ae4c30a4be
lld currently selects the relocation model automatically depending on the link flags specified, but in some cases it'd be useful to allow explicitly overriding the relocation model using a flag. llvm-svn: 366644
306 lines
11 KiB
C++
306 lines
11 KiB
C++
//===- LTO.cpp ------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "LTO.h"
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#include "Config.h"
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#include "InputFiles.h"
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#include "LinkerScript.h"
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#include "SymbolTable.h"
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#include "Symbols.h"
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#include "lld/Common/Args.h"
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#include "lld/Common/ErrorHandler.h"
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#include "lld/Common/TargetOptionsCommandFlags.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/Bitcode/BitcodeReader.h"
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#include "llvm/Bitcode/BitcodeWriter.h"
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#include "llvm/IR/DiagnosticPrinter.h"
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#include "llvm/LTO/Caching.h"
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#include "llvm/LTO/Config.h"
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#include "llvm/LTO/LTO.h"
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#include "llvm/Object/SymbolicFile.h"
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#include "llvm/Support/CodeGen.h"
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#include "llvm/Support/Error.h"
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#include "llvm/Support/FileSystem.h"
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#include "llvm/Support/MemoryBuffer.h"
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#include <algorithm>
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#include <cstddef>
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#include <memory>
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#include <string>
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#include <system_error>
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#include <vector>
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using namespace llvm;
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using namespace llvm::object;
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using namespace llvm::ELF;
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using namespace lld;
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using namespace lld::elf;
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// Creates an empty file to store a list of object files for final
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// linking of distributed ThinLTO.
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static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
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std::error_code ec;
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auto ret =
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llvm::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::F_None);
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if (ec) {
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error("cannot open " + file + ": " + ec.message());
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return nullptr;
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}
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return ret;
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}
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static std::string getThinLTOOutputFile(StringRef modulePath) {
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return lto::getThinLTOOutputFile(modulePath,
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config->thinLTOPrefixReplace.first,
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config->thinLTOPrefixReplace.second);
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}
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static lto::Config createConfig() {
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lto::Config c;
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// LLD supports the new relocations and address-significance tables.
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c.Options = initTargetOptionsFromCodeGenFlags();
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c.Options.RelaxELFRelocations = true;
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c.Options.EmitAddrsig = true;
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// Always emit a section per function/datum with LTO.
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c.Options.FunctionSections = true;
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c.Options.DataSections = true;
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if (auto relocModel = getRelocModelFromCMModel())
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c.RelocModel = *relocModel;
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else if (config->relocatable)
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c.RelocModel = None;
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else if (config->isPic)
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c.RelocModel = Reloc::PIC_;
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else
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c.RelocModel = Reloc::Static;
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c.CodeModel = getCodeModelFromCMModel();
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c.DisableVerify = config->disableVerify;
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c.DiagHandler = diagnosticHandler;
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c.OptLevel = config->ltoo;
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c.CPU = getCPUStr();
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c.MAttrs = getMAttrs();
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c.CGOptLevel = args::getCGOptLevel(config->ltoo);
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// Set up a custom pipeline if we've been asked to.
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c.OptPipeline = config->ltoNewPmPasses;
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c.AAPipeline = config->ltoAAPipeline;
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// Set up optimization remarks if we've been asked to.
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c.RemarksFilename = config->optRemarksFilename;
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c.RemarksPasses = config->optRemarksPasses;
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c.RemarksWithHotness = config->optRemarksWithHotness;
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c.RemarksFormat = config->optRemarksFormat;
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c.SampleProfile = config->ltoSampleProfile;
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c.UseNewPM = config->ltoNewPassManager;
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c.DebugPassManager = config->ltoDebugPassManager;
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c.DwoDir = config->dwoDir;
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c.CSIRProfile = config->ltoCSProfileFile;
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c.RunCSIRInstr = config->ltoCSProfileGenerate;
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if (config->emitLLVM) {
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c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
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if (std::unique_ptr<raw_fd_ostream> os = openFile(config->outputFile))
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WriteBitcodeToFile(m, *os, false);
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return false;
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};
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}
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if (config->saveTemps)
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checkError(c.addSaveTemps(config->outputFile.str() + ".",
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/*UseInputModulePath*/ true));
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return c;
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}
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BitcodeCompiler::BitcodeCompiler() {
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// Initialize indexFile.
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if (!config->thinLTOIndexOnlyArg.empty())
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indexFile = openFile(config->thinLTOIndexOnlyArg);
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// Initialize ltoObj.
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lto::ThinBackend backend;
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if (config->thinLTOIndexOnly) {
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auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
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backend = lto::createWriteIndexesThinBackend(
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config->thinLTOPrefixReplace.first, config->thinLTOPrefixReplace.second,
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config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
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} else if (config->thinLTOJobs != -1U) {
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backend = lto::createInProcessThinBackend(config->thinLTOJobs);
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}
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ltoObj = llvm::make_unique<lto::LTO>(createConfig(), backend,
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config->ltoPartitions);
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// Initialize usedStartStop.
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symtab->forEachSymbol([&](Symbol *sym) {
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StringRef s = sym->getName();
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for (StringRef prefix : {"__start_", "__stop_"})
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if (s.startswith(prefix))
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usedStartStop.insert(s.substr(prefix.size()));
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});
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}
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BitcodeCompiler::~BitcodeCompiler() = default;
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void BitcodeCompiler::add(BitcodeFile &f) {
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lto::InputFile &obj = *f.obj;
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bool isExec = !config->shared && !config->relocatable;
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if (config->thinLTOIndexOnly)
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thinIndices.insert(obj.getName());
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ArrayRef<Symbol *> syms = f.getSymbols();
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ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
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std::vector<lto::SymbolResolution> resols(syms.size());
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// Provide a resolution to the LTO API for each symbol.
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for (size_t i = 0, e = syms.size(); i != e; ++i) {
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Symbol *sym = syms[i];
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const lto::InputFile::Symbol &objSym = objSyms[i];
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lto::SymbolResolution &r = resols[i];
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// Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
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// reports two symbols for module ASM defined. Without this check, lld
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// flags an undefined in IR with a definition in ASM as prevailing.
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// Once IRObjectFile is fixed to report only one symbol this hack can
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// be removed.
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r.Prevailing = !objSym.isUndefined() && sym->file == &f;
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// We ask LTO to preserve following global symbols:
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// 1) All symbols when doing relocatable link, so that them can be used
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// for doing final link.
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// 2) Symbols that are used in regular objects.
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// 3) C named sections if we have corresponding __start_/__stop_ symbol.
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// 4) Symbols that are defined in bitcode files and used for dynamic linking.
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r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
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(r.Prevailing && sym->includeInDynsym()) ||
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usedStartStop.count(objSym.getSectionName());
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const auto *dr = dyn_cast<Defined>(sym);
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r.FinalDefinitionInLinkageUnit =
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(isExec || sym->visibility != STV_DEFAULT) && dr &&
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// Skip absolute symbols from ELF objects, otherwise PC-rel relocations
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// will be generated by for them, triggering linker errors.
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// Symbol section is always null for bitcode symbols, hence the check
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// for isElf(). Skip linker script defined symbols as well: they have
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// no File defined.
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!(dr->section == nullptr && (!sym->file || sym->file->isElf()));
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if (r.Prevailing)
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sym->replace(Undefined{nullptr, sym->getName(), STB_GLOBAL, STV_DEFAULT,
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sym->type});
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// We tell LTO to not apply interprocedural optimization for wrapped
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// (with --wrap) symbols because otherwise LTO would inline them while
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// their values are still not final.
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r.LinkerRedefined = !sym->canInline;
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}
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checkError(ltoObj->add(std::move(f.obj), resols));
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}
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// If LazyObjFile has not been added to link, emit empty index files.
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// This is needed because this is what GNU gold plugin does and we have a
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// distributed build system that depends on that behavior.
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static void thinLTOCreateEmptyIndexFiles() {
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for (LazyObjFile *f : lazyObjFiles) {
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if (!isBitcode(f->mb))
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continue;
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std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
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std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
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if (!os)
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continue;
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ModuleSummaryIndex m(/*HaveGVs*/ false);
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m.setSkipModuleByDistributedBackend();
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WriteIndexToFile(m, *os);
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if (config->thinLTOEmitImportsFiles)
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openFile(path + ".imports");
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}
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}
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// Merge all the bitcode files we have seen, codegen the result
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// and return the resulting ObjectFile(s).
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std::vector<InputFile *> BitcodeCompiler::compile() {
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unsigned maxTasks = ltoObj->getMaxTasks();
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buf.resize(maxTasks);
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files.resize(maxTasks);
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// The --thinlto-cache-dir option specifies the path to a directory in which
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// to cache native object files for ThinLTO incremental builds. If a path was
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// specified, configure LTO to use it as the cache directory.
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lto::NativeObjectCache cache;
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if (!config->thinLTOCacheDir.empty())
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cache = check(
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lto::localCache(config->thinLTOCacheDir,
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[&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
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files[task] = std::move(mb);
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}));
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if (!bitcodeFiles.empty())
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checkError(ltoObj->run(
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[&](size_t task) {
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return llvm::make_unique<lto::NativeObjectStream>(
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llvm::make_unique<raw_svector_ostream>(buf[task]));
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},
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cache));
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// Emit empty index files for non-indexed files
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for (StringRef s : thinIndices) {
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std::string path = getThinLTOOutputFile(s);
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openFile(path + ".thinlto.bc");
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if (config->thinLTOEmitImportsFiles)
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openFile(path + ".imports");
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}
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if (config->thinLTOIndexOnly) {
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thinLTOCreateEmptyIndexFiles();
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if (!config->ltoObjPath.empty())
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saveBuffer(buf[0], config->ltoObjPath);
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// ThinLTO with index only option is required to generate only the index
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// files. After that, we exit from linker and ThinLTO backend runs in a
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// distributed environment.
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if (indexFile)
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indexFile->close();
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return {};
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}
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if (!config->thinLTOCacheDir.empty())
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pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
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if (!config->ltoObjPath.empty()) {
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saveBuffer(buf[0], config->ltoObjPath);
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for (unsigned i = 1; i != maxTasks; ++i)
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saveBuffer(buf[i], config->ltoObjPath + Twine(i));
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}
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if (config->saveTemps) {
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saveBuffer(buf[0], config->outputFile + ".lto.o");
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for (unsigned i = 1; i != maxTasks; ++i)
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saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
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}
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std::vector<InputFile *> ret;
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for (unsigned i = 0; i != maxTasks; ++i)
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if (!buf[i].empty())
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ret.push_back(createObjectFile(MemoryBufferRef(buf[i], "lto.tmp")));
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for (std::unique_ptr<MemoryBuffer> &file : files)
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if (file)
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ret.push_back(createObjectFile(*file));
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return ret;
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}
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