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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/StringRef.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/Linker/IRMover.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/JSON.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<bool>
ForceImportAll("force-import-all", cl::init(false), cl::Hidden,
cl::desc("Import functions with noinline attribute"));
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' and "
/// 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."));
/// This is a test-only option.
/// If this option is enabled, the ThinLTO indexing step will import each
/// function declaration as a fallback. In a real build this may increase ram
/// usage of the indexing step unnecessarily.
/// TODO: Implement selective import (based on combined summary analysis) to
/// ensure the imported function has a use case in the postlink pipeline.
static cl::opt<bool> ImportDeclaration(
"import-declaration", cl::init(false), cl::Hidden,
cl::desc("If true, import function declaration as fallback if the function "
"definition is not imported."));
/// Pass a workload description file - an example of workload would be the
/// functions executed to satisfy a RPC request. A workload is defined by a root
/// function and the list of functions that are (frequently) needed to satisfy
/// it. The module that defines the root will have all those functions imported.
/// The file contains a JSON dictionary. The keys are root functions, the values
/// are lists of functions to import in the module defining the root. It is
/// assumed -funique-internal-linkage-names was used, thus ensuring function
/// names are unique even for local linkage ones.
static cl::opt<std::string> WorkloadDefinitions(
cl::desc("Pass a workload definition. This is a file containing a JSON "
"dictionary. The keys are root functions, the values are lists of "
"functions to import in the module defining the root. It is "
"assumed -funique-internal-linkage-names was used, to ensure "
"local linkage functions have unique names. For example: \n"
" \"rootFunction_1\": [\"function_to_import_1\", "
"\"function_to_import_2\"], \n"
" \"rootFunction_2\": [\"function_to_import_3\", "
"\"function_to_import_4\"] \n"
namespace llvm {
extern cl::opt<bool> EnableMemProfContextDisambiguation;
// 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, qualify the
/// legality of importing each. The return is a range of pairs. Each pair
/// corresponds to a candidate. The first value is the ImportFailureReason for
/// that candidate, the second is the candidate.
static auto qualifyCalleeCandidates(
const ModuleSummaryIndex &Index,
ArrayRef<std::unique_ptr<GlobalValueSummary>> CalleeSummaryList,
StringRef CallerModulePath) {
return llvm::map_range(
[&Index, CalleeSummaryList,
CallerModulePath](const std::unique_ptr<GlobalValueSummary> &SummaryPtr)
-> std::pair<FunctionImporter::ImportFailureReason,
const GlobalValueSummary *> {
auto *GVSummary = SummaryPtr.get();
if (!Index.isGlobalValueLive(GVSummary))
return {FunctionImporter::ImportFailureReason::NotLive, GVSummary};
if (GlobalValue::isInterposableLinkage(GVSummary->linkage()))
return {FunctionImporter::ImportFailureReason::InterposableLinkage,
auto *Summary = dyn_cast<FunctionSummary>(GVSummary->getBaseObject());
// Ignore any callees that aren't actually functions. This could happen
// in the case of GUID hash collisions. It could also happen in theory
// for SamplePGO profiles collected on old versions of the code after
// renaming, since we synthesize edges to any inlined callees appearing
// in the profile.
if (!Summary)
return {FunctionImporter::ImportFailureReason::GlobalVar, GVSummary};
// 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)
return {
// Skip if it isn't legal to import (e.g. may reference unpromotable
// locals).
if (Summary->notEligibleToImport())
return {FunctionImporter::ImportFailureReason::NotEligible,
return {FunctionImporter::ImportFailureReason::None, GVSummary};
/// Given a list of possible callee implementation for a call site, select one
/// that fits the \p Threshold for function definition import. If none are
/// found, the Reason will give the last reason for the failure (last, in the
/// order of CalleeSummaryList entries). While looking for a callee definition,
/// sets \p TooLargeOrNoInlineSummary to the last seen too-large or noinline
/// candidate; other modules may want to know the function summary or
/// declaration even if a definition is not needed.
/// 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,
const GlobalValueSummary *&TooLargeOrNoInlineSummary,
FunctionImporter::ImportFailureReason &Reason) {
// Records the last summary with reason noinline or too-large.
TooLargeOrNoInlineSummary = nullptr;
auto QualifiedCandidates =
qualifyCalleeCandidates(Index, CalleeSummaryList, CallerModulePath);
for (auto QualifiedValue : QualifiedCandidates) {
Reason = QualifiedValue.first;
// Skip a summary if its import is not (proved to be) legal.
if (Reason != FunctionImporter::ImportFailureReason::None)
auto *Summary =
// Don't bother importing the definition if the chance of inlining it is
// not high enough (except under `--force-import-all`).
if ((Summary->instCount() > Threshold) && !Summary->fflags().AlwaysInline &&
!ForceImportAll) {
TooLargeOrNoInlineSummary = Summary;
Reason = FunctionImporter::ImportFailureReason::TooLarge;
// Don't bother importing the definition if we can't inline it anyway.
if (Summary->fflags().NoInline && !ForceImportAll) {
TooLargeOrNoInlineSummary = Summary;
Reason = FunctionImporter::ImportFailureReason::NoInline;
return Summary;
return nullptr;
namespace {
using EdgeInfo = std::tuple<const FunctionSummary *, unsigned /* Threshold */>;
} // anonymous namespace
/// Import globals referenced by a function or other globals that are being
/// imported, if importing such global is possible.
class GlobalsImporter final {
const ModuleSummaryIndex &Index;
const GVSummaryMapTy &DefinedGVSummaries;
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
FunctionImporter::ImportMapTy &ImportList;
DenseMap<StringRef, FunctionImporter::ExportSetTy> *const ExportLists;
bool shouldImportGlobal(const ValueInfo &VI) {
const auto &GVS = DefinedGVSummaries.find(VI.getGUID());
if (GVS == DefinedGVSummaries.end())
return true;
// We should not skip import if the module contains a non-prevailing
// definition with interposable linkage type. This is required for
// correctness in the situation where 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 &&
GlobalValue::isInterposableLinkage(GVS->second->linkage()) &&
!IsPrevailing(VI.getGUID(), GVS->second))
return true;
return false;
onImportingSummaryImpl(const GlobalValueSummary &Summary,
SmallVectorImpl<const GlobalVarSummary *> &Worklist) {
for (const auto &VI : Summary.refs()) {
if (!shouldImportGlobal(VI)) {
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 (const auto &RefSummary : VI.getSummaryList()) {
const auto *GVS = dyn_cast<GlobalVarSummary>(RefSummary.get());
// Functions could be referenced by global vars - e.g. a vtable; but we
// don't currently imagine a reason those would be imported here, rather
// than as part of the logic deciding which functions to import (i.e.
// based on profile information). Should we decide to handle them here,
// we can refactor accordingly at that time.
if (!GVS || !Index.canImportGlobalVar(GVS, /* AnalyzeRefs */ true) ||
// If there isn't an entry for GUID, insert <GUID, Definition> pair.
// Otherwise, definition should take precedence over declaration.
auto [Iter, Inserted] =
VI.getGUID(), GlobalValueSummary::Definition);
// Only update stat and exports if we haven't already imported this
// variable.
if (!Inserted) {
// Set the value to 'std::min(existing-value, new-value)' to make
// sure a definition takes precedence over a declaration.
Iter->second = std::min(GlobalValueSummary::Definition, Iter->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)
(*ExportLists)[RefSummary->modulePath()][VI] =
// If variable is not writeonly we attempt to recursively analyze
// its references in order to import referenced constants.
if (!Index.isWriteOnly(GVS))
const ModuleSummaryIndex &Index, const GVSummaryMapTy &DefinedGVSummaries,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
FunctionImporter::ImportMapTy &ImportList,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists)
: Index(Index), DefinedGVSummaries(DefinedGVSummaries),
IsPrevailing(IsPrevailing), ImportList(ImportList),
ExportLists(ExportLists) {}
void onImportingSummary(const GlobalValueSummary &Summary) {
SmallVector<const GlobalVarSummary *, 128> Worklist;
onImportingSummaryImpl(Summary, Worklist);
while (!Worklist.empty())
onImportingSummaryImpl(*Worklist.pop_back_val(), Worklist);
static const char *getFailureName(FunctionImporter::ImportFailureReason Reason);
/// Determine the list of imports and exports for each module.
class ModuleImportsManager {
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
const ModuleSummaryIndex &Index;
DenseMap<StringRef, FunctionImporter::ExportSetTy> *const ExportLists;
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
const ModuleSummaryIndex &Index,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists = nullptr)
: IsPrevailing(IsPrevailing), Index(Index), ExportLists(ExportLists) {}
virtual ~ModuleImportsManager() = default;
/// 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).
virtual void
computeImportForModule(const GVSummaryMapTy &DefinedGVSummaries,
StringRef ModName,
FunctionImporter::ImportMapTy &ImportList);
static std::unique_ptr<ModuleImportsManager>
create(function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
const ModuleSummaryIndex &Index,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists =
/// A ModuleImportsManager that operates based on a workload definition (see
/// -thinlto-workload-def). For modules that do not define workload roots, it
/// applies the base ModuleImportsManager import policy.
class WorkloadImportsManager : public ModuleImportsManager {
// Keep a module name -> value infos to import association. We use it to
// determine if a module's import list should be done by the base
// ModuleImportsManager or by us.
StringMap<DenseSet<ValueInfo>> Workloads;
computeImportForModule(const GVSummaryMapTy &DefinedGVSummaries,
StringRef ModName,
FunctionImporter::ImportMapTy &ImportList) override {
auto SetIter = Workloads.find(ModName);
if (SetIter == Workloads.end()) {
LLVM_DEBUG(dbgs() << "[Workload] " << ModName
<< " does not contain the root of any context.\n");
return ModuleImportsManager::computeImportForModule(DefinedGVSummaries,
ModName, ImportList);
LLVM_DEBUG(dbgs() << "[Workload] " << ModName
<< " contains the root(s) of context(s).\n");
GlobalsImporter GVI(Index, DefinedGVSummaries, IsPrevailing, ImportList,
auto &ValueInfos = SetIter->second;
SmallVector<EdgeInfo, 128> GlobWorklist;
for (auto &VI : llvm::make_early_inc_range(ValueInfos)) {
auto It = DefinedGVSummaries.find(VI.getGUID());
if (It != DefinedGVSummaries.end() &&
IsPrevailing(VI.getGUID(), It->second)) {
dbgs() << "[Workload] " <<
<< " has the prevailing variant already in the module "
<< ModName << ". No need to import\n");
auto Candidates =
qualifyCalleeCandidates(Index, VI.getSummaryList(), ModName);
const GlobalValueSummary *GVS = nullptr;
auto PotentialCandidates = llvm::map_range(
[&](const auto &Candidate) {
LLVM_DEBUG(dbgs() << "[Workflow] Candidate for " <<
<< " from " << Candidate.second->modulePath()
<< " ImportFailureReason: "
<< getFailureName(Candidate.first) << "\n");
return Candidate.first ==
[](const auto &Candidate) { return Candidate.second; });
if (PotentialCandidates.empty()) {
LLVM_DEBUG(dbgs() << "[Workload] Not importing " <<
<< " because can't find eligible Callee. Guid is: "
<< Function::getGUID( << "\n");
/// We will prefer importing the prevailing candidate, if not, we'll
/// still pick the first available candidate. The reason we want to make
/// sure we do import the prevailing candidate is because the goal of
/// workload-awareness is to enable optimizations specializing the call
/// graph of that workload. Suppose a function is already defined in the
/// module, but it's not the prevailing variant. Suppose also we do not
/// inline it (in fact, if it were interposable, we can't inline it),
/// but we could specialize it to the workload in other ways. However,
/// the linker would drop it in the favor of the prevailing copy.
/// Instead, by importing the prevailing variant (assuming also the use
/// of `-avail-extern-to-local`), we keep the specialization. We could
/// alteranatively make the non-prevailing variant local, but the
/// prevailing one is also the one for which we would have previously
/// collected profiles, making it preferrable.
auto PrevailingCandidates = llvm::make_filter_range(
PotentialCandidates, [&](const auto *Candidate) {
return IsPrevailing(VI.getGUID(), Candidate);
if (PrevailingCandidates.empty()) {
GVS = *PotentialCandidates.begin();
if (!llvm::hasSingleElement(PotentialCandidates) &&
<< "[Workload] Found multiple non-prevailing candidates for "
<< ". This is unexpected. Are module paths passed to the "
"compiler unique for the modules passed to the linker?");
// We could in theory have multiple (interposable) copies of a symbol
// when there is no prevailing candidate, if say the prevailing copy was
// in a native object being linked in. However, we should in theory be
// marking all of these non-prevailing IR copies dead in that case, in
// which case they won't be candidates.
} else {
GVS = *PrevailingCandidates.begin();
auto ExportingModule = GVS->modulePath();
// We checked that for the prevailing case, but if we happen to have for
// example an internal that's defined in this module, it'd have no
// PrevailingCandidates.
if (ExportingModule == ModName) {
LLVM_DEBUG(dbgs() << "[Workload] Not importing " <<
<< " because its defining module is the same as the "
"current module\n");
LLVM_DEBUG(dbgs() << "[Workload][Including]" << << " from "
<< ExportingModule << " : "
<< Function::getGUID( << "\n");
ImportList[ExportingModule][VI.getGUID()] =
if (ExportLists)
(*ExportLists)[ExportingModule][VI] = GlobalValueSummary::Definition;
LLVM_DEBUG(dbgs() << "[Workload] Done\n");
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
const ModuleSummaryIndex &Index,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists)
: ModuleImportsManager(IsPrevailing, Index, ExportLists) {
// Since the workload def uses names, we need a quick lookup
// name->ValueInfo.
StringMap<ValueInfo> NameToValueInfo;
StringSet<> AmbiguousNames;
for (auto &I : Index) {
ValueInfo VI = Index.getValueInfo(I);
if (!NameToValueInfo.insert(std::make_pair(, VI)).second)
auto DbgReportIfAmbiguous = [&](StringRef Name) {
LLVM_DEBUG(if (AmbiguousNames.count(Name) > 0) {
dbgs() << "[Workload] Function name " << Name
<< " present in the workload definition is ambiguous. Consider "
"compiling with -funique-internal-linkage-names.";
std::error_code EC;
auto BufferOrErr = MemoryBuffer::getFileOrSTDIN(WorkloadDefinitions);
if (std::error_code EC = BufferOrErr.getError()) {
report_fatal_error("Failed to open context file");
auto Buffer = std::move(BufferOrErr.get());
std::map<std::string, std::vector<std::string>> WorkloadDefs;
json::Path::Root NullRoot;
// The JSON is supposed to contain a dictionary matching the type of
// WorkloadDefs. For example:
// {
// "rootFunction_1": ["function_to_import_1", "function_to_import_2"],
// "rootFunction_2": ["function_to_import_3", "function_to_import_4"]
// }
auto Parsed = json::parse(Buffer->getBuffer());
if (!Parsed)
if (!json::fromJSON(*Parsed, WorkloadDefs, NullRoot))
report_fatal_error("Invalid thinlto contextual profile format.");
for (const auto &Workload : WorkloadDefs) {
const auto &Root = Workload.first;
LLVM_DEBUG(dbgs() << "[Workload] Root: " << Root << "\n");
const auto &AllCallees = Workload.second;
auto RootIt = NameToValueInfo.find(Root);
if (RootIt == NameToValueInfo.end()) {
LLVM_DEBUG(dbgs() << "[Workload] Root " << Root
<< " not found in this linkage unit.\n");
auto RootVI = RootIt->second;
if (RootVI.getSummaryList().size() != 1) {
LLVM_DEBUG(dbgs() << "[Workload] Root " << Root
<< " should have exactly one summary, but has "
<< RootVI.getSummaryList().size() << ". Skipping.\n");
StringRef RootDefiningModule =
LLVM_DEBUG(dbgs() << "[Workload] Root defining module for " << Root
<< " is : " << RootDefiningModule << "\n");
auto &Set = Workloads[RootDefiningModule];
for (const auto &Callee : AllCallees) {
LLVM_DEBUG(dbgs() << "[Workload] " << Callee << "\n");
auto ElemIt = NameToValueInfo.find(Callee);
if (ElemIt == NameToValueInfo.end()) {
LLVM_DEBUG(dbgs() << "[Workload] " << Callee << " not found\n");
dbgs() << "[Workload] Root: " << Root << " we have " << Set.size()
<< " distinct callees.\n";
for (const auto &VI : Set) {
dbgs() << "[Workload] Root: " << Root
<< " Would include: " << VI.getGUID() << "\n";
std::unique_ptr<ModuleImportsManager> ModuleImportsManager::create(
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
const ModuleSummaryIndex &Index,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists) {
if (WorkloadDefinitions.empty()) {
LLVM_DEBUG(dbgs() << "[Workload] Using the regular imports manager.\n");
return std::unique_ptr<ModuleImportsManager>(
new ModuleImportsManager(IsPrevailing, Index, ExportLists));
LLVM_DEBUG(dbgs() << "[Workload] Using the contextual imports manager.\n");
return std::make_unique<WorkloadImportsManager>(IsPrevailing, Index,
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,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
SmallVectorImpl<EdgeInfo> &Worklist, GlobalsImporter &GVImporter,
FunctionImporter::ImportMapTy &ImportList,
DenseMap<StringRef, FunctionImporter::ExportSetTy> *ExportLists,
FunctionImporter::ImportThresholdsTy &ImportThresholds) {
static int ImportCount = 0;
for (const 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");
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{};
// `SummaryForDeclImport` is an summary eligible for declaration import.
const GlobalValueSummary *SummaryForDeclImport = nullptr;
CalleeSummary =
selectCallee(Index, VI.getSummaryList(), NewThreshold,
Summary.modulePath(), SummaryForDeclImport, Reason);
if (!CalleeSummary) {
// There isn't a callee for definition import but one for declaration
// import.
if (ImportDeclaration && SummaryForDeclImport) {
StringRef DeclSourceModule = SummaryForDeclImport->modulePath();
// Since definition takes precedence over declaration for the same VI,
// try emplace <VI, declaration> pair without checking insert result.
// If insert doesn't happen, there must be an existing entry keyed by
// VI.
if (ExportLists)
VI, GlobalValueSummary::Declaration);
VI.getGUID(), GlobalValueSummary::Declaration);
// 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);
if (ForceImportAll) {
std::string Msg = std::string("Failed to import function ") + + " due to " +
auto Error = make_error<StringError>(
Msg, make_error_code(errc::not_supported));
logAllUnhandledErrors(std::move(Error), errs(),
"Error importing module: ");
} else {
<< "ignored! No qualifying callee with summary found.\n");
// "Resolve" the summary
CalleeSummary = CalleeSummary->getBaseObject();
ResolvedCalleeSummary = cast<FunctionSummary>(CalleeSummary);
assert((ResolvedCalleeSummary->fflags().AlwaysInline || ForceImportAll ||
(ResolvedCalleeSummary->instCount() <= NewThreshold)) &&
"selectCallee() didn't honor the threshold");
auto ExportModulePath = ResolvedCalleeSummary->modulePath();
// Try emplace the definition entry, and update stats based on insertion
// status.
auto [Iter, Inserted] = ImportList[ExportModulePath].try_emplace(
VI.getGUID(), GlobalValueSummary::Definition);
// We previously decided to import this GUID definition if it was already
// inserted in the set of imports from the exporting module.
if (Inserted || Iter->second == GlobalValueSummary::Declaration) {
if (IsHotCallsite)
if (IsCriticalCallsite)
if (Iter->second == GlobalValueSummary::Declaration)
Iter->second = GlobalValueSummary::Definition;
// 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)
(*ExportLists)[ExportModulePath][VI] = GlobalValueSummary::Definition;
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);
void ModuleImportsManager::computeImportForModule(
const GVSummaryMapTy &DefinedGVSummaries, StringRef ModName,
FunctionImporter::ImportMapTy &ImportList) {
// 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;
GlobalsImporter GVI(Index, DefinedGVSummaries, IsPrevailing, ImportList,
FunctionImporter::ImportThresholdsTy ImportThresholds;
// Populate the worklist with the import for the functions in the current
// module
for (const 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, IsPrevailing, Worklist, GVI,
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,
IsPrevailing, Worklist, GVI, ImportList,
ExportLists, ImportThresholds);
// 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 &DefinedGVS,
unsigned &DefinedFS) {
unsigned NumGVS = 0;
DefinedGVS = 0;
DefinedFS = 0;
for (auto &[GUID, Type] : Cont) {
if (isGlobalVarSummary(Index, GUID)) {
if (Type == GlobalValueSummary::Definition)
} else if (Type == GlobalValueSummary::Definition)
return NumGVS;
#ifndef NDEBUG
static bool checkVariableImport(
const ModuleSummaryIndex &Index,
DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists) {
DenseSet<GlobalValue::GUID> FlattenedImports;
for (auto &ImportPerModule : ImportLists)
for (auto &ExportPerModule : ImportPerModule.second)
for (auto &[GUID, Type] : ExportPerModule.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. The exception would be if it has a linkage type indicating
// that there may have been a copy existing in the importing module (e.g.
// linkonce_odr). In that case we cannot accurately do this checking.
auto IsReadOrWriteOnlyVarNeedingImporting = [&](StringRef ModulePath,
const ValueInfo &VI) {
auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
Index.findSummaryInModule(VI, ModulePath));
return GVS && (Index.isReadOnly(GVS) || Index.isWriteOnly(GVS)) &&
!(GVS->linkage() == GlobalValue::AvailableExternallyLinkage ||
GVS->linkage() == GlobalValue::WeakODRLinkage ||
GVS->linkage() == GlobalValue::LinkOnceODRLinkage);
for (auto &ExportPerModule : ExportLists)
for (auto &[VI, Unused] : ExportPerModule.second)
if (!FlattenedImports.count(VI.getGUID()) &&
IsReadOrWriteOnlyVarNeedingImporting(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 DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
DenseMap<StringRef, FunctionImporter::ImportMapTy> &ImportLists,
DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists) {
auto MIS = ModuleImportsManager::create(isPrevailing, Index, &ExportLists);
// For each module that has function defined, compute the import/export lists.
for (const auto &DefinedGVSummaries : ModuleToDefinedGVSummaries) {
auto &ImportList = ImportLists[DefinedGVSummaries.first];
LLVM_DEBUG(dbgs() << "Computing import for Module '"
<< DefinedGVSummaries.first << "'\n");
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, Type] : ELI.second) {
// If a variable is exported as a declaration, its 'refs' and 'calls' are
// not further exported.
if (Type == GlobalValueSummary::Declaration)
// 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()) {
// Try to emplace the declaration entry. If a definition entry
// already exists for key `VI`, this is a no-op.
NewExports.try_emplace(VI, GlobalValueSummary::Declaration);
} else {
auto *FS = cast<FunctionSummary>(S);
for (const auto &Edge : FS->calls()) {
// Try to emplace the declaration entry. If a definition entry
// already exists for key `VI`, this is a no-op.
NewExports.try_emplace(Edge.first, GlobalValueSummary::Declaration);
for (const auto &Ref : FS->refs()) {
// Try to emplace the declaration entry. If a definition entry
// already exists for key `VI`, this is a no-op.
NewExports.try_emplace(Ref, GlobalValueSummary::Declaration);
// 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->first.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 DefinedGVS = 0, DefinedFS = 0;
unsigned NumGVS =
numGlobalVarSummaries(Index, Exports, DefinedGVS, DefinedFS);
LLVM_DEBUG(dbgs() << "* Module " << ModName << " exports " << DefinedFS
<< " function as definitions, "
<< Exports.size() - NumGVS - DefinedFS
<< " functions as declarations, " << DefinedGVS
<< " var definitions and " << NumGVS - DefinedGVS
<< " var declarations. Imports from "
<< ModuleImports.second.size() << " modules.\n");
for (auto &Src : ModuleImports.second) {
auto SrcModName = Src.first;
unsigned DefinedGVS = 0, DefinedFS = 0;
unsigned NumGVSPerMod =
numGlobalVarSummaries(Index, Src.second, DefinedGVS, DefinedFS);
LLVM_DEBUG(dbgs() << " - " << DefinedFS << " function definitions and "
<< Src.second.size() - NumGVSPerMod - DefinedFS
<< " function declarations imported from " << SrcModName
<< "\n");
LLVM_DEBUG(dbgs() << " - " << DefinedGVS << " global vars definition and "
<< NumGVSPerMod - DefinedGVS
<< " global vars declaration 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 DefinedGVS = 0, DefinedFS = 0;
unsigned NumGVSPerMod =
numGlobalVarSummaries(Index, Src.second, DefinedGVS, DefinedFS);
LLVM_DEBUG(dbgs() << " - " << DefinedFS << " function definitions and "
<< Src.second.size() - DefinedFS - NumGVSPerMod
<< " function declarations imported from " << SrcModName
<< "\n");
LLVM_DEBUG(dbgs() << " - " << DefinedGVS << " var definitions and "
<< NumGVSPerMod - DefinedGVS
<< " var declarations imported from " << SrcModName
<< "\n");
/// Compute all the imports for the given module using the Index.
/// \p isPrevailing is a callback that will be called with a global value's GUID
/// and summary and should return whether the module corresponding to the
/// summary contains the linker-prevailing copy of that value.
/// \p ImportList will be populated with a map that can be passed to
/// FunctionImporter::importFunctions() above (see description there).
static void ComputeCrossModuleImportForModuleForTest(
StringRef ModulePath,
function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
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");
auto MIS = ModuleImportsManager::create(isPrevailing, Index);
MIS->computeImportForModule(FunctionSummaryMap, ModulePath, ImportList);
#ifndef NDEBUG
dumpImportListForModule(Index, ModulePath, ImportList);
/// Mark all external summaries in \p Index for import into the given module.
/// Used for testing the case of distributed builds using a distributed index.
/// \p ImportList will be populated with a map that can be passed to
/// FunctionImporter::importFunctions() above (see description there).
static void ComputeCrossModuleImportForModuleFromIndexForTest(
StringRef ModulePath, const ModuleSummaryIndex &Index,
FunctionImporter::ImportMapTy &ImportList) {
for (const 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.
auto [Iter, Inserted] = ImportList[Summary->modulePath()].try_emplace(
GUID, Summary->importType());
if (!Inserted) {
// Use 'std::min' to make sure definition (with enum value 0) takes
// precedence over declaration (with enum value 1).
Iter->second = std::min(Iter->second, Summary->importType());
#ifndef NDEBUG
dumpImportListForModule(Index, ModulePath, ImportList);
// 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, and fix up the edges
// accordingly.
void updateValueInfoForIndirectCalls(ModuleSummaryIndex &Index,
FunctionSummary *FS) {
for (auto &EI : FS->mutableCalls()) {
if (!EI.first.getSummaryList().empty())
auto GUID = Index.getGUIDFromOriginalID(EI.first.getGUID());
if (GUID == 0)
// Update the edge to point directly to the correct GUID.
auto VI = Index.getValueInfo(GUID);
if (llvm::any_of(
[&](const std::unique_ptr<GlobalValueSummary> &SummaryPtr) {
// 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 static variable in 2) will be found,
// which needs to be filtered out.
return SummaryPtr->getSummaryKind() ==
EI.first = VI;
void llvm::updateIndirectCalls(ModuleSummaryIndex &Index) {
for (const auto &Entry : Index) {
for (const auto &S : Entry.second.SummaryList) {
if (auto *FS = dyn_cast<FunctionSummary>(S.get()))
updateValueInfoForIndirectCalls(Index, FS);
void llvm::computeDeadSymbolsAndUpdateIndirectCalls(
ModuleSummaryIndex &Index,
const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing) {
if (!ComputeDead ||
// Don't do anything when nothing is live, this is friendly with tests.
GUIDPreservedSymbols.empty()) {
// Still need to update indirect calls.
unsigned LiveSymbols = 0;
SmallVector<ValueInfo, 128> Worklist;
Worklist.reserve(GUIDPreservedSymbols.size() * 2);
for (auto GUID : GUIDPreservedSymbols) {
ValueInfo VI = Index.getValueInfo(GUID);
if (!VI)
for (const 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 (const auto &S : Entry.second.SummaryList) {
if (auto *FS = dyn_cast<FunctionSummary>(S.get()))
updateValueInfoForIndirectCalls(Index, FS);
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.
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 (const 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 (const auto &S : VI.getSummaryList())
while (!Worklist.empty()) {
auto VI = Worklist.pop_back_val();
for (const 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) {
computeDeadSymbolsAndUpdateIndirectCalls(Index, GUIDPreservedSymbols,
if (ImportEnabled)
/// Compute the set of summaries needed for a ThinLTO backend compilation of
/// \p ModulePath.
void llvm::gatherImportedSummariesForModule(
StringRef ModulePath,
const DenseMap<StringRef, 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 (const auto &ILI : ImportList) {
auto &SummariesForIndex = ModuleToSummariesForIndex[std::string(ILI.first)];
const auto &DefinedGVSummaries =
for (const auto &[GUID, Type] : ILI.second) {
const auto &DS = DefinedGVSummaries.find(GUID);
assert(DS != DefinedGVSummaries.end() &&
"Expected a defined summary for imported global value");
if (Type == GlobalValueSummary::Declaration)
SummariesForIndex[GUID] = 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 (const 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::thinLTOFinalizeInModule(Module &TheModule,
const GVSummaryMapTy &DefinedGlobals,
bool PropagateAttrs) {
DenseSet<Comdat *> NonPrevailingComdats;
auto FinalizeInModule = [&](GlobalValue &GV, bool Propagate = false) {
// See if the global summary analysis computed a new resolved linkage.
const auto &GS = DefinedGlobals.find(GV.getGUID());
if (GS == DefinedGlobals.end())
if (Propagate)
if (FunctionSummary *FS = dyn_cast<FunctionSummary>(GS->second)) {
if (Function *F = dyn_cast<Function>(&GV)) {
// TODO: propagate ReadNone and ReadOnly.
if (FS->fflags().ReadNone && !F->doesNotAccessMemory())
if (FS->fflags().ReadOnly && !F->onlyReadsMemory())
if (FS->fflags().NoRecurse && !F->doesNotRecurse())
if (FS->fflags().NoUnwind && !F->doesNotThrow())
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, or if all of them had local unnamed addr linkage
// and are constants, then 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()) {
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()) {
if (GO->getComdat()->getName() == GO->getName())
// Process functions and global now
for (auto &GV : TheModule)
FinalizeInModule(GV, PropagateAttrs);
for (auto &GV : TheModule.globals())
for (auto &GV : TheModule.aliases())
// For a non-prevailing comdat, all its members must be available_externally.
// FinalizeInModule has handled non-local-linkage GlobalValues. Here we handle
// local linkage GlobalValues.
if (NonPrevailingComdats.empty())
for (auto &GO : TheModule.global_objects()) {
if (auto *C = GO.getComdat(); C && NonPrevailingComdats.count(C)) {
bool Changed;
do {
Changed = false;
// If an alias references a GlobalValue in a non-prevailing comdat, change
// it to available_externally. For simplicity we only handle GlobalValue and
// ConstantExpr with a base object. ConstantExpr without a base object is
// unlikely used in a COMDAT.
for (auto &GA : TheModule.aliases()) {
if (GA.hasAvailableExternallyLinkage())
GlobalObject *Obj = GA.getAliaseeObject();
assert(Obj && "aliasee without an base object is unimplemented");
if (Obj->hasAvailableExternallyLinkage()) {
Changed = true;
} while (Changed);
/// 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 {
// It may be the case that GV is on a chain of an ifunc, its alias and
// subsequent aliases. In this case, the summary for the value is not
// available.
if (isa<GlobalIFunc>(&GV) ||
(isa<GlobalAlias>(&GV) &&
return true;
// 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->getAliaseeObject());
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).
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 (const auto &FunctionsToImportPerModule : ImportList) {
auto getImportType = [&](const FunctionsToImportTy &GUIDToImportType,
GlobalValue::GUID GUID)
-> std::optional<GlobalValueSummary::ImportKind> {
auto Iter = GUIDToImportType.find(GUID);
if (Iter == GUIDToImportType.end())
return std::nullopt;
return Iter->second;
for (const 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 MaybeImportType = getImportType(ImportGUIDs, GUID);
bool ImportDefinition =
(MaybeImportType &&
(*MaybeImportType == GlobalValueSummary::Definition));
LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
<< " importing function"
<< (ImportDefinition
? " definition "
: (MaybeImportType ? " declaration " : " "))
<< GUID << " " << F.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (ImportDefinition) {
if (Error Err = F.materialize())
return std::move(Err);
// MemProf should match function's definition and summary,
// 'thinlto_src_module' is needed.
if (EnableImportMetadata || EnableMemProfContextDisambiguation) {
// Add 'thinlto_src_module' and 'thinlto_src_file' metadata for
// statistics and debugging.
for (GlobalVariable &GV : SrcModule->globals()) {
if (!GV.hasName())
auto GUID = GV.getGUID();
auto MaybeImportType = getImportType(ImportGUIDs, GUID);
bool ImportDefinition =
(MaybeImportType &&
(*MaybeImportType == GlobalValueSummary::Definition));
LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
<< " importing global"
<< (ImportDefinition
? " definition "
: (MaybeImportType ? " declaration " : " "))
<< GUID << " " << GV.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (ImportDefinition) {
if (Error Err = GV.materialize())
return std::move(Err);
ImportedGVCount += GlobalsToImport.insert(&GV);
for (GlobalAlias &GA : SrcModule->aliases()) {
if (!GA.hasName() || isa<GlobalIFunc>(GA.getAliaseeObject()))
auto GUID = GA.getGUID();
auto MaybeImportType = getImportType(ImportGUIDs, GUID);
bool ImportDefinition =
(MaybeImportType &&
(*MaybeImportType == GlobalValueSummary::Definition));
LLVM_DEBUG(dbgs() << (MaybeImportType ? "Is" : "Not")
<< " importing alias"
<< (ImportDefinition
? " definition "
: (MaybeImportType ? " declaration " : " "))
<< GUID << " " << GA.getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (ImportDefinition) {
if (Error Err = GA.materialize())
return std::move(Err);
// Import alias as a copy of its aliasee.
GlobalObject *GO = GA.getAliaseeObject();
if (Error Err = GO->materialize())
return std::move(Err);
auto *Fn = replaceAliasWithAliasee(SrcModule.get(), &GA);
LLVM_DEBUG(dbgs() << "Is importing aliasee fn " << GO->getGUID() << " "
<< GO->getName() << " from "
<< SrcModule->getSourceFileName() << "\n");
if (EnableImportMetadata || EnableMemProfContextDisambiguation) {
// Add 'thinlto_src_module' and 'thinlto_src_file' 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(), nullptr,
return createStringError(errc::invalid_argument,
Twine("Function Import: link error: ") +
ImportedCount += GlobalsToImport.size();
NumImportedFunctions += (ImportedCount - ImportedGVCount);
NumImportedGlobalVars += ImportedGVCount;
// TODO: Print counters for definitions and declarations in the debugging log.
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 doImportingForModuleForTest(
Module &M, function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
isPrevailing) {
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)
*Index, ImportList);
isPrevailing, *Index, ImportList);
// 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 true;
// 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 true;
return true;
PreservedAnalyses FunctionImportPass::run(Module &M,
ModuleAnalysisManager &AM) {
// This is only used for testing the function import pass via opt, where we
// don't have prevailing information from the LTO context available, so just
// conservatively assume everything is prevailing (which is fine for the very
// limited use of prevailing checking in this pass).
auto isPrevailing = [](GlobalValue::GUID, const GlobalValueSummary *) {
return true;
if (!doImportingForModuleForTest(M, isPrevailing))
return PreservedAnalyses::all();
return PreservedAnalyses::none();