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| //===- LTO.cpp ------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#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;
namespace lld {
namespace 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(path,
config->thinLTOPrefixReplace.first,
config->thinLTOPrefixReplace.second);
}
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;
else
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);
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->thinLTOPrefixReplace.first, config->thinLTOPrefixReplace.second,
config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite);
} else if (config->thinLTOJobs != 0) {
backend = lto::createInProcessThinBackend(config->thinLTOJobs);
}
ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
config->ltoPartitions);
}
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)
thinIndices.insert(obj.getName());
// 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];
++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)
undefine(sym);
}
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<StringRef> BitcodeCompiler::compile() {
unsigned maxTasks = ltoObj->getMaxTasks();
buf.resize(maxTasks);
files.resize(maxTasks);
// 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);
}));
checkError(ltoObj->run(
[&](size_t task) {
return std::make_unique<lto::NativeObjectStream>(
std::make_unique<raw_svector_ostream>(buf[task]));
},
cache));
// 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)
indexFile->close();
return {};
}
if (!config->ltoCache.empty())
pruneCache(config->ltoCache, config->ltoCachePolicy);
std::vector<StringRef> ret;
for (unsigned i = 0; i != maxTasks; ++i) {
if (buf[i].empty())
continue;
if (config->saveTemps) {
if (i == 0)
saveBuffer(buf[i], config->outputFile + ".lto.obj");
else
saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.obj");
}
ret.emplace_back(buf[i].data(), buf[i].size());
}
for (std::unique_ptr<MemoryBuffer> &file : files)
if (file)
ret.push_back(file->getBuffer());
return ret;
}
} // namespace coff
} // namespace lld
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