C++ SmallDenseMap类代码示例

static void shuffleValueUseLists(Value *V, std::minstd_rand0 &Gen,
                                 DenseSet<Value *> &Seen) {
  if (!Seen.insert(V).second)
    return;

  if (auto *C = dyn_cast<Constant>(V))
    if (!isa<GlobalValue>(C))
      for (Value *Op : C->operands())
        shuffleValueUseLists(Op, Gen, Seen);

  if (V->use_empty() || std::next(V->use_begin()) == V->use_end())
    // Nothing to shuffle for 0 or 1 users.
    return;

  // Generate random numbers between 10 and 99, which will line up nicely in
  // debug output.  We're not worried about collisons here.
  DEBUG(dbgs() << "V = "; V->dump());
  std::uniform_int_distribution<short> Dist(10, 99);
  SmallDenseMap<const Use *, short, 16> Order;
  for (const Use &U : V->uses()) {
    auto I = Dist(Gen);
    Order[&U] = I;
    DEBUG(dbgs() << " - order: " << I << ", U = "; U.getUser()->dump());
  }

  DEBUG(dbgs() << " => shuffle\n");
  V->sortUseList(
      [&Order](const Use &L, const Use &R) { return Order[&L] < Order[&R]; });

  DEBUG({
    for (const Use &U : V->uses())
      DEBUG(dbgs() << " - order: " << Order.lookup(&U) << ", U = ";
            U.getUser()->dump());
  });

/// Sort local variables so that variables appearing inside of helper
/// expressions come first.
static SmallVector<DbgVariable *, 8>
sortLocalVars(SmallVectorImpl<DbgVariable *> &Input) {
  SmallVector<DbgVariable *, 8> Result;
  SmallVector<PointerIntPair<DbgVariable *, 1>, 8> WorkList;
  // Map back from a DIVariable to its containing DbgVariable.
  SmallDenseMap<const DILocalVariable *, DbgVariable *> DbgVar;
  // Set of DbgVariables in Result.
  SmallDenseSet<DbgVariable *, 8> Visited;
  // For cycle detection.
  SmallDenseSet<DbgVariable *, 8> Visiting;

  // Initialize the worklist and the DIVariable lookup table.
  for (auto Var : reverse(Input)) {
    DbgVar.insert({Var->getVariable(), Var});
    WorkList.push_back({Var, 0});
  }

  // Perform a stable topological sort by doing a DFS.
  while (!WorkList.empty()) {
    auto Item = WorkList.back();
    DbgVariable *Var = Item.getPointer();
    bool visitedAllDependencies = Item.getInt();
    WorkList.pop_back();

    // Dependency is in a different lexical scope or a global.
    if (!Var)
      continue;

    // Already handled.
    if (Visited.count(Var))
      continue;

    // Add to Result if all dependencies are visited.
    if (visitedAllDependencies) {
      Visited.insert(Var);
      Result.push_back(Var);
      continue;
    }

    // Detect cycles.
    auto Res = Visiting.insert(Var);
    if (!Res.second) {
      assert(false && "dependency cycle in local variables");
      return Result;
    }

    // Push dependencies and this node onto the worklist, so that this node is
    // visited again after all of its dependencies are handled.
    WorkList.push_back({Var, 1});
    for (auto *Dependency : dependencies(Var)) {
      auto Dep = dyn_cast_or_null<const DILocalVariable>(Dependency);
      WorkList.push_back({DbgVar[Dep], 0});
    }
  }
  return Result;
}

// This function calculates the number of iterations after which the given Phi
// becomes an invariant. The pre-calculated values are memorized in the map. The
// function (shortcut is I) is calculated according to the following definition:
// Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
//   If %y is a loop invariant, then I(%x) = 1.
//   If %y is a Phi from the loop header, I(%x) = I(%y) + 1.
//   Otherwise, I(%x) is infinite.
// TODO: Actually if %y is an expression that depends only on Phi %z and some
//       loop invariants, we can estimate I(%x) = I(%z) + 1. The example
//       looks like:
//         %x = phi(0, %a),  <-- becomes invariant starting from 3rd iteration.
//         %y = phi(0, 5),
//         %a = %y + 1.
static unsigned calculateIterationsToInvariance(
    PHINode *Phi, Loop *L, BasicBlock *BackEdge,
    SmallDenseMap<PHINode *, unsigned> &IterationsToInvariance) {
  assert(Phi->getParent() == L->getHeader() &&
         "Non-loop Phi should not be checked for turning into invariant.");
  assert(BackEdge == L->getLoopLatch() && "Wrong latch?");
  // If we already know the answer, take it from the map.
  auto I = IterationsToInvariance.find(Phi);
  if (I != IterationsToInvariance.end())
    return I->second;

  // Otherwise we need to analyze the input from the back edge.
  Value *Input = Phi->getIncomingValueForBlock(BackEdge);
  // Place infinity to map to avoid infinite recursion for cycled Phis. Such
  // cycles can never stop on an invariant.
  IterationsToInvariance[Phi] = InfiniteIterationsToInvariance;
  unsigned ToInvariance = InfiniteIterationsToInvariance;

  if (L->isLoopInvariant(Input))
    ToInvariance = 1u;
  else if (PHINode *IncPhi = dyn_cast<PHINode>(Input)) {
    // Only consider Phis in header block.
    if (IncPhi->getParent() != L->getHeader())
      return InfiniteIterationsToInvariance;
    // If the input becomes an invariant after X iterations, then our Phi
    // becomes an invariant after X + 1 iterations.
    unsigned InputToInvariance = calculateIterationsToInvariance(
        IncPhi, L, BackEdge, IterationsToInvariance);
    if (InputToInvariance != InfiniteIterationsToInvariance)
      ToInvariance = InputToInvariance + 1u;
  }

  // If we found that this Phi lies in an invariant chain, update the map.
  if (ToInvariance != InfiniteIterationsToInvariance)
    IterationsToInvariance[Phi] = ToInvariance;
  return ToInvariance;
}

static bool IsEquivalentPHI(PHINode *PHI,
                          SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
  unsigned PHINumValues = PHI->getNumIncomingValues();
  if (PHINumValues != ValueMapping.size())
    return false;

  // Scan the phi to see if it matches.
  for (unsigned i = 0, e = PHINumValues; i != e; ++i)
    if (ValueMapping[PHI->getIncomingBlock(i)] !=
        PHI->getIncomingValue(i)) {
      return false;
    }

  return true;
}

/// Remove dead functions that are not included in DNR (Do Not Remove) list.
bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) {
  SmallVector<CallGraphNode*, 16> FunctionsToRemove;
  SmallVector<CallGraphNode *, 16> DeadFunctionsInComdats;
  SmallDenseMap<const Comdat *, int, 16> ComdatEntriesAlive;

  auto RemoveCGN = [&](CallGraphNode *CGN) {
    // Remove any call graph edges from the function to its callees.
    CGN->removeAllCalledFunctions();

    // Remove any edges from the external node to the function's call graph
    // node.  These edges might have been made irrelegant due to
    // optimization of the program.
    CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);

    // Removing the node for callee from the call graph and delete it.
    FunctionsToRemove.push_back(CGN);
  };

  // Scan for all of the functions, looking for ones that should now be removed
  // from the program.  Insert the dead ones in the FunctionsToRemove set.
  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
    CallGraphNode *CGN = I->second;
    Function *F = CGN->getFunction();
    if (!F || F->isDeclaration())
      continue;

    // Handle the case when this function is called and we only want to care
    // about always-inline functions. This is a bit of a hack to share code
    // between here and the InlineAlways pass.
    if (AlwaysInlineOnly && !F->hasFnAttribute(Attribute::AlwaysInline))
      continue;

    // If the only remaining users of the function are dead constants, remove
    // them.
    F->removeDeadConstantUsers();

    if (!F->isDefTriviallyDead())
      continue;

    // It is unsafe to drop a function with discardable linkage from a COMDAT
    // without also dropping the other members of the COMDAT.
    // The inliner doesn't visit non-function entities which are in COMDAT
    // groups so it is unsafe to do so *unless* the linkage is local.
    if (!F->hasLocalLinkage()) {
      if (const Comdat *C = F->getComdat()) {
        --ComdatEntriesAlive[C];
        DeadFunctionsInComdats.push_back(CGN);
        continue;
      }
    }

    RemoveCGN(CGN);
  }
  if (!DeadFunctionsInComdats.empty()) {
    // Count up all the entities in COMDAT groups
    auto ComdatGroupReferenced = [&](const Comdat *C) {
      auto I = ComdatEntriesAlive.find(C);
      if (I != ComdatEntriesAlive.end())
        ++(I->getSecond());
    };
    for (const Function &F : CG.getModule())
      if (const Comdat *C = F.getComdat())
        ComdatGroupReferenced(C);
    for (const GlobalVariable &GV : CG.getModule().globals())
      if (const Comdat *C = GV.getComdat())
        ComdatGroupReferenced(C);
    for (const GlobalAlias &GA : CG.getModule().aliases())
      if (const Comdat *C = GA.getComdat())
        ComdatGroupReferenced(C);
    for (CallGraphNode *CGN : DeadFunctionsInComdats) {
      Function *F = CGN->getFunction();
      const Comdat *C = F->getComdat();
      int NumAlive = ComdatEntriesAlive[C];
      // We can remove functions in a COMDAT group if the entire group is dead.
      assert(NumAlive >= 0);
      if (NumAlive > 0)
        continue;

      RemoveCGN(CGN);
    }
  }

  if (FunctionsToRemove.empty())
    return false;

  // Now that we know which functions to delete, do so.  We didn't want to do
  // this inline, because that would invalidate our CallGraph::iterator
  // objects. :(
  //
  // Note that it doesn't matter that we are iterating over a non-stable order
  // here to do this, it doesn't matter which order the functions are deleted
  // in.
  array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end());
  FunctionsToRemove.erase(std::unique(FunctionsToRemove.begin(),
                                      FunctionsToRemove.end()),
                          FunctionsToRemove.end());
  for (SmallVectorImpl<CallGraphNode *>::iterator I = FunctionsToRemove.begin(),
                                                  E = FunctionsToRemove.end();
       I != E; ++I) {
//.........这里部分代码省略.........

//.........这里部分代码省略.........
      EmitDiag(" with run-time trip count");
    }
    DEBUG(dbgs() << "!\n");
  }

  bool ContinueOnTrue = L->contains(BI->getSuccessor(0));
  BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue);

  // For the first iteration of the loop, we should use the precloned values for
  // PHI nodes.  Insert associations now.
  ValueToValueMapTy LastValueMap;
  std::vector<PHINode*> OrigPHINode;
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    OrigPHINode.push_back(cast<PHINode>(I));
  }

  std::vector<BasicBlock*> Headers;
  std::vector<BasicBlock*> Latches;
  Headers.push_back(Header);
  Latches.push_back(LatchBlock);

  // The current on-the-fly SSA update requires blocks to be processed in
  // reverse postorder so that LastValueMap contains the correct value at each
  // exit.
  LoopBlocksDFS DFS(L);
  DFS.perform(LI);

  // Stash the DFS iterators before adding blocks to the loop.
  LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
  LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();

  for (unsigned It = 1; It != Count; ++It) {
    std::vector<BasicBlock*> NewBlocks;
    SmallDenseMap<const Loop *, Loop *, 4> NewLoops;
    NewLoops[L] = L;

    for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
      ValueToValueMapTy VMap;
      BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
      Header->getParent()->getBasicBlockList().push_back(New);

      // Tell LI about New.
      if (*BB == Header) {
        assert(LI->getLoopFor(*BB) == L && "Header should not be in a sub-loop");
        L->addBasicBlockToLoop(New, *LI);
      } else {
        // Figure out which loop New is in.
        const Loop *OldLoop = LI->getLoopFor(*BB);
        assert(OldLoop && "Should (at least) be in the loop being unrolled!");

        Loop *&NewLoop = NewLoops[OldLoop];
        if (!NewLoop) {
          // Found a new sub-loop.
          assert(*BB == OldLoop->getHeader() &&
                 "Header should be first in RPO");

          Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop());
          assert(NewLoopParent &&
                 "Expected parent loop before sub-loop in RPO");
          NewLoop = new Loop;
          NewLoopParent->addChildLoop(NewLoop);

          // Forget the old loop, since its inputs may have changed.
          if (SE)
            SE->forgetLoop(OldLoop);
        }

// Sinks \p I from the loop \p L's preheader to its uses. Returns true if
// sinking is successful.
// \p LoopBlockNumber is used to sort the insertion blocks to ensure
// determinism.
static bool sinkInstruction(Loop &L, Instruction &I,
                            const SmallVectorImpl<BasicBlock *> &ColdLoopBBs,
                            const SmallDenseMap<BasicBlock *, int, 16> &LoopBlockNumber,
                            LoopInfo &LI, DominatorTree &DT,
                            BlockFrequencyInfo &BFI) {
  // Compute the set of blocks in loop L which contain a use of I.
  SmallPtrSet<BasicBlock *, 2> BBs;
  for (auto &U : I.uses()) {
    Instruction *UI = cast<Instruction>(U.getUser());
    // We cannot sink I to PHI-uses.
    if (dyn_cast<PHINode>(UI))
      return false;
    // We cannot sink I if it has uses outside of the loop.
    if (!L.contains(LI.getLoopFor(UI->getParent())))
      return false;
    BBs.insert(UI->getParent());
  }

  // findBBsToSinkInto is O(BBs.size() * ColdLoopBBs.size()). We cap the max
  // BBs.size() to avoid expensive computation.
  // FIXME: Handle code size growth for min_size and opt_size.
  if (BBs.size() > MaxNumberOfUseBBsForSinking)
    return false;

  // Find the set of BBs that we should insert a copy of I.
  SmallPtrSet<BasicBlock *, 2> BBsToSinkInto =
      findBBsToSinkInto(L, BBs, ColdLoopBBs, DT, BFI);
  if (BBsToSinkInto.empty())
    return false;

  // Copy the final BBs into a vector and sort them using the total ordering
  // of the loop block numbers as iterating the set doesn't give a useful
  // order. No need to stable sort as the block numbers are a total ordering.
  SmallVector<BasicBlock *, 2> SortedBBsToSinkInto;
  SortedBBsToSinkInto.insert(SortedBBsToSinkInto.begin(), BBsToSinkInto.begin(),
                             BBsToSinkInto.end());
  std::sort(SortedBBsToSinkInto.begin(), SortedBBsToSinkInto.end(),
            [&](BasicBlock *A, BasicBlock *B) {
              return *LoopBlockNumber.find(A) < *LoopBlockNumber.find(B);
            });

  BasicBlock *MoveBB = *SortedBBsToSinkInto.begin();
  // FIXME: Optimize the efficiency for cloned value replacement. The current
  //        implementation is O(SortedBBsToSinkInto.size() * I.num_uses()).
  for (BasicBlock *N : SortedBBsToSinkInto) {
    if (N == MoveBB)
      continue;
    // Clone I and replace its uses.
    Instruction *IC = I.clone();
    IC->setName(I.getName());
    IC->insertBefore(&*N->getFirstInsertionPt());
    // Replaces uses of I with IC in N
    for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE;) {
      Use &U = *UI++;
      auto *I = cast<Instruction>(U.getUser());
      if (I->getParent() == N)
        U.set(IC);
    }
    // Replaces uses of I with IC in blocks dominated by N
    replaceDominatedUsesWith(&I, IC, DT, N);
    DEBUG(dbgs() << "Sinking a clone of " << I << " To: " << N->getName()
                 << '\n');
    NumLoopSunkCloned++;
  }
  DEBUG(dbgs() << "Sinking " << I << " To: " << MoveBB->getName() << '\n');
  NumLoopSunk++;
  I.moveBefore(&*MoveBB->getFirstInsertionPt());

  return true;
}

/// For every instruction from the worklist, check to see if it has any uses
/// that are outside the current loop.  If so, insert LCSSA PHI nodes and
/// rewrite the uses.
bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
                                    DominatorTree &DT, LoopInfo &LI) {
    SmallVector<Use *, 16> UsesToRewrite;
    SmallSetVector<PHINode *, 16> PHIsToRemove;
    PredIteratorCache PredCache;
    bool Changed = false;

    // Cache the Loop ExitBlocks across this loop.  We expect to get a lot of
    // instructions within the same loops, computing the exit blocks is
    // expensive, and we're not mutating the loop structure.
    SmallDenseMap<Loop*, SmallVector<BasicBlock *,1>> LoopExitBlocks;

    while (!Worklist.empty()) {
        UsesToRewrite.clear();

        Instruction *I = Worklist.pop_back_val();
        BasicBlock *InstBB = I->getParent();
        Loop *L = LI.getLoopFor(InstBB);
        if (!LoopExitBlocks.count(L))
            L->getExitBlocks(LoopExitBlocks[L]);
        assert(LoopExitBlocks.count(L));
        const SmallVectorImpl<BasicBlock *> &ExitBlocks = LoopExitBlocks[L];

        if (ExitBlocks.empty())
            continue;

        // Tokens cannot be used in PHI nodes, so we skip over them.
        // We can run into tokens which are live out of a loop with catchswitch
        // instructions in Windows EH if the catchswitch has one catchpad which
        // is inside the loop and another which is not.
        if (I->getType()->isTokenTy())
            continue;

        for (Use &U : I->uses()) {
            Instruction *User = cast<Instruction>(U.getUser());
            BasicBlock *UserBB = User->getParent();
            if (PHINode *PN = dyn_cast<PHINode>(User))
                UserBB = PN->getIncomingBlock(U);

            if (InstBB != UserBB && !L->contains(UserBB))
                UsesToRewrite.push_back(&U);
        }

        // If there are no uses outside the loop, exit with no change.
        if (UsesToRewrite.empty())
            continue;

        ++NumLCSSA; // We are applying the transformation

        // Invoke instructions are special in that their result value is not
        // available along their unwind edge. The code below tests to see whether
        // DomBB dominates the value, so adjust DomBB to the normal destination
        // block, which is effectively where the value is first usable.
        BasicBlock *DomBB = InstBB;
        if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
            DomBB = Inv->getNormalDest();

        DomTreeNode *DomNode = DT.getNode(DomBB);

        SmallVector<PHINode *, 16> AddedPHIs;
        SmallVector<PHINode *, 8> PostProcessPHIs;

        SmallVector<PHINode *, 4> InsertedPHIs;
        SSAUpdater SSAUpdate(&InsertedPHIs);
        SSAUpdate.Initialize(I->getType(), I->getName());

        // Insert the LCSSA phi's into all of the exit blocks dominated by the
        // value, and add them to the Phi's map.
        for (BasicBlock *ExitBB : ExitBlocks) {
            if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
                continue;

            // If we already inserted something for this BB, don't reprocess it.
            if (SSAUpdate.HasValueForBlock(ExitBB))
                continue;

            PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
                                          I->getName() + ".lcssa", &ExitBB->front());

            // Add inputs from inside the loop for this PHI.
            for (BasicBlock *Pred : PredCache.get(ExitBB)) {
                PN->addIncoming(I, Pred);

                // If the exit block has a predecessor not within the loop, arrange for
                // the incoming value use corresponding to that predecessor to be
                // rewritten in terms of a different LCSSA PHI.
                if (!L->contains(Pred))
                    UsesToRewrite.push_back(
                        &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                                               PN->getNumIncomingValues() - 1)));
            }

            AddedPHIs.push_back(PN);

            // Remember that this phi makes the value alive in this block.
            SSAUpdate.AddAvailableValue(ExitBB, PN);

//.........这里部分代码省略.........

// Create output section objects and add them to OutputSections.
template <class ELFT> void Writer<ELFT>::createSections() {
  // .interp needs to be on the first page in the output file.
  if (needsInterpSection())
    OutputSections.push_back(Out<ELFT>::Interp);

  SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSectionBase<ELFT> *> Map;

  std::vector<OutputSectionBase<ELFT> *> RegularSections;

  for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
    for (InputSectionBase<ELFT> *C : F->getSections()) {
      if (isDiscarded(C))
        continue;
      const Elf_Shdr *H = C->getSectionHdr();
      uintX_t OutFlags = H->sh_flags & ~SHF_GROUP;
      // For SHF_MERGE we create different output sections for each sh_entsize.
      // This makes each output section simple and keeps a single level
      // mapping from input to output.
      typename InputSectionBase<ELFT>::Kind K = C->SectionKind;
      uintX_t EntSize = K != InputSectionBase<ELFT>::Merge ? 0 : H->sh_entsize;
      uint32_t OutType = H->sh_type;
      if (OutType == SHT_PROGBITS && C->getSectionName() == ".eh_frame" &&
          Config->EMachine == EM_X86_64)
        OutType = SHT_X86_64_UNWIND;
      SectionKey<ELFT::Is64Bits> Key{getOutputSectionName(C->getSectionName()),
                                     OutType, OutFlags, EntSize};
      OutputSectionBase<ELFT> *&Sec = Map[Key];
      if (!Sec) {
        switch (K) {
        case InputSectionBase<ELFT>::Regular:
          Sec = new (SecAlloc.Allocate())
              OutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
          break;
        case InputSectionBase<ELFT>::EHFrame:
          Sec = new (EHSecAlloc.Allocate())
              EHOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
          break;
        case InputSectionBase<ELFT>::Merge:
          Sec = new (MSecAlloc.Allocate())
              MergeOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
          break;
        }
        OutputSections.push_back(Sec);
        RegularSections.push_back(Sec);
      }
      switch (K) {
      case InputSectionBase<ELFT>::Regular:
        static_cast<OutputSection<ELFT> *>(Sec)
            ->addSection(cast<InputSection<ELFT>>(C));
        break;
      case InputSectionBase<ELFT>::EHFrame:
        static_cast<EHOutputSection<ELFT> *>(Sec)
            ->addSection(cast<EHInputSection<ELFT>>(C));
        break;
      case InputSectionBase<ELFT>::Merge:
        static_cast<MergeOutputSection<ELFT> *>(Sec)
            ->addSection(cast<MergeInputSection<ELFT>>(C));
        break;
      }
    }
  }

  Out<ELFT>::Bss = static_cast<OutputSection<ELFT> *>(
      Map[{".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE, 0}]);

  Out<ELFT>::Dynamic->PreInitArraySec = Map.lookup(
      {".preinit_array", SHT_PREINIT_ARRAY, SHF_WRITE | SHF_ALLOC, 0});
  Out<ELFT>::Dynamic->InitArraySec =
      Map.lookup({".init_array", SHT_INIT_ARRAY, SHF_WRITE | SHF_ALLOC, 0});
  Out<ELFT>::Dynamic->FiniArraySec =
      Map.lookup({".fini_array", SHT_FINI_ARRAY, SHF_WRITE | SHF_ALLOC, 0});

  auto AddStartEnd = [&](StringRef Start, StringRef End,
                         OutputSectionBase<ELFT> *OS) {
    if (OS) {
      Symtab.addSyntheticSym(Start, *OS, 0);
      Symtab.addSyntheticSym(End, *OS, OS->getSize());
    } else {
      Symtab.addIgnoredSym(Start);
      Symtab.addIgnoredSym(End);
    }
  };

  AddStartEnd("__preinit_array_start", "__preinit_array_end",
              Out<ELFT>::Dynamic->PreInitArraySec);
  AddStartEnd("__init_array_start", "__init_array_end",
              Out<ELFT>::Dynamic->InitArraySec);
  AddStartEnd("__fini_array_start", "__fini_array_end",
              Out<ELFT>::Dynamic->FiniArraySec);

  for (OutputSectionBase<ELFT> *Sec : RegularSections)
    addStartStopSymbols(Sec);

  // __tls_get_addr is defined by the dynamic linker for dynamic ELFs. For
  // static linking the linker is required to optimize away any references to
  // __tls_get_addr, so it's not defined anywhere. Create a hidden definition
  // to avoid the undefined symbol error.
  if (!isOutputDynamic())
    Symtab.addIgnoredSym("__tls_get_addr");
//.........这里部分代码省略.........