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//===- llvm-link.cpp - Low-level LLVM linker ------------------------------===//
// 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
// This utility may be invoked in the following manner:
// llvm-link a.bc b.bc c.bc -o x.bc
#include "llvm/ADT/STLExtras.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/IR/AutoUpgrade.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ModuleSummaryIndex.h"
#include "llvm/IR/Verifier.h"
#include "llvm/IRReader/IRReader.h"
#include "llvm/Linker/Linker.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/SystemUtils.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Transforms/IPO/FunctionImport.h"
#include "llvm/Transforms/IPO/Internalize.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include <memory>
#include <utility>
using namespace llvm;
static cl::list<std::string>
InputFilenames(cl::Positional, cl::OneOrMore,
cl::desc("<input bitcode files>"));
static cl::list<std::string> OverridingInputs(
"override", cl::ZeroOrMore, cl::value_desc("filename"),
"input bitcode file which can override previously defined symbol(s)"));
// Option to simulate function importing for testing. This enables using
// llvm-link to simulate ThinLTO backend processes.
static cl::list<std::string> Imports(
"import", cl::ZeroOrMore, cl::value_desc("function:filename"),
cl::desc("Pair of function name and filename, where function should be "
"imported from bitcode in filename"));
// Option to support testing of function importing. The module summary
// must be specified in the case were we request imports via the -import
// option, as well as when compiling any module with functions that may be
// exported (imported by a different llvm-link -import invocation), to ensure
// consistent promotion and renaming of locals.
static cl::opt<std::string>
SummaryIndex("summary-index", cl::desc("Module summary index filename"),
cl::init(""), cl::value_desc("filename"));
static cl::opt<std::string>
OutputFilename("o", cl::desc("Override output filename"), cl::init("-"),
static cl::opt<bool>
Internalize("internalize", cl::desc("Internalize linked symbols"));
static cl::opt<bool>
cl::desc("Don't use a uniquing type map for debug info"));
static cl::opt<bool>
OnlyNeeded("only-needed", cl::desc("Link only needed symbols"));
static cl::opt<bool>
Force("f", cl::desc("Enable binary output on terminals"));
static cl::opt<bool>
cl::desc("Disable lazy module loading"));
static cl::opt<bool>
OutputAssembly("S", cl::desc("Write output as LLVM assembly"), cl::Hidden);
static cl::opt<bool>
Verbose("v", cl::desc("Print information about actions taken"));
static cl::opt<bool>
DumpAsm("d", cl::desc("Print assembly as linked"), cl::Hidden);
static cl::opt<bool>
SuppressWarnings("suppress-warnings", cl::desc("Suppress all linking warnings"),
static cl::opt<bool> PreserveBitcodeUseListOrder(
cl::desc("Preserve use-list order when writing LLVM bitcode."),
cl::init(true), cl::Hidden);
static cl::opt<bool> PreserveAssemblyUseListOrder(
cl::desc("Preserve use-list order when writing LLVM assembly."),
cl::init(false), cl::Hidden);
static ExitOnError ExitOnErr;
// Read the specified bitcode file in and return it. This routine searches the
// link path for the specified file to try to find it...
static std::unique_ptr<Module> loadFile(const char *argv0,
const std::string &FN,
LLVMContext &Context,
bool MaterializeMetadata = true) {
SMDiagnostic Err;
if (Verbose)
errs() << "Loading '" << FN << "'\n";
std::unique_ptr<Module> Result;
if (DisableLazyLoad)
Result = parseIRFile(FN, Err, Context);
Result = getLazyIRFileModule(FN, Err, Context, !MaterializeMetadata);
if (!Result) {
Err.print(argv0, errs());
return nullptr;
if (MaterializeMetadata) {
return Result;
namespace {
/// Helper to load on demand a Module from file and cache it for subsequent
/// queries during function importing.
class ModuleLazyLoaderCache {
/// Cache of lazily loaded module for import.
StringMap<std::unique_ptr<Module>> ModuleMap;
/// Retrieve a Module from the cache or lazily load it on demand.
std::function<std::unique_ptr<Module>(const char *argv0,
const std::string &FileName)>
/// Create the loader, Module will be initialized in \p Context.
const char *argv0, const std::string &FileName)>
: createLazyModule(std::move(createLazyModule)) {}
/// Retrieve a Module from the cache or lazily load it on demand.
Module &operator()(const char *argv0, const std::string &FileName);
std::unique_ptr<Module> takeModule(const std::string &FileName) {
auto I = ModuleMap.find(FileName);
assert(I != ModuleMap.end());
std::unique_ptr<Module> Ret = std::move(I->second);
return Ret;
// Get a Module for \p FileName from the cache, or load it lazily.
Module &ModuleLazyLoaderCache::operator()(const char *argv0,
const std::string &Identifier) {
auto &Module = ModuleMap[Identifier];
if (!Module)
Module = createLazyModule(argv0, Identifier);
return *Module;
} // anonymous namespace
namespace {
struct LLVMLinkDiagnosticHandler : public DiagnosticHandler {
bool handleDiagnostics(const DiagnosticInfo &DI) override {
unsigned Severity = DI.getSeverity();
switch (Severity) {
case DS_Error:
case DS_Warning:
if (SuppressWarnings)
return true;
case DS_Remark:
case DS_Note:
llvm_unreachable("Only expecting warnings and errors");
DiagnosticPrinterRawOStream DP(errs());
errs() << '\n';
return true;
/// Import any functions requested via the -import option.
static bool importFunctions(const char *argv0, Module &DestModule) {
if (SummaryIndex.empty())
return true;
std::unique_ptr<ModuleSummaryIndex> Index =
// Map of Module -> List of globals to import from the Module
FunctionImporter::ImportMapTy ImportList;
auto ModuleLoader = [&DestModule](const char *argv0,
const std::string &Identifier) {
return loadFile(argv0, Identifier, DestModule.getContext(), false);
ModuleLazyLoaderCache ModuleLoaderCache(ModuleLoader);
for (const auto &Import : Imports) {
// Identify the requested function and its bitcode source file.
size_t Idx = Import.find(':');
if (Idx == std::string::npos) {
errs() << "Import parameter bad format: " << Import << "\n";
return false;
std::string FunctionName = Import.substr(0, Idx);
std::string FileName = Import.substr(Idx + 1, std::string::npos);
// Load the specified source module.
auto &SrcModule = ModuleLoaderCache(argv0, FileName);
if (verifyModule(SrcModule, &errs())) {
errs() << argv0 << ": " << FileName;
WithColor::error() << "input module is broken!\n";
return false;
Function *F = SrcModule.getFunction(FunctionName);
if (!F) {
errs() << "Ignoring import request for non-existent function "
<< FunctionName << " from " << FileName << "\n";
// We cannot import weak_any functions without possibly affecting the
// order they are seen and selected by the linker, changing program
// semantics.
if (F->hasWeakAnyLinkage()) {
errs() << "Ignoring import request for weak-any function " << FunctionName
<< " from " << FileName << "\n";
if (Verbose)
errs() << "Importing " << FunctionName << " from " << FileName << "\n";
auto &Entry = ImportList[FileName];
auto CachedModuleLoader = [&](StringRef Identifier) {
return ModuleLoaderCache.takeModule(Identifier);
FunctionImporter Importer(*Index, CachedModuleLoader);
ExitOnErr(Importer.importFunctions(DestModule, ImportList));
return true;
static bool linkFiles(const char *argv0, LLVMContext &Context, Linker &L,
const cl::list<std::string> &Files,
unsigned Flags) {
// Filter out flags that don't apply to the first file we load.
unsigned ApplicableFlags = Flags & Linker::Flags::OverrideFromSrc;
// Similar to some flags, internalization doesn't apply to the first file.
bool InternalizeLinkedSymbols = false;
for (const auto &File : Files) {
std::unique_ptr<Module> M = loadFile(argv0, File, Context);
if (!M.get()) {
errs() << argv0 << ": ";
WithColor::error() << " loading file '" << File << "'\n";
return false;
// Note that when ODR merging types cannot verify input files in here When
// doing that debug metadata in the src module might already be pointing to
// the destination.
if (DisableDITypeMap && verifyModule(*M, &errs())) {
errs() << argv0 << ": " << File << ": ";
WithColor::error() << "input module is broken!\n";
return false;
// If a module summary index is supplied, load it so linkInModule can treat
// local functions/variables as exported and promote if necessary.
if (!SummaryIndex.empty()) {
std::unique_ptr<ModuleSummaryIndex> Index =
// Conservatively mark all internal values as promoted, since this tool
// does not do the ThinLink that would normally determine what values to
// promote.
for (auto &I : *Index) {
for (auto &S : I.second.SummaryList) {
if (GlobalValue::isLocalLinkage(S->linkage()))
// Promotion
if (renameModuleForThinLTO(*M, *Index))
return true;
if (Verbose)
errs() << "Linking in '" << File << "'\n";
bool Err = false;
if (InternalizeLinkedSymbols) {
Err = L.linkInModule(
std::move(M), ApplicableFlags, [](Module &M, const StringSet<> &GVS) {
internalizeModule(M, [&GVS](const GlobalValue &GV) {
return !GV.hasName() || (GVS.count(GV.getName()) == 0);
} else {
Err = L.linkInModule(std::move(M), ApplicableFlags);
if (Err)
return false;
// Internalization applies to linking of subsequent files.
InternalizeLinkedSymbols = Internalize;
// All linker flags apply to linking of subsequent files.
ApplicableFlags = Flags;
return true;
int main(int argc, char **argv) {
InitLLVM X(argc, argv);
ExitOnErr.setBanner(std::string(argv[0]) + ": ");
LLVMContext Context;
std::make_unique<LLVMLinkDiagnosticHandler>(), true);
cl::ParseCommandLineOptions(argc, argv, "llvm linker\n");
if (!DisableDITypeMap)
auto Composite = std::make_unique<Module>("llvm-link", Context);
Linker L(*Composite);
unsigned Flags = Linker::Flags::None;
if (OnlyNeeded)
Flags |= Linker::Flags::LinkOnlyNeeded;
// First add all the regular input files
if (!linkFiles(argv[0], Context, L, InputFilenames, Flags))
return 1;
// Next the -override ones.
if (!linkFiles(argv[0], Context, L, OverridingInputs,
Flags | Linker::Flags::OverrideFromSrc))
return 1;
// Import any functions requested via -import
if (!importFunctions(argv[0], *Composite))
return 1;
if (DumpAsm)
errs() << "Here's the assembly:\n" << *Composite;
std::error_code EC;
ToolOutputFile Out(OutputFilename, EC, sys::fs::OF_None);
if (EC) {
WithColor::error() << EC.message() << '\n';
return 1;
if (verifyModule(*Composite, &errs())) {
errs() << argv[0] << ": ";
WithColor::error() << "linked module is broken!\n";
return 1;
if (Verbose)
errs() << "Writing bitcode...\n";
if (OutputAssembly) {
Composite->print(Out.os(), nullptr, PreserveAssemblyUseListOrder);
} else if (Force || !CheckBitcodeOutputToConsole(Out.os(), true))
WriteBitcodeToFile(*Composite, Out.os(), PreserveBitcodeUseListOrder);
// Declare success.
return 0;