLinkage;
if (keyFunction->isInlined())
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::LinkOnceODRLinkage :
return llvm::GlobalVariable::ExternalLinkage;
case TSK_ImplicitInstantiation:
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::LinkOnceODRLinkage :
case TSK_ExplicitInstantiationDefinition:
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::WeakODRLinkage :
case TSK_ExplicitInstantiationDeclaration:
llvm_unreachable("Should not have been asked to emit this");
// -fapple-kext mode does not support weak linkage, so we must use
// internal linkage.
if (Context.getLangOpts().AppleKext)
return llvm::Function::InternalLinkage;
llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
if (RD->hasAttr<DLLExportAttr>()) {
// Cannot discard exported vtables.
DiscardableODRLinkage = NonDiscardableODRLinkage;
} else if (RD->hasAttr<DLLImportAttr>()) {
// Imported vtables are available externally.
DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
switch (RD->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
case TSK_ImplicitInstantiation:
return DiscardableODRLinkage;
case TSK_ExplicitInstantiationDeclaration:
// Explicit instantiations in MSVC do not provide vtables, so we must emit
// our own.
if (getTarget().getCXXABI().isMicrosoft())
return DiscardableODRLinkage;
return shouldEmitAvailableExternallyVTable(*this, RD)
? llvm::GlobalVariable::AvailableExternallyLinkage
: llvm::GlobalVariable::ExternalLinkage;
case TSK_ExplicitInstantiationDefinition:
return NonDiscardableODRLinkage;
llvm_unreachable("Invalid TemplateSpecializationKind!");
/// This is a callback from Sema to tell us that that a particular vtable is
/// required to be emitted in this translation unit.
/// This is only called for vtables that _must_ be emitted (mainly due to key
/// functions). For weak vtables, CodeGen tracks when they are needed and
/// emits them as-needed.
void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
if (RD->getNumVBases())
CGM.getCXXABI().emitVTableDefinitions(*this, RD);
/// At this point in the translation unit, does it appear that can we
/// rely on the vtable being defined elsewhere in the program?
/// The response is really only definitive when called at the end of
/// the translation unit.
/// The only semantic restriction here is that the object file should
/// not contain a vtable definition when that vtable is defined
/// strongly elsewhere. Otherwise, we'd just like to avoid emitting
/// vtables when unnecessary.
bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
// We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
// emit them even if there is an explicit template instantiation.
if (CGM.getTarget().getCXXABI().isMicrosoft())
return false;
// If we have an explicit instantiation declaration (and not a
// definition), the vtable is defined elsewhere.
TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
if (TSK == TSK_ExplicitInstantiationDeclaration)
return true;
// Otherwise, if the class is an instantiated template, the
// vtable must be defined here.
if (TSK == TSK_ImplicitInstantiation ||
TSK == TSK_ExplicitInstantiationDefinition)
return false;
// Otherwise, if the class doesn't have a key function (possibly
// anymore), the vtable must be defined here.
const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
if (!keyFunction)
return false;
// Otherwise, if we don't have a definition of the key function, the
// vtable must be defined somewhere else.
return !keyFunction->hasBody();
/// Given that we're currently at the end of the translation unit, and
/// we've emitted a reference to the vtable for this class, should
/// we define that vtable?
static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
const CXXRecordDecl *RD) {
// If vtable is internal then it has to be done.
if (!CGM.getVTables().isVTableExternal(RD))
return true;
// If it's external then maybe we will need it as available_externally.
return shouldEmitAvailableExternallyVTable(CGM, RD);
/// Given that at some point we emitted a reference to one or more
/// vtables, and that we are now at the end of the translation unit,
/// decide whether we should emit them.
void CodeGenModule::EmitDeferredVTables() {
#ifndef NDEBUG
// Remember the size of DeferredVTables, because we're going to assume
// that this entire operation doesn't modify it.
size_t savedSize = DeferredVTables.size();
for (const CXXRecordDecl *RD : DeferredVTables)
if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
assert(savedSize == DeferredVTables.size() &&
"deferred extra vtables during vtable emission?");
bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
LinkageInfo LV = RD->getLinkageAndVisibility();
if (!isExternallyVisible(LV.getLinkage()))
return true;
if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
return false;
if (getTriple().isOSBinFormatCOFF()) {
if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
return false;
} else {
if (LV.getVisibility() != HiddenVisibility)
return false;
if (getCodeGenOpts().LTOVisibilityPublicStd) {
const DeclContext *DC = RD;
while (1) {
auto *D = cast<Decl>(DC);
DC = DC->getParent();
if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
if (auto *ND = dyn_cast<NamespaceDecl>(D))
if (const IdentifierInfo *II = ND->getIdentifier())
if (II->isStr("std") || II->isStr("stdext"))
return false;
return true;
void CodeGenModule::EmitVTableTypeMetadata(llvm::GlobalVariable *VTable,
const VTableLayout &VTLayout) {
if (!getCodeGenOpts().PrepareForLTO)
CharUnits PointerWidth =
typedef std::pair<const CXXRecordDecl *, unsigned> BSEntry;
std::vector<BSEntry> BitsetEntries;
// Create a bit set entry for each address point.
for (auto &&AP : VTLayout.getAddressPoints())
VTLayout.getVTableOffset(AP.second.VTableIndex) +
// Sort the bit set entries for determinism.
std::sort(BitsetEntries.begin(), BitsetEntries.end(),
[this](const BSEntry &E1, const BSEntry &E2) {
if (&E1 == &E2)
return false;
std::string S1;
llvm::raw_string_ostream O1(S1);
QualType(E1.first->getTypeForDecl(), 0), O1);
std::string S2;
llvm::raw_string_ostream O2(S2);
QualType(E2.first->getTypeForDecl(), 0), O2);
if (S1 < S2)
return true;
if (S1 != S2)
return false;
return E1.second < E2.second;
for (auto BitsetEntry : BitsetEntries)
AddVTableTypeMetadata(VTable, PointerWidth * BitsetEntry.second,