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//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This contains code dealing with C++ code generation of virtual tables.
#include "CGCXXABI.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/AST/Attr.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Basic/CodeGenOptions.h"
#include "clang/CodeGen/CGFunctionInfo.h"
#include "clang/CodeGen/ConstantInitBuilder.h"
#include "llvm/IR/IntrinsicInst.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(StringRef Name, llvm::Type *FnTy,
GlobalDecl GD) {
return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
/*DontDefer=*/true, /*IsThunk=*/true);
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.
CGM.setGVProperties(ThunkFn, GD);
if (!CGM.getCXXABI().exportThunk()) {
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 clones a function's DISubprogram node and enters it into
/// a value map with the intent that the map can be utilized by the cloner
/// to short-circuit Metadata node mapping.
/// Furthermore, the function resolves any DILocalVariable nodes referenced
/// by dbg.value intrinsics so they can be properly mapped during cloning.
static void resolveTopLevelMetadata(llvm::Function *Fn,
llvm::ValueToValueMapTy &VMap) {
// Clone the DISubprogram node and put it into the Value map.
auto *DIS = Fn->getSubprogram();
if (!DIS)
auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
// Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
// they are referencing.
for (auto &BB : Fn->getBasicBlockList()) {
for (auto &I : BB) {
if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
auto *DILocal = DII->getVariable();
if (!DILocal->isResolved())
// 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()->castAs<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);
// Cloning can't work if we don't have a definition. The Microsoft ABI may
// require thunks when a definition is not available. Emit an error in these
// cases.
if (!MD->isDefined()) {
CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
return Fn;
assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
// Clone to thunk.
llvm::ValueToValueMapTy VMap;
// We are cloning a function while some Metadata nodes are still unresolved.
// Ensure that the value mapper does not encounter any of them.
resolveTopLevelMetadata(BaseFn, 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);
AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
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,
bool IsUnprototyped) {
assert(!CurGD.getDecl() && "CurGD was already set!");
CurGD = GD;
CurFuncIsThunk = true;
// Build FunctionArgs.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
QualType ThisType = MD->getThisType();
QualType ResultType;
if (IsUnprototyped)
ResultType = CGM.getContext().VoidTy;
else if (CGM.getCXXABI().HasThisReturn(GD))
ResultType = ThisType;
else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
ResultType = CGM.getContext().VoidPtrTy;
ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
FunctionArgList FunctionArgs;
// Create the implicit 'this' parameter declaration.
CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
// Add the rest of the parameters, if we have a prototype to work with.
if (!IsUnprototyped) {
FunctionArgs.append(MD->param_begin(), MD->param_end());
if (isa<CXXDestructorDecl>(MD))
CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
// 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::FunctionCallee Callee,
const ThunkInfo *Thunk,
bool IsUnprototyped) {
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 perfect forwarding is required a variadic method, a method using
// inalloca, or an unprototyped thunk, use musttail. Emit an error if this
// thunk requires a return adjustment, since that is impossible with musttail.
if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
if (Thunk && !Thunk->Return.isEmpty()) {
if (IsUnprototyped)
MD, "return-adjusting thunk with incomplete parameter type");
else if (CurFnInfo->isVariadic())
llvm_unreachable("shouldn't try to emit musttail return-adjusting "
"thunks for variadic functions");
MD, "non-trivial argument copy for return-adjusting thunk");
EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
// Start building CallArgs.
CallArgList CallArgs;
QualType ThisType = MD->getThisType();
CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
if (isa<CXXDestructorDecl>(MD))
CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
#ifndef NDEBUG
unsigned PrefixArgs = CallArgs.size() - 1;
// Add the rest of the arguments.
for (const ParmVarDecl *PD : MD->parameters())
EmitDelegateCallArg(CallArgs, PD, SourceLocation());
const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
#ifndef NDEBUG
const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
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(),
/*IsUnused=*/false, /*IsExternallyDestructed=*/true);
// Now emit our call.
llvm::CallBase *CallOrInvoke;
RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), 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(GlobalDecl GD,
llvm::Value *AdjustedThisPtr,
llvm::FunctionCallee Callee) {
// 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(Callee, Args);
// Apply the standard set of call attributes.
unsigned CallingConv;
llvm::AttributeList Attrs;
CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
Attrs, CallingConv, /*AttrOnCallSite=*/true);
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,
bool IsUnprototyped) {
StartThunk(Fn, GD, FnInfo, IsUnprototyped);
// Create a scope with an artificial location for the body of this function.
auto AL = ApplyDebugLocation::CreateArtificial(*this);
// Get our callee. Use a placeholder type if this method is unprototyped so
// that CodeGenModule doesn't try to set attributes.
llvm::Type *Ty;
if (IsUnprototyped)
Ty = llvm::StructType::get(getLLVMContext());
Ty = CGM.getTypes().GetFunctionType(FnInfo);
llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
// Fix up the function type for an unprototyped musttail call.
if (IsUnprototyped)
Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
// Make the call and return the result.
EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
&Thunk, IsUnprototyped);
static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
bool IsUnprototyped, bool ForVTable) {
// Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
// provide thunks for us.
if (CGM.getTarget().getCXXABI().isMicrosoft())
return true;
// In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
// definitions of the main method. Therefore, emitting thunks with the vtable
// is purely an optimization. Emit the thunk if optimizations are enabled and
// all of the parameter types are complete.
if (ForVTable)
return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
// Always emit thunks along with the method definition.
return true;
llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
const ThunkInfo &TI,
bool ForVTable) {
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
// First, get a declaration. Compute the mangled name. Don't worry about
// getting the function prototype right, since we may only need this
// declaration to fill in a vtable slot.
SmallString<256> Name;
MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
llvm::raw_svector_ostream Out(Name);
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
MCtx.mangleThunk(MD, TI, Out);
llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
// If we don't need to emit a definition, return this declaration as is.
bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
return Thunk;
// Arrange a function prototype appropriate for a function definition. In some
// cases in the MS ABI, we may need to build an unprototyped musttail thunk.
const CGFunctionInfo &FnInfo =
IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
: CGM.getTypes().arrangeGlobalDeclaration(GD);
llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
// If the type of the underlying GlobalValue is wrong, we'll have to replace
// it. It should be a declaration.
llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
if (ThunkFn->getFunctionType() != ThunkFnTy) {
llvm::GlobalValue *OldThunkFn = ThunkFn;
assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
// Remove the name from the old thunk function and get a new thunk.
ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
Name.str(), &CGM.getModule());
CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
// If needed, replace the old thunk with a bitcast.
if (!OldThunkFn->use_empty()) {
llvm::Constant *NewPtrForOldDecl =
llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
// Remove the old thunk.
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.
return ThunkFn;
setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
return ThunkFn;
// If this will be unprototyped, add the "thunk" attribute so that LLVM knows
// that the return type is meaningless. These thunks can be used to call
// functions with differing return types, and the caller is required to cast
// the prototype appropriately to extract the correct value.
if (IsUnprototyped)
CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
// Thunks for variadic methods are special because in general variadic
// arguments cannot be perfectly forwarded. In the general case, clang
// implements such thunks by cloning the original function body. However, for
// thunks with no return adjustment on targets that support musttail, we can
// use musttail to perfectly forward the variadic arguments.
bool ShouldCloneVarArgs = false;
if (!IsUnprototyped && ThunkFn->isVarArg()) {
ShouldCloneVarArgs = true;
if (TI.Return.isEmpty()) {
switch (CGM.getTriple().getArch()) {
case llvm::Triple::x86_64:
case llvm::Triple::x86:
case llvm::Triple::aarch64:
ShouldCloneVarArgs = false;
if (ShouldCloneVarArgs) {
if (UseAvailableExternallyLinkage)
return ThunkFn;
ThunkFn =
CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
} else {
// Normal thunk body generation.
CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
return ThunkFn;
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)
maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
llvm::Constant *component,
unsigned vtableAddressPoint,
bool vtableHasLocalLinkage,
bool isCompleteDtor) const {
// No need to get the offset of a nullptr.
if (component->isNullValue())
return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));
auto *globalVal =
llvm::Module &module = CGM.getModule();
// We don't want to copy the linkage of the vtable exactly because we still
// want the stub/proxy to be emitted for properly calculating the offset.
// Examples where there would be no symbol emitted are available_externally
// and private linkages.
auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
: llvm::GlobalValue::ExternalLinkage;
llvm::Constant *target;
if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
target = llvm::DSOLocalEquivalent::get(func);
} else {
llvm::SmallString<16> rttiProxyName(globalVal->getName());
// The RTTI component may not always be emitted in the same linkage unit as
// the vtable. As a general case, we can make a dso_local proxy to the RTTI
// that points to the actual RTTI struct somewhere. This will result in a
// GOTPCREL relocation when taking the relative offset to the proxy.
llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);
if (!proxy) {
proxy = new llvm::GlobalVariable(module, globalVal->getType(),
/*isConstant=*/true, stubLinkage,
globalVal, rttiProxyName);
if (!proxy->hasLocalLinkage()) {
target = proxy;
builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,
bool CodeGenVTables::useRelativeLayout() const {
return CGM.getTarget().getCXXABI().isItaniumFamily() &&
llvm::Type *CodeGenVTables::getVTableComponentType() const {
if (useRelativeLayout())
return CGM.Int32Ty;
return CGM.Int8PtrTy;
static void AddPointerLayoutOffset(const CodeGenModule &CGM,
ConstantArrayBuilder &builder,
CharUnits offset) {
llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
ConstantArrayBuilder &builder,
CharUnits offset) {
builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));
void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
const VTableLayout &layout,
unsigned componentIndex,
llvm::Constant *rtti,
unsigned &nextVTableThunkIndex,
unsigned vtableAddressPoint,
bool vtableHasLocalLinkage) {
auto &component = layout.vtable_components()[componentIndex];
auto addOffsetConstant =
useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
switch (component.getKind()) {
case VTableComponent::CK_VCallOffset:
return addOffsetConstant(CGM, builder, component.getVCallOffset());
case VTableComponent::CK_VBaseOffset:
return addOffsetConstant(CGM, builder, component.getVBaseOffset());
case VTableComponent::CK_OffsetToTop:
return addOffsetConstant(CGM, builder, component.getOffsetToTop());
case VTableComponent::CK_RTTI:
if (useRelativeLayout())
return addRelativeComponent(builder, rtti, vtableAddressPoint,
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.add(llvm::ConstantExpr::getNullValue(CGM.Int8PtrTy));
// Method is acceptable, continue processing as usual.
auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
// FIXME(PR43094): When merging comdat groups, lld can select a local
// symbol as the signature symbol even though it cannot be accessed
// outside that symbol's TU. The relative vtables ABI would make
// __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
// depending on link order, the comdat groups could resolve to the one
// with the local symbol. As a temporary solution, fill these components
// with zero. We shouldn't be calling these in the first place anyway.
if (useRelativeLayout())
return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
// For NVPTX devices in OpenMP emit special functon as null pointers,
// otherwise linking ends up with unresolved references.
if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
llvm::FunctionType *fnTy =
llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
llvm::Constant *fn = cast<llvm::Constant>(
CGM.CreateRuntimeFunction(fnTy, name).getCallee());
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 ==
componentIndex) {
auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
// Otherwise we can use the method definition directly.
} else {
llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
if (useRelativeLayout()) {
return addRelativeComponent(
builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
component.getKind() == VTableComponent::CK_CompleteDtorPointer);
} else
return builder.add(llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy));
case VTableComponent::CK_UnusedFunctionPointer:
if (useRelativeLayout())
return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));
return builder.addNullPointer(CGM.Int8PtrTy);
llvm_unreachable("Unexpected vtable component kind");
llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
SmallVector<llvm::Type *, 4> tys;
llvm::Type *componentType = getVTableComponentType();
for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));
return llvm::StructType::get(CGM.getLLVMContext(), tys);
void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
const VTableLayout &layout,
llvm::Constant *rtti,
bool vtableHasLocalLinkage) {
llvm::Type *componentType = getVTableComponentType();
const auto &addressPoints = layout.getAddressPointIndices();
unsigned nextVTableThunkIndex = 0;
for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
vtableIndex != endIndex; ++vtableIndex) {
auto vtableElem = builder.beginArray(componentType);
size_t vtableStart = layout.getVTableOffset(vtableIndex);
size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);
for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
++componentIndex) {
addVTableComponent(vtableElem, layout, componentIndex, rtti,
nextVTableThunkIndex, addressPoints[vtableIndex],
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);
SmallString<256> Name(OutName);
bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();
bool VTableAliasExists =
UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
if (VTableAliasExists) {
// We previously made the vtable hidden and changed its name.
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;
unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
// Create the variable that will hold the construction vtable.
llvm::GlobalVariable *VTable =
CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
// 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,
// Set properties only after the initializer has been set to ensure that the
// GV is treated as definition and not declaration.
assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
CGM.setGVProperties(VTable, RD);
CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
if (UsingRelativeLayout && !VTable->isDSOLocal())
GenerateRelativeVTableAlias(VTable, OutName);
return VTable;
// If the VTable is not dso_local, then we will not be able to indicate that
// the VTable does not need a relocation and move into rodata. A frequent
// time this can occur is for classes that should be made public from a DSO
// (like in libc++). For cases like these, we can make the vtable hidden or
// private and create a public alias with the same visibility and linkage as
// the original vtable type.
void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
llvm::StringRef AliasNameRef) {
assert(getItaniumVTableContext().isRelativeLayout() &&
"Can only use this if the relative vtable ABI is used");
assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
"not guaranteed to be dso_local");
// If the vtable is available_externally, we shouldn't (or need to) generate
// an alias for it in the first place since the vtable won't actually by
// emitted in this compilation unit.
if (VTable->hasAvailableExternallyLinkage())
// Create a new string in the event the alias is already the name of the
// vtable. Using the reference directly could lead to use of an inititialized
// value in the module's StringMap.
llvm::SmallString<256> AliasName(AliasNameRef);
VTable->setName(AliasName + ".local");
auto Linkage = VTable->getLinkage();
assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
"Invalid vtable alias linkage");
llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);
if (!VTableAlias) {
VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),
VTable->getAddressSpace(), Linkage,
AliasName, &CGM.getModule());
} else {
assert(VTableAlias->getValueType() == VTable->getValueType());
assert(VTableAlias->getLinkage() == Linkage);
// Both of these imply dso_local for the vtable.
if (!VTable->hasComdat()) {
// If this is in a comdat, then we shouldn't make the linkage private due to
// an issue in lld where private symbols can be used as the key symbol when
// choosing the prevelant group. This leads to "relocation refers to a
// symbol in a discarded section".
} else {
// We should at least make this hidden since we don't want to expose it.
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 ||
CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
"Shouldn't query vtable linkage without key function, "
"optimizations, or debug info");
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 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))
else if (shouldOpportunisticallyEmitVTables())
assert(savedSize == DeferredVTables.size() &&
"deferred extra vtables during vtable emission?");
bool CodeGenModule::HasLTOVisibilityPublicStd(const CXXRecordDecl *RD) {
if (!getCodeGenOpts().LTOVisibilityPublicStd)
return false;
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 true;
return false;
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;
return !HasLTOVisibilityPublicStd(RD);
llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
// If we have already visited this RD (which means this is a recursive call
// since the initial call should have an empty Visited set), return the max
// visibility. The recursive calls below compute the min between the result
// of the recursive call and the current TypeVis, so returning the max here
// ensures that it will have no effect on the current TypeVis.
if (!Visited.insert(RD).second)
return llvm::GlobalObject::VCallVisibilityTranslationUnit;
LinkageInfo LV = RD->getLinkageAndVisibility();
llvm::GlobalObject::VCallVisibility TypeVis;
if (!isExternallyVisible(LV.getLinkage()))
TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
else if (HasHiddenLTOVisibility(RD))
TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
for (auto B : RD->bases())
if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
TypeVis = std::min(
GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
for (auto B : RD->vbases())
if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
TypeVis = std::min(
GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
return TypeVis;
void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
llvm::GlobalVariable *VTable,
const VTableLayout &VTLayout) {
if (!getCodeGenOpts().LTOUnit)
CharUnits PointerWidth =
typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
std::vector<AddressPoint> AddressPoints;
for (auto &&AP : VTLayout.getAddressPoints())
AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
// Sort the address points for determinism.
llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
const AddressPoint &AP2) {
if (&AP1 == &AP2)
return false;
std::string S1;
llvm::raw_string_ostream O1(S1);
QualType(AP1.first->getTypeForDecl(), 0), O1);
std::string S2;
llvm::raw_string_ostream O2(S2);
QualType(AP2.first->getTypeForDecl(), 0), O2);
if (S1 < S2)
return true;
if (S1 != S2)
return false;
return AP1.second < AP2.second;
ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
for (auto AP : AddressPoints) {
// Create type metadata for the address point.
AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
// The class associated with each address point could also potentially be
// used for indirect calls via a member function pointer, so we need to
// annotate the address of each function pointer with the appropriate member
// function pointer type.
for (unsigned I = 0; I != Comps.size(); ++I) {
if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
if (getCodeGenOpts().VirtualFunctionElimination ||
getCodeGenOpts().WholeProgramVTables) {
llvm::DenseSet<const CXXRecordDecl *> Visited;
llvm::GlobalObject::VCallVisibility TypeVis =
GetVCallVisibilityLevel(RD, Visited);
if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)