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//===- FunctionImport.cpp - ThinLTO Summary-based Function Import ---------===//
// 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 file implements Function import based on summaries.
#include "llvm/Transforms/IPO/FunctionImport.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/IR/AutoUpgrade.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ModuleSummaryIndex.h"
#include "llvm/IRReader/IRReader.h"
#include "llvm/InitializePasses.h"
#include "llvm/Linker/IRMover.h"
#include "llvm/Object/ModuleSymbolTable.h"
#include "llvm/Object/SymbolicFile.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/IPO/Internalize.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <cassert>
#include <memory>
#include <set>
#include <string>
#include <system_error>
#include <tuple>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "function-import"
"Number of functions thin link decided to import");
"Number of hot functions thin link decided to import");
"Number of critical functions thin link decided to import");
"Number of global variables thin link decided to import");
STATISTIC(NumImportedFunctions, "Number of functions imported in backend");
"Number of global variables imported in backend");
STATISTIC(NumImportedModules, "Number of modules imported from");
STATISTIC(NumDeadSymbols, "Number of dead stripped symbols in index");
STATISTIC(NumLiveSymbols, "Number of live symbols in index");
/// Limit on instruction count of imported functions.
static cl::opt<unsigned> ImportInstrLimit(
"import-instr-limit", cl::init(100), cl::Hidden, cl::value_desc("N"),
cl::desc("Only import functions with less than N instructions"));
static cl::opt<int> ImportCutoff(
"import-cutoff", cl::init(-1), cl::Hidden, cl::value_desc("N"),
cl::desc("Only import first N functions if N>=0 (default -1)"));
static cl::opt<float>
ImportInstrFactor("import-instr-evolution-factor", cl::init(0.7),
cl::Hidden, cl::value_desc("x"),
cl::desc("As we import functions, multiply the "
"`import-instr-limit` threshold by this factor "
"before processing newly imported functions"));
static cl::opt<float> ImportHotInstrFactor(
"import-hot-evolution-factor", cl::init(1.0), cl::Hidden,
cl::desc("As we import functions called from hot callsite, multiply the "
"`import-instr-limit` threshold by this factor "
"before processing newly imported functions"));
static cl::opt<float> ImportHotMultiplier(
"import-hot-multiplier", cl::init(10.0), cl::Hidden, cl::value_desc("x"),
cl::desc("Multiply the `import-instr-limit` threshold for hot callsites"));
static cl::opt<float> ImportCriticalMultiplier(
"import-critical-multiplier", cl::init(100.0), cl::Hidden,
"Multiply the `import-instr-limit` threshold for critical callsites"));
// FIXME: This multiplier was not really tuned up.
static cl::opt<float> ImportColdMultiplier(
"import-cold-multiplier", cl::init(0), cl::Hidden, cl::value_desc("N"),
cl::desc("Multiply the `import-instr-limit` threshold for cold callsites"));
static cl::opt<bool> PrintImports("print-imports", cl::init(false), cl::Hidden,
cl::desc("Print imported functions"));
static cl::opt<bool> PrintImportFailures(
"print-import-failures", cl::init(false), cl::Hidden,
cl::desc("Print information for functions rejected for importing"));
static cl::opt<bool> ComputeDead("compute-dead", cl::init(true), cl::Hidden,
cl::desc("Compute dead symbols"));
static cl::opt<bool> EnableImportMetadata(
"enable-import-metadata", cl::init(false), cl::Hidden,
cl::desc("Enable import metadata like 'thinlto_src_module'"));
/// Summary file to use for function importing when using -function-import from
/// the command line.
static cl::opt<std::string>
cl::desc("The summary file to use for function importing."));
/// Used when testing importing from distributed indexes via opt
// -function-import.
static cl::opt<bool>
cl::desc("Import all external functions in index."));
// Load lazily a module from \p FileName in \p Context.
static std::unique_ptr<Module> loadFile(const std::string &FileName,
LLVMContext &Context) {
SMDiagnostic Err;
LLVM_DEBUG(dbgs() << "Loading '" << FileName << "'\n");
// Metadata isn't loaded until functions are imported, to minimize
// the memory overhead.
std::unique_ptr<Module> Result =
getLazyIRFileModule(FileName, Err, Context,
/* ShouldLazyLoadMetadata = */ true);
if (!Result) {
Err.print("function-import", errs());
return Result;
/// Given a list of possible callee implementation for a call site, select one
/// that fits the \p Threshold.
/// FIXME: select "best" instead of first that fits. But what is "best"?
/// - The smallest: more likely to be inlined.
/// - The one with the least outgoing edges (already well optimized).
/// - One from a module already being imported from in order to reduce the
/// number of source modules parsed/linked.
/// - One that has PGO data attached.
/// - [insert you fancy metric here]
static const GlobalValueSummary *
selectCallee(const ModuleSummaryIndex &Index,
ArrayRef<std::unique_ptr<GlobalValueSummary>> CalleeSummaryList,
unsigned Threshold, StringRef CallerModulePath,
FunctionImporter::ImportFailureReason &Reason,
GlobalValue::GUID GUID) {
Reason = FunctionImporter::ImportFailureReason::None;
auto It = llvm::find_if(
[&](const std::unique_ptr<GlobalValueSummary> &SummaryPtr) {
auto *GVSummary = SummaryPtr.get();
if (!Index.isGlobalValueLive(GVSummary)) {
Reason = FunctionImporter::ImportFailureReason::NotLive;
return false;
// For SamplePGO, in computeImportForFunction the OriginalId
// may have been used to locate the callee summary list (See
// comment there).
// The mapping from OriginalId to GUID may return a GUID
// that corresponds to a static variable. Filter it out here.
// This can happen when
// 1) There is a call to a library function which is not defined
// in the index.
// 2) There is a static variable with the OriginalGUID identical
// to the GUID of the library function in 1);
// When this happens, the logic for SamplePGO kicks in and
// the static variable in 2) will be found, which needs to be
// filtered out.
if (GVSummary->getSummaryKind() == GlobalValueSummary::GlobalVarKind) {
Reason = FunctionImporter::ImportFailureReason::GlobalVar;
return false;
if (GlobalValue::isInterposableLinkage(GVSummary->linkage())) {
Reason = FunctionImporter::ImportFailureReason::InterposableLinkage;
// There is no point in importing these, we can't inline them
return false;
auto *Summary = cast<FunctionSummary>(GVSummary->getBaseObject());
// If this is a local function, make sure we import the copy
// in the caller's module. The only time a local function can
// share an entry in the index is if there is a local with the same name
// in another module that had the same source file name (in a different
// directory), where each was compiled in their own directory so there
// was not distinguishing path.
// However, do the import from another module if there is only one
// entry in the list - in that case this must be a reference due
// to indirect call profile data, since a function pointer can point to
// a local in another module.
if (GlobalValue::isLocalLinkage(Summary->linkage()) &&
CalleeSummaryList.size() > 1 &&
Summary->modulePath() != CallerModulePath) {
Reason =
return false;
if ((Summary->instCount() > Threshold) &&
!Summary->fflags().AlwaysInline) {
Reason = FunctionImporter::ImportFailureReason::TooLarge;
return false;
// Skip if it isn't legal to import (e.g. may reference unpromotable
// locals).
if (Summary->notEligibleToImport()) {
Reason = FunctionImporter::ImportFailureReason::NotEligible;
return false;
// Don't bother importing if we can't inline it anyway.
if (Summary->fflags().NoInline) {
Reason = FunctionImporter::ImportFailureReason::NoInline;
return false;
return true;
if (It == CalleeSummaryList.end())
return nullptr;
return cast<GlobalValueSummary>(It->get());
namespace {
using EdgeInfo =
std::tuple<const GlobalValueSummary *, unsigned /* Threshold */>;
} // anonymous namespace
static ValueInfo
updateValueInfoForIndirectCalls(const ModuleSummaryIndex &Index, ValueInfo VI) {
if (!VI.getSummaryList().empty())
return VI;
// For SamplePGO, the indirect call targets for local functions will
// have its original name annotated in profile. We try to find the
// corresponding PGOFuncName as the GUID.
// FIXME: Consider updating the edges in the graph after building
// it, rather than needing to perform this mapping on each walk.
auto GUID = Index.getGUIDFromOriginalID(VI.getGUID());
if (GUID == 0)
return ValueInfo();
return Index.getValueInfo(GUID);
static bool shouldImportGlobal(const ValueInfo &VI,
const GVSummaryMapTy &DefinedGVSummaries) {
const auto &GVS = DefinedGVSummaries.find(VI.getGUID());
if (GVS == DefinedGVSummaries.end())
return true;
// We should not skip import if the module contains a definition with
// interposable linkage type. This is required for correctness in
// the situation with two following conditions:
// * the def with interposable linkage is non-prevailing,
// * there is a prevailing def available for import and marked read-only.
// In this case, the non-prevailing def will be converted to a declaration,
// while the prevailing one becomes internal, thus no definitions will be
// available for linking. In order to prevent undefined symbol link error,
// the prevailing definition must be imported.
// FIXME: Consider adding a check that the suitable prevailing definition
// exists and marked read-only.
if (VI.getSummaryList().size() > 1 &&
return true;
return false;
static void computeImportForReferencedGlobals(
const GlobalValueSummary &Summary, const ModuleSummaryIndex &Index,
const GVSummaryMapTy &DefinedGVSummaries,
SmallVectorImpl<EdgeInfo> &Worklist,
FunctionImporter::ImportMapTy &ImportList,
StringMap<FunctionImporter::ExportSetTy> *ExportLists) {
for (auto &VI : Summary.refs()) {
if (!shouldImportGlobal(VI, DefinedGVSummaries)) {
dbgs() << "Ref ignored! Target already in destination module.\n");
LLVM_DEBUG(dbgs() << " ref -> " << VI << "\n");
// If this is a local variable, make sure we import the copy
// in the caller's module. The only time a local variable can
// share an entry in the index is if there is a local with the same name
// in another module that had the same source file name (in a different
// directory), where each was compiled in their own directory so there
// was not distinguishing path.
auto LocalNotInModule = [&](const GlobalValueSummary *RefSummary) -> bool {
return GlobalValue::isLocalLinkage(RefSummary->linkage()) &&
RefSummary->modulePath() != Summary.modulePath();
for (auto &RefSummary : VI.getSummaryList())
if (isa<GlobalVarSummary>(RefSummary.get()) &&
Index.canImportGlobalVar(RefSummary.get(), /* AnalyzeRefs */ true) &&
!LocalNotInModule(RefSummary.get())) {
auto ILI = ImportList[RefSummary->modulePath()].insert(VI.getGUID());
// Only update stat and exports if we haven't already imported this
// variable.
if (!ILI.second)
// Any references made by this variable will be marked exported later,
// in ComputeCrossModuleImport, after import decisions are complete,
// which is more efficient than adding them here.
if (ExportLists)
// If variable is not writeonly we attempt to recursively analyze
// its references in order to import referenced constants.
if (!Index.isWriteOnly(cast<GlobalVarSummary>(RefSummary.get())))
Worklist.emplace_back(RefSummary.get(), 0);
static const char *
getFailureName(FunctionImporter::ImportFailureReason Reason) {
switch (Reason) {
case FunctionImporter::ImportFailureReason::None:
return "None";
case FunctionImporter::ImportFailureReason::GlobalVar:
return "GlobalVar";
case FunctionImporter::ImportFailureReason::NotLive:
return "NotLive";
case FunctionImporter::ImportFailureReason::TooLarge:
return "TooLarge";
case FunctionImporter::ImportFailureReason::InterposableLinkage:
return "InterposableLinkage";
case FunctionImporter::ImportFailureReason::LocalLinkageNotInModule:
return "LocalLinkageNotInModule";
case FunctionImporter::ImportFailureReason::NotEligible:
return "NotEligible";
case FunctionImporter::ImportFailureReason::NoInline:
return "NoInline";
llvm_unreachable("invalid reason");
/// Compute the list of functions to import for a given caller. Mark these
/// imported functions and the symbols they reference in their source module as
/// exported from their source module.
static void computeImportForFunction(
const FunctionSummary &Summary, const ModuleSummaryIndex &Index,
const unsigned Threshold, const GVSummaryMapTy &DefinedGVSummaries,
SmallVectorImpl<EdgeInfo> &Worklist,
FunctionImporter::ImportMapTy &ImportList,
StringMap<FunctionImporter::ExportSetTy> *ExportLists,
FunctionImporter::ImportThresholdsTy &ImportThresholds) {
computeImportForReferencedGlobals(Summary, Index, DefinedGVSummaries,
Worklist, ImportList, ExportLists);
static int ImportCount = 0;
for (auto &Edge : Summary.calls()) {
ValueInfo VI = Edge.first;
LLVM_DEBUG(dbgs() << " edge -> " << VI << " Threshold:" << Threshold
<< "\n");
if (ImportCutoff >= 0 && ImportCount >= ImportCutoff) {
LLVM_DEBUG(dbgs() << "ignored! import-cutoff value of " << ImportCutoff
<< " reached.\n");
VI = updateValueInfoForIndirectCalls(Index, VI);
if (!VI)
if (DefinedGVSummaries.count(VI.getGUID())) {
// FIXME: Consider not skipping import if the module contains
// a non-prevailing def with interposable linkage. The prevailing copy
// can safely be imported (see shouldImportGlobal()).
LLVM_DEBUG(dbgs() << "ignored! Target already in destination module.\n");
auto GetBonusMultiplier = [](CalleeInfo::HotnessType Hotness) -> float {
if (Hotness == CalleeInfo::HotnessType::Hot)
return ImportHotMultiplier;
if (Hotness == CalleeInfo::HotnessType::Cold)
return ImportColdMultiplier;
if (Hotness == CalleeInfo::HotnessType::Critical)
return ImportCriticalMultiplier;
return 1.0;
const auto NewThreshold =
Threshold * GetBonusMultiplier(Edge.second.getHotness());
auto IT = ImportThresholds.insert(std::make_pair(
VI.getGUID(), std::make_tuple(NewThreshold, nullptr, nullptr)));
bool PreviouslyVisited = !IT.second;
auto &ProcessedThreshold = std::get<0>(IT.first->second);
auto &CalleeSummary = std::get<1>(IT.first->second);
auto &FailureInfo = std::get<2>(IT.first->second);
bool IsHotCallsite =
Edge.second.getHotness() == CalleeInfo::HotnessType::Hot;
bool IsCriticalCallsite =
Edge.second.getHotness() == CalleeInfo::HotnessType::Critical;
const FunctionSummary *ResolvedCalleeSummary = nullptr;
if (CalleeSummary) {
// Since the traversal of the call graph is DFS, we can revisit a function
// a second time with a higher threshold. In this case, it is added back
// to the worklist with the new threshold (so that its own callee chains
// can be considered with the higher threshold).
if (NewThreshold <= ProcessedThreshold) {
dbgs() << "ignored! Target was already imported with Threshold "
<< ProcessedThreshold << "\n");
// Update with new larger threshold.
ProcessedThreshold = NewThreshold;
ResolvedCalleeSummary = cast<FunctionSummary>(CalleeSummary);
} else {
// If we already rejected importing a callee at the same or higher
// threshold, don't waste time calling selectCallee.
if (PreviouslyVisited && NewThreshold <= ProcessedThreshold) {
dbgs() << "ignored! Target was already rejected with Threshold "
<< ProcessedThreshold << "\n");
if (PrintImportFailures) {
assert(FailureInfo &&
"Expected FailureInfo for previously rejected candidate");
FunctionImporter::ImportFailureReason Reason;
CalleeSummary = selectCallee(Index, VI.getSummaryList(), NewThreshold,
Summary.modulePath(), Reason, VI.getGUID());
if (!CalleeSummary) {
// Update with new larger threshold if this was a retry (otherwise
// we would have already inserted with NewThreshold above). Also
// update failure info if requested.
if (PreviouslyVisited) {
ProcessedThreshold = NewThreshold;
if (PrintImportFailures) {
assert(FailureInfo &&
"Expected FailureInfo for previously rejected candidate");
FailureInfo->Reason = Reason;
FailureInfo->MaxHotness =
std::max(FailureInfo->MaxHotness, Edge.second.getHotness());
} else if (PrintImportFailures) {
assert(!FailureInfo &&
"Expected no FailureInfo for newly rejected candidate");
FailureInfo = std::make_unique<FunctionImporter::ImportFailureInfo>(
VI, Edge.second.getHotness(), Reason, 1);
dbgs() << "ignored! No qualifying callee with summary found.\n");
// "Resolve" the summary
CalleeSummary = CalleeSummary->getBaseObject();
ResolvedCalleeSummary = cast<FunctionSummary>(CalleeSummary);
assert((ResolvedCalleeSummary->fflags().AlwaysInline ||
(ResolvedCalleeSummary->instCount() <= NewThreshold)) &&
"selectCallee() didn't honor the threshold");
auto ExportModulePath = ResolvedCalleeSummary->modulePath();
auto ILI = ImportList[ExportModulePath].insert(VI.getGUID());
// We previously decided to import this GUID definition if it was already
// inserted in the set of imports from the exporting module.
bool PreviouslyImported = !ILI.second;
if (!PreviouslyImported) {
if (IsHotCallsite)
if (IsCriticalCallsite)
// Any calls/references made by this function will be marked exported
// later, in ComputeCrossModuleImport, after import decisions are
// complete, which is more efficient than adding them here.
if (ExportLists)
auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
// Adjust the threshold for next level of imported functions.
// The threshold is different for hot callsites because we can then
// inline chains of hot calls.
if (IsHotCallsite)
return Threshold * ImportHotInstrFactor;
return Threshold * ImportInstrFactor;
const auto AdjThreshold = GetAdjustedThreshold(Threshold, IsHotCallsite);
// Insert the newly imported function to the worklist.
Worklist.emplace_back(ResolvedCalleeSummary, AdjThreshold);
/// Given the list of globals defined in a module, compute the list of imports
/// as well as the list of "exports", i.e. the list of symbols referenced from
/// another module (that may require promotion).
static void ComputeImportForModule(
const GVSummaryMapTy &DefinedGVSummaries, const ModuleSummaryIndex &Index,
StringRef ModName, FunctionImporter::ImportMapTy &ImportList,
StringMap<FunctionImporter::ExportSetTy> *ExportLists = nullptr) {
// Worklist contains the list of function imported in this module, for which
// we will analyse the callees and may import further down the callgraph.
SmallVector<EdgeInfo, 128> Worklist;
FunctionImporter::ImportThresholdsTy ImportThresholds;
// Populate the worklist with the import for the functions in the current
// module
for (auto &GVSummary : DefinedGVSummaries) {
#ifndef NDEBUG
// FIXME: Change the GVSummaryMapTy to hold ValueInfo instead of GUID
// so this map look up (and possibly others) can be avoided.
auto VI = Index.getValueInfo(GVSummary.first);
if (!Index.isGlobalValueLive(GVSummary.second)) {
LLVM_DEBUG(dbgs() << "Ignores Dead GUID: " << VI << "\n");
auto *FuncSummary =
if (!FuncSummary)
// Skip import for global variables
LLVM_DEBUG(dbgs() << "Initialize import for " << VI << "\n");
computeImportForFunction(*FuncSummary, Index, ImportInstrLimit,
DefinedGVSummaries, Worklist, ImportList,
ExportLists, ImportThresholds);
// Process the newly imported functions and add callees to the worklist.
while (!Worklist.empty()) {
auto GVInfo = Worklist.pop_back_val();
auto *Summary = std::get<0>(GVInfo);
auto Threshold = std::get<1>(GVInfo);
if (auto *FS = dyn_cast<FunctionSummary>(Summary))
computeImportForFunction(*FS, Index, Threshold, DefinedGVSummaries,
Worklist, ImportList, ExportLists,
computeImportForReferencedGlobals(*Summary, Index, DefinedGVSummaries,
Worklist, ImportList, ExportLists);
// Print stats about functions considered but rejected for importing
// when requested.
if (PrintImportFailures) {
dbgs() << "Missed imports into module " << ModName << "\n";
for (auto &I : ImportThresholds) {
auto &ProcessedThreshold = std::get<0>(I.second);
auto &CalleeSummary = std::get<1>(I.second);
auto &FailureInfo = std::get<2>(I.second);
if (CalleeSummary)
continue; // We are going to import.
FunctionSummary *FS = nullptr;
if (!FailureInfo->VI.getSummaryList().empty())
FS = dyn_cast<FunctionSummary>(
dbgs() << FailureInfo->VI
<< ": Reason = " << getFailureName(FailureInfo->Reason)
<< ", Threshold = " << ProcessedThreshold
<< ", Size = " << (FS ? (int)FS->instCount() : -1)
<< ", MaxHotness = " << getHotnessName(FailureInfo->MaxHotness)
<< ", Attempts = " << FailureInfo->Attempts << "\n";
#ifndef NDEBUG
static bool isGlobalVarSummary(const ModuleSummaryIndex &Index, ValueInfo VI) {
auto SL = VI.getSummaryList();
return SL.empty()
? false
: SL[0]->getSummaryKind() == GlobalValueSummary::GlobalVarKind;
static bool isGlobalVarSummary(const ModuleSummaryIndex &Index,
GlobalValue::GUID G) {
if (const auto &VI = Index.getValueInfo(G))
return isGlobalVarSummary(Index, VI);
return false;
template <class T>
static unsigned numGlobalVarSummaries(const ModuleSummaryIndex &Index,
T &Cont) {
unsigned NumGVS = 0;
for (auto &V : Cont)
if (isGlobalVarSummary(Index, V))
return NumGVS;
#ifndef NDEBUG
static bool
checkVariableImport(const ModuleSummaryIndex &Index,
StringMap<FunctionImporter::ImportMapTy> &ImportLists,
StringMap<FunctionImporter::ExportSetTy> &ExportLists) {
DenseSet<GlobalValue::GUID> FlattenedImports;
for (auto &ImportPerModule : ImportLists)
for (auto &ExportPerModule : ImportPerModule.second)
// Checks that all GUIDs of read/writeonly vars we see in export lists
// are also in the import lists. Otherwise we my face linker undefs,
// because readonly and writeonly vars are internalized in their
// source modules.
auto IsReadOrWriteOnlyVar = [&](StringRef ModulePath, const ValueInfo &VI) {
auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
Index.findSummaryInModule(VI, ModulePath));
return GVS && (Index.isReadOnly(GVS) || Index.isWriteOnly(GVS));
for (auto &ExportPerModule : ExportLists)
for (auto &VI : ExportPerModule.second)
if (!FlattenedImports.count(VI.getGUID()) &&
IsReadOrWriteOnlyVar(ExportPerModule.first(), VI))
return false;
return true;
/// Compute all the import and export for every module using the Index.
void llvm::ComputeCrossModuleImport(
const ModuleSummaryIndex &Index,
const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
StringMap<FunctionImporter::ImportMapTy> &ImportLists,
StringMap<FunctionImporter::ExportSetTy> &ExportLists) {
// For each module that has function defined, compute the import/export lists.
for (auto &DefinedGVSummaries : ModuleToDefinedGVSummaries) {
auto &ImportList = ImportLists[DefinedGVSummaries.first()];
LLVM_DEBUG(dbgs() << "Computing import for Module '"
<< DefinedGVSummaries.first() << "'\n");
ComputeImportForModule(DefinedGVSummaries.second, Index,
DefinedGVSummaries.first(), ImportList,
// When computing imports we only added the variables and functions being
// imported to the export list. We also need to mark any references and calls
// they make as exported as well. We do this here, as it is more efficient
// since we may import the same values multiple times into different modules
// during the import computation.
for (auto &ELI : ExportLists) {
FunctionImporter::ExportSetTy NewExports;
const auto &DefinedGVSummaries =
for (auto &EI : ELI.second) {
// Find the copy defined in the exporting module so that we can mark the
// values it references in that specific definition as exported.
// Below we will add all references and called values, without regard to
// whether they are also defined in this module. We subsequently prune the
// list to only include those defined in the exporting module, see comment
// there as to why.
auto DS = DefinedGVSummaries.find(EI.getGUID());
// Anything marked exported during the import computation must have been
// defined in the exporting module.
assert(DS != DefinedGVSummaries.end());
auto *S = DS->getSecond();
S = S->getBaseObject();
if (auto *GVS = dyn_cast<GlobalVarSummary>(S)) {
// Export referenced functions and variables. We don't export/promote
// objects referenced by writeonly variable initializer, because
// we convert such variables initializers to "zeroinitializer".
// See processGlobalForThinLTO.
if (!Index.isWriteOnly(GVS))
for (const auto &VI : GVS->refs())
} else {
auto *FS = cast<FunctionSummary>(S);
for (auto &Edge : FS->calls())
for (auto &Ref : FS->refs())
// Prune list computed above to only include values defined in the exporting
// module. We do this after the above insertion since we may hit the same
// ref/call target multiple times in above loop, and it is more efficient to
// avoid a set lookup each time.
for (auto EI = NewExports.begin(); EI != NewExports.end();) {
if (!DefinedGVSummaries.count(EI->getGUID()))
ELI.second.insert(NewExports.begin(), NewExports.end());
assert(checkVariableImport(Index, ImportLists, ExportLists));
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "Import/Export lists for " << ImportLists.size()
<< " modules:\n");
for (auto &ModuleImports : ImportLists) {
auto ModName = ModuleImports.first();
auto &Exports = ExportLists[ModName];
unsigned NumGVS = numGlobalVarSummaries(Index, Exports);
LLVM_DEBUG(dbgs() << "* Module " << ModName << " exports "
<< Exports.size() - NumGVS << " functions and " << NumGVS
<< " vars. Imports from " << ModuleImports.second.size()
<< " modules.\n");
for (auto &Src : ModuleImports.second) {
auto SrcModName = Src.first();
unsigned NumGVSPerMod = numGlobalVarSummaries(Index, Src.second);
LLVM_DEBUG(dbgs() << " - " << Src.second.size() - NumGVSPerMod
<< " functions imported from " << SrcModName << "\n");
LLVM_DEBUG(dbgs() << " - " << NumGVSPerMod
<< " global vars imported from " << SrcModName << "\n");
#ifndef NDEBUG
static void dumpImportListForModule(const ModuleSummaryIndex &Index,
StringRef ModulePath,
FunctionImporter::ImportMapTy &ImportList) {
LLVM_DEBUG(dbgs() << "* Module " << ModulePath << " imports from "
<< ImportList.size() << " modules.\n");
for (auto &Src : ImportList) {
auto SrcModName = Src.first();
unsigned NumGVSPerMod = numGlobalVarSummaries(Index, Src.second);
LLVM_DEBUG(dbgs() << " - " << Src.second.size() - NumGVSPerMod
<< " functions imported from " << SrcModName << "\n");
LLVM_DEBUG(dbgs() << " - " << NumGVSPerMod << " vars imported from "
<< SrcModName << "\n");
/// Compute all the imports for the given module in the Index.
void llvm::ComputeCrossModuleImportForModule(
StringRef ModulePath, const ModuleSummaryIndex &Index,
FunctionImporter::ImportMapTy &ImportList) {
// Collect the list of functions this module defines.
// GUID -> Summary
GVSummaryMapTy FunctionSummaryMap;
Index.collectDefinedFunctionsForModule(ModulePath, FunctionSummaryMap);
// Compute the import list for this module.
LLVM_DEBUG(dbgs() << "Computing import for Module '" << ModulePath << "'\n");
ComputeImportForModule(FunctionSummaryMap, Index, ModulePath, ImportList);
#ifndef NDEBUG
dumpImportListForModule(Index, ModulePath, ImportList);
// Mark all external summaries in Index for import into the given module.
// Used for distributed builds using a distributed index.
void llvm::ComputeCrossModuleImportForModuleFromIndex(
StringRef ModulePath, const ModuleSummaryIndex &Index,
FunctionImporter::ImportMapTy &ImportList) {
for (auto &GlobalList : Index) {
// Ignore entries for undefined references.
if (GlobalList.second.SummaryList.empty())
auto GUID = GlobalList.first;
assert(GlobalList.second.SummaryList.size() == 1 &&
"Expected individual combined index to have one summary per GUID");
auto &Summary = GlobalList.second.SummaryList[0];
// Skip the summaries for the importing module. These are included to
// e.g. record required linkage changes.
if (Summary->modulePath() == ModulePath)
// Add an entry to provoke importing by thinBackend.
#ifndef NDEBUG
dumpImportListForModule(Index, ModulePath, ImportList);
void llvm::computeDeadSymbols(
ModuleSummaryIndex &Index,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing) {
if (!ComputeDead)
if (GUIDPreservedSymbols.empty())
// Don't do anything when nothing is live, this is friendly with tests.
unsigned LiveSymbols = 0;
SmallVector<ValueInfo, 128> Worklist;
Worklist.reserve(GUIDPreservedSymbols.size() * 2);
for (auto GUID : GUIDPreservedSymbols) {
ValueInfo VI = Index.getValueInfo(GUID);
if (!VI)
for (auto &S : VI.getSummaryList())
// Add values flagged in the index as live roots to the worklist.
for (const auto &Entry : Index) {
auto VI = Index.getValueInfo(Entry);
for (auto &S : Entry.second.SummaryList)
if (S->isLive()) {
LLVM_DEBUG(dbgs() << "Live root: " << VI << "\n");
// Make value live and add it to the worklist if it was not live before.
auto visit = [&](ValueInfo VI, bool IsAliasee) {
// FIXME: If we knew which edges were created for indirect call profiles,
// we could skip them here. Any that are live should be reached via
// other edges, e.g. reference edges. Otherwise, using a profile collected
// on a slightly different binary might provoke preserving, importing
// and ultimately promoting calls to functions not linked into this
// binary, which increases the binary size unnecessarily. Note that
// if this code changes, the importer needs to change so that edges
// to functions marked dead are skipped.
VI = updateValueInfoForIndirectCalls(Index, VI);
if (!VI)
if (llvm::any_of(VI.getSummaryList(),
[](const std::unique_ptr<llvm::GlobalValueSummary> &S) {
return S->isLive();
// We only keep live symbols that are known to be non-prevailing if any are
// available_externally, linkonceodr, weakodr. Those symbols are discarded
// later in the EliminateAvailableExternally pass and setting them to
// not-live could break downstreams users of liveness information (PR36483)
// or limit optimization opportunities.
if (isPrevailing(VI.getGUID()) == PrevailingType::No) {
bool KeepAliveLinkage = false;
bool Interposable = false;
for (auto &S : VI.getSummaryList()) {
if (S->linkage() == GlobalValue::AvailableExternallyLinkage ||
S->linkage() == GlobalValue::WeakODRLinkage ||
S->linkage() == GlobalValue::LinkOnceODRLinkage)
KeepAliveLinkage = true;
else if (GlobalValue::isInterposableLinkage(S->linkage()))
Interposable = true;
if (!IsAliasee) {
if (!KeepAliveLinkage)
if (Interposable)
"Interposable and available_externally/linkonce_odr/weak_odr "
for (auto &S : VI.getSummaryList())
while (!Worklist.empty()) {
auto VI = Worklist.pop_back_val();
for (auto &Summary : VI.getSummaryList()) {
if (auto *AS = dyn_cast<AliasSummary>(Summary.get())) {
// If this is an alias, visit the aliasee VI to ensure that all copies
// are marked live and it is added to the worklist for further
// processing of its references.
visit(AS->getAliaseeVI(), true);
for (auto Ref : Summary->refs())
visit(Ref, false);
if (auto *FS = dyn_cast<FunctionSummary>(Summary.get()))
for (auto Call : FS->calls())
visit(Call.first, false);
unsigned DeadSymbols = Index.size() - LiveSymbols;
LLVM_DEBUG(dbgs() << LiveSymbols << " symbols Live, and " << DeadSymbols
<< " symbols Dead \n");
NumDeadSymbols += DeadSymbols;
NumLiveSymbols += LiveSymbols;
// Compute dead symbols and propagate constants in combined index.
void llvm::computeDeadSymbolsWithConstProp(
ModuleSummaryIndex &Index,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing,
bool ImportEnabled) {
computeDeadSymbols(Index, GUIDPreservedSymbols, isPrevailing);
if (ImportEnabled)
/// Compute the set of summaries needed for a ThinLTO backend compilation of
/// \p ModulePath.
void llvm::gatherImportedSummariesForModule(
StringRef ModulePath,
const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
const FunctionImporter::ImportMapTy &ImportList,
std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
// Include all summaries from the importing module.
ModuleToSummariesForIndex[std::string(ModulePath)] =
// Include summaries for imports.
for (auto &ILI : ImportList) {
auto &SummariesForIndex =
const auto &DefinedGVSummaries =
for (auto &GI : ILI.second) {
const auto &DS = DefinedGVSummaries.find(GI);
assert(DS != DefinedGVSummaries.end() &&
"Expected a defined summary for imported global value");
SummariesForIndex[GI] = DS->second;
/// Emit the files \p ModulePath will import from into \p OutputFilename.
std::error_code llvm::EmitImportsFiles(
StringRef ModulePath, StringRef OutputFilename,
const std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex) {
std::error_code EC;
raw_fd_ostream ImportsOS(OutputFilename, EC, sys::fs::OpenFlags::OF_None);
if (EC)
return EC;
for (auto &ILI : ModuleToSummariesForIndex)
// The ModuleToSummariesForIndex map includes an entry for the current
// Module (needed for writing out the index files). We don't want to
// include it in the imports file, however, so filter it out.
if (ILI.first != ModulePath)
ImportsOS << ILI.first << "\n";
return std::error_code();
bool llvm::convertToDeclaration(GlobalValue &GV) {
LLVM_DEBUG(dbgs() << "Converting to a declaration: `" << GV.getName()
<< "\n");
if (Function *F = dyn_cast<Function>(&GV)) {
} else if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
} else {
GlobalValue *NewGV;
if (GV.getValueType()->isFunctionTy())
NewGV =
GlobalValue::ExternalLinkage, GV.getAddressSpace(),
"", GV.getParent());
NewGV =
new GlobalVariable(*GV.getParent(), GV.getValueType(),
/*isConstant*/ false, GlobalValue::ExternalLinkage,
/*init*/ nullptr, "",
/*insertbefore*/ nullptr, GV.getThreadLocalMode(),
return false;
if (!GV.isImplicitDSOLocal())
return true;
void llvm::thinLTOResolvePrevailingInModule(
Module &TheModule, const GVSummaryMapTy &DefinedGlobals) {
auto updateLinkage = [&](GlobalValue &GV) {
// See if the global summary analysis computed a new resolved linkage.
const auto &GS = DefinedGlobals.find(GV.getGUID());
if (GS == DefinedGlobals.end())
auto NewLinkage = GS->second->linkage();
if (GlobalValue::isLocalLinkage(GV.getLinkage()) ||
// Don't internalize anything here, because the code below
// lacks necessary correctness checks. Leave this job to
// LLVM 'internalize' pass.
GlobalValue::isLocalLinkage(NewLinkage) ||
// In case it was dead and already converted to declaration.
// Set the potentially more constraining visibility computed from summaries.
// The DefaultVisibility condition is because older GlobalValueSummary does
// not record DefaultVisibility and we don't want to change protected/hidden
// to default.
if (GS->second->getVisibility() != GlobalValue::DefaultVisibility)
if (NewLinkage == GV.getLinkage())
// Check for a non-prevailing def that has interposable linkage
// (e.g. non-odr weak or linkonce). In that case we can't simply
// convert to available_externally, since it would lose the
// interposable property and possibly get inlined. Simply drop
// the definition in that case.
if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
GlobalValue::isInterposableLinkage(GV.getLinkage())) {
if (!convertToDeclaration(GV))
// FIXME: Change this to collect replaced GVs and later erase
// them from the parent module once thinLTOResolvePrevailingGUID is
// changed to enable this for aliases.
llvm_unreachable("Expected GV to be converted");
} else {
// If all copies of the original symbol had global unnamed addr and
// linkonce_odr linkage, it should be an auto hide symbol. In that case
// the thin link would have marked it as CanAutoHide. Add hidden visibility
// to the symbol to preserve the property.
if (NewLinkage == GlobalValue::WeakODRLinkage &&
GS->second->canAutoHide()) {
assert(GV.hasLinkOnceODRLinkage() && GV.hasGlobalUnnamedAddr());
LLVM_DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName()
<< "` from " << GV.getLinkage() << " to " << NewLinkage
<< "\n");
// Remove declarations from comdats, including available_externally
// as this is a declaration for the linker, and will be dropped eventually.
// It is illegal for comdats to contain declarations.
auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
if (GO && GO->isDeclarationForLinker() && GO->hasComdat())
// Process functions and global now
for (auto &GV : TheModule)
for (auto &GV : TheModule.globals())
for (auto &GV : TheModule.aliases())
/// Run internalization on \p TheModule based on symmary analysis.
void llvm::thinLTOInternalizeModule(Module &TheModule,
const GVSummaryMapTy &DefinedGlobals) {
// Declare a callback for the internalize pass that will ask for every
// candidate GlobalValue if it can be internalized or not.
auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {
// Lookup the linkage recorded in the summaries during global analysis.
auto GS = DefinedGlobals.find(GV.getGUID());
if (GS == DefinedGlobals.end()) {
// Must have been promoted (possibly conservatively). Find original
// name so that we can access the correct summary and see if it can
// be internalized again.
// FIXME: Eventually we should control promotion instead of promoting
// and internalizing again.
StringRef OrigName =
std::string OrigId = GlobalValue::getGlobalIdentifier(
OrigName, GlobalValue::InternalLinkage,
GS = DefinedGlobals.find(GlobalValue::getGUID(OrigId));
if (GS == DefinedGlobals.end()) {
// Also check the original non-promoted non-globalized name. In some
// cases a preempted weak value is linked in as a local copy because
// it is referenced by an alias (IRLinker::linkGlobalValueProto).
// In that case, since it was originally not a local value, it was
// recorded in the index using the original name.
// FIXME: This may not be needed once PR27866 is fixed.
GS = DefinedGlobals.find(GlobalValue::getGUID(OrigName));
assert(GS != DefinedGlobals.end());
return !GlobalValue::isLocalLinkage(GS->second->linkage());
// FIXME: See if we can just internalize directly here via linkage changes
// based on the index, rather than invoking internalizeModule.
internalizeModule(TheModule, MustPreserveGV);
/// Make alias a clone of its aliasee.
static Function *replaceAliasWithAliasee(Module *SrcModule, GlobalAlias *GA) {
Function *Fn = cast<Function>(GA->getBaseObject());
ValueToValueMapTy VMap;
Function *NewFn = CloneFunction(Fn, VMap);
// Clone should use the original alias's linkage, visibility and name, and we
// ensure all uses of alias instead use the new clone (casted if necessary).
GA->replaceAllUsesWith(ConstantExpr::getBitCast(NewFn, GA->getType()));
return NewFn;
// Internalize values that we marked with specific attribute
// in processGlobalForThinLTO.
static void internalizeGVsAfterImport(Module &M) {
for (auto &GV : M.globals())
// Skip GVs which have been converted to declarations
// by dropDeadSymbols.
if (!GV.isDeclaration() && GV.hasAttribute("thinlto-internalize")) {
// Automatically import functions in Module \p DestModule based on the summaries
// index.
Expected<bool> FunctionImporter::importFunctions(
Module &DestModule, const FunctionImporter::ImportMapTy &ImportList) {
LLVM_DEBUG(dbgs() << "Starting import for Module "
<< DestModule.getModuleIdentifier() << "\n");
unsigned ImportedCount = 0, ImportedGVCount = 0;
IRMover Mover(DestModule);
// Do the actual import of functions now, one Module at a time
std::set<StringRef> ModuleNameOrderedList;
for (auto &FunctionsToImportPerModule : ImportList) {
for (auto &Name : ModuleNameOrderedList) {
// Get the module for the import
const auto &FunctionsToImportPerModule = ImportList.find(Name);
assert(FunctionsToImportPerModule != ImportList.end());
Expected<std::unique_ptr<Module>> SrcModuleOrErr = ModuleLoader(Name);
if (!SrcModuleOrErr)
return SrcModuleOrErr.takeError();
std::unique_ptr<Module> SrcModule = std::move(*SrcModuleOrErr);
assert(&DestModule.getContext() == &SrcModule->getContext() &&
"Context mismatch");
// If modules were created with lazy metadata loading, materialize it
// now, before linking it (otherwise this will be a noop).
if (Error Err = SrcModule->materializeMetadata())
return std::move(Err);
auto &ImportGUIDs = FunctionsToImportPerModule->second;
// Find the globals to import
SetVector<GlobalValue *> GlobalsToImport;
for (Function &F : *SrcModule) {
if (!F.hasName())
auto GUID = F.getGUID();
auto Import = ImportGUIDs.count(GUID);
LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing function "
<< GUID << " " << F.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (Import) {
if (Error Err = F.materialize())
return std::move(Err);
if (EnableImportMetadata) {
// Add 'thinlto_src_module' metadata for statistics and debugging.
for (GlobalVariable &GV : SrcModule->globals()) {
if (!GV.hasName())
auto GUID = GV.getGUID();
auto Import = ImportGUIDs.count(GUID);
LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing global "
<< GUID << " " << GV.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (Import) {
if (Error Err = GV.materialize())
return std::move(Err);
ImportedGVCount += GlobalsToImport.insert(&GV);
for (GlobalAlias &GA : SrcModule->aliases()) {
if (!GA.hasName())
auto GUID = GA.getGUID();
auto Import = ImportGUIDs.count(GUID);
LLVM_DEBUG(dbgs() << (Import ? "Is" : "Not") << " importing alias "
<< GUID << " " << GA.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (Import) {
if (Error Err = GA.materialize())
return std::move(Err);
// Import alias as a copy of its aliasee.
GlobalObject *Base = GA.getBaseObject();
if (Error Err = Base->materialize())
return std::move(Err);
auto *Fn = replaceAliasWithAliasee(SrcModule.get(), &GA);
LLVM_DEBUG(dbgs() << "Is importing aliasee fn " << Base->getGUID()
<< " " << Base->getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (EnableImportMetadata) {
// Add 'thinlto_src_module' metadata for statistics and debugging.
// Upgrade debug info after we're done materializing all the globals and we
// have loaded all the required metadata!
// Set the partial sample profile ratio in the profile summary module flag
// of the imported source module, if applicable, so that the profile summary
// module flag will match with that of the destination module when it's
// imported.
// Link in the specified functions.
if (renameModuleForThinLTO(*SrcModule, Index, ClearDSOLocalOnDeclarations,
return true;
if (PrintImports) {
for (const auto *GV : GlobalsToImport)
dbgs() << DestModule.getSourceFileName() << ": Import " << GV->getName()
<< " from " << SrcModule->getSourceFileName() << "\n";
if (Error Err = Mover.move(
std::move(SrcModule), GlobalsToImport.getArrayRef(),
[](GlobalValue &, IRMover::ValueAdder) {},
report_fatal_error("Function Import: link error: " +
ImportedCount += GlobalsToImport.size();
NumImportedFunctions += (ImportedCount - ImportedGVCount);
NumImportedGlobalVars += ImportedGVCount;
LLVM_DEBUG(dbgs() << "Imported " << ImportedCount - ImportedGVCount
<< " functions for Module "
<< DestModule.getModuleIdentifier() << "\n");
LLVM_DEBUG(dbgs() << "Imported " << ImportedGVCount
<< " global variables for Module "
<< DestModule.getModuleIdentifier() << "\n");
return ImportedCount;
static bool doImportingForModule(Module &M) {
if (SummaryFile.empty())
report_fatal_error("error: -function-import requires -summary-file\n");
Expected<std::unique_ptr<ModuleSummaryIndex>> IndexPtrOrErr =
if (!IndexPtrOrErr) {
logAllUnhandledErrors(IndexPtrOrErr.takeError(), errs(),
"Error loading file '" + SummaryFile + "': ");
return false;
std::unique_ptr<ModuleSummaryIndex> Index = std::move(*IndexPtrOrErr);
// First step is collecting the import list.
FunctionImporter::ImportMapTy ImportList;
// If requested, simply import all functions in the index. This is used
// when testing distributed backend handling via the opt tool, when
// we have distributed indexes containing exactly the summaries to import.
if (ImportAllIndex)
ComputeCrossModuleImportForModuleFromIndex(M.getModuleIdentifier(), *Index,
ComputeCrossModuleImportForModule(M.getModuleIdentifier(), *Index,
// Conservatively mark all internal values as promoted. This interface is
// only used when doing importing via the function importing pass. The pass
// is only enabled when testing importing via the 'opt' tool, which 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()))
// Next we need to promote to global scope and rename any local values that
// are potentially exported to other modules.
if (renameModuleForThinLTO(M, *Index, /*ClearDSOLocalOnDeclarations=*/false,
/*GlobalsToImport=*/nullptr)) {
errs() << "Error renaming module\n";
return false;
// Perform the import now.
auto ModuleLoader = [&M](StringRef Identifier) {
return loadFile(std::string(Identifier), M.getContext());
FunctionImporter Importer(*Index, ModuleLoader,
Expected<bool> Result = Importer.importFunctions(M, ImportList);
// FIXME: Probably need to propagate Errors through the pass manager.
if (!Result) {
logAllUnhandledErrors(Result.takeError(), errs(),
"Error importing module: ");
return false;
return *Result;
namespace {
/// Pass that performs cross-module function import provided a summary file.
class FunctionImportLegacyPass : public ModulePass {
/// Pass identification, replacement for typeid
static char ID;
explicit FunctionImportLegacyPass() : ModulePass(ID) {}
/// Specify pass name for debug output
StringRef getPassName() const override { return "Function Importing"; }
bool runOnModule(Module &M) override {
if (skipModule(M))
return false;
return doImportingForModule(M);
} // end anonymous namespace
PreservedAnalyses FunctionImportPass::run(Module &M,
ModuleAnalysisManager &AM) {
if (!doImportingForModule(M))
return PreservedAnalyses::all();
return PreservedAnalyses::none();
char FunctionImportLegacyPass::ID = 0;
INITIALIZE_PASS(FunctionImportLegacyPass, "function-import",
"Summary Based Function Import", false, false)
namespace llvm {
Pass *createFunctionImportPass() {
return new FunctionImportLegacyPass();
} // end namespace llvm