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//===-- Internalize.cpp - Mark functions internal -------------------------===//
// 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 pass loops over all of the functions and variables in the input module.
// If the function or variable does not need to be preserved according to the
// client supplied callback, it is marked as internal.
// This transformation would not be legal in a regular compilation, but it gets
// extra information from the linker about what is safe.
// For example: Internalizing a function with external linkage. Only if we are
// told it is only used from within this module, it is safe to do it.
#include "llvm/Transforms/IPO/Internalize.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GlobPattern.h"
#include "llvm/Support/LineIterator.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/Triple.h"
#include "llvm/Transforms/IPO.h"
using namespace llvm;
#define DEBUG_TYPE "internalize"
STATISTIC(NumAliases, "Number of aliases internalized");
STATISTIC(NumFunctions, "Number of functions internalized");
STATISTIC(NumGlobals, "Number of global vars internalized");
// APIFile - A file which contains a list of symbol glob patterns that should
// not be marked external.
static cl::opt<std::string>
APIFile("internalize-public-api-file", cl::value_desc("filename"),
cl::desc("A file containing list of symbol names to preserve"));
// APIList - A list of symbol glob patterns that should not be marked internal.
static cl::list<std::string>
APIList("internalize-public-api-list", cl::value_desc("list"),
cl::desc("A list of symbol names to preserve"), cl::CommaSeparated);
namespace {
// Helper to load an API list to preserve from file and expose it as a functor
// for internalization.
class PreserveAPIList {
PreserveAPIList() {
if (!APIFile.empty())
for (StringRef Pattern : APIList)
bool operator()(const GlobalValue &GV) {
return llvm::any_of(
ExternalNames, [&](GlobPattern &GP) { return GP.match(GV.getName()); });
// Contains the set of symbols loaded from file
SmallVector<GlobPattern> ExternalNames;
void addGlob(StringRef Pattern) {
auto GlobOrErr = GlobPattern::create(Pattern);
if (!GlobOrErr) {
errs() << "WARNING: when loading pattern: '"
<< toString(GlobOrErr.takeError()) << "' ignoring";
void LoadFile(StringRef Filename) {
// Load the APIFile...
ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrErr =
if (!BufOrErr) {
errs() << "WARNING: Internalize couldn't load file '" << Filename
<< "'! Continuing as if it's empty.\n";
return; // Just continue as if the file were empty
Buf = std::move(*BufOrErr);
for (line_iterator I(*Buf, true), E; I != E; ++I)
std::shared_ptr<MemoryBuffer> Buf;
} // end anonymous namespace
bool InternalizePass::shouldPreserveGV(const GlobalValue &GV) {
// Function must be defined here
if (GV.isDeclaration())
return true;
// Available externally is really just a "declaration with a body".
if (GV.hasAvailableExternallyLinkage())
return true;
// Assume that dllexported symbols are referenced elsewhere
if (GV.hasDLLExportStorageClass())
return true;
// As the name suggests, externally initialized variables need preserving as
// they would be initialized elsewhere externally.
if (const auto *G = dyn_cast<GlobalVariable>(&GV))
if (G->isExternallyInitialized())
return true;
// Already local, has nothing to do.
if (GV.hasLocalLinkage())
return false;
// Check some special cases
if (AlwaysPreserved.count(GV.getName()))
return true;
return MustPreserveGV(GV);
bool InternalizePass::maybeInternalize(
GlobalValue &GV, DenseMap<const Comdat *, ComdatInfo> &ComdatMap) {
SmallString<0> ComdatName;
if (Comdat *C = GV.getComdat()) {
// For GlobalAlias, C is the aliasee object's comdat which may have been
// redirected. So ComdatMap may not contain C.
if (ComdatMap.lookup(C).External)
return false;
if (auto *GO = dyn_cast<GlobalObject>(&GV)) {
// If a comdat with one member is not externally visible, we can drop it.
// Otherwise, the comdat can be used to establish dependencies among the
// group of sections. Thus we have to keep the comdat but switch it to
// nodeduplicate.
// Note: nodeduplicate is not necessary for COFF. wasm doesn't support
// nodeduplicate.
ComdatInfo &Info = ComdatMap.find(C)->second;
if (Info.Size == 1)
else if (!IsWasm)
if (GV.hasLocalLinkage())
return false;
} else {
if (GV.hasLocalLinkage())
return false;
if (shouldPreserveGV(GV))
return false;
return true;
// If GV is part of a comdat and is externally visible, update the comdat size
// and keep track of its comdat so that we don't internalize any of its members.
void InternalizePass::checkComdat(
GlobalValue &GV, DenseMap<const Comdat *, ComdatInfo> &ComdatMap) {
Comdat *C = GV.getComdat();
if (!C)
ComdatInfo &Info = ComdatMap.try_emplace(C).first->second;
if (shouldPreserveGV(GV))
Info.External = true;
bool InternalizePass::internalizeModule(Module &M) {
bool Changed = false;
SmallVector<GlobalValue *, 4> Used;
collectUsedGlobalVariables(M, Used, false);
// Collect comdat size and visiblity information for the module.
DenseMap<const Comdat *, ComdatInfo> ComdatMap;
if (!M.getComdatSymbolTable().empty()) {
for (Function &F : M)
checkComdat(F, ComdatMap);
for (GlobalVariable &GV : M.globals())
checkComdat(GV, ComdatMap);
for (GlobalAlias &GA : M.aliases())
checkComdat(GA, ComdatMap);
// We must assume that globals in llvm.used have a reference that not even
// the linker can see, so we don't internalize them.
// For llvm.compiler.used the situation is a bit fuzzy. The assembler and
// linker can drop those symbols. If this pass is running as part of LTO,
// one might think that it could just drop llvm.compiler.used. The problem
// is that even in LTO llvm doesn't see every reference. For example,
// we don't see references from function local inline assembly. To be
// conservative, we internalize symbols in llvm.compiler.used, but we
// keep llvm.compiler.used so that the symbol is not deleted by llvm.
for (GlobalValue *V : Used) {
// Never internalize the llvm.used symbol. It is used to implement
// attribute((used)).
// FIXME: Shouldn't this just filter on llvm.metadata section??
// Never internalize anchors used by the machine module info, else the info
// won't find them. (see MachineModuleInfo.)
// Never internalize symbols code-gen inserts.
// FIXME: We should probably add this (and the __stack_chk_guard) via some
// type of call-back in CodeGen.
if (Triple(M.getTargetTriple()).isOSAIX())
// Mark all functions not in the api as internal.
IsWasm = Triple(M.getTargetTriple()).isOSBinFormatWasm();
for (Function &I : M) {
if (!maybeInternalize(I, ComdatMap))
Changed = true;
LLVM_DEBUG(dbgs() << "Internalizing func " << I.getName() << "\n");
// Mark all global variables with initializers that are not in the api as
// internal as well.
for (auto &GV : M.globals()) {
if (!maybeInternalize(GV, ComdatMap))
Changed = true;
LLVM_DEBUG(dbgs() << "Internalized gvar " << GV.getName() << "\n");
// Mark all aliases that are not in the api as internal as well.
for (auto &GA : M.aliases()) {
if (!maybeInternalize(GA, ComdatMap))
Changed = true;
LLVM_DEBUG(dbgs() << "Internalized alias " << GA.getName() << "\n");
return Changed;
InternalizePass::InternalizePass() : MustPreserveGV(PreserveAPIList()) {}
PreservedAnalyses InternalizePass::run(Module &M, ModuleAnalysisManager &AM) {
if (!internalizeModule(M))
return PreservedAnalyses::all();
return PreservedAnalyses::none();