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LTO.cpp
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//===-LTO.cpp - LLVM Link Time Optimizer ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements functions and classes used to support LTO.
//
//===----------------------------------------------------------------------===//
#include "llvm/LTO/LTO.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/StackSafetyAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/AutoUpgrade.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMRemarkStreamer.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/RuntimeLibcalls.h"
#include "llvm/LTO/LTOBackend.h"
#include "llvm/LTO/SummaryBasedOptimizations.h"
#include "llvm/Linker/IRMover.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Object/IRObjectFile.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SHA1.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/Threading.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/VCSRevision.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/MemProfContextDisambiguation.h"
#include "llvm/Transforms/IPO/WholeProgramDevirt.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include "llvm/Transforms/Utils/SplitModule.h"
#include <optional>
#include <set>
using namespace llvm;
using namespace lto;
using namespace object;
#define DEBUG_TYPE "lto"
extern cl::opt<bool> UseNewDbgInfoFormat;
static cl::opt<bool>
DumpThinCGSCCs("dump-thin-cg-sccs", cl::init(false), cl::Hidden,
cl::desc("Dump the SCCs in the ThinLTO index's callgraph"));
namespace llvm {
/// Enable global value internalization in LTO.
cl::opt<bool> EnableLTOInternalization(
"enable-lto-internalization", cl::init(true), cl::Hidden,
cl::desc("Enable global value internalization in LTO"));
/// Indicate we are linking with an allocator that supports hot/cold operator
/// new interfaces.
extern cl::opt<bool> SupportsHotColdNew;
/// Enable MemProf context disambiguation for thin link.
extern cl::opt<bool> EnableMemProfContextDisambiguation;
} // namespace llvm
// Computes a unique hash for the Module considering the current list of
// export/import and other global analysis results.
// Returns the hash in its hexadecimal representation.
std::string llvm::computeLTOCacheKey(
const Config &Conf, const ModuleSummaryIndex &Index, StringRef ModuleID,
const FunctionImporter::ImportMapTy &ImportList,
const FunctionImporter::ExportSetTy &ExportList,
const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
const GVSummaryMapTy &DefinedGlobals,
const DenseSet<GlobalValue::GUID> &CfiFunctionDefs,
const DenseSet<GlobalValue::GUID> &CfiFunctionDecls) {
// Compute the unique hash for this entry.
// This is based on the current compiler version, the module itself, the
// export list, the hash for every single module in the import list, the
// list of ResolvedODR for the module, and the list of preserved symbols.
SHA1 Hasher;
// Start with the compiler revision
Hasher.update(LLVM_VERSION_STRING);
#ifdef LLVM_REVISION
Hasher.update(LLVM_REVISION);
#endif
// Include the parts of the LTO configuration that affect code generation.
auto AddString = [&](StringRef Str) {
Hasher.update(Str);
Hasher.update(ArrayRef<uint8_t>{0});
};
auto AddUnsigned = [&](unsigned I) {
uint8_t Data[4];
support::endian::write32le(Data, I);
Hasher.update(Data);
};
auto AddUint64 = [&](uint64_t I) {
uint8_t Data[8];
support::endian::write64le(Data, I);
Hasher.update(Data);
};
auto AddUint8 = [&](const uint8_t I) {
Hasher.update(ArrayRef<uint8_t>((const uint8_t *)&I, 1));
};
AddString(Conf.CPU);
// FIXME: Hash more of Options. For now all clients initialize Options from
// command-line flags (which is unsupported in production), but may set
// X86RelaxRelocations. The clang driver can also pass FunctionSections,
// DataSections and DebuggerTuning via command line flags.
AddUnsigned(Conf.Options.MCOptions.X86RelaxRelocations);
AddUnsigned(Conf.Options.FunctionSections);
AddUnsigned(Conf.Options.DataSections);
AddUnsigned((unsigned)Conf.Options.DebuggerTuning);
for (auto &A : Conf.MAttrs)
AddString(A);
if (Conf.RelocModel)
AddUnsigned(*Conf.RelocModel);
else
AddUnsigned(-1);
if (Conf.CodeModel)
AddUnsigned(*Conf.CodeModel);
else
AddUnsigned(-1);
for (const auto &S : Conf.MllvmArgs)
AddString(S);
AddUnsigned(static_cast<int>(Conf.CGOptLevel));
AddUnsigned(static_cast<int>(Conf.CGFileType));
AddUnsigned(Conf.OptLevel);
AddUnsigned(Conf.Freestanding);
AddString(Conf.OptPipeline);
AddString(Conf.AAPipeline);
AddString(Conf.OverrideTriple);
AddString(Conf.DefaultTriple);
AddString(Conf.DwoDir);
// Include the hash for the current module
auto ModHash = Index.getModuleHash(ModuleID);
Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
// TODO: `ExportList` is determined by `ImportList`. Since `ImportList` is
// used to compute cache key, we could omit hashing `ExportList` here.
std::vector<uint64_t> ExportsGUID;
ExportsGUID.reserve(ExportList.size());
for (const auto &VI : ExportList)
ExportsGUID.push_back(VI.getGUID());
// Sort the export list elements GUIDs.
llvm::sort(ExportsGUID);
for (auto GUID : ExportsGUID)
Hasher.update(ArrayRef<uint8_t>((uint8_t *)&GUID, sizeof(GUID)));
// Include the hash for every module we import functions from. The set of
// imported symbols for each module may affect code generation and is
// sensitive to link order, so include that as well.
using ImportMapIteratorTy =
FunctionImporter::ImportMapTy::ImportMapTyImpl::const_iterator;
struct ImportModule {
ImportMapIteratorTy ModIt;
const ModuleSummaryIndex::ModuleInfo *ModInfo;
StringRef getIdentifier() const { return ModIt->getFirst(); }
const FunctionImporter::FunctionsToImportTy &getFunctions() const {
return ModIt->second;
}
const ModuleHash &getHash() const { return ModInfo->second; }
};
std::vector<ImportModule> ImportModulesVector;
ImportModulesVector.reserve(ImportList.getImportMap().size());
for (ImportMapIteratorTy It = ImportList.getImportMap().begin();
It != ImportList.getImportMap().end(); ++It) {
ImportModulesVector.push_back({It, Index.getModule(It->getFirst())});
}
// Order using module hash, to be both independent of module name and
// module order.
llvm::sort(ImportModulesVector,
[](const ImportModule &Lhs, const ImportModule &Rhs) -> bool {
return Lhs.getHash() < Rhs.getHash();
});
std::vector<std::pair<uint64_t, uint8_t>> ImportedGUIDs;
for (const ImportModule &Entry : ImportModulesVector) {
auto ModHash = Entry.getHash();
Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
AddUint64(Entry.getFunctions().size());
ImportedGUIDs.clear();
for (auto &[Fn, ImportType] : Entry.getFunctions())
ImportedGUIDs.push_back(std::make_pair(Fn, ImportType));
llvm::sort(ImportedGUIDs);
for (auto &[GUID, Type] : ImportedGUIDs) {
AddUint64(GUID);
AddUint8(Type);
}
}
// Include the hash for the resolved ODR.
for (auto &Entry : ResolvedODR) {
Hasher.update(ArrayRef<uint8_t>((const uint8_t *)&Entry.first,
sizeof(GlobalValue::GUID)));
Hasher.update(ArrayRef<uint8_t>((const uint8_t *)&Entry.second,
sizeof(GlobalValue::LinkageTypes)));
}
// Members of CfiFunctionDefs and CfiFunctionDecls that are referenced or
// defined in this module.
std::set<GlobalValue::GUID> UsedCfiDefs;
std::set<GlobalValue::GUID> UsedCfiDecls;
// Typeids used in this module.
std::set<GlobalValue::GUID> UsedTypeIds;
auto AddUsedCfiGlobal = [&](GlobalValue::GUID ValueGUID) {
if (CfiFunctionDefs.contains(ValueGUID))
UsedCfiDefs.insert(ValueGUID);
if (CfiFunctionDecls.contains(ValueGUID))
UsedCfiDecls.insert(ValueGUID);
};
auto AddUsedThings = [&](GlobalValueSummary *GS) {
if (!GS) return;
AddUnsigned(GS->getVisibility());
AddUnsigned(GS->isLive());
AddUnsigned(GS->canAutoHide());
for (const ValueInfo &VI : GS->refs()) {
AddUnsigned(VI.isDSOLocal(Index.withDSOLocalPropagation()));
AddUsedCfiGlobal(VI.getGUID());
}
if (auto *GVS = dyn_cast<GlobalVarSummary>(GS)) {
AddUnsigned(GVS->maybeReadOnly());
AddUnsigned(GVS->maybeWriteOnly());
}
if (auto *FS = dyn_cast<FunctionSummary>(GS)) {
for (auto &TT : FS->type_tests())
UsedTypeIds.insert(TT);
for (auto &TT : FS->type_test_assume_vcalls())
UsedTypeIds.insert(TT.GUID);
for (auto &TT : FS->type_checked_load_vcalls())
UsedTypeIds.insert(TT.GUID);
for (auto &TT : FS->type_test_assume_const_vcalls())
UsedTypeIds.insert(TT.VFunc.GUID);
for (auto &TT : FS->type_checked_load_const_vcalls())
UsedTypeIds.insert(TT.VFunc.GUID);
for (auto &ET : FS->calls()) {
AddUnsigned(ET.first.isDSOLocal(Index.withDSOLocalPropagation()));
AddUsedCfiGlobal(ET.first.getGUID());
}
}
};
// Include the hash for the linkage type to reflect internalization and weak
// resolution, and collect any used type identifier resolutions.
for (auto &GS : DefinedGlobals) {
GlobalValue::LinkageTypes Linkage = GS.second->linkage();
Hasher.update(
ArrayRef<uint8_t>((const uint8_t *)&Linkage, sizeof(Linkage)));
AddUsedCfiGlobal(GS.first);
AddUsedThings(GS.second);
}
// Imported functions may introduce new uses of type identifier resolutions,
// so we need to collect their used resolutions as well.
for (const ImportModule &ImpM : ImportModulesVector)
for (auto &[GUID, UnusedImportType] : ImpM.getFunctions()) {
GlobalValueSummary *S =
Index.findSummaryInModule(GUID, ImpM.getIdentifier());
AddUsedThings(S);
// If this is an alias, we also care about any types/etc. that the aliasee
// may reference.
if (auto *AS = dyn_cast_or_null<AliasSummary>(S))
AddUsedThings(AS->getBaseObject());
}
auto AddTypeIdSummary = [&](StringRef TId, const TypeIdSummary &S) {
AddString(TId);
AddUnsigned(S.TTRes.TheKind);
AddUnsigned(S.TTRes.SizeM1BitWidth);
AddUint64(S.TTRes.AlignLog2);
AddUint64(S.TTRes.SizeM1);
AddUint64(S.TTRes.BitMask);
AddUint64(S.TTRes.InlineBits);
AddUint64(S.WPDRes.size());
for (auto &WPD : S.WPDRes) {
AddUnsigned(WPD.first);
AddUnsigned(WPD.second.TheKind);
AddString(WPD.second.SingleImplName);
AddUint64(WPD.second.ResByArg.size());
for (auto &ByArg : WPD.second.ResByArg) {
AddUint64(ByArg.first.size());
for (uint64_t Arg : ByArg.first)
AddUint64(Arg);
AddUnsigned(ByArg.second.TheKind);
AddUint64(ByArg.second.Info);
AddUnsigned(ByArg.second.Byte);
AddUnsigned(ByArg.second.Bit);
}
}
};
// Include the hash for all type identifiers used by this module.
for (GlobalValue::GUID TId : UsedTypeIds) {
auto TidIter = Index.typeIds().equal_range(TId);
for (const auto &I : make_range(TidIter))
AddTypeIdSummary(I.second.first, I.second.second);
}
AddUnsigned(UsedCfiDefs.size());
for (auto &V : UsedCfiDefs)
AddUint64(V);
AddUnsigned(UsedCfiDecls.size());
for (auto &V : UsedCfiDecls)
AddUint64(V);
if (!Conf.SampleProfile.empty()) {
auto FileOrErr = MemoryBuffer::getFile(Conf.SampleProfile);
if (FileOrErr) {
Hasher.update(FileOrErr.get()->getBuffer());
if (!Conf.ProfileRemapping.empty()) {
FileOrErr = MemoryBuffer::getFile(Conf.ProfileRemapping);
if (FileOrErr)
Hasher.update(FileOrErr.get()->getBuffer());
}
}
}
return toHex(Hasher.result());
}
static void thinLTOResolvePrevailingGUID(
const Config &C, ValueInfo VI,
DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
isPrevailing,
function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
recordNewLinkage,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
GlobalValue::VisibilityTypes Visibility =
C.VisibilityScheme == Config::ELF ? VI.getELFVisibility()
: GlobalValue::DefaultVisibility;
for (auto &S : VI.getSummaryList()) {
GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
// Ignore local and appending linkage values since the linker
// doesn't resolve them.
if (GlobalValue::isLocalLinkage(OriginalLinkage) ||
GlobalValue::isAppendingLinkage(S->linkage()))
continue;
// We need to emit only one of these. The prevailing module will keep it,
// but turned into a weak, while the others will drop it when possible.
// This is both a compile-time optimization and a correctness
// transformation. This is necessary for correctness when we have exported
// a reference - we need to convert the linkonce to weak to
// ensure a copy is kept to satisfy the exported reference.
// FIXME: We may want to split the compile time and correctness
// aspects into separate routines.
if (isPrevailing(VI.getGUID(), S.get())) {
if (GlobalValue::isLinkOnceLinkage(OriginalLinkage)) {
S->setLinkage(GlobalValue::getWeakLinkage(
GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
// The kept copy is eligible for auto-hiding (hidden visibility) if all
// copies were (i.e. they were all linkonce_odr global unnamed addr).
// If any copy is not (e.g. it was originally weak_odr), then the symbol
// must remain externally available (e.g. a weak_odr from an explicitly
// instantiated template). Additionally, if it is in the
// GUIDPreservedSymbols set, that means that it is visibile outside
// the summary (e.g. in a native object or a bitcode file without
// summary), and in that case we cannot hide it as it isn't possible to
// check all copies.
S->setCanAutoHide(VI.canAutoHide() &&
!GUIDPreservedSymbols.count(VI.getGUID()));
}
if (C.VisibilityScheme == Config::FromPrevailing)
Visibility = S->getVisibility();
}
// Alias and aliasee can't be turned into available_externally.
else if (!isa<AliasSummary>(S.get()) &&
!GlobalInvolvedWithAlias.count(S.get()))
S->setLinkage(GlobalValue::AvailableExternallyLinkage);
// For ELF, set visibility to the computed visibility from summaries. We
// don't track visibility from declarations so this may be more relaxed than
// the most constraining one.
if (C.VisibilityScheme == Config::ELF)
S->setVisibility(Visibility);
if (S->linkage() != OriginalLinkage)
recordNewLinkage(S->modulePath(), VI.getGUID(), S->linkage());
}
if (C.VisibilityScheme == Config::FromPrevailing) {
for (auto &S : VI.getSummaryList()) {
GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
if (GlobalValue::isLocalLinkage(OriginalLinkage) ||
GlobalValue::isAppendingLinkage(S->linkage()))
continue;
S->setVisibility(Visibility);
}
}
}
/// Resolve linkage for prevailing symbols in the \p Index.
//
// We'd like to drop these functions if they are no longer referenced in the
// current module. However there is a chance that another module is still
// referencing them because of the import. We make sure we always emit at least
// one copy.
void llvm::thinLTOResolvePrevailingInIndex(
const Config &C, ModuleSummaryIndex &Index,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
isPrevailing,
function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
recordNewLinkage,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
// We won't optimize the globals that are referenced by an alias for now
// Ideally we should turn the alias into a global and duplicate the definition
// when needed.
DenseSet<GlobalValueSummary *> GlobalInvolvedWithAlias;
for (auto &I : Index)
for (auto &S : I.second.SummaryList)
if (auto AS = dyn_cast<AliasSummary>(S.get()))
GlobalInvolvedWithAlias.insert(&AS->getAliasee());
for (auto &I : Index)
thinLTOResolvePrevailingGUID(C, Index.getValueInfo(I),
GlobalInvolvedWithAlias, isPrevailing,
recordNewLinkage, GUIDPreservedSymbols);
}
static void thinLTOInternalizeAndPromoteGUID(
ValueInfo VI, function_ref<bool(StringRef, ValueInfo)> isExported,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
isPrevailing) {
auto ExternallyVisibleCopies =
llvm::count_if(VI.getSummaryList(),
[](const std::unique_ptr<GlobalValueSummary> &Summary) {
return !GlobalValue::isLocalLinkage(Summary->linkage());
});
for (auto &S : VI.getSummaryList()) {
// First see if we need to promote an internal value because it is not
// exported.
if (isExported(S->modulePath(), VI)) {
if (GlobalValue::isLocalLinkage(S->linkage()))
S->setLinkage(GlobalValue::ExternalLinkage);
continue;
}
// Otherwise, see if we can internalize.
if (!EnableLTOInternalization)
continue;
// Non-exported values with external linkage can be internalized.
if (GlobalValue::isExternalLinkage(S->linkage())) {
S->setLinkage(GlobalValue::InternalLinkage);
continue;
}
// Non-exported function and variable definitions with a weak-for-linker
// linkage can be internalized in certain cases. The minimum legality
// requirements would be that they are not address taken to ensure that we
// don't break pointer equality checks, and that variables are either read-
// or write-only. For functions, this is the case if either all copies are
// [local_]unnamed_addr, or we can propagate reference edge attributes
// (which is how this is guaranteed for variables, when analyzing whether
// they are read or write-only).
//
// However, we only get to this code for weak-for-linkage values in one of
// two cases:
// 1) The prevailing copy is not in IR (it is in native code).
// 2) The prevailing copy in IR is not exported from its module.
// Additionally, at least for the new LTO API, case 2 will only happen if
// there is exactly one definition of the value (i.e. in exactly one
// module), as duplicate defs are result in the value being marked exported.
// Likely, users of the legacy LTO API are similar, however, currently there
// are llvm-lto based tests of the legacy LTO API that do not mark
// duplicate linkonce_odr copies as exported via the tool, so we need
// to handle that case below by checking the number of copies.
//
// Generally, we only want to internalize a weak-for-linker value in case
// 2, because in case 1 we cannot see how the value is used to know if it
// is read or write-only. We also don't want to bloat the binary with
// multiple internalized copies of non-prevailing linkonce/weak functions.
// Note if we don't internalize, we will convert non-prevailing copies to
// available_externally anyway, so that we drop them after inlining. The
// only reason to internalize such a function is if we indeed have a single
// copy, because internalizing it won't increase binary size, and enables
// use of inliner heuristics that are more aggressive in the face of a
// single call to a static (local). For variables, internalizing a read or
// write only variable can enable more aggressive optimization. However, we
// already perform this elsewhere in the ThinLTO backend handling for
// read or write-only variables (processGlobalForThinLTO).
//
// Therefore, only internalize linkonce/weak if there is a single copy, that
// is prevailing in this IR module. We can do so aggressively, without
// requiring the address to be insignificant, or that a variable be read or
// write-only.
if (!GlobalValue::isWeakForLinker(S->linkage()) ||
GlobalValue::isExternalWeakLinkage(S->linkage()))
continue;
if (isPrevailing(VI.getGUID(), S.get()) && ExternallyVisibleCopies == 1)
S->setLinkage(GlobalValue::InternalLinkage);
}
}
// Update the linkages in the given \p Index to mark exported values
// as external and non-exported values as internal.
void llvm::thinLTOInternalizeAndPromoteInIndex(
ModuleSummaryIndex &Index,
function_ref<bool(StringRef, ValueInfo)> isExported,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
isPrevailing) {
for (auto &I : Index)
thinLTOInternalizeAndPromoteGUID(Index.getValueInfo(I), isExported,
isPrevailing);
}
// Requires a destructor for std::vector<InputModule>.
InputFile::~InputFile() = default;
Expected<std::unique_ptr<InputFile>> InputFile::create(MemoryBufferRef Object) {
std::unique_ptr<InputFile> File(new InputFile);
Expected<IRSymtabFile> FOrErr = readIRSymtab(Object);
if (!FOrErr)
return FOrErr.takeError();
File->TargetTriple = FOrErr->TheReader.getTargetTriple();
File->SourceFileName = FOrErr->TheReader.getSourceFileName();
File->COFFLinkerOpts = FOrErr->TheReader.getCOFFLinkerOpts();
File->DependentLibraries = FOrErr->TheReader.getDependentLibraries();
File->ComdatTable = FOrErr->TheReader.getComdatTable();
for (unsigned I = 0; I != FOrErr->Mods.size(); ++I) {
size_t Begin = File->Symbols.size();
for (const irsymtab::Reader::SymbolRef &Sym :
FOrErr->TheReader.module_symbols(I))
// Skip symbols that are irrelevant to LTO. Note that this condition needs
// to match the one in Skip() in LTO::addRegularLTO().
if (Sym.isGlobal() && !Sym.isFormatSpecific())
File->Symbols.push_back(Sym);
File->ModuleSymIndices.push_back({Begin, File->Symbols.size()});
}
File->Mods = FOrErr->Mods;
File->Strtab = std::move(FOrErr->Strtab);
return std::move(File);
}
StringRef InputFile::getName() const {
return Mods[0].getModuleIdentifier();
}
BitcodeModule &InputFile::getSingleBitcodeModule() {
assert(Mods.size() == 1 && "Expect only one bitcode module");
return Mods[0];
}
LTO::RegularLTOState::RegularLTOState(unsigned ParallelCodeGenParallelismLevel,
const Config &Conf)
: ParallelCodeGenParallelismLevel(ParallelCodeGenParallelismLevel),
Ctx(Conf), CombinedModule(std::make_unique<Module>("ld-temp.o", Ctx)),
Mover(std::make_unique<IRMover>(*CombinedModule)) {
CombinedModule->IsNewDbgInfoFormat = UseNewDbgInfoFormat;
}
LTO::ThinLTOState::ThinLTOState(ThinBackend Backend)
: Backend(Backend), CombinedIndex(/*HaveGVs*/ false) {
if (!Backend)
this->Backend =
createInProcessThinBackend(llvm::heavyweight_hardware_concurrency());
}
LTO::LTO(Config Conf, ThinBackend Backend,
unsigned ParallelCodeGenParallelismLevel, LTOKind LTOMode)
: Conf(std::move(Conf)),
RegularLTO(ParallelCodeGenParallelismLevel, this->Conf),
ThinLTO(std::move(Backend)),
GlobalResolutions(std::make_optional<StringMap<GlobalResolution>>()),
LTOMode(LTOMode) {}
// Requires a destructor for MapVector<BitcodeModule>.
LTO::~LTO() = default;
// Add the symbols in the given module to the GlobalResolutions map, and resolve
// their partitions.
void LTO::addModuleToGlobalRes(ArrayRef<InputFile::Symbol> Syms,
ArrayRef<SymbolResolution> Res,
unsigned Partition, bool InSummary) {
auto *ResI = Res.begin();
auto *ResE = Res.end();
(void)ResE;
const Triple TT(RegularLTO.CombinedModule->getTargetTriple());
for (const InputFile::Symbol &Sym : Syms) {
assert(ResI != ResE);
SymbolResolution Res = *ResI++;
auto &GlobalRes = (*GlobalResolutions)[Sym.getName()];
GlobalRes.UnnamedAddr &= Sym.isUnnamedAddr();
if (Res.Prevailing) {
assert(!GlobalRes.Prevailing &&
"Multiple prevailing defs are not allowed");
GlobalRes.Prevailing = true;
GlobalRes.IRName = std::string(Sym.getIRName());
} else if (!GlobalRes.Prevailing && GlobalRes.IRName.empty()) {
// Sometimes it can be two copies of symbol in a module and prevailing
// symbol can have no IR name. That might happen if symbol is defined in
// module level inline asm block. In case we have multiple modules with
// the same symbol we want to use IR name of the prevailing symbol.
// Otherwise, if we haven't seen a prevailing symbol, set the name so that
// we can later use it to check if there is any prevailing copy in IR.
GlobalRes.IRName = std::string(Sym.getIRName());
}
// In rare occasion, the symbol used to initialize GlobalRes has a different
// IRName from the inspected Symbol. This can happen on macOS + iOS, when a
// symbol is referenced through its mangled name, say @"\01_symbol" while
// the IRName is @symbol (the prefix underscore comes from MachO mangling).
// In that case, we have the same actual Symbol that can get two different
// GUID, leading to some invalid internalization. Workaround this by marking
// the GlobalRes external.
// FIXME: instead of this check, it would be desirable to compute GUIDs
// based on mangled name, but this requires an access to the Target Triple
// and would be relatively invasive on the codebase.
if (GlobalRes.IRName != Sym.getIRName()) {
GlobalRes.Partition = GlobalResolution::External;
GlobalRes.VisibleOutsideSummary = true;
}
// Set the partition to external if we know it is re-defined by the linker
// with -defsym or -wrap options, used elsewhere, e.g. it is visible to a
// regular object, is referenced from llvm.compiler.used/llvm.used, or was
// already recorded as being referenced from a different partition.
if (Res.LinkerRedefined || Res.VisibleToRegularObj || Sym.isUsed() ||
(GlobalRes.Partition != GlobalResolution::Unknown &&
GlobalRes.Partition != Partition)) {
GlobalRes.Partition = GlobalResolution::External;
} else
// First recorded reference, save the current partition.
GlobalRes.Partition = Partition;
// Flag as visible outside of summary if visible from a regular object or
// from a module that does not have a summary.
GlobalRes.VisibleOutsideSummary |=
(Res.VisibleToRegularObj || Sym.isUsed() || !InSummary);
GlobalRes.ExportDynamic |= Res.ExportDynamic;
}
}
static void writeToResolutionFile(raw_ostream &OS, InputFile *Input,
ArrayRef<SymbolResolution> Res) {
StringRef Path = Input->getName();
OS << Path << '\n';
auto ResI = Res.begin();
for (const InputFile::Symbol &Sym : Input->symbols()) {
assert(ResI != Res.end());
SymbolResolution Res = *ResI++;
OS << "-r=" << Path << ',' << Sym.getName() << ',';
if (Res.Prevailing)
OS << 'p';
if (Res.FinalDefinitionInLinkageUnit)
OS << 'l';
if (Res.VisibleToRegularObj)
OS << 'x';
if (Res.LinkerRedefined)
OS << 'r';
OS << '\n';
}
OS.flush();
assert(ResI == Res.end());
}
Error LTO::add(std::unique_ptr<InputFile> Input,
ArrayRef<SymbolResolution> Res) {
assert(!CalledGetMaxTasks);
if (Conf.ResolutionFile)
writeToResolutionFile(*Conf.ResolutionFile, Input.get(), Res);
if (RegularLTO.CombinedModule->getTargetTriple().empty()) {
RegularLTO.CombinedModule->setTargetTriple(Input->getTargetTriple());
if (Triple(Input->getTargetTriple()).isOSBinFormatELF())
Conf.VisibilityScheme = Config::ELF;
}
const SymbolResolution *ResI = Res.begin();
for (unsigned I = 0; I != Input->Mods.size(); ++I)
if (Error Err = addModule(*Input, I, ResI, Res.end()))
return Err;
assert(ResI == Res.end());
return Error::success();
}
Error LTO::addModule(InputFile &Input, unsigned ModI,
const SymbolResolution *&ResI,
const SymbolResolution *ResE) {
Expected<BitcodeLTOInfo> LTOInfo = Input.Mods[ModI].getLTOInfo();
if (!LTOInfo)
return LTOInfo.takeError();
if (EnableSplitLTOUnit) {
// If only some modules were split, flag this in the index so that
// we can skip or error on optimizations that need consistently split
// modules (whole program devirt and lower type tests).
if (*EnableSplitLTOUnit != LTOInfo->EnableSplitLTOUnit)
ThinLTO.CombinedIndex.setPartiallySplitLTOUnits();
} else
EnableSplitLTOUnit = LTOInfo->EnableSplitLTOUnit;
BitcodeModule BM = Input.Mods[ModI];
if ((LTOMode == LTOK_UnifiedRegular || LTOMode == LTOK_UnifiedThin) &&
!LTOInfo->UnifiedLTO)
return make_error<StringError>(
"unified LTO compilation must use "
"compatible bitcode modules (use -funified-lto)",
inconvertibleErrorCode());
if (LTOInfo->UnifiedLTO && LTOMode == LTOK_Default)
LTOMode = LTOK_UnifiedThin;
bool IsThinLTO = LTOInfo->IsThinLTO && (LTOMode != LTOK_UnifiedRegular);
auto ModSyms = Input.module_symbols(ModI);
addModuleToGlobalRes(ModSyms, {ResI, ResE},
IsThinLTO ? ThinLTO.ModuleMap.size() + 1 : 0,
LTOInfo->HasSummary);
if (IsThinLTO)
return addThinLTO(BM, ModSyms, ResI, ResE);
RegularLTO.EmptyCombinedModule = false;
Expected<RegularLTOState::AddedModule> ModOrErr =
addRegularLTO(BM, ModSyms, ResI, ResE);
if (!ModOrErr)
return ModOrErr.takeError();
if (!LTOInfo->HasSummary)
return linkRegularLTO(std::move(*ModOrErr), /*LivenessFromIndex=*/false);
// Regular LTO module summaries are added to a dummy module that represents
// the combined regular LTO module.
if (Error Err = BM.readSummary(ThinLTO.CombinedIndex, ""))
return Err;
RegularLTO.ModsWithSummaries.push_back(std::move(*ModOrErr));
return Error::success();
}
// Checks whether the given global value is in a non-prevailing comdat
// (comdat containing values the linker indicated were not prevailing,
// which we then dropped to available_externally), and if so, removes
// it from the comdat. This is called for all global values to ensure the
// comdat is empty rather than leaving an incomplete comdat. It is needed for
// regular LTO modules, in case we are in a mixed-LTO mode (both regular
// and thin LTO modules) compilation. Since the regular LTO module will be
// linked first in the final native link, we want to make sure the linker
// doesn't select any of these incomplete comdats that would be left
// in the regular LTO module without this cleanup.
static void
handleNonPrevailingComdat(GlobalValue &GV,
std::set<const Comdat *> &NonPrevailingComdats) {
Comdat *C = GV.getComdat();
if (!C)
return;
if (!NonPrevailingComdats.count(C))
return;
// Additionally need to drop all global values from the comdat to
// available_externally, to satisfy the COMDAT requirement that all members
// are discarded as a unit. The non-local linkage global values avoid
// duplicate definition linker errors.
GV.setLinkage(GlobalValue::AvailableExternallyLinkage);
if (auto GO = dyn_cast<GlobalObject>(&GV))
GO->setComdat(nullptr);
}
// Add a regular LTO object to the link.
// The resulting module needs to be linked into the combined LTO module with
// linkRegularLTO.
Expected<LTO::RegularLTOState::AddedModule>
LTO::addRegularLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
const SymbolResolution *&ResI,
const SymbolResolution *ResE) {
RegularLTOState::AddedModule Mod;
Expected<std::unique_ptr<Module>> MOrErr =
BM.getLazyModule(RegularLTO.Ctx, /*ShouldLazyLoadMetadata*/ true,
/*IsImporting*/ false);
if (!MOrErr)
return MOrErr.takeError();
Module &M = **MOrErr;
Mod.M = std::move(*MOrErr);
if (Error Err = M.materializeMetadata())
return std::move(Err);
// If cfi.functions is present and we are in regular LTO mode, LowerTypeTests
// will rename local functions in the merged module as "<function name>.1".
// This causes linking errors, since other parts of the module expect the
// original function name.
if (LTOMode == LTOK_UnifiedRegular)
if (NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions"))
M.eraseNamedMetadata(CfiFunctionsMD);
UpgradeDebugInfo(M);
ModuleSymbolTable SymTab;
SymTab.addModule(&M);
for (GlobalVariable &GV : M.globals())
if (GV.hasAppendingLinkage())
Mod.Keep.push_back(&GV);
DenseSet<GlobalObject *> AliasedGlobals;
for (auto &GA : M.aliases())
if (GlobalObject *GO = GA.getAliaseeObject())
AliasedGlobals.insert(GO);
// In this function we need IR GlobalValues matching the symbols in Syms
// (which is not backed by a module), so we need to enumerate them in the same
// order. The symbol enumeration order of a ModuleSymbolTable intentionally
// matches the order of an irsymtab, but when we read the irsymtab in
// InputFile::create we omit some symbols that are irrelevant to LTO. The
// Skip() function skips the same symbols from the module as InputFile does
// from the symbol table.
auto MsymI = SymTab.symbols().begin(), MsymE = SymTab.symbols().end();
auto Skip = [&]() {
while (MsymI != MsymE) {
auto Flags = SymTab.getSymbolFlags(*MsymI);
if ((Flags & object::BasicSymbolRef::SF_Global) &&
!(Flags & object::BasicSymbolRef::SF_FormatSpecific))
return;
++MsymI;
}
};
Skip();
std::set<const Comdat *> NonPrevailingComdats;
SmallSet<StringRef, 2> NonPrevailingAsmSymbols;
for (const InputFile::Symbol &Sym : Syms) {
assert(ResI != ResE);
SymbolResolution Res = *ResI++;
assert(MsymI != MsymE);
ModuleSymbolTable::Symbol Msym = *MsymI++;
Skip();
if (GlobalValue *GV = dyn_cast_if_present<GlobalValue *>(Msym)) {
if (Res.Prevailing) {
if (Sym.isUndefined())
continue;
Mod.Keep.push_back(GV);
// For symbols re-defined with linker -wrap and -defsym options,
// set the linkage to weak to inhibit IPO. The linkage will be
// restored by the linker.
if (Res.LinkerRedefined)
GV->setLinkage(GlobalValue::WeakAnyLinkage);
GlobalValue::LinkageTypes OriginalLinkage = GV->getLinkage();
if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
GV->setLinkage(GlobalValue::getWeakLinkage(
GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
} else if (isa<GlobalObject>(GV) &&
(GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage() ||
GV->hasAvailableExternallyLinkage()) &&
!AliasedGlobals.count(cast<GlobalObject>(GV))) {
// Any of the above three types of linkage indicates that the
// chosen prevailing symbol will have the same semantics as this copy of
// the symbol, so we may be able to link it with available_externally
// linkage. We will decide later whether to do that when we link this
// module (in linkRegularLTO), based on whether it is undefined.
Mod.Keep.push_back(GV);
GV->setLinkage(GlobalValue::AvailableExternallyLinkage);
if (GV->hasComdat())
NonPrevailingComdats.insert(GV->getComdat());
cast<GlobalObject>(GV)->setComdat(nullptr);
}
// Set the 'local' flag based on the linker resolution for this symbol.
if (Res.FinalDefinitionInLinkageUnit) {
GV->setDSOLocal(true);
if (GV->hasDLLImportStorageClass())
GV->setDLLStorageClass(GlobalValue::DLLStorageClassTypes::
DefaultStorageClass);
}
} else if (auto *AS =
dyn_cast_if_present<ModuleSymbolTable::AsmSymbol *>(Msym)) {
// Collect non-prevailing symbols.
if (!Res.Prevailing)
NonPrevailingAsmSymbols.insert(AS->first);
} else {
llvm_unreachable("unknown symbol type");
}
// Common resolution: collect the maximum size/alignment over all commons.
// We also record if we see an instance of a common as prevailing, so that
// if none is prevailing we can ignore it later.
if (Sym.isCommon()) {
// FIXME: We should figure out what to do about commons defined by asm.
// For now they aren't reported correctly by ModuleSymbolTable.
auto &CommonRes = RegularLTO.Commons[std::string(Sym.getIRName())];
CommonRes.Size = std::max(CommonRes.Size, Sym.getCommonSize());
if (uint32_t SymAlignValue = Sym.getCommonAlignment()) {
CommonRes.Alignment =
std::max(Align(SymAlignValue), CommonRes.Alignment);
}
CommonRes.Prevailing |= Res.Prevailing;
}
}
if (!M.getComdatSymbolTable().empty())
for (GlobalValue &GV : M.global_values())
handleNonPrevailingComdat(GV, NonPrevailingComdats);
// Prepend ".lto_discard <sym>, <sym>*" directive to each module inline asm
// block.
if (!M.getModuleInlineAsm().empty()) {
std::string NewIA = ".lto_discard";
if (!NonPrevailingAsmSymbols.empty()) {
// Don't dicard a symbol if there is a live .symver for it.
ModuleSymbolTable::CollectAsmSymvers(
M, [&](StringRef Name, StringRef Alias) {
if (!NonPrevailingAsmSymbols.count(Alias))
NonPrevailingAsmSymbols.erase(Name);
});
NewIA += " " + llvm::join(NonPrevailingAsmSymbols, ", ");
}
NewIA += "\n";
M.setModuleInlineAsm(NewIA + M.getModuleInlineAsm());
}
assert(MsymI == MsymE);
return std::move(Mod);
}
Error LTO::linkRegularLTO(RegularLTOState::AddedModule Mod,
bool LivenessFromIndex) {
std::vector<GlobalValue *> Keep;
for (GlobalValue *GV : Mod.Keep) {
if (LivenessFromIndex && !ThinLTO.CombinedIndex.isGUIDLive(GV->getGUID())) {
if (Function *F = dyn_cast<Function>(GV)) {
if (DiagnosticOutputFile) {
if (Error Err = F->materialize())
return Err;
OptimizationRemarkEmitter ORE(F, nullptr);
ORE.emit(OptimizationRemark(DEBUG_TYPE, "deadfunction", F)
<< ore::NV("Function", F)
<< " not added to the combined module ");
}
}
continue;
}
if (!GV->hasAvailableExternallyLinkage()) {
Keep.push_back(GV);
continue;
}
// Only link available_externally definitions if we don't already have a
// definition.
GlobalValue *CombinedGV =
RegularLTO.CombinedModule->getNamedValue(GV->getName());
if (CombinedGV && !CombinedGV->isDeclaration())