C++ SmallPtrSet::empty方法代码示例

void LTOCodeGenerator::applyScopeRestrictions() {
  if (ScopeRestrictionsDone)
    return;
  Module *mergedModule = Linker.getModule();

  // Start off with a verification pass.
  PassManager passes;
  passes.add(createVerifierPass());

  // mark which symbols can not be internalized
  Mangler Mangler(TargetMach);
  std::vector<const char*> MustPreserveList;
  SmallPtrSet<GlobalValue*, 8> AsmUsed;
  std::vector<StringRef> Libcalls;
  TargetLibraryInfo TLI(Triple(TargetMach->getTargetTriple()));
  accumulateAndSortLibcalls(Libcalls, TLI, TargetMach->getTargetLowering());

  for (Module::iterator f = mergedModule->begin(),
         e = mergedModule->end(); f != e; ++f)
    applyRestriction(*f, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (Module::global_iterator v = mergedModule->global_begin(),
         e = mergedModule->global_end(); v !=  e; ++v)
    applyRestriction(*v, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (Module::alias_iterator a = mergedModule->alias_begin(),
         e = mergedModule->alias_end(); a != e; ++a)
    applyRestriction(*a, Libcalls, MustPreserveList, AsmUsed, Mangler);

  GlobalVariable *LLVMCompilerUsed =
    mergedModule->getGlobalVariable("llvm.compiler.used");
  findUsedValues(LLVMCompilerUsed, AsmUsed);
  if (LLVMCompilerUsed)
    LLVMCompilerUsed->eraseFromParent();

  if (!AsmUsed.empty()) {
    llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
    std::vector<Constant*> asmUsed2;
    for (SmallPtrSet<GlobalValue*, 16>::const_iterator i = AsmUsed.begin(),
           e = AsmUsed.end(); i !=e; ++i) {
      GlobalValue *GV = *i;
      Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
      asmUsed2.push_back(c);
    }

    llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
    LLVMCompilerUsed =
      new llvm::GlobalVariable(*mergedModule, ATy, false,
                               llvm::GlobalValue::AppendingLinkage,
                               llvm::ConstantArray::get(ATy, asmUsed2),
                               "llvm.compiler.used");

    LLVMCompilerUsed->setSection("llvm.metadata");
  }

  passes.add(createInternalizePass(MustPreserveList));

  // apply scope restrictions
  passes.run(*mergedModule);

  ScopeRestrictionsDone = true;
}

/// isLiveInButUnusedBefore - Return true if register is livein the MBB not
/// not used before it reaches the MI that defines register.
static bool isLiveInButUnusedBefore(unsigned Reg, MachineInstr *MI,
                                    MachineBasicBlock *MBB,
                                    const TargetRegisterInfo *TRI,
                                    MachineRegisterInfo* MRI) {
  // First check if register is livein.
  bool isLiveIn = false;
  for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(),
         E = MBB->livein_end(); I != E; ++I)
    if (Reg == *I || TRI->isSuperRegister(Reg, *I)) {
      isLiveIn = true;
      break;
    }
  if (!isLiveIn)
    return false;

  // Is there any use of it before the specified MI?
  SmallPtrSet<MachineInstr*, 4> UsesInMBB;
  for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg),
         UE = MRI->use_end(); UI != UE; ++UI) {
    MachineOperand &UseMO = UI.getOperand();
    if (UseMO.isReg() && UseMO.isUndef())
      continue;
    MachineInstr *UseMI = &*UI;
    if (UseMI->getParent() == MBB)
      UsesInMBB.insert(UseMI);
  }
  if (UsesInMBB.empty())
    return true;

  for (MachineBasicBlock::iterator I = MBB->begin(), E = MI; I != E; ++I)
    if (UsesInMBB.count(&*I))
      return false;
  return true;
}

// Calculate the set of virtual registers that must be passed through each basic
// block in order to satisfy the requirements of successor blocks. This is very
// similar to calcRegsPassed, only backwards.
void MachineVerifier::calcRegsRequired() {
  // First push live-in regs to predecessors' vregsRequired.
  SmallPtrSet<const MachineBasicBlock*, 8> todo;
  for (MachineFunction::const_iterator MFI = MF->begin(), MFE = MF->end();
       MFI != MFE; ++MFI) {
    const MachineBasicBlock &MBB(*MFI);
    BBInfo &MInfo = MBBInfoMap[&MBB];
    for (MachineBasicBlock::const_pred_iterator PrI = MBB.pred_begin(),
           PrE = MBB.pred_end(); PrI != PrE; ++PrI) {
      BBInfo &PInfo = MBBInfoMap[*PrI];
      if (PInfo.addRequired(MInfo.vregsLiveIn))
        todo.insert(*PrI);
    }
  }

  // Iteratively push vregsRequired to predecessors. This will converge to the
  // same final state regardless of DenseSet iteration order.
  while (!todo.empty()) {
    const MachineBasicBlock *MBB = *todo.begin();
    todo.erase(MBB);
    BBInfo &MInfo = MBBInfoMap[MBB];
    for (MachineBasicBlock::const_pred_iterator PrI = MBB->pred_begin(),
           PrE = MBB->pred_end(); PrI != PrE; ++PrI) {
      if (*PrI == MBB)
        continue;
      BBInfo &SInfo = MBBInfoMap[*PrI];
      if (SInfo.addRequired(MInfo.vregsRequired))
        todo.insert(*PrI);
    }
  }
}

/// \brief Find an insertion point that dominates all uses.
Instruction *ConstantHoisting::
findConstantInsertionPoint(const ConstantInfo &ConstInfo) const {
  assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
  // Collect all IDoms.
  SmallPtrSet<BasicBlock *, 8> BBs;
  for (auto const &RCI : ConstInfo.RebasedConstants)
    BBs.insert(getIDom(RCI));

  assert(!BBs.empty() && "No dominators!?");

  if (BBs.count(Entry))
    return &Entry->front();

  while (BBs.size() >= 2) {
    BasicBlock *BB, *BB1, *BB2;
    BB1 = *BBs.begin();
    BB2 = *std::next(BBs.begin());
    BB = DT->findNearestCommonDominator(BB1, BB2);
    if (BB == Entry)
      return &Entry->front();
    BBs.erase(BB1);
    BBs.erase(BB2);
    BBs.insert(BB);
  }
  assert((BBs.size() == 1) && "Expected only one element.");
  Instruction &FirstInst = (*BBs.begin())->front();
  return findMatInsertPt(&FirstInst);
}

// Calculate the largest possible vregsPassed sets. These are the registers that
// can pass through an MBB live, but may not be live every time. It is assumed
// that all vregsPassed sets are empty before the call.
void MachineVerifier::calcRegsPassed() {
  // First push live-out regs to successors' vregsPassed. Remember the MBBs that
  // have any vregsPassed.
  SmallPtrSet<const MachineBasicBlock*, 8> todo;
  for (MachineFunction::const_iterator MFI = MF->begin(), MFE = MF->end();
       MFI != MFE; ++MFI) {
    const MachineBasicBlock &MBB(*MFI);
    BBInfo &MInfo = MBBInfoMap[&MBB];
    if (!MInfo.reachable)
      continue;
    for (MachineBasicBlock::const_succ_iterator SuI = MBB.succ_begin(),
           SuE = MBB.succ_end(); SuI != SuE; ++SuI) {
      BBInfo &SInfo = MBBInfoMap[*SuI];
      if (SInfo.addPassed(MInfo.regsLiveOut))
        todo.insert(*SuI);
    }
  }

  // Iteratively push vregsPassed to successors. This will converge to the same
  // final state regardless of DenseSet iteration order.
  while (!todo.empty()) {
    const MachineBasicBlock *MBB = *todo.begin();
    todo.erase(MBB);
    BBInfo &MInfo = MBBInfoMap[MBB];
    for (MachineBasicBlock::const_succ_iterator SuI = MBB->succ_begin(),
           SuE = MBB->succ_end(); SuI != SuE; ++SuI) {
      if (*SuI == MBB)
        continue;
      BBInfo &SInfo = MBBInfoMap[*SuI];
      if (SInfo.addPassed(MInfo.vregsPassed))
        todo.insert(*SuI);
    }
  }
}

/// \brief Calculate edge weights for successors lead to unreachable.
///
/// Predict that a successor which leads necessarily to an
/// unreachable-terminated block as extremely unlikely.
bool BranchProbabilityInfo::calcUnreachableHeuristics(BasicBlock *BB) {
  TerminatorInst *TI = BB->getTerminator();
  if (TI->getNumSuccessors() == 0) {
    if (isa<UnreachableInst>(TI))
      PostDominatedByUnreachable.insert(BB);
    return false;
  }

  SmallPtrSet<BasicBlock *, 4> UnreachableEdges;
  SmallPtrSet<BasicBlock *, 4> ReachableEdges;

  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    if (PostDominatedByUnreachable.count(*I))
      UnreachableEdges.insert(*I);
    else
      ReachableEdges.insert(*I);
  }

  // If all successors are in the set of blocks post-dominated by unreachable,
  // this block is too.
  if (UnreachableEdges.size() == TI->getNumSuccessors())
    PostDominatedByUnreachable.insert(BB);

  // Skip probabilities if this block has a single successor or if all were
  // reachable.
  if (TI->getNumSuccessors() == 1 || UnreachableEdges.empty())
    return false;

  uint32_t UnreachableWeight =
    std::max(UR_TAKEN_WEIGHT / UnreachableEdges.size(), MIN_WEIGHT);
  for (SmallPtrSet<BasicBlock *, 4>::iterator I = UnreachableEdges.begin(),
                                              E = UnreachableEdges.end();
       I != E; ++I)
    setEdgeWeight(BB, *I, UnreachableWeight);

  if (ReachableEdges.empty())
    return true;
  uint32_t ReachableWeight =
    std::max(UR_NONTAKEN_WEIGHT / ReachableEdges.size(), NORMAL_WEIGHT);
  for (SmallPtrSet<BasicBlock *, 4>::iterator I = ReachableEdges.begin(),
                                              E = ReachableEdges.end();
       I != E; ++I)
    setEdgeWeight(BB, *I, ReachableWeight);

  return true;
}

void LTOCodeGenerator::applyScopeRestrictions() {
    if (_scopeRestrictionsDone) return;
    Module *mergedModule = _linker.getModule();

    // Start off with a verification pass.
    PassManager passes;
    passes.add(createVerifierPass());

    // mark which symbols can not be internalized
    MCContext Context(*_target->getMCAsmInfo(), *_target->getRegisterInfo(),NULL);
    Mangler mangler(Context, _target);
    std::vector<const char*> mustPreserveList;
    SmallPtrSet<GlobalValue*, 8> asmUsed;

    for (Module::iterator f = mergedModule->begin(),
            e = mergedModule->end(); f != e; ++f)
        applyRestriction(*f, mustPreserveList, asmUsed, mangler);
    for (Module::global_iterator v = mergedModule->global_begin(),
            e = mergedModule->global_end(); v !=  e; ++v)
        applyRestriction(*v, mustPreserveList, asmUsed, mangler);
    for (Module::alias_iterator a = mergedModule->alias_begin(),
            e = mergedModule->alias_end(); a != e; ++a)
        applyRestriction(*a, mustPreserveList, asmUsed, mangler);

    GlobalVariable *LLVMCompilerUsed =
        mergedModule->getGlobalVariable("llvm.compiler.used");
    findUsedValues(LLVMCompilerUsed, asmUsed);
    if (LLVMCompilerUsed)
        LLVMCompilerUsed->eraseFromParent();

    if (!asmUsed.empty()) {
        llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(_context);
        std::vector<Constant*> asmUsed2;
        for (SmallPtrSet<GlobalValue*, 16>::const_iterator i = asmUsed.begin(),
                e = asmUsed.end(); i !=e; ++i) {
            GlobalValue *GV = *i;
            Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
            asmUsed2.push_back(c);
        }

        llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
        LLVMCompilerUsed =
            new llvm::GlobalVariable(*mergedModule, ATy, false,
                                     llvm::GlobalValue::AppendingLinkage,
                                     llvm::ConstantArray::get(ATy, asmUsed2),
                                     "llvm.compiler.used");

        LLVMCompilerUsed->setSection("llvm.metadata");
    }

    passes.add(createInternalizePass(mustPreserveList));

    // apply scope restrictions
    passes.run(*mergedModule);

    _scopeRestrictionsDone = true;
}

void LTOCodeGenerator::applyScopeRestrictions() {
  if (ScopeRestrictionsDone || !ShouldInternalize)
    return;

  // Start off with a verification pass.
  legacy::PassManager passes;
  passes.add(createVerifierPass());

  // mark which symbols can not be internalized
  Mangler Mangler;
  std::vector<const char*> MustPreserveList;
  SmallPtrSet<GlobalValue*, 8> AsmUsed;
  std::vector<StringRef> Libcalls;
  TargetLibraryInfoImpl TLII(Triple(TargetMach->getTargetTriple()));
  TargetLibraryInfo TLI(TLII);

  accumulateAndSortLibcalls(Libcalls, TLI, *MergedModule, *TargetMach);

  for (Function &f : *MergedModule)
    applyRestriction(f, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (GlobalVariable &v : MergedModule->globals())
    applyRestriction(v, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (GlobalAlias &a : MergedModule->aliases())
    applyRestriction(a, Libcalls, MustPreserveList, AsmUsed, Mangler);

  GlobalVariable *LLVMCompilerUsed =
    MergedModule->getGlobalVariable("llvm.compiler.used");
  findUsedValues(LLVMCompilerUsed, AsmUsed);
  if (LLVMCompilerUsed)
    LLVMCompilerUsed->eraseFromParent();

  if (!AsmUsed.empty()) {
    llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
    std::vector<Constant*> asmUsed2;
    for (auto *GV : AsmUsed) {
      Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
      asmUsed2.push_back(c);
    }

    llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
    LLVMCompilerUsed =
      new llvm::GlobalVariable(*MergedModule, ATy, false,
                               llvm::GlobalValue::AppendingLinkage,
                               llvm::ConstantArray::get(ATy, asmUsed2),
                               "llvm.compiler.used");

    LLVMCompilerUsed->setSection("llvm.metadata");
  }

  passes.add(createInternalizePass(MustPreserveList));

  // apply scope restrictions
  passes.run(*MergedModule);

  ScopeRestrictionsDone = true;
}

// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
// when following the CFG edge to SuccMBB. This needs to be after any def of
// SrcReg, but before any subsequent point where control flow might jump out of
// the basic block.
MachineBasicBlock::iterator
llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
                                          MachineBasicBlock &SuccMBB,
                                          unsigned SrcReg) {
  // Handle the trivial case trivially.
  if (MBB.empty())
    return MBB.begin();

  // Usually, we just want to insert the copy before the first terminator
  // instruction. However, for the edge going to a landing pad, we must insert
  // the copy before the call/invoke instruction.
  if (!SuccMBB.isLandingPad())
    return MBB.getFirstTerminator();

  // Discover any defs/uses in this basic block.
  SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
  for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
         RE = MRI->reg_end(); RI != RE; ++RI) {
    MachineInstr *DefUseMI = &*RI;
    if (DefUseMI->getParent() == &MBB)
      DefUsesInMBB.insert(DefUseMI);
  }

  MachineBasicBlock::iterator InsertPoint;
  if (DefUsesInMBB.empty()) {
    // No defs.  Insert the copy at the start of the basic block.
    InsertPoint = MBB.begin();
  } else if (DefUsesInMBB.size() == 1) {
    // Insert the copy immediately after the def/use.
    InsertPoint = *DefUsesInMBB.begin();
    ++InsertPoint;
  } else {
    // Insert the copy immediately after the last def/use.
    InsertPoint = MBB.end();
    while (!DefUsesInMBB.count(&*--InsertPoint)) {}
    ++InsertPoint;
  }

  // Make sure the copy goes after any phi nodes however.
  return SkipPHIsAndLabels(MBB, InsertPoint);
}

/// This methods creates the SSI representation for the list of values
/// received. It will only create SSI representation if a value is used
/// to decide a branch. Repeated values are created only once.
///
void SSI::createSSI(SmallVectorImpl<Instruction *> &value) {
  init(value);

  SmallPtrSet<Instruction*, 4> needConstruction;
  for (SmallVectorImpl<Instruction*>::iterator I = value.begin(),
       E = value.end(); I != E; ++I)
    if (created.insert(*I))
      needConstruction.insert(*I);

  insertSigmaFunctions(needConstruction);

  // Test if there is a need to transform to SSI
  if (!needConstruction.empty()) {
    insertPhiFunctions(needConstruction);
    renameInit(needConstruction);
    rename(DT_->getRoot());
    fixPhis();
  }

  clean();
}

// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg.
// This needs to be after any def or uses of SrcReg, but before any subsequent
// point where control flow might jump out of the basic block.
MachineBasicBlock::iterator
llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
                                          unsigned SrcReg) {
  // Handle the trivial case trivially.
  if (MBB.empty())
    return MBB.begin();

  // If this basic block does not contain an invoke, then control flow always
  // reaches the end of it, so place the copy there.  The logic below works in
  // this case too, but is more expensive.
  if (!isa<InvokeInst>(MBB.getBasicBlock()->getTerminator()))
    return MBB.getFirstTerminator();

  // Discover any definition/uses in this basic block.
  SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
  for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
       RE = MRI->reg_end(); RI != RE; ++RI) {
    MachineInstr *DefUseMI = &*RI;
    if (DefUseMI->getParent() == &MBB)
      DefUsesInMBB.insert(DefUseMI);
  }

  MachineBasicBlock::iterator InsertPoint;
  if (DefUsesInMBB.empty()) {
    // No def/uses.  Insert the copy at the start of the basic block.
    InsertPoint = MBB.begin();
  } else if (DefUsesInMBB.size() == 1) {
    // Insert the copy immediately after the definition/use.
    InsertPoint = *DefUsesInMBB.begin();
    ++InsertPoint;
  } else {
    // Insert the copy immediately after the last definition/use.
    InsertPoint = MBB.end();
    while (!DefUsesInMBB.count(&*--InsertPoint)) {}
    ++InsertPoint;
  }

  // Make sure the copy goes after any phi nodes however.
  return SkipPHIsAndLabels(MBB, InsertPoint);
}

// findCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
// when following the CFG edge to SuccMBB. This needs to be after any def of
// SrcReg, but before any subsequent point where control flow might jump out of
// the basic block.
MachineBasicBlock::iterator
llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB,
                             unsigned SrcReg) {
    // Handle the trivial case trivially.
    if (MBB->empty())
        return MBB->begin();

    // Usually, we just want to insert the copy before the first terminator
    // instruction. However, for the edge going to a landing pad, we must insert
    // the copy before the call/invoke instruction.
    if (!SuccMBB->isLandingPad())
        return MBB->getFirstTerminator();

    // Discover any defs/uses in this basic block.
    SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
    MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
    for (MachineInstr &RI : MRI.reg_instructions(SrcReg)) {
        if (RI.getParent() == MBB)
            DefUsesInMBB.insert(&RI);
    }

    MachineBasicBlock::iterator InsertPoint;
    if (DefUsesInMBB.empty()) {
        // No defs.  Insert the copy at the start of the basic block.
        InsertPoint = MBB->begin();
    } else if (DefUsesInMBB.size() == 1) {
        // Insert the copy immediately after the def/use.
        InsertPoint = *DefUsesInMBB.begin();
        ++InsertPoint;
    } else {
        // Insert the copy immediately after the last def/use.
        InsertPoint = MBB->end();
        while (!DefUsesInMBB.count(&*--InsertPoint)) {}
        ++InsertPoint;
    }

    // Make sure the copy goes after any phi nodes however.
    return MBB->SkipPHIsAndLabels(InsertPoint);
}

bool ScopedNoAliasAAResult::mayAliasInScopes(const MDNode *Scopes,
                                             const MDNode *NoAlias) const {
  if (!Scopes || !NoAlias)
    return true;

  // Collect the set of scope domains relevant to the noalias scopes.
  SmallPtrSet<const MDNode *, 16> Domains;
  for (const MDOperand &MDOp : NoAlias->operands())
    if (const MDNode *NAMD = dyn_cast<MDNode>(MDOp))
      if (const MDNode *Domain = AliasScopeNode(NAMD).getDomain())
        Domains.insert(Domain);

  // We alias unless, for some domain, the set of noalias scopes in that domain
  // is a superset of the set of alias scopes in that domain.
  for (const MDNode *Domain : Domains) {
    SmallPtrSet<const MDNode *, 16> ScopeNodes;
    collectMDInDomain(Scopes, Domain, ScopeNodes);
    if (ScopeNodes.empty())
      continue;

    SmallPtrSet<const MDNode *, 16> NANodes;
    collectMDInDomain(NoAlias, Domain, NANodes);

    // To not alias, all of the nodes in ScopeNodes must be in NANodes.
    bool FoundAll = true;
    for (const MDNode *SMD : ScopeNodes)
      if (!NANodes.count(SMD)) {
        FoundAll = false;
        break;
      }

    if (FoundAll)
      return false;
  }

  return true;
}

void VirtRegRewriter::rewrite() {
  SmallVector<unsigned, 8> SuperDeads;
  SmallVector<unsigned, 8> SuperDefs;
  SmallVector<unsigned, 8> SuperKills;
  SmallPtrSet<const MachineInstr *, 4> NoReturnInsts;

  // Here we have a SparseSet to hold which PhysRegs are actually encountered
  // in the MF we are about to iterate over so that later when we call
  // setPhysRegUsed, we are only doing it for physRegs that were actually found
  // in the program and not for all of the possible physRegs for the given
  // target architecture. If the target has a lot of physRegs, then for a small
  // program there will be a significant compile time reduction here.
  PhysRegs.clear();
  PhysRegs.setUniverse(TRI->getNumRegs());

  // The function with uwtable should guarantee that the stack unwinder
  // can unwind the stack to the previous frame.  Thus, we can't apply the
  // noreturn optimization if the caller function has uwtable attribute.
  bool HasUWTable = MF->getFunction()->hasFnAttribute(Attribute::UWTable);

  for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
       MBBI != MBBE; ++MBBI) {
    DEBUG(MBBI->print(dbgs(), Indexes));
    bool IsExitBB = MBBI->succ_empty();
    for (MachineBasicBlock::instr_iterator
           MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
      MachineInstr *MI = MII;
      ++MII;

      // Check if this instruction is a call to a noreturn function.  If this
      // is a call to noreturn function and we don't need the stack unwinding
      // functionality (i.e. this function does not have uwtable attribute and
      // the callee function has the nounwind attribute), then we can ignore
      // the definitions set by this instruction.
      if (!HasUWTable && IsExitBB && MI->isCall()) {
        for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
               MOE = MI->operands_end(); MOI != MOE; ++MOI) {
          MachineOperand &MO = *MOI;
          if (!MO.isGlobal())
            continue;
          const Function *Func = dyn_cast<Function>(MO.getGlobal());
          if (!Func || !Func->hasFnAttribute(Attribute::NoReturn) ||
              // We need to keep correct unwind information
              // even if the function will not return, since the
              // runtime may need it.
              !Func->hasFnAttribute(Attribute::NoUnwind))
            continue;
          NoReturnInsts.insert(MI);
          break;
        }
      }

      for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
           MOE = MI->operands_end(); MOI != MOE; ++MOI) {
        MachineOperand &MO = *MOI;

        // Make sure MRI knows about registers clobbered by regmasks.
        if (MO.isRegMask())
          MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());

        // If we encounter a VirtReg or PhysReg then get at the PhysReg and add
        // it to the physreg bitset.  Later we use only the PhysRegs that were
        // actually encountered in the MF to populate the MRI's used physregs.
        if (MO.isReg() && MO.getReg())
          PhysRegs.insert(
              TargetRegisterInfo::isVirtualRegister(MO.getReg()) ?
              VRM->getPhys(MO.getReg()) :
              MO.getReg());

        if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
          continue;
        unsigned VirtReg = MO.getReg();
        unsigned PhysReg = VRM->getPhys(VirtReg);
        assert(PhysReg != VirtRegMap::NO_PHYS_REG &&
               "Instruction uses unmapped VirtReg");
        assert(!MRI->isReserved(PhysReg) && "Reserved register assignment");

        // Preserve semantics of sub-register operands.
        if (MO.getSubReg()) {
          // A virtual register kill refers to the whole register, so we may
          // have to add <imp-use,kill> operands for the super-register.  A
          // partial redef always kills and redefines the super-register.
          if (MO.readsReg() && (MO.isDef() || MO.isKill()))
            SuperKills.push_back(PhysReg);

          if (MO.isDef()) {
            // The <def,undef> flag only makes sense for sub-register defs, and
            // we are substituting a full physreg.  An <imp-use,kill> operand
            // from the SuperKills list will represent the partial read of the
            // super-register.
            MO.setIsUndef(false);

            // Also add implicit defs for the super-register.
            if (MO.isDead())
              SuperDeads.push_back(PhysReg);
            else
              SuperDefs.push_back(PhysReg);
          }

          // PhysReg operands cannot have subregister indexes.
//.........这里部分代码省略.........

/// PromoteArguments - This method checks the specified function to see if there
/// are any promotable arguments and if it is safe to promote the function (for
/// example, all callers are direct).  If safe to promote some arguments, it
/// calls the DoPromotion method.
///
CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
  Function *F = CGN->getFunction();

  // Make sure that it is local to this module.
  if (!F || !F->hasLocalLinkage()) return nullptr;

  // First check: see if there are any pointer arguments!  If not, quick exit.
  SmallVector<Argument*, 16> PointerArgs;
  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
    if (I->getType()->isPointerTy())
      PointerArgs.push_back(I);
  if (PointerArgs.empty()) return nullptr;

  // Second check: make sure that all callers are direct callers.  We can't
  // transform functions that have indirect callers.  Also see if the function
  // is self-recursive.
  bool isSelfRecursive = false;
  for (Use &U : F->uses()) {
    CallSite CS(U.getUser());
    // Must be a direct call.
    if (CS.getInstruction() == nullptr || !CS.isCallee(&U)) return nullptr;
    
    if (CS.getInstruction()->getParent()->getParent() == F)
      isSelfRecursive = true;
  }
  
  // Don't promote arguments for variadic functions. Adding, removing, or
  // changing non-pack parameters can change the classification of pack
  // parameters. Frontends encode that classification at the call site in the
  // IR, while in the callee the classification is determined dynamically based
  // on the number of registers consumed so far.
  if (F->isVarArg()) return nullptr;

  // Check to see which arguments are promotable.  If an argument is promotable,
  // add it to ArgsToPromote.
  SmallPtrSet<Argument*, 8> ArgsToPromote;
  SmallPtrSet<Argument*, 8> ByValArgsToTransform;
  for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
    Argument *PtrArg = PointerArgs[i];
    Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();

    // If this is a byval argument, and if the aggregate type is small, just
    // pass the elements, which is always safe, if the passed value is densely
    // packed or if we can prove the padding bytes are never accessed. This does
    // not apply to inalloca.
    bool isSafeToPromote =
      PtrArg->hasByValAttr() &&
      (isDenselyPacked(AgTy) || !canPaddingBeAccessed(PtrArg));
    if (isSafeToPromote) {
      if (StructType *STy = dyn_cast<StructType>(AgTy)) {
        if (maxElements > 0 && STy->getNumElements() > maxElements) {
          DEBUG(dbgs() << "argpromotion disable promoting argument '"
                << PtrArg->getName() << "' because it would require adding more"
                << " than " << maxElements << " arguments to the function.\n");
          continue;
        }
        
        // If all the elements are single-value types, we can promote it.
        bool AllSimple = true;
        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
          if (!STy->getElementType(i)->isSingleValueType()) {
            AllSimple = false;
            break;
          }
        }

        // Safe to transform, don't even bother trying to "promote" it.
        // Passing the elements as a scalar will allow scalarrepl to hack on
        // the new alloca we introduce.
        if (AllSimple) {
          ByValArgsToTransform.insert(PtrArg);
          continue;
        }
      }
    }

    // If the argument is a recursive type and we're in a recursive
    // function, we could end up infinitely peeling the function argument.
    if (isSelfRecursive) {
      if (StructType *STy = dyn_cast<StructType>(AgTy)) {
        bool RecursiveType = false;
        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
          if (STy->getElementType(i) == PtrArg->getType()) {
            RecursiveType = true;
            break;
          }
        }
        if (RecursiveType)
          continue;
      }
    }
    
    // Otherwise, see if we can promote the pointer to its value.
    if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr()))
      ArgsToPromote.insert(PtrArg);
//.........这里部分代码省略.........