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//===-LTOBackend.cpp - LLVM Link Time Optimizer Backend -------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the "backend" phase of LTO, i.e. it performs
// optimization and code generation on a loaded module. It is generally used
// internally by the LTO class but can also be used independently, for example
// to implement a standalone ThinLTO backend.
#include "llvm/LTO/LTOBackend.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CGSCCPassManager.h"
#include "llvm/Analysis/ModuleSummaryAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/IR/LLVMRemarkStreamer.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Verifier.h"
#include "llvm/LTO/LTO.h"
#include "llvm/MC/SubtargetFeature.h"
#include "llvm/Object/ModuleSymbolTable.h"
#include "llvm/Passes/PassBuilder.h"
#include "llvm/Passes/PassPlugin.h"
#include "llvm/Passes/StandardInstrumentations.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Program.h"
#include "llvm/Support/SmallVectorMemoryBuffer.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"
#include "llvm/Transforms/Scalar/LoopPassManager.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include "llvm/Transforms/Utils/SplitModule.h"
using namespace llvm;
using namespace lto;
#define DEBUG_TYPE "lto-backend"
enum class LTOBitcodeEmbedding {
DoNotEmbed = 0,
EmbedOptimized = 1,
EmbedPostMergePreOptimized = 2
static cl::opt<LTOBitcodeEmbedding> EmbedBitcode(
"lto-embed-bitcode", cl::init(LTOBitcodeEmbedding::DoNotEmbed),
cl::values(clEnumValN(LTOBitcodeEmbedding::DoNotEmbed, "none",
"Do not embed"),
clEnumValN(LTOBitcodeEmbedding::EmbedOptimized, "optimized",
"Embed after all optimization passes"),
"Embed post merge, but before optimizations")),
cl::desc("Embed LLVM bitcode in object files produced by LTO"));
static cl::opt<bool> ThinLTOAssumeMerged(
"thinlto-assume-merged", cl::init(false),
cl::desc("Assume the input has already undergone ThinLTO function "
"importing and the other pre-optimization pipeline changes."));
LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
errs() << "failed to open " << Path << ": " << Msg << '\n';
Error Config::addSaveTemps(std::string OutputFileName,
bool UseInputModulePath) {
ShouldDiscardValueNames = false;
std::error_code EC;
ResolutionFile =
std::make_unique<raw_fd_ostream>(OutputFileName + "resolution.txt", EC,
if (EC) {
return errorCodeToError(EC);
auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
// Keep track of the hook provided by the linker, which also needs to run.
ModuleHookFn LinkerHook = Hook;
Hook = [=](unsigned Task, const Module &M) {
// If the linker's hook returned false, we need to pass that result
// through.
if (LinkerHook && !LinkerHook(Task, M))
return false;
std::string PathPrefix;
// If this is the combined module (not a ThinLTO backend compile) or the
// user hasn't requested using the input module's path, emit to a file
// named from the provided OutputFileName with the Task ID appended.
if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
PathPrefix = OutputFileName;
if (Task != (unsigned)-1)
PathPrefix += utostr(Task) + ".";
} else
PathPrefix = M.getModuleIdentifier() + ".";
std::string Path = PathPrefix + PathSuffix + ".bc";
std::error_code EC;
raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
// Because -save-temps is a debugging feature, we report the error
// directly and exit.
if (EC)
reportOpenError(Path, EC.message());
WriteBitcodeToFile(M, OS, /*ShouldPreserveUseListOrder=*/false);
return true;
setHook("0.preopt", PreOptModuleHook);
setHook("1.promote", PostPromoteModuleHook);
setHook("2.internalize", PostInternalizeModuleHook);
setHook("3.import", PostImportModuleHook);
setHook("4.opt", PostOptModuleHook);
setHook("5.precodegen", PreCodeGenModuleHook);
CombinedIndexHook =
[=](const ModuleSummaryIndex &Index,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
std::string Path = OutputFileName + "index.bc";
std::error_code EC;
raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
// Because -save-temps is a debugging feature, we report the error
// directly and exit.
if (EC)
reportOpenError(Path, EC.message());
WriteIndexToFile(Index, OS);
Path = OutputFileName + "";
raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::OF_None);
if (EC)
reportOpenError(Path, EC.message());
Index.exportToDot(OSDot, GUIDPreservedSymbols);
return true;
return Error::success();
llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
#include "llvm/Support/Extension.def"
static void RegisterPassPlugins(ArrayRef<std::string> PassPlugins,
PassBuilder &PB) {
#include "llvm/Support/Extension.def"
// Load requested pass plugins and let them register pass builder callbacks
for (auto &PluginFN : PassPlugins) {
auto PassPlugin = PassPlugin::Load(PluginFN);
if (!PassPlugin) {
errs() << "Failed to load passes from '" << PluginFN
<< "'. Request ignored.\n";
static std::unique_ptr<TargetMachine>
createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
StringRef TheTriple = M.getTargetTriple();
SubtargetFeatures Features;
for (const std::string &A : Conf.MAttrs)
Optional<Reloc::Model> RelocModel = None;
if (Conf.RelocModel)
RelocModel = *Conf.RelocModel;
else if (M.getModuleFlag("PIC Level"))
RelocModel =
M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
Optional<CodeModel::Model> CodeModel;
if (Conf.CodeModel)
CodeModel = *Conf.CodeModel;
CodeModel = M.getCodeModel();
std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
CodeModel, Conf.CGOptLevel));
assert(TM && "Failed to create target machine");
return TM;
static void runNewPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
unsigned OptLevel, bool IsThinLTO,
ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary) {
Optional<PGOOptions> PGOOpt;
if (!Conf.SampleProfile.empty())
PGOOpt = PGOOptions(Conf.SampleProfile, "", Conf.ProfileRemapping,
PGOOptions::SampleUse, PGOOptions::NoCSAction, true);
else if (Conf.RunCSIRInstr) {
PGOOpt = PGOOptions("", Conf.CSIRProfile, Conf.ProfileRemapping,
PGOOptions::IRUse, PGOOptions::CSIRInstr);
} else if (!Conf.CSIRProfile.empty()) {
PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
PGOOptions::IRUse, PGOOptions::CSIRUse);
LoopAnalysisManager LAM(Conf.DebugPassManager);
FunctionAnalysisManager FAM(Conf.DebugPassManager);
CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
ModuleAnalysisManager MAM(Conf.DebugPassManager);
PassInstrumentationCallbacks PIC;
StandardInstrumentations SI(Conf.DebugPassManager);
SI.registerCallbacks(PIC, &FAM);
PassBuilder PB(Conf.DebugPassManager, TM, Conf.PTO, PGOOpt, &PIC);
RegisterPassPlugins(Conf.PassPlugins, PB);
std::unique_ptr<TargetLibraryInfoImpl> TLII(
new TargetLibraryInfoImpl(Triple(TM->getTargetTriple())));
if (Conf.Freestanding)
FAM.registerPass([&] { return TargetLibraryAnalysis(*TLII); });
AAManager AA;
// Parse a custom AA pipeline if asked to.
if (!Conf.AAPipeline.empty()) {
if (auto Err = PB.parseAAPipeline(AA, Conf.AAPipeline)) {
report_fatal_error("unable to parse AA pipeline description '" +
Conf.AAPipeline + "': " + toString(std::move(Err)));
} else {
AA = PB.buildDefaultAAPipeline();
// Register the AA manager first so that our version is the one used.
FAM.registerPass([&] { return std::move(AA); });
// Register all the basic analyses with the managers.
PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
ModulePassManager MPM(Conf.DebugPassManager);
if (!Conf.DisableVerify)
PassBuilder::OptimizationLevel OL;
switch (OptLevel) {
llvm_unreachable("Invalid optimization level");
case 0:
OL = PassBuilder::OptimizationLevel::O0;
case 1:
OL = PassBuilder::OptimizationLevel::O1;
case 2:
OL = PassBuilder::OptimizationLevel::O2;
case 3:
OL = PassBuilder::OptimizationLevel::O3;
// Parse a custom pipeline if asked to.
if (!Conf.OptPipeline.empty()) {
if (auto Err = PB.parsePassPipeline(MPM, Conf.OptPipeline)) {
report_fatal_error("unable to parse pass pipeline description '" +
Conf.OptPipeline + "': " + toString(std::move(Err)));
} else if (IsThinLTO) {
MPM.addPass(PB.buildThinLTODefaultPipeline(OL, ImportSummary));
} else {
MPM.addPass(PB.buildLTODefaultPipeline(OL, ExportSummary));
if (!Conf.DisableVerify)
MPM.addPass(VerifierPass());, MAM);
static void runOldPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary) {
legacy::PassManager passes;
PassManagerBuilder PMB;
PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
if (Conf.Freestanding)
PMB.Inliner = createFunctionInliningPass();
PMB.ExportSummary = ExportSummary;
PMB.ImportSummary = ImportSummary;
// Unconditionally verify input since it is not verified before this
// point and has unknown origin.
PMB.VerifyInput = true;
PMB.VerifyOutput = !Conf.DisableVerify;
PMB.LoopVectorize = true;
PMB.SLPVectorize = true;
PMB.OptLevel = Conf.OptLevel;
PMB.PGOSampleUse = Conf.SampleProfile;
PMB.EnablePGOCSInstrGen = Conf.RunCSIRInstr;
if (!Conf.RunCSIRInstr && !Conf.CSIRProfile.empty()) {
PMB.EnablePGOCSInstrUse = true;
PMB.PGOInstrUse = Conf.CSIRProfile;
if (IsThinLTO)
bool lto::opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary,
const std::vector<uint8_t> &CmdArgs) {
if (EmbedBitcode == LTOBitcodeEmbedding::EmbedPostMergePreOptimized) {
// FIXME: the motivation for capturing post-merge bitcode and command line
// is replicating the compilation environment from bitcode, without needing
// to understand the dependencies (the functions to be imported). This
// assumes a clang - based invocation, case in which we have the command
// line.
// It's not very clear how the above motivation would map in the
// linker-based case, so we currently don't plumb the command line args in
// that case.
if (CmdArgs.empty())
dbgs() << "Post-(Thin)LTO merge bitcode embedding was requested, but "
"command line arguments are not available");
llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
/*EmbedBitcode*/ true, /*EmbedCmdline*/ true,
/*Cmdline*/ CmdArgs);
// FIXME: Plumb the combined index into the new pass manager.
if (Conf.UseNewPM || !Conf.OptPipeline.empty()) {
runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
} else {
runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
static void codegen(const Config &Conf, TargetMachine *TM,
AddStreamFn AddStream, unsigned Task, Module &Mod,
const ModuleSummaryIndex &CombinedIndex) {
if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
if (EmbedBitcode == LTOBitcodeEmbedding::EmbedOptimized)
llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
/*EmbedBitcode*/ true,
/*EmbedCmdline*/ false,
/*CmdArgs*/ std::vector<uint8_t>());
std::unique_ptr<ToolOutputFile> DwoOut;
SmallString<1024> DwoFile(Conf.SplitDwarfOutput);
if (!Conf.DwoDir.empty()) {
std::error_code EC;
if (auto EC = llvm::sys::fs::create_directories(Conf.DwoDir))
report_fatal_error("Failed to create directory " + Conf.DwoDir + ": " +
DwoFile = Conf.DwoDir;
sys::path::append(DwoFile, std::to_string(Task) + ".dwo");
TM->Options.MCOptions.SplitDwarfFile = std::string(DwoFile);
} else
TM->Options.MCOptions.SplitDwarfFile = Conf.SplitDwarfFile;
if (!DwoFile.empty()) {
std::error_code EC;
DwoOut = std::make_unique<ToolOutputFile>(DwoFile, EC, sys::fs::OF_None);
if (EC)
report_fatal_error("Failed to open " + DwoFile + ": " + EC.message());
auto Stream = AddStream(Task);
legacy::PassManager CodeGenPasses;
if (Conf.PreCodeGenPassesHook)
if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
DwoOut ? &DwoOut->os() : nullptr,
report_fatal_error("Failed to setup codegen");;
if (DwoOut)
static void splitCodeGen(const Config &C, TargetMachine *TM,
AddStreamFn AddStream,
unsigned ParallelCodeGenParallelismLevel, Module &Mod,
const ModuleSummaryIndex &CombinedIndex) {
ThreadPool CodegenThreadPool(
unsigned ThreadCount = 0;
const Target *T = &TM->getTarget();
Mod, ParallelCodeGenParallelismLevel,
[&](std::unique_ptr<Module> MPart) {
// We want to clone the module in a new context to multi-thread the
// codegen. We do it by serializing partition modules to bitcode
// (while still on the main thread, in order to avoid data races) and
// spinning up new threads which deserialize the partitions into
// separate contexts.
// FIXME: Provide a more direct way to do this in LLVM.
SmallString<0> BC;
raw_svector_ostream BCOS(BC);
WriteBitcodeToFile(*MPart, BCOS);
// Enqueue the task
[&](const SmallString<0> &BC, unsigned ThreadId) {
LTOLLVMContext Ctx(C);
Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
MemoryBufferRef(StringRef(, BC.size()), "ld-temp.o"),
if (!MOrErr)
report_fatal_error("Failed to read bitcode");
std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
std::unique_ptr<TargetMachine> TM =
createTargetMachine(C, T, *MPartInCtx);
codegen(C, TM.get(), AddStream, ThreadId, *MPartInCtx,
// Pass BC using std::move to ensure that it get moved rather than
// copied into the thread's context.
std::move(BC), ThreadCount++);
// Because the inner lambda (which runs in a worker thread) captures our local
// variables, we need to wait for the worker threads to terminate before we
// can leave the function scope.
static Expected<const Target *> initAndLookupTarget(const Config &C,
Module &Mod) {
if (!C.OverrideTriple.empty())
else if (Mod.getTargetTriple().empty())
std::string Msg;
const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
if (!T)
return make_error<StringError>(Msg, inconvertibleErrorCode());
return T;
Error lto::finalizeOptimizationRemarks(
std::unique_ptr<ToolOutputFile> DiagOutputFile) {
// Make sure we flush the diagnostic remarks file in case the linker doesn't
// call the global destructors before exiting.
if (!DiagOutputFile)
return Error::success();
return Error::success();
Error lto::backend(const Config &C, AddStreamFn AddStream,
unsigned ParallelCodeGenParallelismLevel, Module &Mod,
ModuleSummaryIndex &CombinedIndex) {
Expected<const Target *> TOrErr = initAndLookupTarget(C, Mod);
if (!TOrErr)
return TOrErr.takeError();
std::unique_ptr<TargetMachine> TM = createTargetMachine(C, *TOrErr, Mod);
if (!C.CodeGenOnly) {
if (!opt(C, TM.get(), 0, Mod, /*IsThinLTO=*/false,
/*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr,
/*CmdArgs*/ std::vector<uint8_t>()))
return Error::success();
if (ParallelCodeGenParallelismLevel == 1) {
codegen(C, TM.get(), AddStream, 0, Mod, CombinedIndex);
} else {
splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel, Mod,
return Error::success();
static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
const ModuleSummaryIndex &Index) {
std::vector<GlobalValue*> DeadGVs;
for (auto &GV : Mod.global_values())
if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
if (!Index.isGlobalValueLive(GVS)) {
// Now that all dead bodies have been dropped, delete the actual objects
// themselves when possible.
for (GlobalValue *GV : DeadGVs) {
// Might reference something defined in native object (i.e. dropped a
// non-prevailing IR def, but we need to keep the declaration).
if (GV->use_empty())
Error lto::thinBackend(const Config &Conf, unsigned Task, AddStreamFn AddStream,
Module &Mod, const ModuleSummaryIndex &CombinedIndex,
const FunctionImporter::ImportMapTy &ImportList,
const GVSummaryMapTy &DefinedGlobals,
MapVector<StringRef, BitcodeModule> *ModuleMap,
const std::vector<uint8_t> &CmdArgs) {
Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
if (!TOrErr)
return TOrErr.takeError();
std::unique_ptr<TargetMachine> TM = createTargetMachine(Conf, *TOrErr, Mod);
// Setup optimization remarks.
auto DiagFileOrErr = lto::setupLLVMOptimizationRemarks(
Mod.getContext(), Conf.RemarksFilename, Conf.RemarksPasses,
Conf.RemarksFormat, Conf.RemarksWithHotness, Conf.RemarksHotnessThreshold,
if (!DiagFileOrErr)
return DiagFileOrErr.takeError();
auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
// Set the partial sample profile ratio in the profile summary module flag of
// the module, if applicable.
if (Conf.CodeGenOnly) {
codegen(Conf, TM.get(), AddStream, Task, Mod, CombinedIndex);
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
auto OptimizeAndCodegen =
[&](Module &Mod, TargetMachine *TM,
std::unique_ptr<ToolOutputFile> DiagnosticOutputFile) {
if (!opt(Conf, TM, Task, Mod, /*IsThinLTO=*/true,
/*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex,
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
codegen(Conf, TM, AddStream, Task, Mod, CombinedIndex);
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
if (ThinLTOAssumeMerged)
return OptimizeAndCodegen(Mod, TM.get(), std::move(DiagnosticOutputFile));
// When linking an ELF shared object, dso_local should be dropped. We
// conservatively do this for -fpic.
bool ClearDSOLocalOnDeclarations =
TM->getTargetTriple().isOSBinFormatELF() &&
TM->getRelocationModel() != Reloc::Static &&
Mod.getPIELevel() == PIELevel::Default;
renameModuleForThinLTO(Mod, CombinedIndex, ClearDSOLocalOnDeclarations);
dropDeadSymbols(Mod, DefinedGlobals, CombinedIndex);
thinLTOResolvePrevailingInModule(Mod, DefinedGlobals);
if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
if (!DefinedGlobals.empty())
thinLTOInternalizeModule(Mod, DefinedGlobals);
if (Conf.PostInternalizeModuleHook &&
!Conf.PostInternalizeModuleHook(Task, Mod))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
auto ModuleLoader = [&](StringRef Identifier) {
assert(Mod.getContext().isODRUniquingDebugTypes() &&
"ODR Type uniquing should be enabled on the context");
if (ModuleMap) {
auto I = ModuleMap->find(Identifier);
assert(I != ModuleMap->end());
return I->second.getLazyModule(Mod.getContext(),
/*IsImporting*/ true);
ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> MBOrErr =
if (!MBOrErr)
return Expected<std::unique_ptr<llvm::Module>>(make_error<StringError>(
Twine("Error loading imported file ") + Identifier + " : ",
Expected<BitcodeModule> BMOrErr = findThinLTOModule(**MBOrErr);
if (!BMOrErr)
return Expected<std::unique_ptr<llvm::Module>>(make_error<StringError>(
Twine("Error loading imported file ") + Identifier + " : " +
Expected<std::unique_ptr<Module>> MOrErr =
/*IsImporting*/ true);
if (MOrErr)
return MOrErr;
FunctionImporter Importer(CombinedIndex, ModuleLoader,
if (Error Err = Importer.importFunctions(Mod, ImportList).takeError())
return Err;
if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
return OptimizeAndCodegen(Mod, TM.get(), std::move(DiagnosticOutputFile));
BitcodeModule *lto::findThinLTOModule(MutableArrayRef<BitcodeModule> BMs) {
if (ThinLTOAssumeMerged && BMs.size() == 1)
return BMs.begin();
for (BitcodeModule &BM : BMs) {
Expected<BitcodeLTOInfo> LTOInfo = BM.getLTOInfo();
if (LTOInfo && LTOInfo->IsThinLTO)
return &BM;
return nullptr;
Expected<BitcodeModule> lto::findThinLTOModule(MemoryBufferRef MBRef) {
Expected<std::vector<BitcodeModule>> BMsOrErr = getBitcodeModuleList(MBRef);
if (!BMsOrErr)
return BMsOrErr.takeError();
// The bitcode file may contain multiple modules, we want the one that is
// marked as being the ThinLTO module.
if (const BitcodeModule *Bm = lto::findThinLTOModule(*BMsOrErr))
return *Bm;
return make_error<StringError>("Could not find module summary",
bool lto::initImportList(const Module &M,
const ModuleSummaryIndex &CombinedIndex,
FunctionImporter::ImportMapTy &ImportList) {
if (ThinLTOAssumeMerged)
return true;
// We can simply import the values mentioned in the combined index, since
// we should only invoke this using the individual indexes written out
// via a WriteIndexesThinBackend.
for (const auto &GlobalList : CombinedIndex) {
// Ignore entries for undefined references.
if (GlobalList.second.SummaryList.empty())
auto GUID = GlobalList.first;
for (const auto &Summary : GlobalList.second.SummaryList) {
// Skip the summaries for the importing module. These are included to
// e.g. record required linkage changes.
if (Summary->modulePath() == M.getModuleIdentifier())
// Add an entry to provoke importing by thinBackend.
return true;