blob: 2fa3536db873d511592e125fe8194eac99048938 [file] [log] [blame]
//===- LTO.cpp ------------------------------------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "LTO.h"
#include "Config.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "lld/Common/Args.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Strings.h"
#include "lld/Common/TargetOptionsCommandFlags.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/LTO/Caching.h"
#include "llvm/LTO/Config.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Object/SymbolicFile.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cstddef>
#include <memory>
#include <string>
#include <system_error>
#include <vector>
using namespace llvm;
using namespace llvm::object;
using namespace lld;
using namespace lld::coff;
// Creates an empty file to and returns a raw_fd_ostream to write to it.
static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
std::error_code ec;
auto ret =
std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
if (ec) {
error("cannot open " + file + ": " + ec.message());
return nullptr;
return ret;
static std::string getThinLTOOutputFile(StringRef path) {
return lto::getThinLTOOutputFile(
std::string(path), std::string(config->thinLTOPrefixReplace.first),
static lto::Config createConfig() {
lto::Config c;
c.Options = initTargetOptionsFromCodeGenFlags();
// Always emit a section per function/datum with LTO. LLVM LTO should get most
// of the benefit of linker GC, but there are still opportunities for ICF.
c.Options.FunctionSections = true;
c.Options.DataSections = true;
// Use static reloc model on 32-bit x86 because it usually results in more
// compact code, and because there are also known code generation bugs when
// using the PIC model (see PR34306).
if (config->machine == COFF::IMAGE_FILE_MACHINE_I386)
c.RelocModel = Reloc::Static;
c.RelocModel = Reloc::PIC_;
c.DisableVerify = true;
c.DiagHandler = diagnosticHandler;
c.OptLevel = config->ltoo;
c.CPU = getCPUStr();
c.MAttrs = getMAttrs();
c.CGOptLevel = args::getCGOptLevel(config->ltoo);
c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
c.UseNewPM = config->ltoNewPassManager;
c.DebugPassManager = config->ltoDebugPassManager;
if (config->saveTemps)
checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
/*UseInputModulePath*/ true));
return c;
BitcodeCompiler::BitcodeCompiler() {
// Initialize indexFile.
if (!config->thinLTOIndexOnlyArg.empty())
indexFile = openFile(config->thinLTOIndexOnlyArg);
// Initialize ltoObj.
lto::ThinBackend backend;
if (config->thinLTOIndexOnly) {
auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); };
backend = lto::createWriteIndexesThinBackend(
config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
} else {
backend = lto::createInProcessThinBackend(
ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
BitcodeCompiler::~BitcodeCompiler() = default;
static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); }
void BitcodeCompiler::add(BitcodeFile &f) {
lto::InputFile &obj = *f.obj;
unsigned symNum = 0;
std::vector<Symbol *> symBodies = f.getSymbols();
std::vector<lto::SymbolResolution> resols(symBodies.size());
if (config->thinLTOIndexOnly)
// Provide a resolution to the LTO API for each symbol.
for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
Symbol *sym = symBodies[symNum];
lto::SymbolResolution &r = resols[symNum];
// Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
// reports two symbols for module ASM defined. Without this check, lld
// flags an undefined in IR with a definition in ASM as prevailing.
// Once IRObjectFile is fixed to report only one symbol this hack can
// be removed.
r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
r.VisibleToRegularObj = sym->isUsedInRegularObj;
if (r.Prevailing)
// We tell LTO to not apply interprocedural optimization for wrapped
// (with -wrap) symbols because otherwise LTO would inline them while
// their values are still not final.
r.LinkerRedefined = !sym->canInline;
checkError(ltoObj->add(std::move(f.obj), resols));
// Merge all the bitcode files we have seen, codegen the result
// and return the resulting objects.
std::vector<InputFile *> BitcodeCompiler::compile() {
unsigned maxTasks = ltoObj->getMaxTasks();
// The /lldltocache option specifies the path to a directory in which to cache
// native object files for ThinLTO incremental builds. If a path was
// specified, configure LTO to use it as the cache directory.
lto::NativeObjectCache cache;
if (!config->ltoCache.empty())
cache = check(lto::localCache(
config->ltoCache, [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
files[task] = std::move(mb);
[&](size_t task) {
return std::make_unique<lto::NativeObjectStream>(
// Emit empty index files for non-indexed files
for (StringRef s : thinIndices) {
std::string path = getThinLTOOutputFile(s);
openFile(path + ".thinlto.bc");
if (config->thinLTOEmitImportsFiles)
openFile(path + ".imports");
// ThinLTO with index only option is required to generate only the index
// files. After that, we exit from linker and ThinLTO backend runs in a
// distributed environment.
if (config->thinLTOIndexOnly) {
if (!config->ltoObjPath.empty())
saveBuffer(buf[0], config->ltoObjPath);
if (indexFile)
return {};
if (!config->ltoCache.empty())
pruneCache(config->ltoCache, config->ltoCachePolicy);
std::vector<InputFile *> ret;
for (unsigned i = 0; i != maxTasks; ++i) {
// Assign unique names to LTO objects. This ensures they have unique names
// in the PDB if one is produced. The names should look like:
// - foo.exe.lto.obj
// - foo.exe.lto.1.obj
// - ...
StringRef ltoObjName =>outputFile) + ".lto" +
(i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
// Get the native object contents either from the cache or from memory. Do
// not use the cached MemoryBuffer directly, or the PDB will not be
// deterministic.
StringRef objBuf;
if (files[i])
objBuf = files[i]->getBuffer();
objBuf = buf[i];
if (objBuf.empty())
if (config->saveTemps)
saveBuffer(buf[i], ltoObjName);
ret.push_back(make<ObjFile>(MemoryBufferRef(objBuf, ltoObjName)));
return ret;