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llvm-project/llvm/lib/LTO/ThinLTOCodeGenerator.cpp

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//===-ThinLTOCodeGenerator.cpp - LLVM Link Time Optimizer -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the Thin Link Time Optimization library. This library is
// intended to be used by linker to optimize code at link time.
//
//===----------------------------------------------------------------------===//
#include "llvm/LTO/ThinLTOCodeGenerator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/ModuleSummaryAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/BitcodeWriterPass.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/ExecutionEngine/ObjectMemoryBuffer.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IRReader/IRReader.h"
#include "llvm/Linker/Linker.h"
#include "llvm/MC/SubtargetFeature.h"
#include "llvm/Object/ModuleSummaryIndexObjectFile.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/FunctionImport.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"
#include "llvm/Transforms/ObjCARC.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
using namespace llvm;
#define DEBUG_TYPE "thinlto"
namespace llvm {
// Flags -discard-value-names, defined in LTOCodeGenerator.cpp
extern cl::opt<bool> LTODiscardValueNames;
}
namespace {
static cl::opt<int> ThreadCount("threads",
cl::init(std::thread::hardware_concurrency()));
static void diagnosticHandler(const DiagnosticInfo &DI) {
DiagnosticPrinterRawOStream DP(errs());
DI.print(DP);
errs() << '\n';
}
// Simple helper to load a module from bitcode
static std::unique_ptr<Module>
loadModuleFromBuffer(const MemoryBufferRef &Buffer, LLVMContext &Context,
bool Lazy) {
SMDiagnostic Err;
ErrorOr<std::unique_ptr<Module>> ModuleOrErr(nullptr);
if (Lazy) {
ModuleOrErr =
getLazyBitcodeModule(MemoryBuffer::getMemBuffer(Buffer, false), Context,
/* ShouldLazyLoadMetadata */ Lazy);
} else {
ModuleOrErr = parseBitcodeFile(Buffer, Context);
}
if (std::error_code EC = ModuleOrErr.getError()) {
Err = SMDiagnostic(Buffer.getBufferIdentifier(), SourceMgr::DK_Error,
EC.message());
Err.print("ThinLTO", errs());
report_fatal_error("Can't load module, abort.");
}
return std::move(ModuleOrErr.get());
}
// Simple helper to save temporary files for debug.
static void saveTempBitcode(const Module &TheModule, StringRef TempDir,
unsigned count, StringRef Suffix) {
if (TempDir.empty())
return;
// User asked to save temps, let dump the bitcode file after import.
auto SaveTempPath = TempDir + llvm::utostr(count) + Suffix;
std::error_code EC;
raw_fd_ostream OS(SaveTempPath.str(), EC, sys::fs::F_None);
if (EC)
report_fatal_error(Twine("Failed to open ") + SaveTempPath +
" to save optimized bitcode\n");
WriteBitcodeToFile(&TheModule, OS, /* ShouldPreserveUseListOrder */ true);
}
bool IsFirstDefinitionForLinker(const GlobalValueInfoList &GVInfo,
const ModuleSummaryIndex &Index,
StringRef ModulePath) {
// Get the first *linker visible* definition for this global in the summary
// list.
auto FirstDefForLinker = llvm::find_if(
GVInfo, [](const std::unique_ptr<GlobalValueInfo> &FuncInfo) {
auto Linkage = FuncInfo->summary()->linkage();
return !GlobalValue::isAvailableExternallyLinkage(Linkage);
});
// If \p GV is not the first definition, give up...
if ((*FirstDefForLinker)->summary()->modulePath() != ModulePath)
return false;
// If there is any strong definition anywhere, do not bother emitting this.
if (llvm::any_of(
GVInfo, [](const std::unique_ptr<GlobalValueInfo> &FuncInfo) {
auto Linkage = FuncInfo->summary()->linkage();
return !GlobalValue::isAvailableExternallyLinkage(Linkage) &&
!GlobalValue::isWeakForLinker(Linkage);
}))
return false;
return true;
}
static GlobalValue::LinkageTypes ResolveODR(const ModuleSummaryIndex &Index,
StringRef ModuleIdentifier,
GlobalValue::GUID GUID,
const GlobalValueSummary &GV) {
auto HasMultipleCopies =
[&](const GlobalValueInfoList &GVInfo) { return GVInfo.size() > 1; };
auto OriginalLinkage = GV.linkage();
switch (OriginalLinkage) {
case GlobalValue::ExternalLinkage:
case GlobalValue::AvailableExternallyLinkage:
case GlobalValue::AppendingLinkage:
case GlobalValue::InternalLinkage:
case GlobalValue::PrivateLinkage:
case GlobalValue::ExternalWeakLinkage:
case GlobalValue::CommonLinkage:
case GlobalValue::LinkOnceAnyLinkage:
case GlobalValue::WeakAnyLinkage:
break;
case GlobalValue::LinkOnceODRLinkage:
case GlobalValue::WeakODRLinkage: {
auto &GVInfo = Index.findGlobalValueInfoList(GUID)->second;
// We need to emit only one of these, the first module will keep
// it, but turned into a weak while the others will drop it.
if (!HasMultipleCopies(GVInfo))
break;
if (IsFirstDefinitionForLinker(GVInfo, Index, ModuleIdentifier))
return GlobalValue::WeakODRLinkage;
else
return GlobalValue::AvailableExternallyLinkage;
break;
}
}
return OriginalLinkage;
}
/// Resolve LinkOnceODR and WeakODR.
///
/// We'd like to drop these function 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.
static void ResolveODR(
const ModuleSummaryIndex &Index,
const std::map<GlobalValue::GUID, GlobalValueSummary *> &DefinedGlobals,
StringRef ModuleIdentifier,
DenseMap<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR) {
if (Index.modulePaths().size() == 1)
// Nothing to do if we don't have multiple modules
return;
// 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 &GA : DefinedGlobals) {
if (auto AS = dyn_cast<AliasSummary>(GA.second))
GlobalInvolvedWithAlias.insert(&AS->getAliasee());
}
for (auto &GV : DefinedGlobals) {
if (GlobalInvolvedWithAlias.count(GV.second))
continue;
auto NewLinkage = ResolveODR(Index, ModuleIdentifier, GV.first, *GV.second);
if (NewLinkage != GV.second->linkage()) {
ResolvedODR[GV.first] = NewLinkage;
}
}
}
/// Fixup linkage, see ResolveODR() above.
void fixupODR(
Module &TheModule,
const DenseMap<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR) {
// Process functions and global now
for (auto &GV : TheModule) {
auto NewLinkage = ResolvedODR.find(GV.getGUID());
if (NewLinkage == ResolvedODR.end())
continue;
DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName() << "` from "
<< GV.getLinkage() << " to " << NewLinkage->second << "\n");
GV.setLinkage(NewLinkage->second);
}
for (auto &GV : TheModule.globals()) {
auto NewLinkage = ResolvedODR.find(GV.getGUID());
if (NewLinkage == ResolvedODR.end())
continue;
DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName() << "` from "
<< GV.getLinkage() << " to " << NewLinkage->second << "\n");
GV.setLinkage(NewLinkage->second);
}
}
static StringMap<MemoryBufferRef>
generateModuleMap(const std::vector<MemoryBufferRef> &Modules) {
StringMap<MemoryBufferRef> ModuleMap;
for (auto &ModuleBuffer : Modules) {
assert(ModuleMap.find(ModuleBuffer.getBufferIdentifier()) ==
ModuleMap.end() &&
"Expect unique Buffer Identifier");
ModuleMap[ModuleBuffer.getBufferIdentifier()] = ModuleBuffer;
}
return ModuleMap;
}
/// Provide a "loader" for the FunctionImporter to access function from other
/// modules.
class ModuleLoader {
/// The context that will be used for importing.
LLVMContext &Context;
/// Map from Module identifier to MemoryBuffer. Used by clients like the
/// FunctionImported to request loading a Module.
StringMap<MemoryBufferRef> &ModuleMap;
public:
ModuleLoader(LLVMContext &Context, StringMap<MemoryBufferRef> &ModuleMap)
: Context(Context), ModuleMap(ModuleMap) {}
/// Load a module on demand.
std::unique_ptr<Module> operator()(StringRef Identifier) {
return loadModuleFromBuffer(ModuleMap[Identifier], Context, /*Lazy*/ true);
}
};
static void promoteModule(Module &TheModule, const ModuleSummaryIndex &Index) {
if (renameModuleForThinLTO(TheModule, Index))
report_fatal_error("renameModuleForThinLTO failed");
}
static void
crossImportIntoModule(Module &TheModule, const ModuleSummaryIndex &Index,
StringMap<MemoryBufferRef> &ModuleMap,
const FunctionImporter::ImportMapTy &ImportList) {
ModuleLoader Loader(TheModule.getContext(), ModuleMap);
FunctionImporter Importer(Index, Loader);
Importer.importFunctions(TheModule, ImportList);
}
static void optimizeModule(Module &TheModule, TargetMachine &TM) {
// Populate the PassManager
PassManagerBuilder PMB;
PMB.LibraryInfo = new TargetLibraryInfoImpl(TM.getTargetTriple());
PMB.Inliner = createFunctionInliningPass();
// FIXME: should get it from the bitcode?
PMB.OptLevel = 3;
PMB.LoopVectorize = true;
PMB.SLPVectorize = true;
PMB.VerifyInput = true;
PMB.VerifyOutput = false;
legacy::PassManager PM;
// Add the TTI (required to inform the vectorizer about register size for
// instance)
PM.add(createTargetTransformInfoWrapperPass(TM.getTargetIRAnalysis()));
// Add optimizations
PMB.populateThinLTOPassManager(PM);
PM.run(TheModule);
}
std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
TargetMachine &TM) {
SmallVector<char, 128> OutputBuffer;
// CodeGen
{
raw_svector_ostream OS(OutputBuffer);
legacy::PassManager PM;
// If the bitcode files contain ARC code and were compiled with optimization,
// the ObjCARCContractPass must be run, so do it unconditionally here.
PM.add(createObjCARCContractPass());
// Setup the codegen now.
if (TM.addPassesToEmitFile(PM, OS, TargetMachine::CGFT_ObjectFile,
/* DisableVerify */ true))
report_fatal_error("Failed to setup codegen");
// Run codegen now. resulting binary is in OutputBuffer.
PM.run(TheModule);
}
return make_unique<ObjectMemoryBuffer>(std::move(OutputBuffer));
}
static std::unique_ptr<MemoryBuffer> ProcessThinLTOModule(
Module &TheModule, const ModuleSummaryIndex &Index,
StringMap<MemoryBufferRef> &ModuleMap, TargetMachine &TM,
const FunctionImporter::ImportMapTy &ImportList,
DenseMap<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
ThinLTOCodeGenerator::CachingOptions CacheOptions, bool DisableCodeGen,
StringRef SaveTempsDir, unsigned count) {
// Save temps: after IPO.
saveTempBitcode(TheModule, SaveTempsDir, count, ".1.IPO.bc");
// "Benchmark"-like optimization: single-source case
bool SingleModule = (ModuleMap.size() == 1);
if (!SingleModule) {
promoteModule(TheModule, Index);
// Resolve the LinkOnce/Weak ODR, trying to turn them into
// "available_externally" when possible.
// This is a compile-time optimization.
fixupODR(TheModule, ResolvedODR);
// Save temps: after promotion.
saveTempBitcode(TheModule, SaveTempsDir, count, ".2.promoted.bc");
crossImportIntoModule(TheModule, Index, ModuleMap, ImportList);
// Save temps: after cross-module import.
saveTempBitcode(TheModule, SaveTempsDir, count, ".3.imported.bc");
}
optimizeModule(TheModule, TM);
saveTempBitcode(TheModule, SaveTempsDir, count, ".3.opt.bc");
if (DisableCodeGen) {
// Configured to stop before CodeGen, serialize the bitcode and return.
SmallVector<char, 128> OutputBuffer;
{
raw_svector_ostream OS(OutputBuffer);
ModuleSummaryIndexBuilder IndexBuilder(&TheModule);
WriteBitcodeToFile(&TheModule, OS, true, &IndexBuilder.getIndex());
}
return make_unique<ObjectMemoryBuffer>(std::move(OutputBuffer));
}
return codegenModule(TheModule, TM);
}
// Initialize the TargetMachine builder for a given Triple
static void initTMBuilder(TargetMachineBuilder &TMBuilder,
const Triple &TheTriple) {
// Set a default CPU for Darwin triples (copied from LTOCodeGenerator).
// FIXME this looks pretty terrible...
if (TMBuilder.MCpu.empty() && TheTriple.isOSDarwin()) {
if (TheTriple.getArch() == llvm::Triple::x86_64)
TMBuilder.MCpu = "core2";
else if (TheTriple.getArch() == llvm::Triple::x86)
TMBuilder.MCpu = "yonah";
else if (TheTriple.getArch() == llvm::Triple::aarch64)
TMBuilder.MCpu = "cyclone";
}
TMBuilder.TheTriple = std::move(TheTriple);
}
} // end anonymous namespace
void ThinLTOCodeGenerator::addModule(StringRef Identifier, StringRef Data) {
MemoryBufferRef Buffer(Data, Identifier);
if (Modules.empty()) {
// First module added, so initialize the triple and some options
LLVMContext Context;
Triple TheTriple(getBitcodeTargetTriple(Buffer, Context));
initTMBuilder(TMBuilder, Triple(TheTriple));
}
#ifndef NDEBUG
else {
LLVMContext Context;
assert(TMBuilder.TheTriple.str() ==
getBitcodeTargetTriple(Buffer, Context) &&
"ThinLTO modules with different triple not supported");
}
#endif
Modules.push_back(Buffer);
}
void ThinLTOCodeGenerator::preserveSymbol(StringRef Name) {
PreservedSymbols.insert(Name);
}
void ThinLTOCodeGenerator::crossReferenceSymbol(StringRef Name) {
CrossReferencedSymbols.insert(Name);
}
// TargetMachine factory
std::unique_ptr<TargetMachine> TargetMachineBuilder::create() const {
std::string ErrMsg;
const Target *TheTarget =
TargetRegistry::lookupTarget(TheTriple.str(), ErrMsg);
if (!TheTarget) {
report_fatal_error("Can't load target for this Triple: " + ErrMsg);
}
// Use MAttr as the default set of features.
SubtargetFeatures Features(MAttr);
Features.getDefaultSubtargetFeatures(TheTriple);
std::string FeatureStr = Features.getString();
return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
TheTriple.str(), MCpu, FeatureStr, Options, RelocModel,
CodeModel::Default, CGOptLevel));
}
/**
* Produce the combined summary index from all the bitcode files:
* "thin-link".
*/
std::unique_ptr<ModuleSummaryIndex> ThinLTOCodeGenerator::linkCombinedIndex() {
std::unique_ptr<ModuleSummaryIndex> CombinedIndex;
uint64_t NextModuleId = 0;
for (auto &ModuleBuffer : Modules) {
ErrorOr<std::unique_ptr<object::ModuleSummaryIndexObjectFile>> ObjOrErr =
object::ModuleSummaryIndexObjectFile::create(ModuleBuffer,
diagnosticHandler, false);
if (std::error_code EC = ObjOrErr.getError()) {
// FIXME diagnose
errs() << "error: can't create ModuleSummaryIndexObjectFile for buffer: "
<< EC.message() << "\n";
return nullptr;
}
auto Index = (*ObjOrErr)->takeIndex();
if (CombinedIndex) {
CombinedIndex->mergeFrom(std::move(Index), ++NextModuleId);
} else {
CombinedIndex = std::move(Index);
}
}
return CombinedIndex;
}
/**
* Perform promotion and renaming of exported internal functions.
*/
void ThinLTOCodeGenerator::promote(Module &TheModule,
ModuleSummaryIndex &Index) {
auto ModuleIdentifier = TheModule.getModuleIdentifier();
// Collect for each module the list of function it defines (GUID -> Summary).
StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
ModuleToDefinedGVSummaries;
Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
// Resolve the LinkOnceODR, trying to turn them into "available_externally"
// where possible.
// This is a compile-time optimization.
DenseMap<GlobalValue::GUID, GlobalValue::LinkageTypes> ResolvedODR;
ResolveODR(Index, ModuleToDefinedGVSummaries[ModuleIdentifier],
ModuleIdentifier, ResolvedODR);
fixupODR(TheModule, ResolvedODR);
promoteModule(TheModule, Index);
}
/**
* Perform cross-module importing for the module identified by ModuleIdentifier.
*/
void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
ModuleSummaryIndex &Index) {
auto ModuleMap = generateModuleMap(Modules);
auto ModuleCount = Index.modulePaths().size();
// Collect for each module the list of function it defines (GUID -> Summary).
StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
ModuleToDefinedGVSummaries(ModuleCount);
Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
// Generate import/export list
StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
ExportLists);
auto &ImportList = ImportLists[TheModule.getModuleIdentifier()];
crossImportIntoModule(TheModule, Index, ModuleMap, ImportList);
}
/**
* Perform post-importing ThinLTO optimizations.
*/
void ThinLTOCodeGenerator::optimize(Module &TheModule) {
initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
optimizeModule(TheModule, *TMBuilder.create());
}
/**
* Perform ThinLTO CodeGen.
*/
std::unique_ptr<MemoryBuffer> ThinLTOCodeGenerator::codegen(Module &TheModule) {
initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
return codegenModule(TheModule, *TMBuilder.create());
}
// Main entry point for the ThinLTO processing
void ThinLTOCodeGenerator::run() {
if (CodeGenOnly) {
// Perform only parallel codegen and return.
ThreadPool Pool;
assert(ProducedBinaries.empty() && "The generator should not be reused");
ProducedBinaries.resize(Modules.size());
int count = 0;
for (auto &ModuleBuffer : Modules) {
Pool.async([&](int count) {
LLVMContext Context;
Context.setDiscardValueNames(LTODiscardValueNames);
// Parse module now
auto TheModule = loadModuleFromBuffer(ModuleBuffer, Context, false);
// CodeGen
ProducedBinaries[count] = codegen(*TheModule);
}, count++);
}
return;
}
// Sequential linking phase
auto Index = linkCombinedIndex();
// Save temps: index.
if (!SaveTempsDir.empty()) {
auto SaveTempPath = SaveTempsDir + "index.bc";
std::error_code EC;
raw_fd_ostream OS(SaveTempPath, EC, sys::fs::F_None);
if (EC)
report_fatal_error(Twine("Failed to open ") + SaveTempPath +
" to save optimized bitcode\n");
WriteIndexToFile(*Index, OS);
}
// Prepare the resulting object vector
assert(ProducedBinaries.empty() && "The generator should not be reused");
ProducedBinaries.resize(Modules.size());
// Prepare the module map.
auto ModuleMap = generateModuleMap(Modules);
auto ModuleCount = Modules.size();
// Collect for each module the list of function it defines (GUID -> Summary).
StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
ModuleToDefinedGVSummaries(ModuleCount);
Index->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
// Collect the import/export lists for all modules from the call-graph in the
// combined index.
StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
ComputeCrossModuleImport(*Index, ModuleToDefinedGVSummaries, ImportLists,
ExportLists);
// Parallel optimizer + codegen
{
ThreadPool Pool(ThreadCount);
int count = 0;
for (auto &ModuleBuffer : Modules) {
Pool.async([&](int count) {
LLVMContext Context;
Context.setDiscardValueNames(LTODiscardValueNames);
Context.enableDebugTypeODRUniquing();
auto ModuleIdentifier = ModuleBuffer.getBufferIdentifier();
DenseMap<GlobalValue::GUID, GlobalValue::LinkageTypes> ResolvedODR;
ResolveODR(*Index, ModuleToDefinedGVSummaries[ModuleIdentifier],
ModuleIdentifier, ResolvedODR);
// Parse module now
auto TheModule = loadModuleFromBuffer(ModuleBuffer, Context, false);
// Save temps: original file.
if (!SaveTempsDir.empty()) {
saveTempBitcode(*TheModule, SaveTempsDir, count, ".0.original.bc");
}
auto &ImportList = ImportLists[ModuleIdentifier];
ProducedBinaries[count] = ProcessThinLTOModule(
*TheModule, *Index, ModuleMap, *TMBuilder.create(), ImportList,
ResolvedODR, CacheOptions, DisableCodeGen, SaveTempsDir, count);
}, count);
count++;
}
}
// If statistics were requested, print them out now.
if (llvm::AreStatisticsEnabled())
llvm::PrintStatistics();
}
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