text: //===-- SystemZLDCleanup.cpp - Clean up local-dynamic TLS accesses --------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This pass combines multiple accesses to local-dynamic TLS variables so that
  // the TLS base address for the module is only fetched once per execution path
  // through the function.
  //
  //===----------------------------------------------------------------------===//
  
  #include "SystemZMachineFunctionInfo.h"
  #include "SystemZTargetMachine.h"
  #include "llvm/CodeGen/MachineDominators.h"
  #include "llvm/CodeGen/MachineFunctionPass.h"
  #include "llvm/CodeGen/MachineInstrBuilder.h"
  #include "llvm/CodeGen/MachineRegisterInfo.h"
  #include "llvm/Target/TargetInstrInfo.h"
  #include "llvm/Target/TargetMachine.h"
  #include "llvm/Target/TargetRegisterInfo.h"
  
  using namespace llvm;
  
  namespace {
  
  class SystemZLDCleanup : public MachineFunctionPass {
  public:
    static char ID;
    SystemZLDCleanup(const SystemZTargetMachine &tm)
      : MachineFunctionPass(ID), TII(nullptr), MF(nullptr) {}
  
    StringRef getPassName() const override {
      return "SystemZ Local Dynamic TLS Access Clean-up";
    }
  
    bool runOnMachineFunction(MachineFunction &MF) override;
    void getAnalysisUsage(AnalysisUsage &AU) const override;
  
  private:
    bool VisitNode(MachineDomTreeNode *Node, unsigned TLSBaseAddrReg);
    MachineInstr *ReplaceTLSCall(MachineInstr *I, unsigned TLSBaseAddrReg);
    MachineInstr *SetRegister(MachineInstr *I, unsigned *TLSBaseAddrReg);
  
    const SystemZInstrInfo *TII;
    MachineFunction *MF;
  };
  
  char SystemZLDCleanup::ID = 0;
  
  } // end anonymous namespace
  
  FunctionPass *llvm::createSystemZLDCleanupPass(SystemZTargetMachine &TM) {
    return new SystemZLDCleanup(TM);
  }
  
  void SystemZLDCleanup::getAnalysisUsage(AnalysisUsage &AU) const {
    AU.setPreservesCFG();
    AU.addRequired<MachineDominatorTree>();
    MachineFunctionPass::getAnalysisUsage(AU);
  }
  
  bool SystemZLDCleanup::runOnMachineFunction(MachineFunction &F) {
    if (skipFunction(*F.getFunction()))
      return false;
  
    TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
    MF = &F;
  
    SystemZMachineFunctionInfo* MFI = F.getInfo<SystemZMachineFunctionInfo>();
    if (MFI->getNumLocalDynamicTLSAccesses() < 2) {
      // No point folding accesses if there isn't at least two.
      return false;
    }
  
    MachineDominatorTree *DT = &getAnalysis<MachineDominatorTree>();
    return VisitNode(DT->getRootNode(), 0);
  }
  
  // Visit the dominator subtree rooted at Node in pre-order.
  // If TLSBaseAddrReg is non-null, then use that to replace any
  // TLS_LDCALL instructions. Otherwise, create the register
  // when the first such instruction is seen, and then use it
  // as we encounter more instructions.
  bool SystemZLDCleanup::VisitNode(MachineDomTreeNode *Node,
                                   unsigned TLSBaseAddrReg) {
    MachineBasicBlock *BB = Node->getBlock();
    bool Changed = false;
  
    // Traverse the current block.
    for (auto I = BB->begin(), E = BB->end(); I != E; ++I) {
      switch (I->getOpcode()) {
        case SystemZ::TLS_LDCALL:
          if (TLSBaseAddrReg)
            I = ReplaceTLSCall(&*I, TLSBaseAddrReg);
          else
            I = SetRegister(&*I, &TLSBaseAddrReg);
          Changed = true;
          break;
        default:
          break;
      }
    }
  
    // Visit the children of this block in the dominator tree.
    for (auto I = Node->begin(), E = Node->end(); I != E; ++I)
      Changed |= VisitNode(*I, TLSBaseAddrReg);
  
    return Changed;
  }
  
  // Replace the TLS_LDCALL instruction I with a copy from TLSBaseAddrReg,
  // returning the new instruction.
  MachineInstr *SystemZLDCleanup::ReplaceTLSCall(MachineInstr *I,
                                                 unsigned TLSBaseAddrReg) {
    // Insert a Copy from TLSBaseAddrReg to R2.
    MachineInstr *Copy = BuildMI(*I->getParent(), I, I->getDebugLoc(),
                                 TII->get(TargetOpcode::COPY), SystemZ::R2D)
                                 .addReg(TLSBaseAddrReg);
  
    // Erase the TLS_LDCALL instruction.
    I->eraseFromParent();
  
    return Copy;
  }
  
  // Create a virtual register in *TLSBaseAddrReg, and populate it by
  // inserting a copy instruction after I. Returns the new instruction.
  MachineInstr *SystemZLDCleanup::SetRegister(MachineInstr *I,
                                              unsigned *TLSBaseAddrReg) {
    // Create a virtual register for the TLS base address.
    MachineRegisterInfo &RegInfo = MF->getRegInfo();
    *TLSBaseAddrReg = RegInfo.createVirtualRegister(&SystemZ::GR64BitRegClass);
  
    // Insert a copy from R2 to TLSBaseAddrReg.
    MachineInstr *Next = I->getNextNode();
    MachineInstr *Copy = BuildMI(*I->getParent(), Next, I->getDebugLoc(),
                                 TII->get(TargetOpcode::COPY), *TLSBaseAddrReg)
                                 .addReg(SystemZ::R2D);
  
    return Copy;
  }
  
  