lib/Transforms/Utils/FunctionImportUtils.cpp - llvm-project/llvm - Git at Google

 //===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt 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) {
   assert(SGV->hasLocalLinkage());
   // 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;
 }
 #endif

 std::string
 FunctionImportGlobalProcessing::getPromotedName(const GlobalValue *SGV) {
   assert(SGV->hasLocalLinkage());
   // 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(
       SGV->getName(),
       ImportIndex.getModuleHash(SGV->getParent()->getModuleIdentifier()));
 }

 GlobalValue::LinkageTypes
 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.
     assert(!doImportAsDefinition(SGV));
     // 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;
     else
       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;
       else
         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.
     assert(!doImportAsDefinition(SGV));
     // 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()) {
               F->setEntryCount(Function::ProfileCount(FS->entryCount(),
                                                       Function::PCT_Synthetic));
               break;
             }
           }
         }
       }
     }
   }

   // 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))) {
         V->addAttribute("thinlto-internalize");
         // 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))
           V->setInitializer(Constant::getNullValue(V->getValueType()));
       }
     }
   }

   if (GV.hasLocalLinkage() && shouldPromoteLocalToGlobal(&GV, VI)) {
     // Save the original name string before we rename GV below.
     auto Name = GV.getName().str();
     GV.setName(getPromotedName(&GV));
     GV.setLinkage(getLinkage(&GV, /* DoPromote */ true));
     assert(!GV.hasLocalLinkage());
     GV.setVisibility(GlobalValue::HiddenVisibility);

     // 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()) {
     GV.setDSOLocal(false);
   } else if (VI && VI.isDSOLocal(ImportIndex.withDSOLocalPropagation())) {
     // If all summaries are dso_local, symbol gets resolved to a known local
     // definition.
     GV.setDSOLocal(true);
     if (GV.hasDLLImportStorageClass())
       GV.setDLLStorageClass(GlobalValue::DefaultStorageClass);
   }

   // 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)");
     GO->setComdat(nullptr);
   }
 }

 void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
   for (GlobalVariable &GV : M.globals())
     processGlobalForThinLTO(GV);
   for (Function &SF : M)
     processGlobalForThinLTO(SF);
   for (GlobalAlias &GA : M.aliases())
     processGlobalForThinLTO(GA);

   // 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())
           GO.setComdat(Replacement->second);
       }
 }

 bool FunctionImportGlobalProcessing::run() {
   processGlobalsForThinLTO();
   return false;
 }

 bool llvm::renameModuleForThinLTO(Module &M, const ModuleSummaryIndex &Index,
                                   bool ClearDSOLocalOnDeclarations,
                                   SetVector<GlobalValue *> *GlobalsToImport) {
   FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport,
                                                    ClearDSOLocalOnDeclarations);
   return ThinLTOProcessing.run();
 }
	//===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt 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) {
	assert(SGV->hasLocalLinkage());
	// 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;
	}
	#endif

	std::string
	FunctionImportGlobalProcessing::getPromotedName(const GlobalValue *SGV) {
	assert(SGV->hasLocalLinkage());
	// 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(
	SGV->getName(),
	ImportIndex.getModuleHash(SGV->getParent()->getModuleIdentifier()));
	}

	GlobalValue::LinkageTypes
	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.
	assert(!doImportAsDefinition(SGV));
	// 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;
	else
	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;
	else
	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.
	assert(!doImportAsDefinition(SGV));
	// 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()) {
	F->setEntryCount(Function::ProfileCount(FS->entryCount(),
	Function::PCT_Synthetic));
	break;
	}
	}
	}
	}
	}
	}

	// 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))) {
	V->addAttribute("thinlto-internalize");
	// 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))
	V->setInitializer(Constant::getNullValue(V->getValueType()));
	}
	}
	}

	if (GV.hasLocalLinkage() && shouldPromoteLocalToGlobal(&GV, VI)) {
	// Save the original name string before we rename GV below.
	auto Name = GV.getName().str();
	GV.setName(getPromotedName(&GV));
	GV.setLinkage(getLinkage(&GV, /* DoPromote */ true));
	assert(!GV.hasLocalLinkage());
	GV.setVisibility(GlobalValue::HiddenVisibility);

	// 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()) {
	GV.setDSOLocal(false);
	} else if (VI && VI.isDSOLocal(ImportIndex.withDSOLocalPropagation())) {
	// If all summaries are dso_local, symbol gets resolved to a known local
	// definition.
	GV.setDSOLocal(true);
	if (GV.hasDLLImportStorageClass())
	GV.setDLLStorageClass(GlobalValue::DefaultStorageClass);
	}

	// 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)");
	GO->setComdat(nullptr);
	}
	}

	void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
	for (GlobalVariable &GV : M.globals())
	processGlobalForThinLTO(GV);
	for (Function &SF : M)
	processGlobalForThinLTO(SF);
	for (GlobalAlias &GA : M.aliases())
	processGlobalForThinLTO(GA);

	// 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())
	GO.setComdat(Replacement->second);
	}
	}

	bool FunctionImportGlobalProcessing::run() {
	processGlobalsForThinLTO();
	return false;
	}

	bool llvm::renameModuleForThinLTO(Module &M, const ModuleSummaryIndex &Index,
	bool ClearDSOLocalOnDeclarations,
	SetVector<GlobalValue > GlobalsToImport) {
	FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport,
	ClearDSOLocalOnDeclarations);
	return ThinLTOProcessing.run();
	}