C++ GlobalValue::isDeclaration方法代码示例

void LTOCodeGenerator::
applyRestriction(GlobalValue &GV,
                 ArrayRef<StringRef> Libcalls,
                 std::vector<const char*> &MustPreserveList,
                 SmallPtrSetImpl<GlobalValue*> &AsmUsed,
                 Mangler &Mangler) {
  // There are no restrictions to apply to declarations.
  if (GV.isDeclaration())
    return;

  // There is nothing more restrictive than private linkage.
  if (GV.hasPrivateLinkage())
    return;

  SmallString<64> Buffer;
  TargetMach->getNameWithPrefix(Buffer, &GV, Mangler);

  if (MustPreserveSymbols.count(Buffer))
    MustPreserveList.push_back(GV.getName().data());
  if (AsmUndefinedRefs.count(Buffer))
    AsmUsed.insert(&GV);

  // Conservatively append user-supplied runtime library functions to
  // llvm.compiler.used.  These could be internalized and deleted by
  // optimizations like -globalopt, causing problems when later optimizations
  // add new library calls (e.g., llvm.memset => memset and printf => puts).
  // Leave it to the linker to remove any dead code (e.g. with -dead_strip).
  if (isa<Function>(GV) &&
      std::binary_search(Libcalls.begin(), Libcalls.end(), GV.getName()))
    AsmUsed.insert(&GV);
}

static bool isDeclaration(const GlobalValue &V) {
  if (V.hasAvailableExternallyLinkage())
    return true;
  if (V.isMaterializable())
    return false;
  return V.isDeclaration();
}

static bool shouldInternalize(const GlobalValue &GV,
                              const std::set<std::string> &ExternalNames,
                              bool OnlyHidden) {
  if (OnlyHidden && !GV.hasHiddenVisibility())
    return false;

  // Function must be defined here
  if (GV.isDeclaration())
    return false;

  // Available externally is really just a "declaration with a body".
  if (GV.hasAvailableExternallyLinkage())
    return false;

  // Assume that dllexported symbols are referenced elsewhere
  if (GV.hasDLLExportStorageClass())
    return false;

  // Already has internal linkage
  if (GV.hasLocalLinkage())
    return false;

  // Marked to keep external?
  if (ExternalNames.count(GV.getName()))
    return false;

  return true;
}

static bool shouldInternalize(const GlobalValue &GV,
                              const std::set<std::string> &ExternalNames,
                              const std::set<std::string> &DSONames) {
  // Function must be defined here
  if (GV.isDeclaration())
    return false;

  // Available externally is really just a "declaration with a body".
  if (GV.hasAvailableExternallyLinkage())
    return false;

  // Already has internal linkage
  if (GV.hasLocalLinkage())
    return false;

  // Marked to keep external?
  if (ExternalNames.count(GV.getName()))
    return false;

  // Not needed for the symbol table?
  if (!DSONames.count(GV.getName()))
    return true;

  // Not a linkonce. Someone can depend on it being on the symbol table.
  if (!GV.hasLinkOnceLinkage())
    return false;

  // The address is not important, we can hide it.
  if (GV.hasUnnamedAddr())
    return true;

  // FIXME: Check if the address is used.
  return false;
}

// llvm_mark_decl_weak - Used by varasm.c, called when a decl is found to be
// weak, but it already had an llvm object created for it. This marks the LLVM
// object weak as well.
void llvm_mark_decl_weak(tree decl) {
  assert(DECL_LLVM_SET_P(decl) && DECL_WEAK(decl) &&
         isa<GlobalValue>(DECL_LLVM(decl)) && "Decl isn't marked weak!");
  GlobalValue *GV = cast<GlobalValue>(DECL_LLVM(decl));

  // Do not mark something that is already known to be linkonce or internal.
  if (GV->hasExternalLinkage()) {
    if (GV->isDeclaration())
      GV->setLinkage(GlobalValue::ExternalWeakLinkage);
    else
      GV->setLinkage(GlobalValue::WeakLinkage);
  }
}

void LTOCodeGenerator::
applyRestriction(GlobalValue &GV,
                 std::vector<const char*> &mustPreserveList,
                 SmallPtrSet<GlobalValue*, 8> &asmUsed,
                 Mangler &mangler) {
  SmallString<64> Buffer;
  mangler.getNameWithPrefix(Buffer, &GV, false);

  if (GV.isDeclaration())
    return;
  if (_mustPreserveSymbols.count(Buffer))
    mustPreserveList.push_back(GV.getName().data());
  if (_asmUndefinedRefs.count(Buffer))
    asmUsed.insert(&GV);
}

static char TypeCharForSymbol(GlobalValue &GV) {
  if (GV.isDeclaration())                                  return 'U';
  if (GV.hasLinkOnceLinkage())                             return 'C';
  if (GV.hasCommonLinkage())                               return 'C';
  if (GV.hasWeakLinkage())                                 return 'W';
  if (isa<Function>(GV) && GV.hasInternalLinkage())        return 't';
  if (isa<Function>(GV))                                   return 'T';
  if (isa<GlobalVariable>(GV) && GV.hasInternalLinkage())  return 'd';
  if (isa<GlobalVariable>(GV))                             return 'D';
  if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(&GV)) {
    const GlobalValue *AliasedGV = GA->getAliasedGlobal();
    if (isa<Function>(AliasedGV))                          return 'T';
    if (isa<GlobalVariable>(AliasedGV))                    return 'D';
  }
                                                           return '?';
}

static bool useExistingDest(GlobalValue &SGV, GlobalValue *DGV,
                            bool ShouldLink) {
  if (!DGV)
    return false;

  if (SGV.isDeclaration())
    return true;

  if (DGV->isDeclarationForLinker() && !SGV.isDeclarationForLinker())
    return false;

  if (ShouldLink)
    return false;

  return true;
}

void AlphaAsmPrinter::printOp(const MachineOperand &MO, bool IsCallOp) {
  const TargetRegisterInfo &RI = *TM.getRegisterInfo();

  switch (MO.getType()) {
  case MachineOperand::MO_Register:
    O << RI.get(MO.getReg()).AsmName;
    return;

  case MachineOperand::MO_Immediate:
    cerr << "printOp() does not handle immediate values\n";
    abort();
    return;

  case MachineOperand::MO_MachineBasicBlock:
    printBasicBlockLabel(MO.getMBB());
    return;

  case MachineOperand::MO_ConstantPoolIndex:
    O << TAI->getPrivateGlobalPrefix() << "CPI" << getFunctionNumber() << "_"
      << MO.getIndex();
    return;

  case MachineOperand::MO_ExternalSymbol:
    O << MO.getSymbolName();
    return;

  case MachineOperand::MO_GlobalAddress: {
    GlobalValue *GV = MO.getGlobal();
    O << Mang->getValueName(GV);
    if (GV->isDeclaration() && GV->hasExternalWeakLinkage())
      ExtWeakSymbols.insert(GV);
    return;
  }

  case MachineOperand::MO_JumpTableIndex:
    O << TAI->getPrivateGlobalPrefix() << "JTI" << getFunctionNumber()
      << '_' << MO.getIndex();
    return;

  default:
    O << "<unknown operand type: " << MO.getType() << ">";
    return;
  }
}

bool IRLinker::shouldLink(GlobalValue *DGV, GlobalValue &SGV) {
  if (ValuesToLink.count(&SGV) || SGV.hasLocalLinkage())
    return true;

  if (DGV && !DGV->isDeclarationForLinker())
    return false;

  if (SGV.hasAvailableExternallyLinkage())
    return true;

  if (SGV.isDeclaration() || DoneLinkingBodies)
    return false;

  // Callback to the client to give a chance to lazily add the Global to the
  // list of value to link.
  bool LazilyAdded = false;
  AddLazyFor(SGV, [this, &LazilyAdded](GlobalValue &GV) {
    maybeAdd(&GV);
    LazilyAdded = true;
  });
  return LazilyAdded;
}

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()) {
            FunctionSummary *FS = dyn_cast<FunctionSummary>(S->getBaseObject());
            if (FS->modulePath() == M.getModuleIdentifier()) {
              F->setEntryCount(Function::ProfileCount(FS->entryCount(),
                                                      Function::PCT_Synthetic));
              break;
            }
          }
        }
      }
    }
    // Check the summaries to see if the symbol gets resolved to a known local
    // definition.
    if (VI && VI.isDSOLocal()) {
      GV.setDSOLocal(true);
      if (GV.hasDLLImportStorageClass())
        GV.setDLLStorageClass(GlobalValue::DefaultStorageClass);
    }
  }

  // Mark read-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 internalizeImmutableGVs.
  //
  // 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.withGlobalValueDeadStripping()) {
    const auto &SL = VI.getSummaryList();
    auto *GVS = SL.empty() ? nullptr : dyn_cast<GlobalVarSummary>(SL[0].get());
    if (GVS && GVS->isReadOnly())
      cast<GlobalVariable>(&GV)->addAttribute("thinlto-internalize");
  }

  bool DoPromote = false;
  if (GV.hasLocalLinkage() &&
      ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
    // Save the original name string before we rename GV below.
    auto Name = GV.getName().str();
    // Once we change the name or linkage it is difficult to determine
    // again whether we should promote since shouldPromoteLocalToGlobal needs
    // to locate the summary (based on GUID from name and linkage). Therefore,
    // use DoPromote result saved above.
    GV.setName(getName(&GV, DoPromote));
    GV.setLinkage(getLinkage(&GV, DoPromote));
    if (!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));

  // 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);
  }
}

// destructively move the contents of src into dest
// this assumes that the targets of the two modules are the same
// including the DataLayout and ModuleFlags (for example)
// and that there is no module-level assembly
static void jl_merge_module(Module *dest, std::unique_ptr<Module> src)
{
    assert(dest != src.get());
    for (Module::global_iterator I = src->global_begin(), E = src->global_end(); I != E;) {
        GlobalVariable *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        // Replace a declaration with the definition:
        if (dG) {
            if (sG->isDeclaration()) {
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        // Reparent the global variable:
        sG->removeFromParent();
        dest->getGlobalList().push_back(sG);
        // Comdat is owned by the Module, recreate it in the new parent:
        addComdat(sG);
    }

    for (Module::iterator I = src->begin(), E = src->end(); I != E;) {
        Function *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        // Replace a declaration with the definition:
        if (dG) {
            if (sG->isDeclaration()) {
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        // Reparent the global variable:
        sG->removeFromParent();
        dest->getFunctionList().push_back(sG);
        // Comdat is owned by the Module, recreate it in the new parent:
        addComdat(sG);
    }

    for (Module::alias_iterator I = src->alias_begin(), E = src->alias_end(); I != E;) {
        GlobalAlias *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        if (dG) {
            if (!dG->isDeclaration()) { // aliases are always definitions, so this test is reversed from the above two
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        sG->removeFromParent();
        dest->getAliasList().push_back(sG);
    }

    // metadata nodes need to be explicitly merged not just copied
    // so there are special passes here for each known type of metadata
    NamedMDNode *sNMD = src->getNamedMetadata("llvm.dbg.cu");
    if (sNMD) {
        NamedMDNode *dNMD = dest->getOrInsertNamedMetadata("llvm.dbg.cu");
#ifdef LLVM35
        for (NamedMDNode::op_iterator I = sNMD->op_begin(), E = sNMD->op_end(); I != E; ++I) {
            dNMD->addOperand(*I);
        }
#else
        for (unsigned i = 0, l = sNMD->getNumOperands(); i < l; i++) {
            dNMD->addOperand(sNMD->getOperand(i));
        }
#endif
    }
}

ModuleSummaryIndex llvm::buildModuleSummaryIndex(
    const Module &M,
    std::function<BlockFrequencyInfo *(const Function &F)> GetBFICallback,
    ProfileSummaryInfo *PSI) {
  ModuleSummaryIndex Index;

  // Identify the local values in the llvm.used and llvm.compiler.used sets,
  // which should not be exported as they would then require renaming and
  // promotion, but we may have opaque uses e.g. in inline asm. We collect them
  // here because we use this information to mark functions containing inline
  // assembly calls as not importable.
  SmallPtrSet<GlobalValue *, 8> LocalsUsed;
  SmallPtrSet<GlobalValue *, 8> Used;
  // First collect those in the llvm.used set.
  collectUsedGlobalVariables(M, Used, /*CompilerUsed*/ false);
  // Next collect those in the llvm.compiler.used set.
  collectUsedGlobalVariables(M, Used, /*CompilerUsed*/ true);
  DenseSet<GlobalValue::GUID> CantBePromoted;
  for (auto *V : Used) {
    if (V->hasLocalLinkage()) {
      LocalsUsed.insert(V);
      CantBePromoted.insert(V->getGUID());
    }
  }

  // Compute summaries for all functions defined in module, and save in the
  // index.
  for (auto &F : M) {
    if (F.isDeclaration())
      continue;

    BlockFrequencyInfo *BFI = nullptr;
    std::unique_ptr<BlockFrequencyInfo> BFIPtr;
    if (GetBFICallback)
      BFI = GetBFICallback(F);
    else if (F.getEntryCount().hasValue()) {
      LoopInfo LI{DominatorTree(const_cast<Function &>(F))};
      BranchProbabilityInfo BPI{F, LI};
      BFIPtr = llvm::make_unique<BlockFrequencyInfo>(F, BPI, LI);
      BFI = BFIPtr.get();
    }

    computeFunctionSummary(Index, M, F, BFI, PSI, !LocalsUsed.empty(),
                           CantBePromoted);
  }

  // Compute summaries for all variables defined in module, and save in the
  // index.
  for (const GlobalVariable &G : M.globals()) {
    if (G.isDeclaration())
      continue;
    computeVariableSummary(Index, G, CantBePromoted);
  }

  // Compute summaries for all aliases defined in module, and save in the
  // index.
  for (const GlobalAlias &A : M.aliases())
    computeAliasSummary(Index, A, CantBePromoted);

  for (auto *V : LocalsUsed) {
    auto *Summary = Index.getGlobalValueSummary(*V);
    assert(Summary && "Missing summary for global value");
    Summary->setNotEligibleToImport();
  }

  // The linker doesn't know about these LLVM produced values, so we need
  // to flag them as live in the index to ensure index-based dead value
  // analysis treats them as live roots of the analysis.
  setLiveRoot(Index, "llvm.used");
  setLiveRoot(Index, "llvm.compiler.used");
  setLiveRoot(Index, "llvm.global_ctors");
  setLiveRoot(Index, "llvm.global_dtors");
  setLiveRoot(Index, "llvm.global.annotations");

  if (!M.getModuleInlineAsm().empty()) {
    // Collect the local values defined by module level asm, and set up
    // summaries for these symbols so that they can be marked as NoRename,
    // to prevent export of any use of them in regular IR that would require
    // renaming within the module level asm. Note we don't need to create a
    // summary for weak or global defs, as they don't need to be flagged as
    // NoRename, and defs in module level asm can't be imported anyway.
    // Also, any values used but not defined within module level asm should
    // be listed on the llvm.used or llvm.compiler.used global and marked as
    // referenced from there.
    ModuleSymbolTable::CollectAsmSymbols(
        Triple(M.getTargetTriple()), M.getModuleInlineAsm(),
        [&M, &Index, &CantBePromoted](StringRef Name,
                                      object::BasicSymbolRef::Flags Flags) {
          // Symbols not marked as Weak or Global are local definitions.
          if (Flags & (object::BasicSymbolRef::SF_Weak |
                       object::BasicSymbolRef::SF_Global))
            return;
          GlobalValue *GV = M.getNamedValue(Name);
          if (!GV)
            return;
          assert(GV->isDeclaration() && "Def in module asm already has definition");
          GlobalValueSummary::GVFlags GVFlags(GlobalValue::InternalLinkage,
                                              /* NotEligibleToImport */ true,
                                              /* LiveRoot */ true);
          CantBePromoted.insert(GlobalValue::getGUID(Name));
//.........这里部分代码省略.........

bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
  GlobalValue *DGV = getLinkedToGlobal(&GV);

  if (shouldLinkOnlyNeeded() && !(DGV && DGV->isDeclaration()))
    return false;

  if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
    auto *DGVar = dyn_cast<GlobalVariable>(DGV);
    auto *SGVar = dyn_cast<GlobalVariable>(&GV);
    if (DGVar && SGVar) {
      if (DGVar->isDeclaration() && SGVar->isDeclaration() &&
          (!DGVar->isConstant() || !SGVar->isConstant())) {
        DGVar->setConstant(false);
        SGVar->setConstant(false);
      }
      if (DGVar->hasCommonLinkage() && SGVar->hasCommonLinkage()) {
        unsigned Align = std::max(DGVar->getAlignment(), SGVar->getAlignment());
        SGVar->setAlignment(Align);
        DGVar->setAlignment(Align);
      }
    }

    GlobalValue::VisibilityTypes Visibility =
        getMinVisibility(DGV->getVisibility(), GV.getVisibility());
    DGV->setVisibility(Visibility);
    GV.setVisibility(Visibility);

    bool HasUnnamedAddr = GV.hasUnnamedAddr() && DGV->hasUnnamedAddr();
    DGV->setUnnamedAddr(HasUnnamedAddr);
    GV.setUnnamedAddr(HasUnnamedAddr);
  }

  // Don't want to append to global_ctors list, for example, when we
  // are importing for ThinLTO, otherwise the global ctors and dtors
  // get executed multiple times for local variables (the latter causing
  // double frees).
  if (GV.hasAppendingLinkage() && isPerformingImport())
    return false;

  if (isPerformingImport()) {
    if (!doImportAsDefinition(&GV))
      return false;
  } else if (!DGV && !shouldOverrideFromSrc() &&
             (GV.hasLocalLinkage() || GV.hasLinkOnceLinkage() ||
              GV.hasAvailableExternallyLinkage()))
    return false;

  if (GV.isDeclaration())
    return false;

  if (const Comdat *SC = GV.getComdat()) {
    bool LinkFromSrc;
    Comdat::SelectionKind SK;
    std::tie(SK, LinkFromSrc) = ComdatsChosen[SC];
    if (!LinkFromSrc)
      return false;
  }

  bool LinkFromSrc = true;
  if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, GV))
    return true;
  if (LinkFromSrc)
    ValuesToLink.insert(&GV);
  return false;
}

bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
                                        const GlobalValue &Dest,
                                        const GlobalValue &Src) {

  // Should we unconditionally use the Src?
  if (shouldOverrideFromSrc()) {
    LinkFromSrc = true;
    return false;
  }

  // We always have to add Src if it has appending linkage.
  if (Src.hasAppendingLinkage()) {
    // Should have prevented importing for appending linkage in linkIfNeeded.
    assert(!isPerformingImport());
    LinkFromSrc = true;
    return false;
  }

  if (isPerformingImport()) {
    // LinkFromSrc iff this is a global requested for importing.
    LinkFromSrc = GlobalsToImport->count(&Src);
    return false;
  }

  bool SrcIsDeclaration = Src.isDeclarationForLinker();
  bool DestIsDeclaration = Dest.isDeclarationForLinker();

  if (SrcIsDeclaration) {
    // If Src is external or if both Src & Dest are external..  Just link the
    // external globals, we aren't adding anything.
    if (Src.hasDLLImportStorageClass()) {
      // If one of GVs is marked as DLLImport, result should be dllimport'ed.
      LinkFromSrc = DestIsDeclaration;
      return false;
    }
    // If the Dest is weak, use the source linkage.
    if (Dest.hasExternalWeakLinkage()) {
      LinkFromSrc = true;
      return false;
    }
    // Link an available_externally over a declaration.
    LinkFromSrc = !Src.isDeclaration() && Dest.isDeclaration();
    return false;
  }

  if (DestIsDeclaration) {
    // If Dest is external but Src is not:
    LinkFromSrc = true;
    return false;
  }

  if (Src.hasCommonLinkage()) {
    if (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage()) {
      LinkFromSrc = true;
      return false;
    }

    if (!Dest.hasCommonLinkage()) {
      LinkFromSrc = false;
      return false;
    }

    const DataLayout &DL = Dest.getParent()->getDataLayout();
    uint64_t DestSize = DL.getTypeAllocSize(Dest.getValueType());
    uint64_t SrcSize = DL.getTypeAllocSize(Src.getValueType());
    LinkFromSrc = SrcSize > DestSize;
    return false;
  }

  if (Src.isWeakForLinker()) {
    assert(!Dest.hasExternalWeakLinkage());
    assert(!Dest.hasAvailableExternallyLinkage());

    if (Dest.hasLinkOnceLinkage() && Src.hasWeakLinkage()) {
      LinkFromSrc = true;
      return false;
    }

    LinkFromSrc = false;
    return false;
  }

  if (Dest.isWeakForLinker()) {
    assert(Src.hasExternalLinkage());
    LinkFromSrc = true;
    return false;
  }

  assert(!Src.hasExternalWeakLinkage());
  assert(!Dest.hasExternalWeakLinkage());
  assert(Dest.hasExternalLinkage() && Src.hasExternalLinkage() &&
         "Unexpected linkage type!");
  return emitError("Linking globals named '" + Src.getName() +
                   "': symbol multiply defined!");
}