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

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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 https://llvm.org/LICENSE.txt 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/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.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/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/raw_ostream.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/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;
LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
errs() << "failed to open " << Path << ": " << Msg << '\n';
errs().flush();
exit(1);
}
Error Config::addSaveTemps(std::string OutputFileName,
bool UseInputModulePath) {
ShouldDiscardValueNames = false;
std::error_code EC;
ResolutionFile = llvm::make_unique<raw_fd_ostream>(
OutputFileName + "resolution.txt", EC, sys::fs::OpenFlags::F_Text);
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::F_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) {
std::string Path = OutputFileName + "index.bc";
std::error_code EC;
raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_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 + "index.dot";
raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::F_None);
if (EC)
reportOpenError(Path, EC.message());
Index.exportToDot(OSDot);
return true;
};
return Error::success();
}
namespace {
std::unique_ptr<TargetMachine>
createTargetMachine(Config &Conf, const Target *TheTarget, Module &M) {
StringRef TheTriple = M.getTargetTriple();
SubtargetFeatures Features;
Features.getDefaultSubtargetFeatures(Triple(TheTriple));
for (const std::string &A : Conf.MAttrs)
Features.AddFeature(A);
Reloc::Model RelocModel;
if (Conf.RelocModel)
RelocModel = *Conf.RelocModel;
else
RelocModel =
M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
Optional<CodeModel::Model> CodeModel;
if (Conf.CodeModel)
CodeModel = *Conf.CodeModel;
else
CodeModel = M.getCodeModel();
return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
CodeModel, Conf.CGOptLevel));
}
static void runNewPMPasses(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);
}
PassBuilder PB(TM, PipelineTuningOptions(), PGOOpt);
AAManager AA;
// Parse a custom AA pipeline if asked to.
if (auto Err = PB.parseAAPipeline(AA, "default"))
report_fatal_error("Error parsing default AA pipeline");
LoopAnalysisManager LAM(Conf.DebugPassManager);
FunctionAnalysisManager FAM(Conf.DebugPassManager);
CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
ModuleAnalysisManager MAM(Conf.DebugPassManager);
// 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.registerModuleAnalyses(MAM);
PB.registerCGSCCAnalyses(CGAM);
PB.registerFunctionAnalyses(FAM);
PB.registerLoopAnalyses(LAM);
PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
ModulePassManager MPM(Conf.DebugPassManager);
// FIXME (davide): verify the input.
PassBuilder::OptimizationLevel OL;
switch (OptLevel) {
default:
llvm_unreachable("Invalid optimization level");
case 0:
OL = PassBuilder::O0;
break;
case 1:
OL = PassBuilder::O1;
break;
case 2:
OL = PassBuilder::O2;
break;
case 3:
OL = PassBuilder::O3;
break;
}
if (IsThinLTO)
MPM = PB.buildThinLTODefaultPipeline(OL, Conf.DebugPassManager,
ImportSummary);
else
MPM = PB.buildLTODefaultPipeline(OL, Conf.DebugPassManager, ExportSummary);
MPM.run(Mod, MAM);
// FIXME (davide): verify the output.
}
static void runNewPMCustomPasses(Module &Mod, TargetMachine *TM,
std::string PipelineDesc,
std::string AAPipelineDesc,
bool DisableVerify) {
PassBuilder PB(TM);
AAManager AA;
// Parse a custom AA pipeline if asked to.
if (!AAPipelineDesc.empty())
if (auto Err = PB.parseAAPipeline(AA, AAPipelineDesc))
report_fatal_error("unable to parse AA pipeline description '" +
AAPipelineDesc + "': " + toString(std::move(Err)));
LoopAnalysisManager LAM;
FunctionAnalysisManager FAM;
CGSCCAnalysisManager CGAM;
ModuleAnalysisManager MAM;
// 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.registerModuleAnalyses(MAM);
PB.registerCGSCCAnalyses(CGAM);
PB.registerFunctionAnalyses(FAM);
PB.registerLoopAnalyses(LAM);
PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
ModulePassManager MPM;
// Always verify the input.
MPM.addPass(VerifierPass());
// Now, add all the passes we've been requested to.
if (auto Err = PB.parsePassPipeline(MPM, PipelineDesc))
report_fatal_error("unable to parse pass pipeline description '" +
PipelineDesc + "': " + toString(std::move(Err)));
if (!DisableVerify)
MPM.addPass(VerifierPass());
MPM.run(Mod, MAM);
}
static void runOldPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary) {
legacy::PassManager passes;
passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
PassManagerBuilder PMB;
PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
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)
PMB.populateThinLTOPassManager(passes);
else
PMB.populateLTOPassManager(passes);
passes.run(Mod);
}
bool opt(Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
const ModuleSummaryIndex *ImportSummary) {
// FIXME: Plumb the combined index into the new pass manager.
if (!Conf.OptPipeline.empty())
runNewPMCustomPasses(Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
Conf.DisableVerify);
else if (Conf.UseNewPM)
runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
ImportSummary);
else
runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
}
void codegen(Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
unsigned Task, Module &Mod) {
if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
return;
std::unique_ptr<ToolOutputFile> DwoOut;
SmallString<1024> DwoFile(Conf.DwoPath);
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 + ": " +
EC.message());
DwoFile = Conf.DwoDir;
sys::path::append(DwoFile, std::to_string(Task) + ".dwo");
}
if (!DwoFile.empty()) {
std::error_code EC;
TM->Options.MCOptions.SplitDwarfFile = DwoFile.str().str();
DwoOut = llvm::make_unique<ToolOutputFile>(DwoFile, EC, sys::fs::F_None);
if (EC)
report_fatal_error("Failed to open " + DwoFile + ": " + EC.message());
}
auto Stream = AddStream(Task);
legacy::PassManager CodeGenPasses;
if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
DwoOut ? &DwoOut->os() : nullptr,
Conf.CGFileType))
report_fatal_error("Failed to setup codegen");
CodeGenPasses.run(Mod);
if (DwoOut)
DwoOut->keep();
}
void splitCodeGen(Config &C, TargetMachine *TM, AddStreamFn AddStream,
unsigned ParallelCodeGenParallelismLevel,
std::unique_ptr<Module> Mod) {
ThreadPool CodegenThreadPool(ParallelCodeGenParallelismLevel);
unsigned ThreadCount = 0;
const Target *T = &TM->getTarget();
SplitModule(
std::move(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
CodegenThreadPool.async(
[&](const SmallString<0> &BC, unsigned ThreadId) {
LTOLLVMContext Ctx(C);
Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
Ctx);
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++);
},
false);
// 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.
CodegenThreadPool.wait();
}
Expected<const Target *> initAndLookupTarget(Config &C, Module &Mod) {
if (!C.OverrideTriple.empty())
Mod.setTargetTriple(C.OverrideTriple);
else if (Mod.getTargetTriple().empty())
Mod.setTargetTriple(C.DefaultTriple);
std::string Msg;
const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
if (!T)
return make_error<StringError>(Msg, inconvertibleErrorCode());
return T;
}
}
static Error
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();
DiagOutputFile->keep();
DiagOutputFile->os().flush();
return Error::success();
}
Error lto::backend(Config &C, AddStreamFn AddStream,
unsigned ParallelCodeGenParallelismLevel,
std::unique_ptr<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);
// Setup optimization remarks.
auto DiagFileOrErr =
lto::setupOptimizationRemarks(Mod->getContext(), C.RemarksFilename,
C.RemarksPasses, C.RemarksWithHotness);
if (!DiagFileOrErr)
return DiagFileOrErr.takeError();
auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
if (!C.CodeGenOnly) {
if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false,
/*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
}
if (ParallelCodeGenParallelismLevel == 1) {
codegen(C, TM.get(), AddStream, 0, *Mod);
} else {
splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
std::move(Mod));
}
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
}
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)) {
DeadGVs.push_back(&GV);
convertToDeclaration(GV);
}
// Now that all dead bodies have been dropped, delete the actual objects
// themselves when possible.
for (GlobalValue *GV : DeadGVs) {
GV->removeDeadConstantUsers();
// 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())
GV->eraseFromParent();
}
}
Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
Module &Mod, const ModuleSummaryIndex &CombinedIndex,
const FunctionImporter::ImportMapTy &ImportList,
const GVSummaryMapTy &DefinedGlobals,
MapVector<StringRef, BitcodeModule> &ModuleMap) {
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::setupOptimizationRemarks(
Mod.getContext(), Conf.RemarksFilename, Conf.RemarksPasses,
Conf.RemarksWithHotness, Task);
if (!DiagFileOrErr)
return DiagFileOrErr.takeError();
auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
if (Conf.CodeGenOnly) {
codegen(Conf, TM.get(), AddStream, Task, Mod);
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
}
if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
renameModuleForThinLTO(Mod, CombinedIndex);
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");
auto I = ModuleMap.find(Identifier);
assert(I != ModuleMap.end());
return I->second.getLazyModule(Mod.getContext(),
/*ShouldLazyLoadMetadata=*/true,
/*IsImporting*/ true);
};
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));
if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true,
/*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex))
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
codegen(Conf, TM.get(), AddStream, Task, Mod);
return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
}
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