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llvm-project/clang/lib/CodeGen/CGVTables.cpp

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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 "CodeGenFunction.h"
#include "CGCXXABI.h"
#include "CodeGenModule.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Support/Compiler.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()) { }
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);
else
getCXXABI().getMangleContext().mangleThunk(MD, Thunk, Out);
Out.flush();
llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true);
}
static llvm::Value *PerformTypeAdjustment(CodeGenFunction &CGF,
llvm::Value *Ptr,
int64_t NonVirtualAdjustment,
int64_t VirtualAdjustment,
bool IsReturnAdjustment) {
if (!NonVirtualAdjustment && !VirtualAdjustment)
return Ptr;
llvm::Type *Int8PtrTy = CGF.Int8PtrTy;
llvm::Value *V = CGF.Builder.CreateBitCast(Ptr, Int8PtrTy);
if (NonVirtualAdjustment && !IsReturnAdjustment) {
// Perform the non-virtual adjustment for a base-to-derived cast.
V = CGF.Builder.CreateConstInBoundsGEP1_64(V, NonVirtualAdjustment);
}
if (VirtualAdjustment) {
llvm::Type *PtrDiffTy =
CGF.ConvertType(CGF.getContext().getPointerDiffType());
// Perform the virtual adjustment.
llvm::Value *VTablePtrPtr =
CGF.Builder.CreateBitCast(V, Int8PtrTy->getPointerTo());
llvm::Value *VTablePtr = CGF.Builder.CreateLoad(VTablePtrPtr);
llvm::Value *OffsetPtr =
CGF.Builder.CreateConstInBoundsGEP1_64(VTablePtr, VirtualAdjustment);
OffsetPtr = CGF.Builder.CreateBitCast(OffsetPtr, PtrDiffTy->getPointerTo());
// Load the adjustment offset from the vtable.
llvm::Value *Offset = CGF.Builder.CreateLoad(OffsetPtr);
// Adjust our pointer.
V = CGF.Builder.CreateInBoundsGEP(V, Offset);
}
if (NonVirtualAdjustment && IsReturnAdjustment) {
// Perform the non-virtual adjustment for a derived-to-base cast.
V = CGF.Builder.CreateConstInBoundsGEP1_64(V, NonVirtualAdjustment);
}
// Cast back to the original type.
return CGF.Builder.CreateBitCast(V, Ptr->getType());
}
static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
const ThunkInfo &Thunk, llvm::Function *Fn) {
CGM.setGlobalVisibility(Fn, MD);
if (!CGM.getCodeGenOpts().HiddenWeakVTables)
return;
// If the thunk has weak/linkonce linkage, but the function must be
// emitted in every translation unit that references it, then we can
// emit its thunks with hidden visibility, since its thunks must be
// emitted when the function is.
// This follows CodeGenModule::setTypeVisibility; see the comments
// there for explanation.
if ((Fn->getLinkage() != llvm::GlobalVariable::LinkOnceODRLinkage &&
Fn->getLinkage() != llvm::GlobalVariable::WeakODRLinkage) ||
Fn->getVisibility() != llvm::GlobalVariable::DefaultVisibility)
return;
if (MD->getExplicitVisibility(ValueDecl::VisibilityForValue))
return;
switch (MD->getTemplateSpecializationKind()) {
case TSK_ExplicitInstantiationDefinition:
case TSK_ExplicitInstantiationDeclaration:
return;
case TSK_Undeclared:
break;
case TSK_ExplicitSpecialization:
case TSK_ImplicitInstantiation:
return;
break;
}
// If there's an explicit definition, and that definition is
// out-of-line, then we can't assume that all users will have a
// definition to emit.
const FunctionDecl *Def = 0;
if (MD->hasBody(Def) && Def->isOutOfLine())
return;
Fn->setVisibility(llvm::GlobalValue::HiddenVisibility);
}
#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))));
}
#endif
static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
QualType ResultType, RValue RV,
const ThunkInfo &Thunk) {
// Emit the return adjustment.
bool NullCheckValue = !ResultType->isReferenceType();
llvm::BasicBlock *AdjustNull = 0;
llvm::BasicBlock *AdjustNotNull = 0;
llvm::BasicBlock *AdjustEnd = 0;
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);
CGF.EmitBlock(AdjustNotNull);
}
ReturnValue = PerformTypeAdjustment(CGF, ReturnValue,
Thunk.Return.NonVirtual,
Thunk.Return.VBaseOffsetOffset,
/*IsReturnAdjustment*/true);
if (NullCheckValue) {
CGF.Builder.CreateBr(AdjustEnd);
CGF.EmitBlock(AdjustNull);
CGF.Builder.CreateBr(AdjustEnd);
CGF.EmitBlock(AdjustEnd);
llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
PHI->addIncoming(ReturnValue, AdjustNotNull);
PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
AdjustNull);
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.
void 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->getResultType();
// Get the original function
assert(FnInfo.isVariadic());
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,
/*ModuleLevelChanges=*/false);
CGM.getModule().getFunctionList().push_back(NewFn);
Fn->replaceAllUsesWith(NewFn);
NewFn->takeName(Fn);
Fn->eraseFromParent();
Fn = NewFn;
// "Initialize" CGF (minimally).
CurFn = Fn;
// Get the "this" value
llvm::Function::arg_iterator AI = Fn->arg_begin();
if (CGM.ReturnTypeUsesSRet(FnInfo))
++AI;
// Find the first store of "this", which will be to the alloca associated
// with "this".
llvm::Value *ThisPtr = &*AI;
llvm::BasicBlock *EntryBB = Fn->begin();
llvm::Instruction *ThisStore = 0;
for (llvm::BasicBlock::iterator I = EntryBB->begin(), E = EntryBB->end();
I != E; I++) {
if (isa<llvm::StoreInst>(I) && I->getOperand(0) == ThisPtr) {
ThisStore = cast<llvm::StoreInst>(I);
break;
}
}
assert(ThisStore && "Store of this should be in entry block?");
// Adjust "this", if necessary.
Builder.SetInsertPoint(ThisStore);
llvm::Value *AdjustedThisPtr =
PerformTypeAdjustment(*this, ThisPtr,
Thunk.This.NonVirtual,
Thunk.This.VCallOffsetOffset,
/*IsReturnAdjustment*/false);
ThisStore->setOperand(0, AdjustedThisPtr);
if (!Thunk.Return.isEmpty()) {
// Fix up the returned value, if necessary.
for (llvm::Function::iterator I = Fn->begin(), E = Fn->end(); I != E; I++) {
llvm::Instruction *T = I->getTerminator();
if (isa<llvm::ReturnInst>(T)) {
RValue RV = RValue::get(T->getOperand(0));
T->eraseFromParent();
Builder.SetInsertPoint(&*I);
RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
Builder.CreateRet(RV.getScalarVal());
break;
}
}
}
}
void CodeGenFunction::GenerateThunk(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->getResultType();
QualType ThisType = MD->getThisType(getContext());
FunctionArgList FunctionArgs;
// FIXME: It would be nice if more of this code could be shared with
// CodeGenFunction::GenerateCode.
// Create the implicit 'this' parameter declaration.
CurGD = GD;
CGM.getCXXABI().BuildInstanceFunctionParams(*this, ResultType, FunctionArgs);
// Add the rest of the parameters.
for (FunctionDecl::param_const_iterator I = MD->param_begin(),
E = MD->param_end(); I != E; ++I) {
ParmVarDecl *Param = *I;
FunctionArgs.push_back(Param);
}
// Initialize debug info if needed.
maybeInitializeDebugInfo();
StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
SourceLocation());
CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
CXXThisValue = CXXABIThisValue;
// Adjust the 'this' pointer if necessary.
llvm::Value *AdjustedThisPtr =
PerformTypeAdjustment(*this, LoadCXXThis(),
Thunk.This.NonVirtual,
Thunk.This.VCallOffsetOffset,
/*IsReturnAdjustment*/false);
CallArgList CallArgs;
// Add our adjusted 'this' pointer.
CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
// Add the rest of the parameters.
for (FunctionDecl::param_const_iterator I = MD->param_begin(),
E = MD->param_end(); I != E; ++I) {
ParmVarDecl *param = *I;
EmitDelegateCallArg(CallArgs, param);
}
// Get our callee.
llvm::Type *Ty =
CGM.getTypes().GetFunctionType(CGM.getTypes().arrangeGlobalDeclaration(GD));
llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
#ifndef NDEBUG
const CGFunctionInfo &CallFnInfo =
CGM.getTypes().arrangeCXXMethodCall(CallArgs, FPT,
RequiredArgs::forPrototypePlus(FPT, 1));
assert(CallFnInfo.getRegParm() == FnInfo.getRegParm() &&
CallFnInfo.isNoReturn() == FnInfo.isNoReturn() &&
CallFnInfo.getCallingConvention() == FnInfo.getCallingConvention());
assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
FnInfo.getReturnInfo(), FnInfo.getReturnType()));
assert(CallFnInfo.arg_size() == FnInfo.arg_size());
for (unsigned i = 0, e = FnInfo.arg_size(); i != e; ++i)
assert(similar(CallFnInfo.arg_begin()[i].info,
CallFnInfo.arg_begin()[i].type,
FnInfo.arg_begin()[i].info, FnInfo.arg_begin()[i].type));
#endif
// Determine whether we have a return value slot to use.
ReturnValueSlot Slot;
if (!ResultType->isVoidType() &&
FnInfo.getReturnInfo().getKind() == ABIArgInfo::Indirect &&
!hasScalarEvaluationKind(CurFnInfo->getReturnType()))
Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
// Now emit our call.
RValue RV = EmitCall(FnInfo, Callee, Slot, CallArgs, MD);
if (!Thunk.Return.isEmpty())
RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
if (!ResultType->isVoidType() && Slot.isNull())
CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
// Disable the final ARC autorelease.
AutoreleaseResult = false;
FinishFunction();
// Set the right linkage.
CGM.setFunctionLinkage(MD, Fn);
// Set the right visibility.
setThunkVisibility(CGM, MD, Thunk, Fn);
}
void CodeGenVTables::EmitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
bool UseAvailableExternallyLinkage)
{
const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
// FIXME: re-use FnInfo in this computation.
llvm::Constant *Entry = CGM.GetAddrOfThunk(GD, Thunk);
// Strip off a bitcast if we got one back.
if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(Entry)) {
assert(CE->getOpcode() == llvm::Instruction::BitCast);
Entry = CE->getOperand(0);
}
// There's already a declaration with the same name, check if it has the same
// type or if we need to replace it.
if (cast<llvm::GlobalValue>(Entry)->getType()->getElementType() !=
CGM.getTypes().GetFunctionTypeForVTable(GD)) {
llvm::GlobalValue *OldThunkFn = cast<llvm::GlobalValue>(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.
OldThunkFn->setName(StringRef());
Entry = 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());
OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
}
// Remove the old thunk.
OldThunkFn->eraseFromParent();
}
llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
if (!ThunkFn->isDeclaration()) {
if (UseAvailableExternallyLinkage) {
// There is already a thunk emitted for this function, do nothing.
return;
}
// If a function has a body, it should have available_externally linkage.
assert(ThunkFn->hasAvailableExternallyLinkage() &&
"Function should have available_externally linkage!");
// Change the linkage.
CGM.setFunctionLinkage(cast<CXXMethodDecl>(GD.getDecl()), ThunkFn);
return;
}
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)
CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
} else {
// Normal thunk body generation.
CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
}
if (UseAvailableExternallyLinkage)
ThunkFn->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
}
void CodeGenVTables::MaybeEmitThunkAvailableExternally(GlobalDecl GD,
const ThunkInfo &Thunk) {
// We only want to do this when building with optimizations.
if (!CGM.getCodeGenOpts().OptimizationLevel)
return;
// We can't emit thunks for member functions with incomplete types.
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
if (!CGM.getTypes().isFuncTypeConvertible(
cast<FunctionType>(MD->getType().getTypePtr())))
return;
EmitThunk(GD, Thunk, /*UseAvailableExternallyLinkage=*/true);
}
void CodeGenVTables::EmitThunks(GlobalDecl GD)
{
const CXXMethodDecl *MD =
cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
// We don't need to generate thunks for the base destructor.
if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
return;
const VTableContext::ThunkInfoVectorTy *ThunkInfoVector =
VTContext.getThunkInfo(MD);
if (!ThunkInfoVector)
return;
for (unsigned I = 0, E = ThunkInfoVector->size(); I != E; ++I)
EmitThunk(GD, (*ThunkInfoVector)[I],
/*UseAvailableExternallyLinkage=*/false);
}
llvm::Constant *
CodeGenVTables::CreateVTableInitializer(const CXXRecordDecl *RD,
const VTableComponent *Components,
unsigned NumComponents,
const VTableLayout::VTableThunkTy *VTableThunks,
unsigned NumVTableThunks) {
SmallVector<llvm::Constant *, 64> Inits;
llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
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 = 0, *DeletedVirtualFn = 0;
for (unsigned I = 0; I != NumComponents; ++I) {
VTableComponent Component = Components[I];
llvm::Constant *Init = 0;
switch (Component.getKind()) {
case VTableComponent::CK_VCallOffset:
Init = llvm::ConstantInt::get(PtrDiffTy,
Component.getVCallOffset().getQuantity());
Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
break;
case VTableComponent::CK_VBaseOffset:
Init = llvm::ConstantInt::get(PtrDiffTy,
Component.getVBaseOffset().getQuantity());
Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
break;
case VTableComponent::CK_OffsetToTop:
Init = llvm::ConstantInt::get(PtrDiffTy,
Component.getOffsetToTop().getQuantity());
Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
break;
case VTableComponent::CK_RTTI:
Init = llvm::ConstantExpr::getBitCast(RTTI, Int8PtrTy);
break;
case VTableComponent::CK_FunctionPointer:
case VTableComponent::CK_CompleteDtorPointer:
case VTableComponent::CK_DeletingDtorPointer: {
GlobalDecl GD;
// Get the right global decl.
switch (Component.getKind()) {
default:
llvm_unreachable("Unexpected vtable component kind");
case VTableComponent::CK_FunctionPointer:
GD = Component.getFunctionDecl();
break;
case VTableComponent::CK_CompleteDtorPointer:
GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Complete);
break;
case VTableComponent::CK_DeletingDtorPointer:
GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Deleting);
break;
}
if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
// We have a pure virtual member function.
if (!PureVirtualFn) {
llvm::FunctionType *Ty =
llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
CGM.Int8PtrTy);
}
Init = PureVirtualFn;
} else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
if (!DeletedVirtualFn) {
llvm::FunctionType *Ty =
llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
StringRef DeletedCallName =
CGM.getCXXABI().GetDeletedVirtualCallName();
DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
CGM.Int8PtrTy);
}
Init = DeletedVirtualFn;
} else {
// Check if we should use a thunk.
if (NextVTableThunkIndex < NumVTableThunks &&
VTableThunks[NextVTableThunkIndex].first == I) {
const ThunkInfo &Thunk = VTableThunks[NextVTableThunkIndex].second;
MaybeEmitThunkAvailableExternally(GD, Thunk);
Init = CGM.GetAddrOfThunk(GD, Thunk);
NextVTableThunkIndex++;
} else {
llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVTable(GD);
Init = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
}
Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
}
break;
}
case VTableComponent::CK_UnusedFunctionPointer:
Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
break;
};
Inits.push_back(Init);
}
llvm::ArrayType *ArrayType = llvm::ArrayType::get(Int8PtrTy, NumComponents);
return llvm::ConstantArray::get(ArrayType, Inits);
}
llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTable(const CXXRecordDecl *RD) {
llvm::GlobalVariable *&VTable = VTables[RD];
if (VTable)
return VTable;
// Queue up this v-table for possible deferred emission.
CGM.addDeferredVTable(RD);
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
CGM.getCXXABI().getMangleContext().mangleCXXVTable(RD, Out);
Out.flush();
StringRef Name = OutName.str();
llvm::ArrayType *ArrayType =
llvm::ArrayType::get(CGM.Int8PtrTy,
VTContext.getVTableLayout(RD).getNumVTableComponents());
VTable =
CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType,
llvm::GlobalValue::ExternalLinkage);
VTable->setUnnamedAddr(true);
return VTable;
}
void
CodeGenVTables::EmitVTableDefinition(llvm::GlobalVariable *VTable,
llvm::GlobalVariable::LinkageTypes Linkage,
const CXXRecordDecl *RD) {
const VTableLayout &VTLayout = VTContext.getVTableLayout(RD);
// Create and set the initializer.
llvm::Constant *Init =
CreateVTableInitializer(RD,
VTLayout.vtable_component_begin(),
VTLayout.getNumVTableComponents(),
VTLayout.vtable_thunk_begin(),
VTLayout.getNumVTableThunks());
VTable->setInitializer(Init);
// Set the correct linkage.
VTable->setLinkage(Linkage);
// Set the right visibility.
CGM.setTypeVisibility(VTable, RD, CodeGenModule::TVK_ForVTable);
}
llvm::GlobalVariable *
CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
const BaseSubobject &Base,
bool BaseIsVirtual,
llvm::GlobalVariable::LinkageTypes Linkage,
VTableAddressPointsMapTy& AddressPoints) {
OwningPtr<VTableLayout> VTLayout(
VTContext.createConstructionVTableLayout(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);
CGM.getCXXABI().getMangleContext().
mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(), Base.getBase(),
Out);
Out.flush();
StringRef Name = OutName.str();
llvm::ArrayType *ArrayType =
llvm::ArrayType::get(CGM.Int8PtrTy, VTLayout->getNumVTableComponents());
// 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, ArrayType, Linkage);
CGM.setTypeVisibility(VTable, RD, CodeGenModule::TVK_ForConstructionVTable);
// V-tables are always unnamed_addr.
VTable->setUnnamedAddr(true);
// Create and set the initializer.
llvm::Constant *Init =
CreateVTableInitializer(Base.getBase(),
VTLayout->vtable_component_begin(),
VTLayout->getNumVTableComponents(),
VTLayout->vtable_thunk_begin(),
VTLayout->getNumVTableThunks());
VTable->setInitializer(Init);
return VTable;
}
/// Compute the required linkage of the v-table for the given class.
///
/// Note that we only call this at the end of the translation unit.
llvm::GlobalVariable::LinkageTypes
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.
if (const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD)) {
// If this class has a key function, use that to determine the
// linkage of the vtable.
const FunctionDecl *def = 0;
if (keyFunction->hasBody(def))
keyFunction = cast<CXXMethodDecl>(def);
switch (keyFunction->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
// When compiling with optimizations turned on, we emit all vtables,
// even if the key function is not defined in the current translation
// unit. If this is the case, use available_externally linkage.
if (!def && CodeGenOpts.OptimizationLevel)
return llvm::GlobalVariable::AvailableExternallyLinkage;
if (keyFunction->isInlined())
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::LinkOnceODRLinkage :
llvm::Function::InternalLinkage;
return llvm::GlobalVariable::ExternalLinkage;
case TSK_ImplicitInstantiation:
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::LinkOnceODRLinkage :
llvm::Function::InternalLinkage;
case TSK_ExplicitInstantiationDefinition:
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::WeakODRLinkage :
llvm::Function::InternalLinkage;
case TSK_ExplicitInstantiationDeclaration:
return !Context.getLangOpts().AppleKext ?
llvm::GlobalVariable::AvailableExternallyLinkage :
llvm::Function::InternalLinkage;
}
}
// -fapple-kext mode does not support weak linkage, so we must use
// internal linkage.
if (Context.getLangOpts().AppleKext)
return llvm::Function::InternalLinkage;
switch (RD->getTemplateSpecializationKind()) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
case TSK_ImplicitInstantiation:
return llvm::GlobalVariable::LinkOnceODRLinkage;
case TSK_ExplicitInstantiationDeclaration:
return llvm::GlobalVariable::AvailableExternallyLinkage;
case TSK_ExplicitInstantiationDefinition:
return llvm::GlobalVariable::WeakODRLinkage;
}
llvm_unreachable("Invalid TemplateSpecializationKind!");
}
/// This is a callback from Sema to tell us that it believes that a
/// particular v-table is required to be emitted in this translation
/// unit.
///
/// The reason we don't simply trust this callback is because Sema
/// will happily report that something is used even when it's used
/// only in code that we don't actually have to emit.
///
/// \param isRequired - if true, the v-table is mandatory, e.g.
/// because the translation unit defines the key function
void CodeGenModule::EmitVTable(CXXRecordDecl *theClass, bool isRequired) {
if (!isRequired) return;
VTables.GenerateClassData(theClass);
}
void
CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
// First off, check whether we've already emitted the v-table and
// associated stuff.
llvm::GlobalVariable *VTable = GetAddrOfVTable(RD);
if (VTable->hasInitializer())
return;
llvm::GlobalVariable::LinkageTypes Linkage = CGM.getVTableLinkage(RD);
EmitVTableDefinition(VTable, Linkage, RD);
if (RD->getNumVBases()) {
if (!CGM.getTarget().getCXXABI().isMicrosoft()) {
llvm::GlobalVariable *VTT = GetAddrOfVTT(RD);
EmitVTTDefinition(VTT, Linkage, RD);
} else {
// FIXME: Emit vbtables here.
}
}
// If this is the magic class __cxxabiv1::__fundamental_type_info,
// we will emit the typeinfo for the fundamental types. This is the
// same behaviour as GCC.
const DeclContext *DC = RD->getDeclContext();
if (RD->getIdentifier() &&
RD->getIdentifier()->isStr("__fundamental_type_info") &&
isa<NamespaceDecl>(DC) &&
cast<NamespaceDecl>(DC)->getIdentifier() &&
cast<NamespaceDecl>(DC)->getIdentifier()->isStr("__cxxabiv1") &&
DC->getParent()->isTranslationUnit())
CGM.EmitFundamentalRTTIDescriptors();
}
/// 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 v-table definition when that v-table is defined
/// strongly elsewhere. Otherwise, we'd just like to avoid emitting
/// v-tables when unnecessary.
bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
assert(RD->isDynamicClass() && "Non dynamic classes have no VTable.");
// If we have an explicit instantiation declaration (and not a
// definition), the v-table is defined elsewhere.
TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
if (TSK == TSK_ExplicitInstantiationDeclaration)
return true;
// Otherwise, if the class is an instantiated template, the
// v-table 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 v-table 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
// v-table 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 v-table for this class, should
/// we define that v-table?
static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
const CXXRecordDecl *RD) {
// If we're building with optimization, we always emit v-tables
// since that allows for virtual function calls to be devirtualized.
// If the v-table is defined strongly elsewhere, this definition
// will be emitted available_externally.
//
// However, we don't want to do this in -fapple-kext mode, because
// kext mode does not permit devirtualization.
if (CGM.getCodeGenOpts().OptimizationLevel && !CGM.getLangOpts().AppleKext)
return true;
return !CGM.getVTables().isVTableExternal(RD);
}
/// Given that at some point we emitted a reference to one or more
/// v-tables, 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();
#endif
typedef std::vector<const CXXRecordDecl *>::const_iterator const_iterator;
for (const_iterator i = DeferredVTables.begin(),
e = DeferredVTables.end(); i != e; ++i) {
const CXXRecordDecl *RD = *i;
if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
VTables.GenerateClassData(RD);
}
assert(savedSize == DeferredVTables.size() &&
"deferred extra v-tables during v-table emission?");
DeferredVTables.clear();
}
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