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//===- WholeProgramDevirt.cpp - Whole program virtual call optimization ---===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This pass implements whole program optimization of virtual calls in cases
// where we know (via !type metadata) that the list of callees is fixed. This
// includes the following:
// - Single implementation devirtualization: if a virtual call has a single
// possible callee, replace all calls with a direct call to that callee.
// - Virtual constant propagation: if the virtual function's return type is an
// integer <=64 bits and all possible callees are readnone, for each class and
// each list of constant arguments: evaluate the function, store the return
// value alongside the virtual table, and rewrite each virtual call as a load
// from the virtual table.
// - Uniform return value optimization: if the conditions for virtual constant
// propagation hold and each function returns the same constant value, replace
// each virtual call with that constant.
// - Unique return value optimization for i1 return values: if the conditions
// for virtual constant propagation hold and a single vtable's function
// returns 0, or a single vtable's function returns 1, replace each virtual
// call with a comparison of the vptr against that vtable's address.
// This pass is intended to be used during the regular and thin LTO pipelines.
// During regular LTO, the pass determines the best optimization for each
// virtual call and applies the resolutions directly to virtual calls that are
// eligible for virtual call optimization (i.e. calls that use either of the
// llvm.assume(llvm.type.test) or llvm.type.checked.load intrinsics). During
// ThinLTO, the pass operates in two phases:
// - Export phase: this is run during the thin link over a single merged module
// that contains all vtables with !type metadata that participate in the link.
// The pass computes a resolution for each virtual call and stores it in the
// type identifier summary.
// - Import phase: this is run during the thin backends over the individual
// modules. The pass applies the resolutions previously computed during the
// import phase to each eligible virtual call.
#include "llvm/Transforms/IPO/WholeProgramDevirt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/TypeMetadataUtils.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ModuleSummaryIndexYAML.h"
#include "llvm/Pass.h"
#include "llvm/PassRegistry.h"
#include "llvm/PassSupport.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/Utils/Evaluator.h"
#include <algorithm>
#include <cstddef>
#include <map>
#include <set>
#include <string>
using namespace llvm;
using namespace wholeprogramdevirt;
#define DEBUG_TYPE "wholeprogramdevirt"
static cl::opt<PassSummaryAction> ClSummaryAction(
cl::desc("What to do with the summary when running this pass"),
cl::values(clEnumValN(PassSummaryAction::None, "none", "Do nothing"),
clEnumValN(PassSummaryAction::Import, "import",
"Import typeid resolutions from summary and globals"),
clEnumValN(PassSummaryAction::Export, "export",
"Export typeid resolutions to summary and globals")),
static cl::opt<std::string> ClReadSummary(
cl::desc("Read summary from given YAML file before running pass"),
static cl::opt<std::string> ClWriteSummary(
cl::desc("Write summary to given YAML file after running pass"),
// Find the minimum offset that we may store a value of size Size bits at. If
// IsAfter is set, look for an offset before the object, otherwise look for an
// offset after the object.
wholeprogramdevirt::findLowestOffset(ArrayRef<VirtualCallTarget> Targets,
bool IsAfter, uint64_t Size) {
// Find a minimum offset taking into account only vtable sizes.
uint64_t MinByte = 0;
for (const VirtualCallTarget &Target : Targets) {
if (IsAfter)
MinByte = std::max(MinByte, Target.minAfterBytes());
MinByte = std::max(MinByte, Target.minBeforeBytes());
// Build a vector of arrays of bytes covering, for each target, a slice of the
// used region (see AccumBitVector::BytesUsed in
// llvm/Transforms/IPO/WholeProgramDevirt.h) starting at MinByte. Effectively,
// this aligns the used regions to start at MinByte.
// In this example, A, B and C are vtables, # is a byte already allocated for
// a virtual function pointer, AAAA... (etc.) are the used regions for the
// vtables and Offset(X) is the value computed for the Offset variable below
// for X.
// Offset(A)
// | |
// |MinByte
// A: ################AAAAAAAA|AAAAAAAA
// C: ########################|CCCCCCCCCCCCCCCC
// | Offset(B) |
// This code produces the slices of A, B and C that appear after the divider
// at MinByte.
std::vector<ArrayRef<uint8_t>> Used;
for (const VirtualCallTarget &Target : Targets) {
ArrayRef<uint8_t> VTUsed = IsAfter ? Target.TM->Bits->After.BytesUsed
: Target.TM->Bits->Before.BytesUsed;
uint64_t Offset = IsAfter ? MinByte - Target.minAfterBytes()
: MinByte - Target.minBeforeBytes();
// Disregard used regions that are smaller than Offset. These are
// effectively all-free regions that do not need to be checked.
if (VTUsed.size() > Offset)
if (Size == 1) {
// Find a free bit in each member of Used.
for (unsigned I = 0;; ++I) {
uint8_t BitsUsed = 0;
for (auto &&B : Used)
if (I < B.size())
BitsUsed |= B[I];
if (BitsUsed != 0xff)
return (MinByte + I) * 8 +
countTrailingZeros(uint8_t(~BitsUsed), ZB_Undefined);
} else {
// Find a free (Size/8) byte region in each member of Used.
// FIXME: see if alignment helps.
for (unsigned I = 0;; ++I) {
for (auto &&B : Used) {
unsigned Byte = 0;
while ((I + Byte) < B.size() && Byte < (Size / 8)) {
if (B[I + Byte])
goto NextI;
return (MinByte + I) * 8;
void wholeprogramdevirt::setBeforeReturnValues(
MutableArrayRef<VirtualCallTarget> Targets, uint64_t AllocBefore,
unsigned BitWidth, int64_t &OffsetByte, uint64_t &OffsetBit) {
if (BitWidth == 1)
OffsetByte = -(AllocBefore / 8 + 1);
OffsetByte = -((AllocBefore + 7) / 8 + (BitWidth + 7) / 8);
OffsetBit = AllocBefore % 8;
for (VirtualCallTarget &Target : Targets) {
if (BitWidth == 1)
Target.setBeforeBytes(AllocBefore, (BitWidth + 7) / 8);
void wholeprogramdevirt::setAfterReturnValues(
MutableArrayRef<VirtualCallTarget> Targets, uint64_t AllocAfter,
unsigned BitWidth, int64_t &OffsetByte, uint64_t &OffsetBit) {
if (BitWidth == 1)
OffsetByte = AllocAfter / 8;
OffsetByte = (AllocAfter + 7) / 8;
OffsetBit = AllocAfter % 8;
for (VirtualCallTarget &Target : Targets) {
if (BitWidth == 1)
Target.setAfterBytes(AllocAfter, (BitWidth + 7) / 8);
VirtualCallTarget::VirtualCallTarget(Function *Fn, const TypeMemberInfo *TM)
: Fn(Fn), TM(TM),
IsBigEndian(Fn->getParent()->getDataLayout().isBigEndian()), WasDevirt(false) {}
namespace {
// A slot in a set of virtual tables. The TypeID identifies the set of virtual
// tables, and the ByteOffset is the offset in bytes from the address point to
// the virtual function pointer.
struct VTableSlot {
Metadata *TypeID;
uint64_t ByteOffset;
} // end anonymous namespace
namespace llvm {
template <> struct DenseMapInfo<VTableSlot> {
static VTableSlot getEmptyKey() {
return {DenseMapInfo<Metadata *>::getEmptyKey(),
static VTableSlot getTombstoneKey() {
return {DenseMapInfo<Metadata *>::getTombstoneKey(),
static unsigned getHashValue(const VTableSlot &I) {
return DenseMapInfo<Metadata *>::getHashValue(I.TypeID) ^
static bool isEqual(const VTableSlot &LHS,
const VTableSlot &RHS) {
return LHS.TypeID == RHS.TypeID && LHS.ByteOffset == RHS.ByteOffset;
} // end namespace llvm
namespace {
// A virtual call site. VTable is the loaded virtual table pointer, and CS is
// the indirect virtual call.
struct VirtualCallSite {
Value *VTable;
CallSite CS;
// If non-null, this field points to the associated unsafe use count stored in
// the DevirtModule::NumUnsafeUsesForTypeTest map below. See the description
// of that field for details.
unsigned *NumUnsafeUses;
emitRemark(const StringRef OptName, const StringRef TargetName,
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter) {
Function *F = CS.getCaller();
DebugLoc DLoc = CS->getDebugLoc();
BasicBlock *Block = CS.getParent();
// In the new pass manager, we can request the optimization
// remark emitter pass on a per-function-basis, which the
// OREGetter will do for us.
// In the old pass manager, this is harder, so we just build
// a optimization remark emitter on the fly, when we need it.
std::unique_ptr<OptimizationRemarkEmitter> OwnedORE;
OptimizationRemarkEmitter *ORE;
if (OREGetter)
ORE = &OREGetter(F);
else {
OwnedORE = make_unique<OptimizationRemarkEmitter>(F);
ORE = OwnedORE.get();
using namespace ore;
ORE->emit(OptimizationRemark(DEBUG_TYPE, OptName, DLoc, Block)
<< NV("Optimization", OptName) << ": devirtualized a call to "
<< NV("FunctionName", TargetName));
void replaceAndErase(
const StringRef OptName, const StringRef TargetName, bool RemarksEnabled,
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter,
Value *New) {
if (RemarksEnabled)
emitRemark(OptName, TargetName, OREGetter);
if (auto II = dyn_cast<InvokeInst>(CS.getInstruction())) {
BranchInst::Create(II->getNormalDest(), CS.getInstruction());
// This use is no longer unsafe.
if (NumUnsafeUses)
// Call site information collected for a specific VTableSlot and possibly a list
// of constant integer arguments. The grouping by arguments is handled by the
// VTableSlotInfo class.
struct CallSiteInfo {
/// The set of call sites for this slot. Used during regular LTO and the
/// import phase of ThinLTO (as well as the export phase of ThinLTO for any
/// call sites that appear in the merged module itself); in each of these
/// cases we are directly operating on the call sites at the IR level.
std::vector<VirtualCallSite> CallSites;
// These fields are used during the export phase of ThinLTO and reflect
// information collected from function summaries.
/// Whether any function summary contains an llvm.assume(llvm.type.test) for
/// this slot.
bool SummaryHasTypeTestAssumeUsers;
/// CFI-specific: a vector containing the list of function summaries that use
/// the llvm.type.checked.load intrinsic and therefore will require
/// resolutions for llvm.type.test in order to implement CFI checks if
/// devirtualization was unsuccessful. If devirtualization was successful, the
/// pass will clear this vector by calling markDevirt(). If at the end of the
/// pass the vector is non-empty, we will need to add a use of llvm.type.test
/// to each of the function summaries in the vector.
std::vector<FunctionSummary *> SummaryTypeCheckedLoadUsers;
bool isExported() const {
return SummaryHasTypeTestAssumeUsers ||
/// As explained in the comment for SummaryTypeCheckedLoadUsers.
void markDevirt() { SummaryTypeCheckedLoadUsers.clear(); }
// Call site information collected for a specific VTableSlot.
struct VTableSlotInfo {
// The set of call sites which do not have all constant integer arguments
// (excluding "this").
CallSiteInfo CSInfo;
// The set of call sites with all constant integer arguments (excluding
// "this"), grouped by argument list.
std::map<std::vector<uint64_t>, CallSiteInfo> ConstCSInfo;
void addCallSite(Value *VTable, CallSite CS, unsigned *NumUnsafeUses);
CallSiteInfo &findCallSiteInfo(CallSite CS);
CallSiteInfo &VTableSlotInfo::findCallSiteInfo(CallSite CS) {
std::vector<uint64_t> Args;
auto *CI = dyn_cast<IntegerType>(CS.getType());
if (!CI || CI->getBitWidth() > 64 || CS.arg_empty())
return CSInfo;
for (auto &&Arg : make_range(CS.arg_begin() + 1, CS.arg_end())) {
auto *CI = dyn_cast<ConstantInt>(Arg);
if (!CI || CI->getBitWidth() > 64)
return CSInfo;
return ConstCSInfo[Args];
void VTableSlotInfo::addCallSite(Value *VTable, CallSite CS,
unsigned *NumUnsafeUses) {
findCallSiteInfo(CS).CallSites.push_back({VTable, CS, NumUnsafeUses});
struct DevirtModule {
Module &M;
function_ref<AAResults &(Function &)> AARGetter;
ModuleSummaryIndex *ExportSummary;
const ModuleSummaryIndex *ImportSummary;
IntegerType *Int8Ty;
PointerType *Int8PtrTy;
IntegerType *Int32Ty;
IntegerType *Int64Ty;
IntegerType *IntPtrTy;
bool RemarksEnabled;
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter;
MapVector<VTableSlot, VTableSlotInfo> CallSlots;
// This map keeps track of the number of "unsafe" uses of a loaded function
// pointer. The key is the associated llvm.type.test intrinsic call generated
// by this pass. An unsafe use is one that calls the loaded function pointer
// directly. Every time we eliminate an unsafe use (for example, by
// devirtualizing it or by applying virtual constant propagation), we
// decrement the value stored in this map. If a value reaches zero, we can
// eliminate the type check by RAUWing the associated llvm.type.test call with
// true.
std::map<CallInst *, unsigned> NumUnsafeUsesForTypeTest;
DevirtModule(Module &M, function_ref<AAResults &(Function &)> AARGetter,
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter,
ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary)
: M(M), AARGetter(AARGetter), ExportSummary(ExportSummary),
ImportSummary(ImportSummary), Int8Ty(Type::getInt8Ty(M.getContext())),
IntPtrTy(M.getDataLayout().getIntPtrType(M.getContext(), 0)),
RemarksEnabled(areRemarksEnabled()), OREGetter(OREGetter) {
assert(!(ExportSummary && ImportSummary));
bool areRemarksEnabled();
void scanTypeTestUsers(Function *TypeTestFunc, Function *AssumeFunc);
void scanTypeCheckedLoadUsers(Function *TypeCheckedLoadFunc);
void buildTypeIdentifierMap(
std::vector<VTableBits> &Bits,
DenseMap<Metadata *, std::set<TypeMemberInfo>> &TypeIdMap);
Constant *getPointerAtOffset(Constant *I, uint64_t Offset);
tryFindVirtualCallTargets(std::vector<VirtualCallTarget> &TargetsForSlot,
const std::set<TypeMemberInfo> &TypeMemberInfos,
uint64_t ByteOffset);
void applySingleImplDevirt(VTableSlotInfo &SlotInfo, Constant *TheFn,
bool &IsExported);
bool trySingleImplDevirt(MutableArrayRef<VirtualCallTarget> TargetsForSlot,
VTableSlotInfo &SlotInfo,
WholeProgramDevirtResolution *Res);
bool tryEvaluateFunctionsWithArgs(
MutableArrayRef<VirtualCallTarget> TargetsForSlot,
ArrayRef<uint64_t> Args);
void applyUniformRetValOpt(CallSiteInfo &CSInfo, StringRef FnName,
uint64_t TheRetVal);
bool tryUniformRetValOpt(MutableArrayRef<VirtualCallTarget> TargetsForSlot,
CallSiteInfo &CSInfo,
WholeProgramDevirtResolution::ByArg *Res);
// Returns the global symbol name that is used to export information about the
// given vtable slot and list of arguments.
std::string getGlobalName(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name);
bool shouldExportConstantsAsAbsoluteSymbols();
// This function is called during the export phase to create a symbol
// definition containing information about the given vtable slot and list of
// arguments.
void exportGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args, StringRef Name,
Constant *C);
void exportConstant(VTableSlot Slot, ArrayRef<uint64_t> Args, StringRef Name,
uint32_t Const, uint32_t &Storage);
// This function is called during the import phase to create a reference to
// the symbol definition created during the export phase.
Constant *importGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name);
Constant *importConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name, IntegerType *IntTy,
uint32_t Storage);
void applyUniqueRetValOpt(CallSiteInfo &CSInfo, StringRef FnName, bool IsOne,
Constant *UniqueMemberAddr);
bool tryUniqueRetValOpt(unsigned BitWidth,
MutableArrayRef<VirtualCallTarget> TargetsForSlot,
CallSiteInfo &CSInfo,
WholeProgramDevirtResolution::ByArg *Res,
VTableSlot Slot, ArrayRef<uint64_t> Args);
void applyVirtualConstProp(CallSiteInfo &CSInfo, StringRef FnName,
Constant *Byte, Constant *Bit);
bool tryVirtualConstProp(MutableArrayRef<VirtualCallTarget> TargetsForSlot,
VTableSlotInfo &SlotInfo,
WholeProgramDevirtResolution *Res, VTableSlot Slot);
void rebuildGlobal(VTableBits &B);
// Apply the summary resolution for Slot to all virtual calls in SlotInfo.
void importResolution(VTableSlot Slot, VTableSlotInfo &SlotInfo);
// If we were able to eliminate all unsafe uses for a type checked load,
// eliminate the associated type tests by replacing them with true.
void removeRedundantTypeTests();
bool run();
// Lower the module using the action and summary passed as command line
// arguments. For testing purposes only.
static bool runForTesting(
Module &M, function_ref<AAResults &(Function &)> AARGetter,
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter);
struct WholeProgramDevirt : public ModulePass {
static char ID;
bool UseCommandLine = false;
ModuleSummaryIndex *ExportSummary;
const ModuleSummaryIndex *ImportSummary;
WholeProgramDevirt() : ModulePass(ID), UseCommandLine(true) {
WholeProgramDevirt(ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary)
: ModulePass(ID), ExportSummary(ExportSummary),
ImportSummary(ImportSummary) {
bool runOnModule(Module &M) override {
if (skipModule(M))
return false;
auto OREGetter = function_ref<OptimizationRemarkEmitter &(Function *)>();
if (UseCommandLine)
return DevirtModule::runForTesting(M, LegacyAARGetter(*this), OREGetter);
return DevirtModule(M, LegacyAARGetter(*this), OREGetter, ExportSummary,
void getAnalysisUsage(AnalysisUsage &AU) const override {
} // end anonymous namespace
INITIALIZE_PASS_BEGIN(WholeProgramDevirt, "wholeprogramdevirt",
"Whole program devirtualization", false, false)
INITIALIZE_PASS_END(WholeProgramDevirt, "wholeprogramdevirt",
"Whole program devirtualization", false, false)
char WholeProgramDevirt::ID = 0;
ModulePass *
llvm::createWholeProgramDevirtPass(ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary) {
return new WholeProgramDevirt(ExportSummary, ImportSummary);
PreservedAnalyses WholeProgramDevirtPass::run(Module &M,
ModuleAnalysisManager &AM) {
auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
auto AARGetter = [&](Function &F) -> AAResults & {
return FAM.getResult<AAManager>(F);
auto OREGetter = [&](Function *F) -> OptimizationRemarkEmitter & {
return FAM.getResult<OptimizationRemarkEmitterAnalysis>(*F);
if (!DevirtModule(M, AARGetter, OREGetter, nullptr, nullptr).run())
return PreservedAnalyses::all();
return PreservedAnalyses::none();
bool DevirtModule::runForTesting(
Module &M, function_ref<AAResults &(Function &)> AARGetter,
function_ref<OptimizationRemarkEmitter &(Function *)> OREGetter) {
ModuleSummaryIndex Summary;
// Handle the command-line summary arguments. This code is for testing
// purposes only, so we handle errors directly.
if (!ClReadSummary.empty()) {
ExitOnError ExitOnErr("-wholeprogramdevirt-read-summary: " + ClReadSummary +
": ");
auto ReadSummaryFile =
yaml::Input In(ReadSummaryFile->getBuffer());
In >> Summary;
bool Changed =
M, AARGetter, OREGetter,
ClSummaryAction == PassSummaryAction::Export ? &Summary : nullptr,
ClSummaryAction == PassSummaryAction::Import ? &Summary : nullptr)
if (!ClWriteSummary.empty()) {
ExitOnError ExitOnErr(
"-wholeprogramdevirt-write-summary: " + ClWriteSummary + ": ");
std::error_code EC;
raw_fd_ostream OS(ClWriteSummary, EC, sys::fs::F_Text);
yaml::Output Out(OS);
Out << Summary;
return Changed;
void DevirtModule::buildTypeIdentifierMap(
std::vector<VTableBits> &Bits,
DenseMap<Metadata *, std::set<TypeMemberInfo>> &TypeIdMap) {
DenseMap<GlobalVariable *, VTableBits *> GVToBits;
SmallVector<MDNode *, 2> Types;
for (GlobalVariable &GV : M.globals()) {
GV.getMetadata(LLVMContext::MD_type, Types);
if (Types.empty())
VTableBits *&BitsPtr = GVToBits[&GV];
if (!BitsPtr) {
Bits.back().GV = &GV;
Bits.back().ObjectSize =
BitsPtr = &Bits.back();
for (MDNode *Type : Types) {
auto TypeID = Type->getOperand(1).get();
uint64_t Offset =
TypeIdMap[TypeID].insert({BitsPtr, Offset});
Constant *DevirtModule::getPointerAtOffset(Constant *I, uint64_t Offset) {
if (I->getType()->isPointerTy()) {
if (Offset == 0)
return I;
return nullptr;
const DataLayout &DL = M.getDataLayout();
if (auto *C = dyn_cast<ConstantStruct>(I)) {
const StructLayout *SL = DL.getStructLayout(C->getType());
if (Offset >= SL->getSizeInBytes())
return nullptr;
unsigned Op = SL->getElementContainingOffset(Offset);
return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
Offset - SL->getElementOffset(Op));
if (auto *C = dyn_cast<ConstantArray>(I)) {
ArrayType *VTableTy = C->getType();
uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
unsigned Op = Offset / ElemSize;
if (Op >= C->getNumOperands())
return nullptr;
return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
Offset % ElemSize);
return nullptr;
bool DevirtModule::tryFindVirtualCallTargets(
std::vector<VirtualCallTarget> &TargetsForSlot,
const std::set<TypeMemberInfo> &TypeMemberInfos, uint64_t ByteOffset) {
for (const TypeMemberInfo &TM : TypeMemberInfos) {
if (!TM.Bits->GV->isConstant())
return false;
Constant *Ptr = getPointerAtOffset(TM.Bits->GV->getInitializer(),
TM.Offset + ByteOffset);
if (!Ptr)
return false;
auto Fn = dyn_cast<Function>(Ptr->stripPointerCasts());
if (!Fn)
return false;
// We can disregard __cxa_pure_virtual as a possible call target, as
// calls to pure virtuals are UB.
if (Fn->getName() == "__cxa_pure_virtual")
TargetsForSlot.push_back({Fn, &TM});
// Give up if we couldn't find any targets.
return !TargetsForSlot.empty();
void DevirtModule::applySingleImplDevirt(VTableSlotInfo &SlotInfo,
Constant *TheFn, bool &IsExported) {
auto Apply = [&](CallSiteInfo &CSInfo) {
for (auto &&VCallSite : CSInfo.CallSites) {
if (RemarksEnabled)
VCallSite.emitRemark("single-impl", TheFn->getName(), OREGetter);
TheFn, VCallSite.CS.getCalledValue()->getType()));
// This use is no longer unsafe.
if (VCallSite.NumUnsafeUses)
if (CSInfo.isExported()) {
IsExported = true;
for (auto &P : SlotInfo.ConstCSInfo)
bool DevirtModule::trySingleImplDevirt(
MutableArrayRef<VirtualCallTarget> TargetsForSlot,
VTableSlotInfo &SlotInfo, WholeProgramDevirtResolution *Res) {
// See if the program contains a single implementation of this virtual
// function.
Function *TheFn = TargetsForSlot[0].Fn;
for (auto &&Target : TargetsForSlot)
if (TheFn != Target.Fn)
return false;
// If so, update each call site to call that implementation directly.
if (RemarksEnabled)
TargetsForSlot[0].WasDevirt = true;
bool IsExported = false;
applySingleImplDevirt(SlotInfo, TheFn, IsExported);
if (!IsExported)
return false;
// If the only implementation has local linkage, we must promote to external
// to make it visible to thin LTO objects. We can only get here during the
// ThinLTO export phase.
if (TheFn->hasLocalLinkage()) {
std::string NewName = (TheFn->getName() + "$merged").str();
// Since we are renaming the function, any comdats with the same name must
// also be renamed. This is required when targeting COFF, as the comdat name
// must match one of the names of the symbols in the comdat.
if (Comdat *C = TheFn->getComdat()) {
if (C->getName() == TheFn->getName()) {
Comdat *NewC = M.getOrInsertComdat(NewName);
for (GlobalObject &GO : M.global_objects())
if (GO.getComdat() == C)
Res->TheKind = WholeProgramDevirtResolution::SingleImpl;
Res->SingleImplName = TheFn->getName();
return true;
bool DevirtModule::tryEvaluateFunctionsWithArgs(
MutableArrayRef<VirtualCallTarget> TargetsForSlot,
ArrayRef<uint64_t> Args) {
// Evaluate each function and store the result in each target's RetVal
// field.
for (VirtualCallTarget &Target : TargetsForSlot) {
if (Target.Fn->arg_size() != Args.size() + 1)
return false;
Evaluator Eval(M.getDataLayout(), nullptr);
SmallVector<Constant *, 2> EvalArgs;
for (unsigned I = 0; I != Args.size(); ++I) {
auto *ArgTy = dyn_cast<IntegerType>(
Target.Fn->getFunctionType()->getParamType(I + 1));
if (!ArgTy)
return false;
EvalArgs.push_back(ConstantInt::get(ArgTy, Args[I]));
Constant *RetVal;
if (!Eval.EvaluateFunction(Target.Fn, RetVal, EvalArgs) ||
return false;
Target.RetVal = cast<ConstantInt>(RetVal)->getZExtValue();
return true;
void DevirtModule::applyUniformRetValOpt(CallSiteInfo &CSInfo, StringRef FnName,
uint64_t TheRetVal) {
for (auto Call : CSInfo.CallSites)
"uniform-ret-val", FnName, RemarksEnabled, OREGetter,
ConstantInt::get(cast<IntegerType>(Call.CS.getType()), TheRetVal));
bool DevirtModule::tryUniformRetValOpt(
MutableArrayRef<VirtualCallTarget> TargetsForSlot, CallSiteInfo &CSInfo,
WholeProgramDevirtResolution::ByArg *Res) {
// Uniform return value optimization. If all functions return the same
// constant, replace all calls with that constant.
uint64_t TheRetVal = TargetsForSlot[0].RetVal;
for (const VirtualCallTarget &Target : TargetsForSlot)
if (Target.RetVal != TheRetVal)
return false;
if (CSInfo.isExported()) {
Res->TheKind = WholeProgramDevirtResolution::ByArg::UniformRetVal;
Res->Info = TheRetVal;
applyUniformRetValOpt(CSInfo, TargetsForSlot[0].Fn->getName(), TheRetVal);
if (RemarksEnabled)
for (auto &&Target : TargetsForSlot)
Target.WasDevirt = true;
return true;
std::string DevirtModule::getGlobalName(VTableSlot Slot,
ArrayRef<uint64_t> Args,
StringRef Name) {
std::string FullName = "__typeid_";
raw_string_ostream OS(FullName);
OS << cast<MDString>(Slot.TypeID)->getString() << '_' << Slot.ByteOffset;
for (uint64_t Arg : Args)
OS << '_' << Arg;
OS << '_' << Name;
return OS.str();
bool DevirtModule::shouldExportConstantsAsAbsoluteSymbols() {
Triple T(M.getTargetTriple());
return (T.getArch() == Triple::x86 || T.getArch() == Triple::x86_64) &&
T.getObjectFormat() == Triple::ELF;
void DevirtModule::exportGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name, Constant *C) {
GlobalAlias *GA = GlobalAlias::create(Int8Ty, 0, GlobalValue::ExternalLinkage,
getGlobalName(Slot, Args, Name), C, &M);
void DevirtModule::exportConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name, uint32_t Const,
uint32_t &Storage) {
if (shouldExportConstantsAsAbsoluteSymbols()) {
Slot, Args, Name,
ConstantExpr::getIntToPtr(ConstantInt::get(Int32Ty, Const), Int8PtrTy));
Storage = Const;
Constant *DevirtModule::importGlobal(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name) {
Constant *C = M.getOrInsertGlobal(getGlobalName(Slot, Args, Name), Int8Ty);
auto *GV = dyn_cast<GlobalVariable>(C);
if (GV)
return C;
Constant *DevirtModule::importConstant(VTableSlot Slot, ArrayRef<uint64_t> Args,
StringRef Name, IntegerType *IntTy,
uint32_t Storage) {
if (!shouldExportConstantsAsAbsoluteSymbols())
return ConstantInt::get(IntTy, Storage);
Constant *C = importGlobal(Slot, Args, Name);
auto *GV = cast<GlobalVariable>(C->stripPointerCasts());
C = ConstantExpr::getPtrToInt(C, IntTy);
// We only need to set metadata if the global is newly created, in which
// case it would not have hidden visibility.
if (GV->getMetadata(LLVMContext::MD_absolute_symbol))
return C;
auto SetAbsRange = [&](uint64_t Min, uint64_t Max) {
auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntPtrTy, Min));
auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntPtrTy, Max));
MDNode::get(M.getContext(), {MinC, MaxC}));
unsigned AbsWidth = IntTy->getBitWidth();
if (AbsWidth == IntPtrTy->getBitWidth())
SetAbsRange(~0ull, ~0ull); // Full set.
SetAbsRange(0, 1ull << AbsWidth);
return C;
void DevirtModule::applyUniqueRetValOpt(CallSiteInfo &CSInfo, StringRef FnName,
bool IsOne,
Constant *UniqueMemberAddr) {
for (auto &&Call : CSInfo.CallSites) {
IRBuilder<> B(Call.CS.getInstruction());
Value *Cmp =
B.CreateICmp(IsOne ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE,
B.CreateBitCast(Call.VTable, Int8PtrTy), UniqueMemberAddr);
Cmp = B.CreateZExt(Cmp, Call.CS->getType());
Call.replaceAndErase("unique-ret-val", FnName, RemarksEnabled, OREGetter,
bool DevirtModule::tryUniqueRetValOpt(
unsigned BitWidth, MutableArrayRef<VirtualCallTarget> TargetsForSlot,
CallSiteInfo &CSInfo, WholeProgramDevirtResolution::ByArg *Res,
VTableSlot Slot, ArrayRef<uint64_t> Args) {
// IsOne controls whether we look for a 0 or a 1.
auto tryUniqueRetValOptFor = [&](bool IsOne) {
const TypeMemberInfo *UniqueMember = nullptr;
for (const VirtualCallTarget &Target : TargetsForSlot) {
if (Target.RetVal == (IsOne ? 1 : 0)) {
if (UniqueMember)
return false;
UniqueMember = Target.TM;
// We should have found a unique member or bailed out by now. We already
// checked for a uniform return value in tryUniformRetValOpt.
Constant *UniqueMemberAddr =
ConstantExpr::getBitCast(UniqueMember->Bits->GV, Int8PtrTy);
UniqueMemberAddr = ConstantExpr::getGetElementPtr(
Int8Ty, UniqueMemberAddr,
ConstantInt::get(Int64Ty, UniqueMember->Offset));
if (CSInfo.isExported()) {
Res->TheKind = WholeProgramDevirtResolution::ByArg::UniqueRetVal;
Res->Info = IsOne;
exportGlobal(Slot, Args, "unique_member", UniqueMemberAddr);
// Replace each call with the comparison.
applyUniqueRetValOpt(CSInfo, TargetsForSlot[0].Fn->getName(), IsOne,
// Update devirtualization statistics for targets.
if (RemarksEnabled)
for (auto &&Target : TargetsForSlot)
Target.WasDevirt = true;
return true;
if (BitWidth == 1) {
if (tryUniqueRetValOptFor(true))
return true;
if (tryUniqueRetValOptFor(false))
return true;
return false;
void DevirtModule::applyVirtualConstProp(CallSiteInfo &CSInfo, StringRef FnName,
Constant *Byte, Constant *Bit) {
for (auto Call : CSInfo.CallSites) {
auto *RetType = cast<IntegerType>(Call.CS.getType());
IRBuilder<> B(Call.CS.getInstruction());
Value *Addr =
B.CreateGEP(Int8Ty, B.CreateBitCast(Call.VTable, Int8PtrTy), Byte);
if (RetType->getBitWidth() == 1) {
Value *Bits = B.CreateLoad(Addr);
Value *BitsAndBit = B.CreateAnd(Bits, Bit);
auto IsBitSet = B.CreateICmpNE(BitsAndBit, ConstantInt::get(Int8Ty, 0));
Call.replaceAndErase("virtual-const-prop-1-bit", FnName, RemarksEnabled,
OREGetter, IsBitSet);
} else {
Value *ValAddr = B.CreateBitCast(Addr, RetType->getPointerTo());
Value *Val = B.CreateLoad(RetType, ValAddr);
Call.replaceAndErase("virtual-const-prop", FnName, RemarksEnabled,
OREGetter, Val);
bool DevirtModule::tryVirtualConstProp(
MutableArrayRef<VirtualCallTarget> TargetsForSlot, VTableSlotInfo &SlotInfo,
WholeProgramDevirtResolution *Res, VTableSlot Slot) {
// This only works if the function returns an integer.
auto RetType = dyn_cast<IntegerType>(TargetsForSlot[0].Fn->getReturnType());
if (!RetType)
return false;
unsigned BitWidth = RetType->getBitWidth();
if (BitWidth > 64)
return false;
// Make sure that each function is defined, does not access memory, takes at
// least one argument, does not use its first argument (which we assume is
// 'this'), and has the same return type.
// Note that we test whether this copy of the function is readnone, rather
// than testing function attributes, which must hold for any copy of the
// function, even a less optimized version substituted at link time. This is
// sound because the virtual constant propagation optimizations effectively
// inline all implementations of the virtual function into each call site,
// rather than using function attributes to perform local optimization.
for (VirtualCallTarget &Target : TargetsForSlot) {
if (Target.Fn->isDeclaration() ||
computeFunctionBodyMemoryAccess(*Target.Fn, AARGetter(*Target.Fn)) !=
MAK_ReadNone ||
Target.Fn->arg_empty() || !Target.Fn->arg_begin()->use_empty() ||
Target.Fn->getReturnType() != RetType)
return false;
for (auto &&CSByConstantArg : SlotInfo.ConstCSInfo) {
if (!tryEvaluateFunctionsWithArgs(TargetsForSlot, CSByConstantArg.first))
WholeProgramDevirtResolution::ByArg *ResByArg = nullptr;
if (Res)
ResByArg = &Res->ResByArg[CSByConstantArg.first];
if (tryUniformRetValOpt(TargetsForSlot, CSByConstantArg.second, ResByArg))
if (tryUniqueRetValOpt(BitWidth, TargetsForSlot, CSByConstantArg.second,
ResByArg, Slot, CSByConstantArg.first))
// Find an allocation offset in bits in all vtables associated with the
// type.
uint64_t AllocBefore =
findLowestOffset(TargetsForSlot, /*IsAfter=*/false, BitWidth);
uint64_t AllocAfter =
findLowestOffset(TargetsForSlot, /*IsAfter=*/true, BitWidth);
// Calculate the total amount of padding needed to store a value at both
// ends of the object.
uint64_t TotalPaddingBefore = 0, TotalPaddingAfter = 0;
for (auto &&Target : TargetsForSlot) {
TotalPaddingBefore += std::max<int64_t>(
(AllocBefore + 7) / 8 - Target.allocatedBeforeBytes() - 1, 0);
TotalPaddingAfter += std::max<int64_t>(
(AllocAfter + 7) / 8 - Target.allocatedAfterBytes() - 1, 0);
// If the amount of padding is too large, give up.
// FIXME: do something smarter here.
if (std::min(TotalPaddingBefore, TotalPaddingAfter) > 128)
// Calculate the offset to the value as a (possibly negative) byte offset
// and (if applicable) a bit offset, and store the values in the targets.
int64_t OffsetByte;
uint64_t OffsetBit;
if (TotalPaddingBefore <= TotalPaddingAfter)
setBeforeReturnValues(TargetsForSlot, AllocBefore, BitWidth, OffsetByte,
setAfterReturnValues(TargetsForSlot, AllocAfter, BitWidth, OffsetByte,
if (RemarksEnabled)
for (auto &&Target : TargetsForSlot)
Target.WasDevirt = true;
if (CSByConstantArg.second.isExported()) {
ResByArg->TheKind = WholeProgramDevirtResolution::ByArg::VirtualConstProp;
exportConstant(Slot, CSByConstantArg.first, "byte", OffsetByte,
exportConstant(Slot, CSByConstantArg.first, "bit", 1ULL << OffsetBit,
// Rewrite each call to a load from OffsetByte/OffsetBit.
Constant *ByteConst = ConstantInt::get(Int32Ty, OffsetByte);
Constant *BitConst = ConstantInt::get(Int8Ty, 1ULL << OffsetBit);
TargetsForSlot[0].Fn->getName(), ByteConst, BitConst);
return true;
void DevirtModule::rebuildGlobal(VTableBits &B) {
if (B.Before.Bytes.empty() && B.After.Bytes.empty())
// Align each byte array to pointer width.
unsigned PointerSize = M.getDataLayout().getPointerSize();
B.Before.Bytes.resize(alignTo(B.Before.Bytes.size(), PointerSize));
B.After.Bytes.resize(alignTo(B.After.Bytes.size(), PointerSize));
// Before was stored in reverse order; flip it now.
for (size_t I = 0, Size = B.Before.Bytes.size(); I != Size / 2; ++I)
std::swap(B.Before.Bytes[I], B.Before.Bytes[Size - 1 - I]);
// Build an anonymous global containing the before bytes, followed by the
// original initializer, followed by the after bytes.
auto NewInit = ConstantStruct::getAnon(
{ConstantDataArray::get(M.getContext(), B.Before.Bytes),
ConstantDataArray::get(M.getContext(), B.After.Bytes)});
auto NewGV =
new GlobalVariable(M, NewInit->getType(), B.GV->isConstant(),
GlobalVariable::PrivateLinkage, NewInit, "", B.GV);
// Copy the original vtable's metadata to the anonymous global, adjusting
// offsets as required.
NewGV->copyMetadata(B.GV, B.Before.Bytes.size());
// Build an alias named after the original global, pointing at the second
// element (the original initializer).
auto Alias = GlobalAlias::create(
B.GV->getInitializer()->getType(), 0, B.GV->getLinkage(), "",
NewInit->getType(), NewGV,
ArrayRef<Constant *>{ConstantInt::get(Int32Ty, 0),
ConstantInt::get(Int32Ty, 1)}),
bool DevirtModule::areRemarksEnabled() {
const auto &FL = M.getFunctionList();
if (FL.empty())
return false;
const Function &Fn = FL.front();
const auto &BBL = Fn.getBasicBlockList();
if (BBL.empty())
return false;
auto DI = OptimizationRemark(DEBUG_TYPE, "", DebugLoc(), &BBL.front());
return DI.isEnabled();
void DevirtModule::scanTypeTestUsers(Function *TypeTestFunc,
Function *AssumeFunc) {
// Find all virtual calls via a virtual table pointer %p under an assumption
// of the form llvm.assume(llvm.type.test(%p, %md)). This indicates that %p
// points to a member of the type identifier %md. Group calls by (type ID,
// offset) pair (effectively the identity of the virtual function) and store
// to CallSlots.
DenseSet<Value *> SeenPtrs;
for (auto I = TypeTestFunc->use_begin(), E = TypeTestFunc->use_end();
I != E;) {
auto CI = dyn_cast<CallInst>(I->getUser());
if (!CI)
// Search for virtual calls based on %p and add them to DevirtCalls.
SmallVector<DevirtCallSite, 1> DevirtCalls;
SmallVector<CallInst *, 1> Assumes;
findDevirtualizableCallsForTypeTest(DevirtCalls, Assumes, CI);
// If we found any, add them to CallSlots. Only do this if we haven't seen
// the vtable pointer before, as it may have been CSE'd with pointers from
// other call sites, and we don't want to process call sites multiple times.
if (!Assumes.empty()) {
Metadata *TypeId =
Value *Ptr = CI->getArgOperand(0)->stripPointerCasts();
if (SeenPtrs.insert(Ptr).second) {
for (DevirtCallSite Call : DevirtCalls) {
CallSlots[{TypeId, Call.Offset}].addCallSite(Ptr, Call.CS, nullptr);
// We no longer need the assumes or the type test.
for (auto Assume : Assumes)
// We can't use RecursivelyDeleteTriviallyDeadInstructions here because we
// may use the vtable argument later.
if (CI->use_empty())
void DevirtModule::scanTypeCheckedLoadUsers(Function *TypeCheckedLoadFunc) {
Function *TypeTestFunc = Intrinsic::getDeclaration(&M, Intrinsic::type_test);
for (auto I = TypeCheckedLoadFunc->use_begin(),
E = TypeCheckedLoadFunc->use_end();
I != E;) {
auto CI = dyn_cast<CallInst>(I->getUser());
if (!CI)
Value *Ptr = CI->getArgOperand(0);
Value *Offset = CI->getArgOperand(1);
Value *TypeIdValue = CI->getArgOperand(2);
Metadata *TypeId = cast<MetadataAsValue>(TypeIdValue)->getMetadata();
SmallVector<DevirtCallSite, 1> DevirtCalls;
SmallVector<Instruction *, 1> LoadedPtrs;
SmallVector<Instruction *, 1> Preds;
bool HasNonCallUses = false;
findDevirtualizableCallsForTypeCheckedLoad(DevirtCalls, LoadedPtrs, Preds,
HasNonCallUses, CI);
// Start by generating "pessimistic" code that explicitly loads the function
// pointer from the vtable and performs the type check. If possible, we will
// eliminate the load and the type check later.
// If possible, only generate the load at the point where it is used.
// This helps avoid unnecessary spills.
IRBuilder<> LoadB(
(LoadedPtrs.size() == 1 && !HasNonCallUses) ? LoadedPtrs[0] : CI);
Value *GEP = LoadB.CreateGEP(Int8Ty, Ptr, Offset);
Value *GEPPtr = LoadB.CreateBitCast(GEP, PointerType::getUnqual(Int8PtrTy));
Value *LoadedValue = LoadB.CreateLoad(Int8PtrTy, GEPPtr);
for (Instruction *LoadedPtr : LoadedPtrs) {
// Likewise for the type test.
IRBuilder<> CallB((Preds.size() == 1 && !HasNonCallUses) ? Preds[0] : CI);
CallInst *TypeTestCall = CallB.CreateCall(TypeTestFunc, {Ptr, TypeIdValue});
for (Instruction *Pred : Preds) {
// We have already erased any extractvalue instructions that refer to the
// intrinsic call, but the intrinsic may have other non-extractvalue uses
// (although this is unlikely). In that case, explicitly build a pair and
// RAUW it.
if (!CI->use_empty()) {
Value *Pair = UndefValue::get(CI->getType());
IRBuilder<> B(CI);
Pair = B.CreateInsertValue(Pair, LoadedValue, {0});
Pair = B.CreateInsertValue(Pair, TypeTestCall, {1});
// The number of unsafe uses is initially the number of uses.
auto &NumUnsafeUses = NumUnsafeUsesForTypeTest[TypeTestCall];
NumUnsafeUses = DevirtCalls.size();
// If the function pointer has a non-call user, we cannot eliminate the type
// check, as one of those users may eventually call the pointer. Increment
// the unsafe use count to make sure it cannot reach zero.
if (HasNonCallUses)
for (DevirtCallSite Call : DevirtCalls) {
CallSlots[{TypeId, Call.Offset}].addCallSite(Ptr, Call.CS,
void DevirtModule::importResolution(VTableSlot Slot, VTableSlotInfo &SlotInfo) {
const TypeIdSummary *TidSummary =
if (!TidSummary)
auto ResI = TidSummary->WPDRes.find(Slot.ByteOffset);
if (ResI == TidSummary->WPDRes.end())
const WholeProgramDevirtResolution &Res = ResI->second;
if (Res.TheKind == WholeProgramDevirtResolution::SingleImpl) {
// The type of the function in the declaration is irrelevant because every
// call site will cast it to the correct type.
auto *SingleImpl = M.getOrInsertFunction(
Res.SingleImplName, Type::getVoidTy(M.getContext()));
// This is the import phase so we should not be exporting anything.
bool IsExported = false;
applySingleImplDevirt(SlotInfo, SingleImpl, IsExported);
for (auto &CSByConstantArg : SlotInfo.ConstCSInfo) {
auto I = Res.ResByArg.find(CSByConstantArg.first);
if (I == Res.ResByArg.end())
auto &ResByArg = I->second;
// FIXME: We should figure out what to do about the "function name" argument
// to the apply* functions, as the function names are unavailable during the
// importing phase. For now we just pass the empty string. This does not
// impact correctness because the function names are just used for remarks.
switch (ResByArg.TheKind) {
case WholeProgramDevirtResolution::ByArg::UniformRetVal:
applyUniformRetValOpt(CSByConstantArg.second, "", ResByArg.Info);
case WholeProgramDevirtResolution::ByArg::UniqueRetVal: {
Constant *UniqueMemberAddr =
importGlobal(Slot, CSByConstantArg.first, "unique_member");
applyUniqueRetValOpt(CSByConstantArg.second, "", ResByArg.Info,
case WholeProgramDevirtResolution::ByArg::VirtualConstProp: {
Constant *Byte = importConstant(Slot, CSByConstantArg.first, "byte",
Int32Ty, ResByArg.Byte);
Constant *Bit = importConstant(Slot, CSByConstantArg.first, "bit", Int8Ty,
applyVirtualConstProp(CSByConstantArg.second, "", Byte, Bit);
void DevirtModule::removeRedundantTypeTests() {
auto True = ConstantInt::getTrue(M.getContext());
for (auto &&U : NumUnsafeUsesForTypeTest) {
if (U.second == 0) {
bool DevirtModule::run() {
Function *TypeTestFunc =
Function *TypeCheckedLoadFunc =
Function *AssumeFunc = M.getFunction(Intrinsic::getName(Intrinsic::assume));
// Normally if there are no users of the devirtualization intrinsics in the
// module, this pass has nothing to do. But if we are exporting, we also need
// to handle any users that appear only in the function summaries.
if (!ExportSummary &&
(!TypeTestFunc || TypeTestFunc->use_empty() || !AssumeFunc ||
AssumeFunc->use_empty()) &&
(!TypeCheckedLoadFunc || TypeCheckedLoadFunc->use_empty()))
return false;
if (TypeTestFunc && AssumeFunc)
scanTypeTestUsers(TypeTestFunc, AssumeFunc);
if (TypeCheckedLoadFunc)
if (ImportSummary) {
for (auto &S : CallSlots)
importResolution(S.first, S.second);
// The rest of the code is only necessary when exporting or during regular
// LTO, so we are done.
return true;
// Rebuild type metadata into a map for easy lookup.
std::vector<VTableBits> Bits;
DenseMap<Metadata *, std::set<TypeMemberInfo>> TypeIdMap;
buildTypeIdentifierMap(Bits, TypeIdMap);
if (TypeIdMap.empty())
return true;
// Collect information from summary about which calls to try to devirtualize.
if (ExportSummary) {
DenseMap<GlobalValue::GUID, TinyPtrVector<Metadata *>> MetadataByGUID;
for (auto &P : TypeIdMap) {
if (auto *TypeId = dyn_cast<MDString>(P.first))
for (auto &P : *ExportSummary) {
for (auto &S : P.second.SummaryList) {
auto *FS = dyn_cast<FunctionSummary>(S.get());
if (!FS)
// FIXME: Only add live functions.
for (FunctionSummary::VFuncId VF : FS->type_test_assume_vcalls()) {
for (Metadata *MD : MetadataByGUID[VF.GUID]) {
CallSlots[{MD, VF.Offset}].CSInfo.SummaryHasTypeTestAssumeUsers =
for (FunctionSummary::VFuncId VF : FS->type_checked_load_vcalls()) {
for (Metadata *MD : MetadataByGUID[VF.GUID]) {
CallSlots[{MD, VF.Offset}]
for (const FunctionSummary::ConstVCall &VC :
FS->type_test_assume_const_vcalls()) {
for (Metadata *MD : MetadataByGUID[VC.VFunc.GUID]) {
CallSlots[{MD, VC.VFunc.Offset}]
.SummaryHasTypeTestAssumeUsers = true;
for (const FunctionSummary::ConstVCall &VC :
FS->type_checked_load_const_vcalls()) {
for (Metadata *MD : MetadataByGUID[VC.VFunc.GUID]) {
CallSlots[{MD, VC.VFunc.Offset}]
// For each (type, offset) pair:
bool DidVirtualConstProp = false;
std::map<std::string, Function*> DevirtTargets;
for (auto &S : CallSlots) {
// Search each of the members of the type identifier for the virtual
// function implementation at offset S.first.ByteOffset, and add to
// TargetsForSlot.
std::vector<VirtualCallTarget> TargetsForSlot;
if (tryFindVirtualCallTargets(TargetsForSlot, TypeIdMap[S.first.TypeID],
S.first.ByteOffset)) {
WholeProgramDevirtResolution *Res = nullptr;
if (ExportSummary && isa<MDString>(S.first.TypeID))
Res = &ExportSummary
if (!trySingleImplDevirt(TargetsForSlot, S.second, Res) &&
tryVirtualConstProp(TargetsForSlot, S.second, Res, S.first))
DidVirtualConstProp = true;
// Collect functions devirtualized at least for one call site for stats.
if (RemarksEnabled)
for (const auto &T : TargetsForSlot)
if (T.WasDevirt)
DevirtTargets[T.Fn->getName()] = T.Fn;
// CFI-specific: if we are exporting and any llvm.type.checked.load
// intrinsics were *not* devirtualized, we need to add the resulting
// llvm.type.test intrinsics to the function summaries so that the
// LowerTypeTests pass will export them.
if (ExportSummary && isa<MDString>(S.first.TypeID)) {
auto GUID =
for (auto FS : S.second.CSInfo.SummaryTypeCheckedLoadUsers)
for (auto &CCS : S.second.ConstCSInfo)
for (auto FS : CCS.second.SummaryTypeCheckedLoadUsers)
if (RemarksEnabled) {
// Generate remarks for each devirtualized function.
for (const auto &DT : DevirtTargets) {
Function *F = DT.second;
// In the new pass manager, we can request the optimization
// remark emitter pass on a per-function-basis, which the
// OREGetter will do for us.
// In the old pass manager, this is harder, so we just build
// a optimization remark emitter on the fly, when we need it.
std::unique_ptr<OptimizationRemarkEmitter> OwnedORE;
OptimizationRemarkEmitter *ORE;
if (OREGetter)
ORE = &OREGetter(F);
else {
OwnedORE = make_unique<OptimizationRemarkEmitter>(F);
ORE = OwnedORE.get();
using namespace ore;
ORE->emit(OptimizationRemark(DEBUG_TYPE, "Devirtualized", F)
<< "devirtualized " << NV("FunctionName", F->getName()));
// Rebuild each global we touched as part of virtual constant propagation to
// include the before and after bytes.
if (DidVirtualConstProp)
for (VTableBits &B : Bits)
return true;