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

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//===--- CGVtable.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 "CodeGenModule.h"
#include "CodeGenFunction.h"
#include "clang/AST/RecordLayout.h"
using namespace clang;
using namespace CodeGen;
class VtableBuilder {
public:
/// Index_t - Vtable index type.
typedef uint64_t Index_t;
private:
std::vector<llvm::Constant *> &methods;
std::vector<llvm::Constant *> submethods;
llvm::Type *Ptr8Ty;
/// Class - The most derived class that this vtable is being built for.
const CXXRecordDecl *Class;
/// BLayout - Layout for the most derived class that this vtable is being
/// built for.
const ASTRecordLayout &BLayout;
llvm::SmallSet<const CXXRecordDecl *, 32> IndirectPrimary;
llvm::SmallSet<const CXXRecordDecl *, 32> SeenVBase;
llvm::Constant *rtti;
llvm::LLVMContext &VMContext;
CodeGenModule &CGM; // Per-module state.
/// Index - Maps a method decl into a vtable index. Useful for virtual
/// dispatch codegen.
llvm::DenseMap<const CXXMethodDecl *, Index_t> Index;
llvm::DenseMap<const CXXMethodDecl *, Index_t> VCall;
llvm::DenseMap<const CXXMethodDecl *, Index_t> VCallOffset;
llvm::DenseMap<const CXXRecordDecl *, Index_t> VBIndex;
typedef std::pair<Index_t, Index_t> CallOffset;
typedef llvm::DenseMap<const CXXMethodDecl *, CallOffset> Thunks_t;
Thunks_t Thunks;
typedef llvm::DenseMap<const CXXMethodDecl *,
std::pair<std::pair<CallOffset, CallOffset>,
CanQualType> > CovariantThunks_t;
CovariantThunks_t CovariantThunks;
std::vector<Index_t> VCalls;
typedef CXXRecordDecl::method_iterator method_iter;
// FIXME: Linkage should follow vtable
const bool Extern;
const uint32_t LLVMPointerWidth;
Index_t extra;
public:
VtableBuilder(std::vector<llvm::Constant *> &meth,
const CXXRecordDecl *c,
CodeGenModule &cgm)
: methods(meth), Class(c), BLayout(cgm.getContext().getASTRecordLayout(c)),
rtti(cgm.GenerateRtti(c)), VMContext(cgm.getModule().getContext()),
CGM(cgm), Extern(true),
LLVMPointerWidth(cgm.getContext().Target.getPointerWidth(0)) {
Ptr8Ty = llvm::PointerType::get(llvm::Type::getInt8Ty(VMContext), 0);
}
llvm::DenseMap<const CXXMethodDecl *, Index_t> &getIndex() { return Index; }
llvm::DenseMap<const CXXRecordDecl *, Index_t> &getVBIndex()
{ return VBIndex; }
llvm::Constant *wrap(Index_t i) {
llvm::Constant *m;
m = llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext), i);
return llvm::ConstantExpr::getIntToPtr(m, Ptr8Ty);
}
llvm::Constant *wrap(llvm::Constant *m) {
return llvm::ConstantExpr::getBitCast(m, Ptr8Ty);
}
void GenerateVBaseOffsets(std::vector<llvm::Constant *> &offsets,
const CXXRecordDecl *RD, uint64_t Offset,
bool updateVBIndex) {
for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
e = RD->bases_end(); i != e; ++i) {
const CXXRecordDecl *Base =
cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
if (i->isVirtual() && !SeenVBase.count(Base)) {
SeenVBase.insert(Base);
int64_t BaseOffset = -(Offset/8) + BLayout.getVBaseClassOffset(Base)/8;
llvm::Constant *m = wrap(BaseOffset);
m = wrap((0?700:0) + BaseOffset);
if (updateVBIndex)
VBIndex[Base] = (ssize_t)(-(offsets.size()*LLVMPointerWidth/8)
- 3*LLVMPointerWidth/8);
offsets.push_back(m);
}
GenerateVBaseOffsets(offsets, Base, Offset, updateVBIndex);
}
}
void StartNewTable() {
SeenVBase.clear();
}
Index_t VBlookup(CXXRecordDecl *D, CXXRecordDecl *B);
/// getVbaseOffset - Returns the index into the vtable for the virtual base
/// offset for the given (B) virtual base of the derived class D.
Index_t getVbaseOffset(QualType qB, QualType qD) {
qD = qD->getAs<PointerType>()->getPointeeType();
qB = qB->getAs<PointerType>()->getPointeeType();
CXXRecordDecl *D = cast<CXXRecordDecl>(qD->getAs<RecordType>()->getDecl());
CXXRecordDecl *B = cast<CXXRecordDecl>(qB->getAs<RecordType>()->getDecl());
if (D != Class)
return VBlookup(D, B);
llvm::DenseMap<const CXXRecordDecl *, Index_t>::iterator i;
i = VBIndex.find(B);
if (i != VBIndex.end())
return i->second;
assert(false && "FIXME: Locate the containing virtual base first");
return 0;
}
bool OverrideMethod(const CXXMethodDecl *MD, llvm::Constant *m,
bool MorallyVirtual, Index_t Offset) {
typedef CXXMethodDecl::method_iterator meth_iter;
// FIXME: Don't like the nested loops. For very large inheritance
// heirarchies we could have a table on the side with the final overridder
// and just replace each instance of an overridden method once. Would be
// nice to measure the cost/benefit on real code.
for (meth_iter mi = MD->begin_overridden_methods(),
e = MD->end_overridden_methods();
mi != e; ++mi) {
const CXXMethodDecl *OMD = *mi;
llvm::Constant *om;
om = CGM.GetAddrOfFunction(OMD, Ptr8Ty);
om = llvm::ConstantExpr::getBitCast(om, Ptr8Ty);
for (Index_t i = 0, e = submethods.size();
i != e; ++i) {
// FIXME: begin_overridden_methods might be too lax, covariance */
if (submethods[i] != om)
continue;
QualType nc_oret = OMD->getType()->getAs<FunctionType>()->getResultType();
CanQualType oret = CGM.getContext().getCanonicalType(nc_oret);
QualType nc_ret = MD->getType()->getAs<FunctionType>()->getResultType();
CanQualType ret = CGM.getContext().getCanonicalType(nc_ret);
CallOffset ReturnOffset = std::make_pair(0, 0);
if (oret != ret) {
// FIXME: calculate offsets for covariance
Index_t nv = 0;
if (CovariantThunks.count(OMD)) {
oret = CovariantThunks[OMD].second;
CovariantThunks.erase(OMD);
}
ReturnOffset = std::make_pair(nv, getVbaseOffset(oret, ret));
}
Index[MD] = i;
submethods[i] = m;
Thunks.erase(OMD);
if (MorallyVirtual) {
Index_t &idx = VCall[OMD];
if (idx == 0) {
VCallOffset[MD] = Offset/8;
idx = VCalls.size()+1;
VCalls.push_back(0);
} else {
VCallOffset[MD] = VCallOffset[OMD];
VCalls[idx-1] = -VCallOffset[OMD] + Offset/8;
}
VCall[MD] = idx;
CallOffset ThisOffset;
// FIXME: calculate non-virtual offset
ThisOffset = std::make_pair(0, -((idx+extra+2)*LLVMPointerWidth/8));
if (ReturnOffset.first || ReturnOffset.second)
CovariantThunks[MD] = std::make_pair(std::make_pair(ThisOffset,
ReturnOffset),
oret);
else
Thunks[MD] = ThisOffset;
return true;
}
#if 0
// FIXME: finish off
int64_t O = VCallOffset[OMD] - Offset/8;
if (O) {
Thunks[MD] = std::make_pair(O, 0);
}
#endif
return true;
}
}
return false;
}
void InstallThunks() {
for (Thunks_t::iterator i = Thunks.begin(), e = Thunks.end();
i != e; ++i) {
const CXXMethodDecl *MD = i->first;
Index_t idx = Index[MD];
Index_t nv_O = i->second.first;
Index_t v_O = i->second.second;
submethods[idx] = CGM.BuildThunk(MD, Extern, nv_O, v_O);
}
Thunks.clear();
for (CovariantThunks_t::iterator i = CovariantThunks.begin(),
e = CovariantThunks.end();
i != e; ++i) {
const CXXMethodDecl *MD = i->first;
Index_t idx = Index[MD];
Index_t nv_t = i->second.first.first.first;
Index_t v_t = i->second.first.first.second;
Index_t nv_r = i->second.first.second.first;
Index_t v_r = i->second.first.second.second;
submethods[idx] = CGM.BuildCovariantThunk(MD, Extern, nv_t, v_t, nv_r,
v_r);
}
CovariantThunks.clear();
}
void OverrideMethods(std::vector<std::pair<const CXXRecordDecl *,
int64_t> > *Path, bool MorallyVirtual) {
for (std::vector<std::pair<const CXXRecordDecl *,
int64_t> >::reverse_iterator i =Path->rbegin(),
e = Path->rend(); i != e; ++i) {
const CXXRecordDecl *RD = i->first;
int64_t Offset = i->second;
for (method_iter mi = RD->method_begin(), me = RD->method_end(); mi != me;
++mi) {
if (!mi->isVirtual())
continue;
const CXXMethodDecl *MD = *mi;
llvm::Constant *m = 0;
if (const CXXDestructorDecl *Dtor = dyn_cast<CXXDestructorDecl>(MD))
m = wrap(CGM.GetAddrOfCXXDestructor(Dtor, Dtor_Complete));
else {
const FunctionProtoType *FPT =
MD->getType()->getAs<FunctionProtoType>();
const llvm::Type *Ty =
CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(MD),
FPT->isVariadic());
m = wrap(CGM.GetAddrOfFunction(MD, Ty));
}
OverrideMethod(MD, m, MorallyVirtual, Offset);
}
}
}
void AddMethod(const CXXMethodDecl *MD, bool MorallyVirtual, Index_t Offset) {
llvm::Constant *m = 0;
if (const CXXDestructorDecl *Dtor = dyn_cast<CXXDestructorDecl>(MD))
m = wrap(CGM.GetAddrOfCXXDestructor(Dtor, Dtor_Complete));
else {
const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
const llvm::Type *Ty =
CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(MD),
FPT->isVariadic());
m = wrap(CGM.GetAddrOfFunction(MD, Ty));
}
// If we can find a previously allocated slot for this, reuse it.
if (OverrideMethod(MD, m, MorallyVirtual, Offset))
return;
// else allocate a new slot.
Index[MD] = submethods.size();
submethods.push_back(m);
if (MorallyVirtual) {
VCallOffset[MD] = Offset/8;
Index_t &idx = VCall[MD];
// Allocate the first one, after that, we reuse the previous one.
if (idx == 0) {
idx = VCalls.size()+1;
VCalls.push_back(0);
}
}
}
void AddMethods(const CXXRecordDecl *RD, bool MorallyVirtual,
Index_t Offset) {
for (method_iter mi = RD->method_begin(), me = RD->method_end(); mi != me;
++mi)
if (mi->isVirtual())
AddMethod(*mi, MorallyVirtual, Offset);
}
void NonVirtualBases(const CXXRecordDecl *RD, const ASTRecordLayout &Layout,
const CXXRecordDecl *PrimaryBase,
bool PrimaryBaseWasVirtual, bool MorallyVirtual,
int64_t Offset) {
for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
e = RD->bases_end(); i != e; ++i) {
if (i->isVirtual())
continue;
const CXXRecordDecl *Base =
cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
if (Base != PrimaryBase || PrimaryBaseWasVirtual) {
uint64_t o = Offset + Layout.getBaseClassOffset(Base);
StartNewTable();
std::vector<std::pair<const CXXRecordDecl *,
int64_t> > S;
S.push_back(std::make_pair(RD, Offset));
GenerateVtableForBase(Base, MorallyVirtual, o, false, &S);
}
}
}
Index_t end(const CXXRecordDecl *RD, std::vector<llvm::Constant *> &offsets,
const ASTRecordLayout &Layout,
const CXXRecordDecl *PrimaryBase,
bool PrimaryBaseWasVirtual, bool MorallyVirtual,
int64_t Offset, bool ForVirtualBase) {
StartNewTable();
extra = 0;
// FIXME: Cleanup.
if (!ForVirtualBase) {
// then virtual base offsets...
for (std::vector<llvm::Constant *>::reverse_iterator i = offsets.rbegin(),
e = offsets.rend(); i != e; ++i)
methods.push_back(*i);
}
// The vcalls come first...
for (std::vector<Index_t>::reverse_iterator i=VCalls.rbegin(),
e=VCalls.rend();
i != e; ++i)
methods.push_back(wrap((0?600:0) + *i));
VCalls.clear();
if (ForVirtualBase) {
// then virtual base offsets...
for (std::vector<llvm::Constant *>::reverse_iterator i = offsets.rbegin(),
e = offsets.rend(); i != e; ++i)
methods.push_back(*i);
}
methods.push_back(wrap(-(Offset/8)));
methods.push_back(rtti);
Index_t AddressPoint = methods.size();
InstallThunks();
methods.insert(methods.end(), submethods.begin(), submethods.end());
submethods.clear();
// and then the non-virtual bases.
NonVirtualBases(RD, Layout, PrimaryBase, PrimaryBaseWasVirtual,
MorallyVirtual, Offset);
return AddressPoint;
}
void Primaries(const CXXRecordDecl *RD, bool MorallyVirtual, int64_t Offset) {
if (!RD->isDynamicClass())
return;
const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();
// vtables are composed from the chain of primaries.
if (PrimaryBase) {
if (PrimaryBaseWasVirtual)
IndirectPrimary.insert(PrimaryBase);
Primaries(PrimaryBase, PrimaryBaseWasVirtual|MorallyVirtual, Offset);
}
// And add the virtuals for the class to the primary vtable.
AddMethods(RD, MorallyVirtual, Offset);
}
int64_t GenerateVtableForBase(const CXXRecordDecl *RD,
bool MorallyVirtual = false, int64_t Offset = 0,
bool ForVirtualBase = false,
std::vector<std::pair<const CXXRecordDecl *,
int64_t> > *Path = 0) {
if (!RD->isDynamicClass())
return 0;
const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();
std::vector<llvm::Constant *> offsets;
extra = 0;
GenerateVBaseOffsets(offsets, RD, Offset, !ForVirtualBase);
if (ForVirtualBase)
extra = offsets.size();
// vtables are composed from the chain of primaries.
if (PrimaryBase) {
if (PrimaryBaseWasVirtual)
IndirectPrimary.insert(PrimaryBase);
Primaries(PrimaryBase, PrimaryBaseWasVirtual|MorallyVirtual, Offset);
}
// And add the virtuals for the class to the primary vtable.
AddMethods(RD, MorallyVirtual, Offset);
if (Path)
OverrideMethods(Path, MorallyVirtual);
return end(RD, offsets, Layout, PrimaryBase, PrimaryBaseWasVirtual,
MorallyVirtual, Offset, ForVirtualBase);
}
void GenerateVtableForVBases(const CXXRecordDecl *RD,
int64_t Offset = 0,
std::vector<std::pair<const CXXRecordDecl *,
int64_t> > *Path = 0) {
bool alloc = false;
if (Path == 0) {
alloc = true;
Path = new std::vector<std::pair<const CXXRecordDecl *,
int64_t> >;
}
// FIXME: We also need to override using all paths to a virtual base,
// right now, we just process the first path
Path->push_back(std::make_pair(RD, Offset));
for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
e = RD->bases_end(); i != e; ++i) {
const CXXRecordDecl *Base =
cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
if (i->isVirtual() && !IndirectPrimary.count(Base)) {
// Mark it so we don't output it twice.
IndirectPrimary.insert(Base);
StartNewTable();
int64_t BaseOffset = BLayout.getVBaseClassOffset(Base);
GenerateVtableForBase(Base, true, BaseOffset, true, Path);
}
int64_t BaseOffset = Offset;
if (i->isVirtual())
BaseOffset = BLayout.getVBaseClassOffset(Base);
if (Base->getNumVBases())
GenerateVtableForVBases(Base, BaseOffset, Path);
}
Path->pop_back();
if (alloc)
delete Path;
}
};
VtableBuilder::Index_t VtableBuilder::VBlookup(CXXRecordDecl *D,
CXXRecordDecl *B) {
return CGM.getVtableInfo().getVirtualBaseOffsetIndex(D, B);
}
int64_t CGVtableInfo::getMethodVtableIndex(const CXXMethodDecl *MD) {
MD = MD->getCanonicalDecl();
MethodVtableIndicesTy::iterator I = MethodVtableIndices.find(MD);
if (I != MethodVtableIndices.end())
return I->second;
const CXXRecordDecl *RD = MD->getParent();
std::vector<llvm::Constant *> methods;
// FIXME: This seems expensive. Can we do a partial job to get
// just this data.
VtableBuilder b(methods, RD, CGM);
b.GenerateVtableForBase(RD);
b.GenerateVtableForVBases(RD);
MethodVtableIndices.insert(b.getIndex().begin(),
b.getIndex().end());
I = MethodVtableIndices.find(MD);
assert(I != MethodVtableIndices.end() && "Did not find index!");
return I->second;
}
int64_t CGVtableInfo::getVirtualBaseOffsetIndex(const CXXRecordDecl *RD,
const CXXRecordDecl *VBase) {
ClassPairTy ClassPair(RD, VBase);
VirtualBaseClassIndiciesTy::iterator I =
VirtualBaseClassIndicies.find(ClassPair);
if (I != VirtualBaseClassIndicies.end())
return I->second;
std::vector<llvm::Constant *> methods;
// FIXME: This seems expensive. Can we do a partial job to get
// just this data.
VtableBuilder b(methods, RD, CGM);
b.GenerateVtableForBase(RD);
b.GenerateVtableForVBases(RD);
for (llvm::DenseMap<const CXXRecordDecl *, uint64_t>::iterator I =
b.getVBIndex().begin(), E = b.getVBIndex().end(); I != E; ++I) {
// Insert all types.
ClassPairTy ClassPair(RD, I->first);
VirtualBaseClassIndicies.insert(std::make_pair(ClassPair, I->second));
}
I = VirtualBaseClassIndicies.find(ClassPair);
assert(I != VirtualBaseClassIndicies.end() && "Did not find index!");
return I->second;
}
llvm::Value *CodeGenFunction::GenerateVtable(const CXXRecordDecl *RD) {
llvm::SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
mangleCXXVtable(CGM.getMangleContext(), RD, Out);
llvm::GlobalVariable::LinkageTypes linktype;
linktype = llvm::GlobalValue::WeakAnyLinkage;
std::vector<llvm::Constant *> methods;
llvm::Type *Ptr8Ty=llvm::PointerType::get(llvm::Type::getInt8Ty(VMContext),0);
int64_t AddressPoint;
VtableBuilder b(methods, RD, CGM);
// First comes the vtables for all the non-virtual bases...
AddressPoint = b.GenerateVtableForBase(RD);
// then the vtables for all the virtual bases.
b.GenerateVtableForVBases(RD);
llvm::Constant *C;
llvm::ArrayType *type = llvm::ArrayType::get(Ptr8Ty, methods.size());
C = llvm::ConstantArray::get(type, methods);
llvm::Value *vtable = new llvm::GlobalVariable(CGM.getModule(), type, true,
linktype, C, Out.str());
vtable = Builder.CreateBitCast(vtable, Ptr8Ty);
vtable = Builder.CreateGEP(vtable,
llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
AddressPoint*LLVMPointerWidth/8));
return vtable;
}
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