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Diffstat (limited to 'lib/Transforms/Utils/FunctionImportUtils.cpp')
| -rw-r--r-- | lib/Transforms/Utils/FunctionImportUtils.cpp | 243 |
1 files changed, 243 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/FunctionImportUtils.cpp b/lib/Transforms/Utils/FunctionImportUtils.cpp new file mode 100644 index 000000000000..fcb25baf3216 --- /dev/null +++ b/lib/Transforms/Utils/FunctionImportUtils.cpp @@ -0,0 +1,243 @@ +//===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the FunctionImportGlobalProcessing class, used +// to perform the necessary global value handling for function importing. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/ModuleSummaryAnalysis.h" +#include "llvm/Transforms/Utils/FunctionImportUtils.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instructions.h" +using namespace llvm; + +/// Checks if we should import SGV as a definition, otherwise import as a +/// declaration. +bool FunctionImportGlobalProcessing::doImportAsDefinition( + const GlobalValue *SGV, DenseSet<const GlobalValue *> *GlobalsToImport) { + + // For alias, we tie the definition to the base object. Extract it and recurse + if (auto *GA = dyn_cast<GlobalAlias>(SGV)) { + if (GA->hasWeakAnyLinkage()) + return false; + const GlobalObject *GO = GA->getBaseObject(); + if (!GO->hasLinkOnceODRLinkage()) + return false; + return FunctionImportGlobalProcessing::doImportAsDefinition( + GO, GlobalsToImport); + } + // Only import the globals requested for importing. + if (GlobalsToImport->count(SGV)) + return true; + // Otherwise no. + return false; +} + +bool FunctionImportGlobalProcessing::doImportAsDefinition( + const GlobalValue *SGV) { + if (!isPerformingImport()) + return false; + return FunctionImportGlobalProcessing::doImportAsDefinition(SGV, + GlobalsToImport); +} + +bool FunctionImportGlobalProcessing::doPromoteLocalToGlobal( + const GlobalValue *SGV) { + assert(SGV->hasLocalLinkage()); + // Both the imported references and the original local variable must + // be promoted. + if (!isPerformingImport() && !isModuleExporting()) + return false; + + // Local const variables never need to be promoted unless they are address + // taken. The imported uses can simply use the clone created in this module. + // For now we are conservative in determining which variables are not + // address taken by checking the unnamed addr flag. To be more aggressive, + // the address taken information must be checked earlier during parsing + // of the module and recorded in the summary index for use when importing + // from that module. + auto *GVar = dyn_cast<GlobalVariable>(SGV); + if (GVar && GVar->isConstant() && GVar->hasGlobalUnnamedAddr()) + return false; + + if (GVar && GVar->hasSection()) + // Some sections like "__DATA,__cfstring" are "magic" and promotion is not + // allowed. Just disable promotion on any GVar with sections right now. + return false; + + // Eventually we only need to promote functions in the exporting module that + // are referenced by a potentially exported function (i.e. one that is in the + // summary index). + return true; +} + +std::string FunctionImportGlobalProcessing::getName(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. When importing, + // we rename all locals (not just those that are promoted) in order to + // avoid naming conflicts between locals imported from different modules. + if (SGV->hasLocalLinkage() && + (doPromoteLocalToGlobal(SGV) || isPerformingImport())) + return ModuleSummaryIndex::getGlobalNameForLocal( + SGV->getName(), + ImportIndex.getModuleHash(SGV->getParent()->getModuleIdentifier())); + return SGV->getName(); +} + +GlobalValue::LinkageTypes +FunctionImportGlobalProcessing::getLinkage(const GlobalValue *SGV) { + // 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() && doPromoteLocalToGlobal(SGV)) + 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::ExternalLinkage: + // External defnitions 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) && !dyn_cast<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::LinkOnceODRLinkage: + // These both stay the same when importing the definition. + // The ThinLTO pass will eventually force-import their definitions. + return SGV->getLinkage(); + + case GlobalValue::WeakAnyLinkage: + // Can't import weak_any definitions correctly, or we might change the + // program semantics, since the linker will pick the first 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) && !dyn_cast<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 (doPromoteLocalToGlobal(SGV)) { + if (doImportAsDefinition(SGV) && !dyn_cast<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) { + if (GV.hasLocalLinkage() && + (doPromoteLocalToGlobal(&GV) || isPerformingImport())) { + GV.setName(getName(&GV)); + GV.setLinkage(getLinkage(&GV)); + if (!GV.hasLocalLinkage()) + GV.setVisibility(GlobalValue::HiddenVisibility); + } else + GV.setLinkage(getLinkage(&GV)); + + // 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_or_null<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() { + if (!moduleCanBeRenamedForThinLTO(M)) { + // We would have blocked importing from this module by suppressing index + // generation. We still may be able to import into this module though. + assert(!isPerformingImport() && + "Should have blocked importing from module with local used in ASM"); + return; + } + + for (GlobalVariable &GV : M.globals()) + processGlobalForThinLTO(GV); + for (Function &SF : M) + processGlobalForThinLTO(SF); + for (GlobalAlias &GA : M.aliases()) + processGlobalForThinLTO(GA); +} + +bool FunctionImportGlobalProcessing::run() { + processGlobalsForThinLTO(); + return false; +} + +bool llvm::renameModuleForThinLTO( + Module &M, const ModuleSummaryIndex &Index, + DenseSet<const GlobalValue *> *GlobalsToImport) { + FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport); + return ThinLTOProcessing.run(); +} |