636 lines
21 KiB
C++
636 lines
21 KiB
C++
//===- lib/Linker/LinkModules.cpp - Module Linker Implementation ----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the LLVM module linker.
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//
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//===----------------------------------------------------------------------===//
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#include "LinkDiagnosticInfo.h"
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#include "llvm-c/Linker.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/StringSet.h"
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#include "llvm/IR/DiagnosticPrinter.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/Linker/Linker.h"
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#include "llvm/Support/Error.h"
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#include "llvm/Transforms/Utils/FunctionImportUtils.h"
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using namespace llvm;
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namespace {
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/// This is an implementation class for the LinkModules function, which is the
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/// entrypoint for this file.
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class ModuleLinker {
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IRMover &Mover;
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std::unique_ptr<Module> SrcM;
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SetVector<GlobalValue *> ValuesToLink;
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StringSet<> Internalize;
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/// For symbol clashes, prefer those from Src.
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unsigned Flags;
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/// Functions to import from source module, all other functions are
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/// imported as declarations instead of definitions.
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DenseSet<const GlobalValue *> *GlobalsToImport;
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/// Used as the callback for lazy linking.
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/// The mover has just hit GV and we have to decide if it, and other members
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/// of the same comdat, should be linked. Every member to be linked is passed
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/// to Add.
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void addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add);
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bool shouldLinkReferencedLinkOnce() {
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return !(Flags & Linker::DontForceLinkLinkonceODR);
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}
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bool shouldOverrideFromSrc() { return Flags & Linker::OverrideFromSrc; }
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bool shouldLinkOnlyNeeded() { return Flags & Linker::LinkOnlyNeeded; }
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bool shouldInternalizeLinkedSymbols() {
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return Flags & Linker::InternalizeLinkedSymbols;
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}
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bool shouldLinkFromSource(bool &LinkFromSrc, const GlobalValue &Dest,
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const GlobalValue &Src);
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/// Should we have mover and linker error diag info?
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bool emitError(const Twine &Message) {
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SrcM->getContext().diagnose(LinkDiagnosticInfo(DS_Error, Message));
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return true;
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}
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bool getComdatLeader(Module &M, StringRef ComdatName,
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const GlobalVariable *&GVar);
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bool computeResultingSelectionKind(StringRef ComdatName,
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Comdat::SelectionKind Src,
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Comdat::SelectionKind Dst,
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Comdat::SelectionKind &Result,
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bool &LinkFromSrc);
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std::map<const Comdat *, std::pair<Comdat::SelectionKind, bool>>
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ComdatsChosen;
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bool getComdatResult(const Comdat *SrcC, Comdat::SelectionKind &SK,
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bool &LinkFromSrc);
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// Keep track of the lazy linked global members of each comdat in source.
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DenseMap<const Comdat *, std::vector<GlobalValue *>> LazyComdatMembers;
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/// Given a global in the source module, return the global in the
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/// destination module that is being linked to, if any.
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GlobalValue *getLinkedToGlobal(const GlobalValue *SrcGV) {
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Module &DstM = Mover.getModule();
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// If the source has no name it can't link. If it has local linkage,
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// there is no name match-up going on.
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if (!SrcGV->hasName() || GlobalValue::isLocalLinkage(SrcGV->getLinkage()))
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return nullptr;
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// Otherwise see if we have a match in the destination module's symtab.
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GlobalValue *DGV = DstM.getNamedValue(SrcGV->getName());
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if (!DGV)
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return nullptr;
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// If we found a global with the same name in the dest module, but it has
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// internal linkage, we are really not doing any linkage here.
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if (DGV->hasLocalLinkage())
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return nullptr;
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// Otherwise, we do in fact link to the destination global.
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return DGV;
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}
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/// Drop GV if it is a member of a comdat that we are dropping.
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/// This can happen with COFF's largest selection kind.
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void dropReplacedComdat(GlobalValue &GV,
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const DenseSet<const Comdat *> &ReplacedDstComdats);
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bool linkIfNeeded(GlobalValue &GV);
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/// Helper method to check if we are importing from the current source
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/// module.
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bool isPerformingImport() const { return GlobalsToImport != nullptr; }
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/// If we are importing from the source module, checks if we should
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/// import SGV as a definition, otherwise import as a declaration.
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bool doImportAsDefinition(const GlobalValue *SGV);
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public:
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ModuleLinker(IRMover &Mover, std::unique_ptr<Module> SrcM, unsigned Flags,
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DenseSet<const GlobalValue *> *GlobalsToImport = nullptr)
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: Mover(Mover), SrcM(std::move(SrcM)), Flags(Flags),
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GlobalsToImport(GlobalsToImport) {}
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bool run();
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};
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}
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bool ModuleLinker::doImportAsDefinition(const GlobalValue *SGV) {
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if (!isPerformingImport())
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return false;
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return FunctionImportGlobalProcessing::doImportAsDefinition(SGV,
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GlobalsToImport);
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}
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static GlobalValue::VisibilityTypes
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getMinVisibility(GlobalValue::VisibilityTypes A,
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GlobalValue::VisibilityTypes B) {
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if (A == GlobalValue::HiddenVisibility || B == GlobalValue::HiddenVisibility)
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return GlobalValue::HiddenVisibility;
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if (A == GlobalValue::ProtectedVisibility ||
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B == GlobalValue::ProtectedVisibility)
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return GlobalValue::ProtectedVisibility;
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return GlobalValue::DefaultVisibility;
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}
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bool ModuleLinker::getComdatLeader(Module &M, StringRef ComdatName,
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const GlobalVariable *&GVar) {
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const GlobalValue *GVal = M.getNamedValue(ComdatName);
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if (const auto *GA = dyn_cast_or_null<GlobalAlias>(GVal)) {
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GVal = GA->getBaseObject();
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if (!GVal)
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// We cannot resolve the size of the aliasee yet.
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return emitError("Linking COMDATs named '" + ComdatName +
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"': COMDAT key involves incomputable alias size.");
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}
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GVar = dyn_cast_or_null<GlobalVariable>(GVal);
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if (!GVar)
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return emitError(
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"Linking COMDATs named '" + ComdatName +
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"': GlobalVariable required for data dependent selection!");
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return false;
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}
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bool ModuleLinker::computeResultingSelectionKind(StringRef ComdatName,
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Comdat::SelectionKind Src,
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Comdat::SelectionKind Dst,
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Comdat::SelectionKind &Result,
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bool &LinkFromSrc) {
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Module &DstM = Mover.getModule();
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// The ability to mix Comdat::SelectionKind::Any with
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// Comdat::SelectionKind::Largest is a behavior that comes from COFF.
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bool DstAnyOrLargest = Dst == Comdat::SelectionKind::Any ||
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Dst == Comdat::SelectionKind::Largest;
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bool SrcAnyOrLargest = Src == Comdat::SelectionKind::Any ||
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Src == Comdat::SelectionKind::Largest;
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if (DstAnyOrLargest && SrcAnyOrLargest) {
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if (Dst == Comdat::SelectionKind::Largest ||
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Src == Comdat::SelectionKind::Largest)
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Result = Comdat::SelectionKind::Largest;
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else
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Result = Comdat::SelectionKind::Any;
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} else if (Src == Dst) {
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Result = Dst;
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} else {
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return emitError("Linking COMDATs named '" + ComdatName +
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"': invalid selection kinds!");
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}
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switch (Result) {
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case Comdat::SelectionKind::Any:
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// Go with Dst.
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LinkFromSrc = false;
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break;
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case Comdat::SelectionKind::NoDuplicates:
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return emitError("Linking COMDATs named '" + ComdatName +
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"': noduplicates has been violated!");
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case Comdat::SelectionKind::ExactMatch:
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case Comdat::SelectionKind::Largest:
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case Comdat::SelectionKind::SameSize: {
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const GlobalVariable *DstGV;
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const GlobalVariable *SrcGV;
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if (getComdatLeader(DstM, ComdatName, DstGV) ||
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getComdatLeader(*SrcM, ComdatName, SrcGV))
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return true;
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const DataLayout &DstDL = DstM.getDataLayout();
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const DataLayout &SrcDL = SrcM->getDataLayout();
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uint64_t DstSize = DstDL.getTypeAllocSize(DstGV->getValueType());
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uint64_t SrcSize = SrcDL.getTypeAllocSize(SrcGV->getValueType());
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if (Result == Comdat::SelectionKind::ExactMatch) {
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if (SrcGV->getInitializer() != DstGV->getInitializer())
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return emitError("Linking COMDATs named '" + ComdatName +
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"': ExactMatch violated!");
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LinkFromSrc = false;
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} else if (Result == Comdat::SelectionKind::Largest) {
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LinkFromSrc = SrcSize > DstSize;
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} else if (Result == Comdat::SelectionKind::SameSize) {
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if (SrcSize != DstSize)
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return emitError("Linking COMDATs named '" + ComdatName +
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"': SameSize violated!");
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LinkFromSrc = false;
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} else {
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llvm_unreachable("unknown selection kind");
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}
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break;
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}
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}
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return false;
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}
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bool ModuleLinker::getComdatResult(const Comdat *SrcC,
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Comdat::SelectionKind &Result,
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bool &LinkFromSrc) {
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Module &DstM = Mover.getModule();
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Comdat::SelectionKind SSK = SrcC->getSelectionKind();
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StringRef ComdatName = SrcC->getName();
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Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
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Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(ComdatName);
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if (DstCI == ComdatSymTab.end()) {
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// Use the comdat if it is only available in one of the modules.
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LinkFromSrc = true;
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Result = SSK;
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return false;
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}
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const Comdat *DstC = &DstCI->second;
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Comdat::SelectionKind DSK = DstC->getSelectionKind();
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return computeResultingSelectionKind(ComdatName, SSK, DSK, Result,
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LinkFromSrc);
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}
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bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
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const GlobalValue &Dest,
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const GlobalValue &Src) {
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// Should we unconditionally use the Src?
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if (shouldOverrideFromSrc()) {
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LinkFromSrc = true;
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return false;
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}
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// We always have to add Src if it has appending linkage.
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if (Src.hasAppendingLinkage()) {
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// Should have prevented importing for appending linkage in linkIfNeeded.
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assert(!isPerformingImport());
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LinkFromSrc = true;
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return false;
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}
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if (isPerformingImport()) {
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// LinkFromSrc iff this is a global requested for importing.
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LinkFromSrc = GlobalsToImport->count(&Src);
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return false;
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}
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bool SrcIsDeclaration = Src.isDeclarationForLinker();
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bool DestIsDeclaration = Dest.isDeclarationForLinker();
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if (SrcIsDeclaration) {
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// If Src is external or if both Src & Dest are external.. Just link the
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// external globals, we aren't adding anything.
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if (Src.hasDLLImportStorageClass()) {
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// If one of GVs is marked as DLLImport, result should be dllimport'ed.
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LinkFromSrc = DestIsDeclaration;
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return false;
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}
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// If the Dest is weak, use the source linkage.
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if (Dest.hasExternalWeakLinkage()) {
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LinkFromSrc = true;
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return false;
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}
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// Link an available_externally over a declaration.
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LinkFromSrc = !Src.isDeclaration() && Dest.isDeclaration();
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return false;
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}
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if (DestIsDeclaration) {
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// If Dest is external but Src is not:
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LinkFromSrc = true;
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return false;
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}
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if (Src.hasCommonLinkage()) {
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if (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage()) {
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LinkFromSrc = true;
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return false;
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}
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if (!Dest.hasCommonLinkage()) {
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LinkFromSrc = false;
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return false;
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}
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const DataLayout &DL = Dest.getParent()->getDataLayout();
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uint64_t DestSize = DL.getTypeAllocSize(Dest.getValueType());
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uint64_t SrcSize = DL.getTypeAllocSize(Src.getValueType());
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LinkFromSrc = SrcSize > DestSize;
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return false;
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}
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if (Src.isWeakForLinker()) {
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assert(!Dest.hasExternalWeakLinkage());
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assert(!Dest.hasAvailableExternallyLinkage());
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if (Dest.hasLinkOnceLinkage() && Src.hasWeakLinkage()) {
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LinkFromSrc = true;
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return false;
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}
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LinkFromSrc = false;
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return false;
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}
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if (Dest.isWeakForLinker()) {
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assert(Src.hasExternalLinkage());
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LinkFromSrc = true;
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return false;
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}
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assert(!Src.hasExternalWeakLinkage());
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assert(!Dest.hasExternalWeakLinkage());
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assert(Dest.hasExternalLinkage() && Src.hasExternalLinkage() &&
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"Unexpected linkage type!");
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return emitError("Linking globals named '" + Src.getName() +
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"': symbol multiply defined!");
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}
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bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
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GlobalValue *DGV = getLinkedToGlobal(&GV);
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if (shouldLinkOnlyNeeded() && !(DGV && DGV->isDeclaration()))
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return false;
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if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
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auto *DGVar = dyn_cast<GlobalVariable>(DGV);
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auto *SGVar = dyn_cast<GlobalVariable>(&GV);
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if (DGVar && SGVar) {
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if (DGVar->isDeclaration() && SGVar->isDeclaration() &&
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(!DGVar->isConstant() || !SGVar->isConstant())) {
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DGVar->setConstant(false);
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SGVar->setConstant(false);
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}
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if (DGVar->hasCommonLinkage() && SGVar->hasCommonLinkage()) {
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unsigned Align = std::max(DGVar->getAlignment(), SGVar->getAlignment());
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SGVar->setAlignment(Align);
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DGVar->setAlignment(Align);
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}
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}
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GlobalValue::VisibilityTypes Visibility =
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getMinVisibility(DGV->getVisibility(), GV.getVisibility());
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DGV->setVisibility(Visibility);
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GV.setVisibility(Visibility);
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GlobalValue::UnnamedAddr UnnamedAddr = GlobalValue::getMinUnnamedAddr(
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DGV->getUnnamedAddr(), GV.getUnnamedAddr());
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DGV->setUnnamedAddr(UnnamedAddr);
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GV.setUnnamedAddr(UnnamedAddr);
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}
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// Don't want to append to global_ctors list, for example, when we
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// are importing for ThinLTO, otherwise the global ctors and dtors
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// get executed multiple times for local variables (the latter causing
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// double frees).
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if (GV.hasAppendingLinkage() && isPerformingImport())
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return false;
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if (isPerformingImport()) {
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if (!doImportAsDefinition(&GV))
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return false;
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} else if (!DGV && !shouldOverrideFromSrc() &&
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(GV.hasLocalLinkage() || GV.hasLinkOnceLinkage() ||
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GV.hasAvailableExternallyLinkage()))
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return false;
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if (GV.isDeclaration())
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return false;
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if (const Comdat *SC = GV.getComdat()) {
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bool LinkFromSrc;
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Comdat::SelectionKind SK;
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std::tie(SK, LinkFromSrc) = ComdatsChosen[SC];
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if (!LinkFromSrc)
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return false;
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}
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bool LinkFromSrc = true;
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if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, GV))
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return true;
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if (LinkFromSrc)
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ValuesToLink.insert(&GV);
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return false;
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}
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void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
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if (!shouldLinkReferencedLinkOnce())
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// For ThinLTO we don't import more than what was required.
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// The client has to guarantee that the linkonce will be availabe at link
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// time (by promoting it to weak for instance).
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return;
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// Add these to the internalize list
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if (!GV.hasLinkOnceLinkage() && !shouldLinkOnlyNeeded())
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return;
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if (shouldInternalizeLinkedSymbols())
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Internalize.insert(GV.getName());
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Add(GV);
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const Comdat *SC = GV.getComdat();
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if (!SC)
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return;
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for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
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GlobalValue *DGV = getLinkedToGlobal(GV2);
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bool LinkFromSrc = true;
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if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
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return;
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if (!LinkFromSrc)
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continue;
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if (shouldInternalizeLinkedSymbols())
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Internalize.insert(GV2->getName());
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Add(*GV2);
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}
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}
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void ModuleLinker::dropReplacedComdat(
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GlobalValue &GV, const DenseSet<const Comdat *> &ReplacedDstComdats) {
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Comdat *C = GV.getComdat();
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if (!C)
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return;
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if (!ReplacedDstComdats.count(C))
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return;
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if (GV.use_empty()) {
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GV.eraseFromParent();
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return;
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}
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if (auto *F = dyn_cast<Function>(&GV)) {
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F->deleteBody();
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} else if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
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Var->setInitializer(nullptr);
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} else {
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auto &Alias = cast<GlobalAlias>(GV);
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Module &M = *Alias.getParent();
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PointerType &Ty = *cast<PointerType>(Alias.getType());
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GlobalValue *Declaration;
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if (auto *FTy = dyn_cast<FunctionType>(Alias.getValueType())) {
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Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage, "", &M);
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} else {
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Declaration =
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new GlobalVariable(M, Ty.getElementType(), /*isConstant*/ false,
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GlobalValue::ExternalLinkage,
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/*Initializer*/ nullptr);
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}
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Declaration->takeName(&Alias);
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Alias.replaceAllUsesWith(Declaration);
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Alias.eraseFromParent();
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}
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}
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bool ModuleLinker::run() {
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Module &DstM = Mover.getModule();
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DenseSet<const Comdat *> ReplacedDstComdats;
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for (const auto &SMEC : SrcM->getComdatSymbolTable()) {
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const Comdat &C = SMEC.getValue();
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if (ComdatsChosen.count(&C))
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continue;
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Comdat::SelectionKind SK;
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bool LinkFromSrc;
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if (getComdatResult(&C, SK, LinkFromSrc))
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return true;
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ComdatsChosen[&C] = std::make_pair(SK, LinkFromSrc);
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if (!LinkFromSrc)
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continue;
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Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
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Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(C.getName());
|
|
if (DstCI == ComdatSymTab.end())
|
|
continue;
|
|
|
|
// The source comdat is replacing the dest one.
|
|
const Comdat *DstC = &DstCI->second;
|
|
ReplacedDstComdats.insert(DstC);
|
|
}
|
|
|
|
// Alias have to go first, since we are not able to find their comdats
|
|
// otherwise.
|
|
for (auto I = DstM.alias_begin(), E = DstM.alias_end(); I != E;) {
|
|
GlobalAlias &GV = *I++;
|
|
dropReplacedComdat(GV, ReplacedDstComdats);
|
|
}
|
|
|
|
for (auto I = DstM.global_begin(), E = DstM.global_end(); I != E;) {
|
|
GlobalVariable &GV = *I++;
|
|
dropReplacedComdat(GV, ReplacedDstComdats);
|
|
}
|
|
|
|
for (auto I = DstM.begin(), E = DstM.end(); I != E;) {
|
|
Function &GV = *I++;
|
|
dropReplacedComdat(GV, ReplacedDstComdats);
|
|
}
|
|
|
|
for (GlobalVariable &GV : SrcM->globals())
|
|
if (GV.hasLinkOnceLinkage())
|
|
if (const Comdat *SC = GV.getComdat())
|
|
LazyComdatMembers[SC].push_back(&GV);
|
|
|
|
for (Function &SF : *SrcM)
|
|
if (SF.hasLinkOnceLinkage())
|
|
if (const Comdat *SC = SF.getComdat())
|
|
LazyComdatMembers[SC].push_back(&SF);
|
|
|
|
for (GlobalAlias &GA : SrcM->aliases())
|
|
if (GA.hasLinkOnceLinkage())
|
|
if (const Comdat *SC = GA.getComdat())
|
|
LazyComdatMembers[SC].push_back(&GA);
|
|
|
|
// Insert all of the globals in src into the DstM module... without linking
|
|
// initializers (which could refer to functions not yet mapped over).
|
|
for (GlobalVariable &GV : SrcM->globals())
|
|
if (linkIfNeeded(GV))
|
|
return true;
|
|
|
|
for (Function &SF : *SrcM)
|
|
if (linkIfNeeded(SF))
|
|
return true;
|
|
|
|
for (GlobalAlias &GA : SrcM->aliases())
|
|
if (linkIfNeeded(GA))
|
|
return true;
|
|
|
|
for (unsigned I = 0; I < ValuesToLink.size(); ++I) {
|
|
GlobalValue *GV = ValuesToLink[I];
|
|
const Comdat *SC = GV->getComdat();
|
|
if (!SC)
|
|
continue;
|
|
for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
|
|
GlobalValue *DGV = getLinkedToGlobal(GV2);
|
|
bool LinkFromSrc = true;
|
|
if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
|
|
return true;
|
|
if (LinkFromSrc)
|
|
ValuesToLink.insert(GV2);
|
|
}
|
|
}
|
|
|
|
if (shouldInternalizeLinkedSymbols()) {
|
|
for (GlobalValue *GV : ValuesToLink)
|
|
Internalize.insert(GV->getName());
|
|
}
|
|
|
|
// FIXME: Propagate Errors through to the caller instead of emitting
|
|
// diagnostics.
|
|
bool HasErrors = false;
|
|
if (Error E = Mover.move(std::move(SrcM), ValuesToLink.getArrayRef(),
|
|
[this](GlobalValue &GV, IRMover::ValueAdder Add) {
|
|
addLazyFor(GV, Add);
|
|
},
|
|
/* LinkModuleInlineAsm */ !isPerformingImport(),
|
|
/* IsPerformingImport */ isPerformingImport())) {
|
|
handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
|
|
DstM.getContext().diagnose(LinkDiagnosticInfo(DS_Error, EIB.message()));
|
|
HasErrors = true;
|
|
});
|
|
}
|
|
if (HasErrors)
|
|
return true;
|
|
|
|
for (auto &P : Internalize) {
|
|
GlobalValue *GV = DstM.getNamedValue(P.first());
|
|
GV->setLinkage(GlobalValue::InternalLinkage);
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
Linker::Linker(Module &M) : Mover(M) {}
|
|
|
|
bool Linker::linkInModule(std::unique_ptr<Module> Src, unsigned Flags,
|
|
DenseSet<const GlobalValue *> *GlobalsToImport) {
|
|
ModuleLinker ModLinker(Mover, std::move(Src), Flags, GlobalsToImport);
|
|
return ModLinker.run();
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// LinkModules entrypoint.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// This function links two modules together, with the resulting Dest module
|
|
/// modified to be the composite of the two input modules. If an error occurs,
|
|
/// true is returned and ErrorMsg (if not null) is set to indicate the problem.
|
|
/// Upon failure, the Dest module could be in a modified state, and shouldn't be
|
|
/// relied on to be consistent.
|
|
bool Linker::linkModules(Module &Dest, std::unique_ptr<Module> Src,
|
|
unsigned Flags) {
|
|
Linker L(Dest);
|
|
return L.linkInModule(std::move(Src), Flags);
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// C API.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
LLVMBool LLVMLinkModules2(LLVMModuleRef Dest, LLVMModuleRef Src) {
|
|
Module *D = unwrap(Dest);
|
|
std::unique_ptr<Module> M(unwrap(Src));
|
|
return Linker::linkModules(*D, std::move(M));
|
|
}
|