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//===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===//
// 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 the FunctionImportGlobalProcessing class, used
// to perform the necessary global value handling for function importing.
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/InstIterator.h"
using namespace llvm;
/// Checks if we should import SGV as a definition, otherwise import as a
/// declaration.
bool FunctionImportGlobalProcessing::doImportAsDefinition(
const GlobalValue *SGV) {
if (!isPerformingImport())
return false;
// Only import the globals requested for importing.
if (!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)))
return false;
assert(!isa<GlobalAlias>(SGV) &&
"Unexpected global alias in the import list.");
// Otherwise yes.
return true;
bool FunctionImportGlobalProcessing::shouldPromoteLocalToGlobal(
const GlobalValue *SGV, ValueInfo VI) {
// Both the imported references and the original local variable must
// be promoted.
if (!isPerformingImport() && !isModuleExporting())
return false;
if (isPerformingImport()) {
assert((!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)) ||
!isNonRenamableLocal(*SGV)) &&
"Attempting to promote non-renamable local");
// We don't know for sure yet if we are importing this value (as either
// a reference or a def), since we are simply walking all values in the
// module. But by necessity if we end up importing it and it is local,
// it must be promoted, so unconditionally promote all values in the
// importing module.
return true;
// When exporting, consult the index. We can have more than one local
// with the same GUID, in the case of same-named locals in different but
// same-named source files that were compiled in their respective directories
// (so the source file name and resulting GUID is the same). Find the one
// in this module.
auto Summary = ImportIndex.findSummaryInModule(
VI, SGV->getParent()->getModuleIdentifier());
assert(Summary && "Missing summary for global value when exporting");
auto Linkage = Summary->linkage();
if (!GlobalValue::isLocalLinkage(Linkage)) {
assert(!isNonRenamableLocal(*SGV) &&
"Attempting to promote non-renamable local");
return true;
return false;
#ifndef NDEBUG
bool FunctionImportGlobalProcessing::isNonRenamableLocal(
const GlobalValue &GV) const {
if (!GV.hasLocalLinkage())
return false;
// This needs to stay in sync with the logic in buildModuleSummaryIndex.
if (GV.hasSection())
return true;
if (Used.count(const_cast<GlobalValue *>(&GV)))
return true;
return false;
FunctionImportGlobalProcessing::getPromotedName(const GlobalValue *SGV) {
// For locals that must be promoted to global scope, ensure that
// the promoted name uniquely identifies the copy in the original module,
// using the ID assigned during combined index creation.
return ModuleSummaryIndex::getGlobalNameForLocal(
FunctionImportGlobalProcessing::getLinkage(const GlobalValue *SGV,
bool DoPromote) {
// Any local variable that is referenced by an exported function needs
// to be promoted to global scope. Since we don't currently know which
// functions reference which local variables/functions, we must treat
// all as potentially exported if this module is exporting anything.
if (isModuleExporting()) {
if (SGV->hasLocalLinkage() && DoPromote)
return GlobalValue::ExternalLinkage;
return SGV->getLinkage();
// Otherwise, if we aren't importing, no linkage change is needed.
if (!isPerformingImport())
return SGV->getLinkage();
switch (SGV->getLinkage()) {
case GlobalValue::LinkOnceODRLinkage:
case GlobalValue::ExternalLinkage:
// External and linkonce definitions are converted to available_externally
// definitions upon import, so that they are available for inlining
// and/or optimization, but are turned into declarations later
// during the EliminateAvailableExternally pass.
if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(SGV))
return GlobalValue::AvailableExternallyLinkage;
// An imported external declaration stays external.
return SGV->getLinkage();
case GlobalValue::AvailableExternallyLinkage:
// An imported available_externally definition converts
// to external if imported as a declaration.
if (!doImportAsDefinition(SGV))
return GlobalValue::ExternalLinkage;
// An imported available_externally declaration stays that way.
return SGV->getLinkage();
case GlobalValue::LinkOnceAnyLinkage:
case GlobalValue::WeakAnyLinkage:
// Can't import linkonce_any/weak_any definitions correctly, or we might
// change the program semantics, since the linker will pick the first
// linkonce_any/weak_any definition and importing would change the order
// they are seen by the linker. The module linking caller needs to enforce
// this.
// If imported as a declaration, it becomes external_weak.
return SGV->getLinkage();
case GlobalValue::WeakODRLinkage:
// For weak_odr linkage, there is a guarantee that all copies will be
// equivalent, so the issue described above for weak_any does not exist,
// and the definition can be imported. It can be treated similarly
// to an imported externally visible global value.
if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(SGV))
return GlobalValue::AvailableExternallyLinkage;
return GlobalValue::ExternalLinkage;
case GlobalValue::AppendingLinkage:
// It would be incorrect to import an appending linkage variable,
// since it would cause global constructors/destructors to be
// executed multiple times. This should have already been handled
// by linkIfNeeded, and we will assert in shouldLinkFromSource
// if we try to import, so we simply return AppendingLinkage.
return GlobalValue::AppendingLinkage;
case GlobalValue::InternalLinkage:
case GlobalValue::PrivateLinkage:
// If we are promoting the local to global scope, it is handled
// similarly to a normal externally visible global.
if (DoPromote) {
if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(SGV))
return GlobalValue::AvailableExternallyLinkage;
return GlobalValue::ExternalLinkage;
// A non-promoted imported local definition stays local.
// The ThinLTO pass will eventually force-import their definitions.
return SGV->getLinkage();
case GlobalValue::ExternalWeakLinkage:
// External weak doesn't apply to definitions, must be a declaration.
// Linkage stays external_weak.
return SGV->getLinkage();
case GlobalValue::CommonLinkage:
// Linkage stays common on definitions.
// The ThinLTO pass will eventually force-import their definitions.
return SGV->getLinkage();
llvm_unreachable("unknown linkage type");
void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
ValueInfo VI;
if (GV.hasName()) {
VI = ImportIndex.getValueInfo(GV.getGUID());
// Set synthetic function entry counts.
if (VI && ImportIndex.hasSyntheticEntryCounts()) {
if (Function *F = dyn_cast<Function>(&GV)) {
if (!F->isDeclaration()) {
for (auto &S : VI.getSummaryList()) {
auto *FS = cast<FunctionSummary>(S->getBaseObject());
if (FS->modulePath() == M.getModuleIdentifier()) {
// We should always have a ValueInfo (i.e. GV in index) for definitions when
// we are exporting, and also when importing that value.
assert(VI || GV.isDeclaration() ||
(isPerformingImport() && !doImportAsDefinition(&GV)));
// Mark read/write-only variables which can be imported with specific
// attribute. We can't internalize them now because IRMover will fail
// to link variable definitions to their external declarations during
// ThinLTO import. We'll internalize read-only variables later, after
// import is finished. See internalizeGVsAfterImport.
// If global value dead stripping is not enabled in summary then
// propagateConstants hasn't been run. We can't internalize GV
// in such case.
if (!GV.isDeclaration() && VI && ImportIndex.withAttributePropagation()) {
if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
// We can have more than one local with the same GUID, in the case of
// same-named locals in different but same-named source files that were
// compiled in their respective directories (so the source file name
// and resulting GUID is the same). Find the one in this module.
// Handle the case where there is no summary found in this module. That
// can happen in the distributed ThinLTO backend, because the index only
// contains summaries from the source modules if they are being imported.
// We might have a non-null VI and get here even in that case if the name
// matches one in this module (e.g. weak or appending linkage).
auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
ImportIndex.findSummaryInModule(VI, M.getModuleIdentifier()));
if (GVS &&
(ImportIndex.isReadOnly(GVS) || ImportIndex.isWriteOnly(GVS))) {
// Objects referenced by writeonly GV initializer should not be
// promoted, because there is no any kind of read access to them
// on behalf of this writeonly GV. To avoid promotion we convert
// GV initializer to 'zeroinitializer'. This effectively drops
// references in IR module (not in combined index), so we can
// ignore them when computing import. We do not export references
// of writeonly object. See computeImportForReferencedGlobals
if (ImportIndex.isWriteOnly(GVS))
if (GV.hasLocalLinkage() && shouldPromoteLocalToGlobal(&GV, VI)) {
// Save the original name string before we rename GV below.
auto Name = GV.getName().str();
GV.setLinkage(getLinkage(&GV, /* DoPromote */ true));
// If we are renaming a COMDAT leader, ensure that we record the COMDAT
// for later renaming as well. This is required for COFF.
if (const auto *C = GV.getComdat())
if (C->getName() == Name)
RenamedComdats.try_emplace(C, M.getOrInsertComdat(GV.getName()));
} else
GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));
// When ClearDSOLocalOnDeclarations is true, clear dso_local if GV is
// converted to a declaration, to disable direct access. Don't do this if GV
// is implicitly dso_local due to a non-default visibility.
if (ClearDSOLocalOnDeclarations && GV.isDeclarationForLinker() &&
!GV.isImplicitDSOLocal()) {
} else if (VI && VI.isDSOLocal(ImportIndex.withDSOLocalPropagation())) {
// If all summaries are dso_local, symbol gets resolved to a known local
// definition.
if (GV.hasDLLImportStorageClass())
// Remove functions imported as available externally defs from comdats,
// 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<GlobalObject>(&GV);
if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
// The IRMover should not have placed any imported declarations in
// a comdat, so the only declaration that should be in a comdat
// at this point would be a definition imported as available_externally.
assert(GO->hasAvailableExternallyLinkage() &&
"Expected comdat on definition (possibly available external)");
void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
for (GlobalVariable &GV : M.globals())
for (Function &SF : M)
for (GlobalAlias &GA : M.aliases())
// Replace any COMDATS that required renaming (because the COMDAT leader was
// promoted and renamed).
if (!RenamedComdats.empty())
for (auto &GO : M.global_objects())
if (auto *C = GO.getComdat()) {
auto Replacement = RenamedComdats.find(C);
if (Replacement != RenamedComdats.end())
bool FunctionImportGlobalProcessing::run() {
return false;
bool llvm::renameModuleForThinLTO(Module &M, const ModuleSummaryIndex &Index,
bool ClearDSOLocalOnDeclarations,
SetVector<GlobalValue *> *GlobalsToImport) {
FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport,