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//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
// 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.
// We might split this into multiple files if it gets too unwieldy
#include "CGCXXABI.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/Mangle.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/StmtCXX.h"
#include "clang/Basic/CodeGenOptions.h"
#include "llvm/ADT/StringExtras.h"
using namespace clang;
using namespace CodeGen;
/// Try to emit a base destructor as an alias to its primary
/// base-class destructor.
bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
if (!getCodeGenOpts().CXXCtorDtorAliases)
return true;
// Producing an alias to a base class ctor/dtor can degrade debug quality
// as the debugger cannot tell them apart.
if (getCodeGenOpts().OptimizationLevel == 0)
return true;
// If sanitizing memory to check for use-after-dtor, do not emit as
// an alias, unless this class owns no members.
if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
return true;
// If the destructor doesn't have a trivial body, we have to emit it
// separately.
if (!D->hasTrivialBody())
return true;
const CXXRecordDecl *Class = D->getParent();
// We are going to instrument this destructor, so give up even if it is
// currently empty.
if (Class->mayInsertExtraPadding())
return true;
// If we need to manipulate a VTT parameter, give up.
if (Class->getNumVBases()) {
// Extra Credit: passing extra parameters is perfectly safe
// in many calling conventions, so only bail out if the ctor's
// calling convention is nonstandard.
return true;
// If any field has a non-trivial destructor, we have to emit the
// destructor separately.
for (const auto *I : Class->fields())
if (I->getType().isDestructedType())
return true;
// Try to find a unique base class with a non-trivial destructor.
const CXXRecordDecl *UniqueBase = nullptr;
for (const auto &I : Class->bases()) {
// We're in the base destructor, so skip virtual bases.
if (I.isVirtual()) continue;
// Skip base classes with trivial destructors.
const auto *Base =
if (Base->hasTrivialDestructor()) continue;
// If we've already found a base class with a non-trivial
// destructor, give up.
if (UniqueBase) return true;
UniqueBase = Base;
// If we didn't find any bases with a non-trivial destructor, then
// the base destructor is actually effectively trivial, which can
// happen if it was needlessly user-defined or if there are virtual
// bases with non-trivial destructors.
if (!UniqueBase)
return true;
// If the base is at a non-zero offset, give up.
const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
return true;
// Give up if the calling conventions don't match. We could update the call,
// but it is probably not worth it.
const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
return true;
GlobalDecl AliasDecl(D, Dtor_Base);
GlobalDecl TargetDecl(BaseD, Dtor_Base);
// The alias will use the linkage of the referent. If we can't
// support aliases with that linkage, fail.
llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
// We can't use an alias if the linkage is not valid for one.
if (!llvm::GlobalAlias::isValidLinkage(Linkage))
return true;
llvm::GlobalValue::LinkageTypes TargetLinkage =
// Check if we have it already.
StringRef MangledName = getMangledName(AliasDecl);
llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
if (Entry && !Entry->isDeclaration())
return false;
if (Replacements.count(MangledName))
return false;
// Derive the type for the alias.
llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
llvm::PointerType *AliasType = AliasValueType->getPointerTo();
// Find the referent. Some aliases might require a bitcast, in
// which case the caller is responsible for ensuring the soundness
// of these semantics.
auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
llvm::Constant *Aliasee = Ref;
if (Ref->getType() != AliasType)
Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
// Instead of creating as alias to a linkonce_odr, replace all of the uses
// of the aliasee.
if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
!(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
// FIXME: An extern template instantiation will create functions with
// linkage "AvailableExternally". In libc++, some classes also define
// members with attribute "AlwaysInline" and expect no reference to
// be generated. It is desirable to reenable this optimisation after
// corresponding LLVM changes.
addReplacement(MangledName, Aliasee);
return false;
// If we have a weak, non-discardable alias (weak, weak_odr), like an extern
// template instantiation or a dllexported class, avoid forming it on COFF.
// A COFF weak external alias cannot satisfy a normal undefined symbol
// reference from another TU. The other TU must also mark the referenced
// symbol as weak, which we cannot rely on.
if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
getTriple().isOSBinFormatCOFF()) {
return true;
// If we don't have a definition for the destructor yet or the definition is
// avaialable_externally, don't emit an alias. We can't emit aliases to
// declarations; that's just not how aliases work.
if (Ref->isDeclarationForLinker())
return true;
// Don't create an alias to a linker weak symbol. This avoids producing
// different COMDATs in different TUs. Another option would be to
// output the alias both for weak_odr and linkonce_odr, but that
// requires explicit comdat support in the IL.
if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
return true;
// Create the alias with no name.
auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
Aliasee, &getModule());
// Destructors are always unnamed_addr.
// Switch any previous uses to the alias.
if (Entry) {
assert(Entry->getType() == AliasType &&
"declaration exists with different type");
} else {
// Finally, set up the alias with its proper name and attributes.
SetCommonAttributes(AliasDecl, Alias);
return false;
llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
auto *Fn = cast<llvm::Function>(
getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
/*DontDefer=*/true, ForDefinition));
setFunctionLinkage(GD, Fn);
CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
setNonAliasAttributes(GD, Fn);
SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
return Fn;
llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
bool DontDefer, ForDefinition_t IsForDefinition) {
auto *MD = cast<CXXMethodDecl>(GD.getDecl());
if (isa<CXXDestructorDecl>(MD)) {
// Always alias equivalent complete destructors to base destructors in the
// MS ABI.
if (getTarget().getCXXABI().isMicrosoft() &&
GD.getDtorType() == Dtor_Complete &&
MD->getParent()->getNumVBases() == 0)
GD = GD.getWithDtorType(Dtor_Base);
if (!FnType) {
if (!FnInfo)
FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
FnType = getTypes().GetFunctionType(*FnInfo);
llvm::Constant *Ptr = GetOrCreateLLVMFunction(
getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
/*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
return {FnType, Ptr};
static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
GlobalDecl GD,
llvm::Type *Ty,
const CXXRecordDecl *RD) {
assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
"No kext in Microsoft ABI");
CodeGenModule &CGM = CGF.CGM;
llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
Ty = Ty->getPointerTo();
VTable = CGF.Builder.CreateBitCast(VTable, Ty->getPointerTo());
assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
VTableLayout::AddressPointLocation AddressPoint =
VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
llvm::Value *VFuncPtr =
CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
CGCallee Callee(GD, VFunc);
return Callee;
/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
/// indirect call to virtual functions. It makes the call through indexing
/// into the vtable.
CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
NestedNameSpecifier *Qual,
llvm::Type *Ty) {
assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
"BuildAppleKextVirtualCall - bad Qual kind");
const Type *QTy = Qual->getAsType();
QualType T = QualType(QTy, 0);
const RecordType *RT = T->getAs<RecordType>();
assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
/// BuildVirtualCall - This routine makes indirect vtable call for
/// call to virtual destructors. It returns 0 if it could not do it.
const CXXDestructorDecl *DD,
CXXDtorType Type,
const CXXRecordDecl *RD) {
assert(DD->isVirtual() && Type != Dtor_Base);
// Compute the function type we're calling.
const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
GlobalDecl(DD, Dtor_Complete));
llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);