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

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//===-LTOBackend.cpp - LLVM Link Time Optimizer Backend -------------------===//
//
// 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 "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/LTO/legacy/UpdateCompilerUsed.h"
#include "llvm/MC/SubtargetFeature.h"
#include "llvm/Passes/PassBuilder.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.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;
static cl::opt<bool>
LTOUseNewPM("lto-use-new-pm",
cl::desc("Run LTO passes using the new pass manager"),
cl::init(false), cl::Hidden);
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 + 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);
return true;
};
return Error::success();
}
namespace {
std::unique_ptr<TargetMachine>
createTargetMachine(Config &Conf, StringRef TheTriple,
const Target *TheTarget) {
SubtargetFeatures Features;
Features.getDefaultSubtargetFeatures(Triple(TheTriple));
for (const std::string &A : Conf.MAttrs)
Features.AddFeature(A);
return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
TheTriple, Conf.CPU, Features.getString(), Conf.Options, Conf.RelocModel,
Conf.CodeModel, Conf.CGOptLevel));
}
static void runNewPMPasses(Module &Mod, TargetMachine *TM, unsigned OptLevel) {
PassBuilder PB(TM);
AAManager AA;
// Parse a custom AA pipeline if asked to.
assert(PB.parseAAPipeline(AA, "default"));
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;
// 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;
}
MPM = PB.buildLTODefaultPipeline(OL, false /* DebugLogging */);
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 (!PB.parseAAPipeline(AA, AAPipelineDesc))
report_fatal_error("unable to parse AA pipeline description: " +
AAPipelineDesc);
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 (!PB.parsePassPipeline(MPM, PipelineDesc))
report_fatal_error("unable to parse pass pipeline description: " +
PipelineDesc);
if (!DisableVerify)
MPM.addPass(VerifierPass());
MPM.run(Mod, MAM);
}
static void runOldPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
bool IsThinLTO, ModuleSummaryIndex &CombinedIndex) {
legacy::PassManager passes;
passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
PassManagerBuilder PMB;
PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
PMB.Inliner = createFunctionInliningPass();
PMB.Summary = &CombinedIndex;
// 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;
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 &CombinedIndex) {
// There's still no ThinLTO pipeline hooked up in the new pass manager,
// once there is one, we can just remove this.
if (LTOUseNewPM && IsThinLTO)
report_fatal_error("ThinLTO not supported with the new PM yet!");
// 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 (LTOUseNewPM)
runNewPMPasses(Mod, TM, Conf.OptLevel);
else
runOldPMPasses(Conf, Mod, TM, IsThinLTO, CombinedIndex);
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;
auto Stream = AddStream(Task);
legacy::PassManager CodeGenPasses;
if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
TargetMachine::CGFT_ObjectFile))
report_fatal_error("Failed to setup codegen");
CodeGenPasses.run(Mod);
}
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.get(), 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, MPartInCtx->getTargetTriple(), T);
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 void handleAsmUndefinedRefs(Module &Mod, TargetMachine &TM) {
// Collect the list of undefined symbols used in asm and update
// llvm.compiler.used to prevent optimization to drop these from the output.
StringSet<> AsmUndefinedRefs;
ModuleSymbolTable::CollectAsmSymbols(
Triple(Mod.getTargetTriple()), Mod.getModuleInlineAsm(),
[&AsmUndefinedRefs](StringRef Name, object::BasicSymbolRef::Flags Flags) {
if (Flags & object::BasicSymbolRef::SF_Undefined)
AsmUndefinedRefs.insert(Name);
});
updateCompilerUsed(Mod, TM, AsmUndefinedRefs);
}
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, Mod->getTargetTriple(), *TOrErr);
handleAsmUndefinedRefs(*Mod, *TM);
if (!C.CodeGenOnly)
if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false, CombinedIndex))
return Error::success();
if (ParallelCodeGenParallelismLevel == 1) {
codegen(C, TM.get(), AddStream, 0, *Mod);
} else {
splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
std::move(Mod));
}
return Error::success();
}
Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
Module &Mod, 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, Mod.getTargetTriple(), *TOrErr);
handleAsmUndefinedRefs(Mod, *TM);
if (Conf.CodeGenOnly) {
codegen(Conf, TM.get(), AddStream, Task, Mod);
return Error::success();
}
if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
return Error::success();
renameModuleForThinLTO(Mod, CombinedIndex);
thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
return Error::success();
if (!DefinedGlobals.empty())
thinLTOInternalizeModule(Mod, DefinedGlobals);
if (Conf.PostInternalizeModuleHook &&
!Conf.PostInternalizeModuleHook(Task, Mod))
return Error::success();
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 Error::success();
if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true, CombinedIndex))
return Error::success();
codegen(Conf, TM.get(), AddStream, Task, Mod);
return Error::success();
}
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