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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/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/LineIterator.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Utils/GlobalStatus.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 symbols 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 symbols 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())
ExternalNames.insert(APIList.begin(), APIList.end());
bool operator()(const GlobalValue &GV) {
return ExternalNames.count(GV.getName());
// Contains the set of symbols loaded from file
StringSet<> ExternalNames;
void LoadFile(StringRef Filename) {
// Load the APIFile...
ErrorOr<std::unique_ptr<MemoryBuffer>> Buf =
if (!Buf) {
errs() << "WARNING: Internalize couldn't load file '" << Filename
<< "'! Continuing as if it's empty.\n";
return; // Just continue as if the file were empty
for (line_iterator I(*Buf->get(), true), E; I != E; ++I)
} // 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;
// 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, const DenseSet<const Comdat *> &ExternalComdats) {
if (Comdat *C = GV.getComdat()) {
if (ExternalComdats.count(C))
return false;
// If a comdat is not externally visible we can drop it.
if (auto GO = dyn_cast<GlobalObject>(&GV))
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, keep track of its
// comdat so that we don't internalize any of its members.
void InternalizePass::checkComdatVisibility(
GlobalValue &GV, DenseSet<const Comdat *> &ExternalComdats) {
Comdat *C = GV.getComdat();
if (!C)
if (shouldPreserveGV(GV))
bool InternalizePass::internalizeModule(Module &M, CallGraph *CG) {
bool Changed = false;
CallGraphNode *ExternalNode = CG ? CG->getExternalCallingNode() : nullptr;
SmallPtrSet<GlobalValue *, 8> Used;
collectUsedGlobalVariables(M, Used, false);
// Collect comdat visiblity information for the module.
DenseSet<const Comdat *> ExternalComdats;
if (!M.getComdatSymbolTable().empty()) {
for (Function &F : M)
checkComdatVisibility(F, ExternalComdats);
for (GlobalVariable &GV : M.globals())
checkComdatVisibility(GV, ExternalComdats);
for (GlobalAlias &GA : M.aliases())
checkComdatVisibility(GA, ExternalComdats);
// 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) {
// Mark all functions not in the api as internal.
for (Function &I : M) {
if (!maybeInternalize(I, ExternalComdats))
Changed = true;
if (ExternalNode)
// Remove a callgraph edge from the external node to this function.
LLVM_DEBUG(dbgs() << "Internalizing func " << I.getName() << "\n");
// 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.
// Mark all global variables with initializers that are not in the api as
// internal as well.
for (auto &GV : M.globals()) {
if (!maybeInternalize(GV, ExternalComdats))
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, ExternalComdats))
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, AM.getCachedResult<CallGraphAnalysis>(M)))
return PreservedAnalyses::all();
PreservedAnalyses PA;
return PA;
namespace {
class InternalizeLegacyPass : public ModulePass {
// Client supplied callback to control wheter a symbol must be preserved.
std::function<bool(const GlobalValue &)> MustPreserveGV;
static char ID; // Pass identification, replacement for typeid
InternalizeLegacyPass() : ModulePass(ID), MustPreserveGV(PreserveAPIList()) {}
InternalizeLegacyPass(std::function<bool(const GlobalValue &)> MustPreserveGV)
: ModulePass(ID), MustPreserveGV(std::move(MustPreserveGV)) {
bool runOnModule(Module &M) override {
if (skipModule(M))
return false;
CallGraphWrapperPass *CGPass =
CallGraph *CG = CGPass ? &CGPass->getCallGraph() : nullptr;
return internalizeModule(M, MustPreserveGV, CG);
void getAnalysisUsage(AnalysisUsage &AU) const override {
char InternalizeLegacyPass::ID = 0;
INITIALIZE_PASS(InternalizeLegacyPass, "internalize",
"Internalize Global Symbols", false, false)
ModulePass *llvm::createInternalizePass() {
return new InternalizeLegacyPass();
ModulePass *llvm::createInternalizePass(
std::function<bool(const GlobalValue &)> MustPreserveGV) {
return new InternalizeLegacyPass(std::move(MustPreserveGV));