xref: /freebsd-13.1/contrib/llvm-project/llvm/lib/CodeGen/MachineRegisterInfo.cpp (revision 5f7ddb14)

//===- lib/Codegen/MachineRegisterInfo.cpp --------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Implementation of the MachineRegisterInfo class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/LowLevelType.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>

using namespace llvm;

static cl::opt<bool> EnableSubRegLiveness("enable-subreg-liveness", cl::Hidden,
  cl::init(true), cl::desc("Enable subregister liveness tracking."));

// Pin the vtable to this file.
void MachineRegisterInfo::Delegate::anchor() {}

MachineRegisterInfo::MachineRegisterInfo(MachineFunction *MF)
    : MF(MF), TracksSubRegLiveness(MF->getSubtarget().enableSubRegLiveness() &&
                                   EnableSubRegLiveness),
      IsUpdatedCSRsInitialized(false) {
  unsigned NumRegs = getTargetRegisterInfo()->getNumRegs();
  VRegInfo.reserve(256);
  RegAllocHints.reserve(256);
  UsedPhysRegMask.resize(NumRegs);
  PhysRegUseDefLists.reset(new MachineOperand*[NumRegs]());
}

/// setRegClass - Set the register class of the specified virtual register.
///
void
MachineRegisterInfo::setRegClass(Register Reg, const TargetRegisterClass *RC) {
  assert(RC && RC->isAllocatable() && "Invalid RC for virtual register");
  VRegInfo[Reg].first = RC;
}

void MachineRegisterInfo::setRegBank(Register Reg,
                                     const RegisterBank &RegBank) {
  VRegInfo[Reg].first = &RegBank;
}

static const TargetRegisterClass *
constrainRegClass(MachineRegisterInfo &MRI, Register Reg,
                  const TargetRegisterClass *OldRC,
                  const TargetRegisterClass *RC, unsigned MinNumRegs) {
  if (OldRC == RC)
    return RC;
  const TargetRegisterClass *NewRC =
      MRI.getTargetRegisterInfo()->getCommonSubClass(OldRC, RC);
  if (!NewRC || NewRC == OldRC)
    return NewRC;
  if (NewRC->getNumRegs() < MinNumRegs)
    return nullptr;
  MRI.setRegClass(Reg, NewRC);
  return NewRC;
}

const TargetRegisterClass *
MachineRegisterInfo::constrainRegClass(Register Reg,
                                       const TargetRegisterClass *RC,
                                       unsigned MinNumRegs) {
  return ::constrainRegClass(*this, Reg, getRegClass(Reg), RC, MinNumRegs);
}

bool
MachineRegisterInfo::constrainRegAttrs(Register Reg,
                                       Register ConstrainingReg,
                                       unsigned MinNumRegs) {
  const LLT RegTy = getType(Reg);
  const LLT ConstrainingRegTy = getType(ConstrainingReg);
  if (RegTy.isValid() && ConstrainingRegTy.isValid() &&
      RegTy != ConstrainingRegTy)
    return false;
  const auto ConstrainingRegCB = getRegClassOrRegBank(ConstrainingReg);
  if (!ConstrainingRegCB.isNull()) {
    const auto RegCB = getRegClassOrRegBank(Reg);
    if (RegCB.isNull())
      setRegClassOrRegBank(Reg, ConstrainingRegCB);
    else if (RegCB.is<const TargetRegisterClass *>() !=
             ConstrainingRegCB.is<const TargetRegisterClass *>())
      return false;
    else if (RegCB.is<const TargetRegisterClass *>()) {
      if (!::constrainRegClass(
              *this, Reg, RegCB.get<const TargetRegisterClass *>(),
              ConstrainingRegCB.get<const TargetRegisterClass *>(), MinNumRegs))
        return false;
    } else if (RegCB != ConstrainingRegCB)
      return false;
  }
  if (ConstrainingRegTy.isValid())
    setType(Reg, ConstrainingRegTy);
  return true;
}

bool
MachineRegisterInfo::recomputeRegClass(Register Reg) {
  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
  const TargetRegisterClass *OldRC = getRegClass(Reg);
  const TargetRegisterClass *NewRC =
      getTargetRegisterInfo()->getLargestLegalSuperClass(OldRC, *MF);

  // Stop early if there is no room to grow.
  if (NewRC == OldRC)
    return false;

  // Accumulate constraints from all uses.
  for (MachineOperand &MO : reg_nodbg_operands(Reg)) {
    // Apply the effect of the given operand to NewRC.
    MachineInstr *MI = MO.getParent();
    unsigned OpNo = &MO - &MI->getOperand(0);
    NewRC = MI->getRegClassConstraintEffect(OpNo, NewRC, TII,
                                            getTargetRegisterInfo());
    if (!NewRC || NewRC == OldRC)
      return false;
  }
  setRegClass(Reg, NewRC);
  return true;
}

Register MachineRegisterInfo::createIncompleteVirtualRegister(StringRef Name) {
  Register Reg = Register::index2VirtReg(getNumVirtRegs());
  VRegInfo.grow(Reg);
  RegAllocHints.grow(Reg);
  insertVRegByName(Name, Reg);
  return Reg;
}

/// createVirtualRegister - Create and return a new virtual register in the
/// function with the specified register class.
///
Register
MachineRegisterInfo::createVirtualRegister(const TargetRegisterClass *RegClass,
                                           StringRef Name) {
  assert(RegClass && "Cannot create register without RegClass!");
  assert(RegClass->isAllocatable() &&
         "Virtual register RegClass must be allocatable.");

  // New virtual register number.
  Register Reg = createIncompleteVirtualRegister(Name);
  VRegInfo[Reg].first = RegClass;
  if (TheDelegate)
    TheDelegate->MRI_NoteNewVirtualRegister(Reg);
  return Reg;
}

Register MachineRegisterInfo::cloneVirtualRegister(Register VReg,
                                                   StringRef Name) {
  Register Reg = createIncompleteVirtualRegister(Name);
  VRegInfo[Reg].first = VRegInfo[VReg].first;
  setType(Reg, getType(VReg));
  if (TheDelegate)
    TheDelegate->MRI_NoteNewVirtualRegister(Reg);
  return Reg;
}

void MachineRegisterInfo::setType(Register VReg, LLT Ty) {
  VRegToType.grow(VReg);
  VRegToType[VReg] = Ty;
}

Register
MachineRegisterInfo::createGenericVirtualRegister(LLT Ty, StringRef Name) {
  // New virtual register number.
  Register Reg = createIncompleteVirtualRegister(Name);
  // FIXME: Should we use a dummy register class?
  VRegInfo[Reg].first = static_cast<RegisterBank *>(nullptr);
  setType(Reg, Ty);
  if (TheDelegate)
    TheDelegate->MRI_NoteNewVirtualRegister(Reg);
  return Reg;
}

void MachineRegisterInfo::clearVirtRegTypes() { VRegToType.clear(); }

/// clearVirtRegs - Remove all virtual registers (after physreg assignment).
void MachineRegisterInfo::clearVirtRegs() {
#ifndef NDEBUG
  for (unsigned i = 0, e = getNumVirtRegs(); i != e; ++i) {
    Register Reg = Register::index2VirtReg(i);
    if (!VRegInfo[Reg].second)
      continue;
    verifyUseList(Reg);
    llvm_unreachable("Remaining virtual register operands");
  }
#endif
  VRegInfo.clear();
  for (auto &I : LiveIns)
    I.second = 0;
}

void MachineRegisterInfo::verifyUseList(Register Reg) const {
#ifndef NDEBUG
  bool Valid = true;
  for (MachineOperand &M : reg_operands(Reg)) {
    MachineOperand *MO = &M;
    MachineInstr *MI = MO->getParent();
    if (!MI) {
      errs() << printReg(Reg, getTargetRegisterInfo())
             << " use list MachineOperand " << MO
             << " has no parent instruction.\n";
      Valid = false;
      continue;
    }
    MachineOperand *MO0 = &MI->getOperand(0);
    unsigned NumOps = MI->getNumOperands();
    if (!(MO >= MO0 && MO < MO0+NumOps)) {
      errs() << printReg(Reg, getTargetRegisterInfo())
             << " use list MachineOperand " << MO
             << " doesn't belong to parent MI: " << *MI;
      Valid = false;
    }
    if (!MO->isReg()) {
      errs() << printReg(Reg, getTargetRegisterInfo())
             << " MachineOperand " << MO << ": " << *MO
             << " is not a register\n";
      Valid = false;
    }
    if (MO->getReg() != Reg) {
      errs() << printReg(Reg, getTargetRegisterInfo())
             << " use-list MachineOperand " << MO << ": "
             << *MO << " is the wrong register\n";
      Valid = false;
    }
  }
  assert(Valid && "Invalid use list");
#endif
}

void MachineRegisterInfo::verifyUseLists() const {
#ifndef NDEBUG
  for (unsigned i = 0, e = getNumVirtRegs(); i != e; ++i)
    verifyUseList(Register::index2VirtReg(i));
  for (unsigned i = 1, e = getTargetRegisterInfo()->getNumRegs(); i != e; ++i)
    verifyUseList(i);
#endif
}

/// Add MO to the linked list of operands for its register.
void MachineRegisterInfo::addRegOperandToUseList(MachineOperand *MO) {
  assert(!MO->isOnRegUseList() && "Already on list");
  MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
  MachineOperand *const Head = HeadRef;

  // Head points to the first list element.
  // Next is NULL on the last list element.
  // Prev pointers are circular, so Head->Prev == Last.

  // Head is NULL for an empty list.
  if (!Head) {
    MO->Contents.Reg.Prev = MO;
    MO->Contents.Reg.Next = nullptr;
    HeadRef = MO;
    return;
  }
  assert(MO->getReg() == Head->getReg() && "Different regs on the same list!");

  // Insert MO between Last and Head in the circular Prev chain.
  MachineOperand *Last = Head->Contents.Reg.Prev;
  assert(Last && "Inconsistent use list");
  assert(MO->getReg() == Last->getReg() && "Different regs on the same list!");
  Head->Contents.Reg.Prev = MO;
  MO->Contents.Reg.Prev = Last;

  // Def operands always precede uses. This allows def_iterator to stop early.
  // Insert def operands at the front, and use operands at the back.
  if (MO->isDef()) {
    // Insert def at the front.
    MO->Contents.Reg.Next = Head;
    HeadRef = MO;
  } else {
    // Insert use at the end.
    MO->Contents.Reg.Next = nullptr;
    Last->Contents.Reg.Next = MO;
  }
}

/// Remove MO from its use-def list.
void MachineRegisterInfo::removeRegOperandFromUseList(MachineOperand *MO) {
  assert(MO->isOnRegUseList() && "Operand not on use list");
  MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
  MachineOperand *const Head = HeadRef;
  assert(Head && "List already empty");

  // Unlink this from the doubly linked list of operands.
  MachineOperand *Next = MO->Contents.Reg.Next;
  MachineOperand *Prev = MO->Contents.Reg.Prev;

  // Prev links are circular, next link is NULL instead of looping back to Head.
  if (MO == Head)
    HeadRef = Next;
  else
    Prev->Contents.Reg.Next = Next;

  (Next ? Next : Head)->Contents.Reg.Prev = Prev;

  MO->Contents.Reg.Prev = nullptr;
  MO->Contents.Reg.Next = nullptr;
}

/// Move NumOps operands from Src to Dst, updating use-def lists as needed.
///
/// The Dst range is assumed to be uninitialized memory. (Or it may contain
/// operands that won't be destroyed, which is OK because the MO destructor is
/// trivial anyway).
///
/// The Src and Dst ranges may overlap.
void MachineRegisterInfo::moveOperands(MachineOperand *Dst,
                                       MachineOperand *Src,
                                       unsigned NumOps) {
  assert(Src != Dst && NumOps && "Noop moveOperands");

  // Copy backwards if Dst is within the Src range.
  int Stride = 1;
  if (Dst >= Src && Dst < Src + NumOps) {
    Stride = -1;
    Dst += NumOps - 1;
    Src += NumOps - 1;
  }

  // Copy one operand at a time.
  do {
    new (Dst) MachineOperand(*Src);

    // Dst takes Src's place in the use-def chain.
    if (Src->isReg()) {
      MachineOperand *&Head = getRegUseDefListHead(Src->getReg());
      MachineOperand *Prev = Src->Contents.Reg.Prev;
      MachineOperand *Next = Src->Contents.Reg.Next;
      assert(Head && "List empty, but operand is chained");
      assert(Prev && "Operand was not on use-def list");

      // Prev links are circular, next link is NULL instead of looping back to
      // Head.
      if (Src == Head)
        Head = Dst;
      else
        Prev->Contents.Reg.Next = Dst;

      // Update Prev pointer. This also works when Src was pointing to itself
      // in a 1-element list. In that case Head == Dst.
      (Next ? Next : Head)->Contents.Reg.Prev = Dst;
    }

    Dst += Stride;
    Src += Stride;
  } while (--NumOps);
}

/// replaceRegWith - Replace all instances of FromReg with ToReg in the
/// machine function.  This is like llvm-level X->replaceAllUsesWith(Y),
/// except that it also changes any definitions of the register as well.
/// If ToReg is a physical register we apply the sub register to obtain the
/// final/proper physical register.
void MachineRegisterInfo::replaceRegWith(Register FromReg, Register ToReg) {
  assert(FromReg != ToReg && "Cannot replace a reg with itself");

  const TargetRegisterInfo *TRI = getTargetRegisterInfo();

  // TODO: This could be more efficient by bulk changing the operands.
  for (reg_iterator I = reg_begin(FromReg), E = reg_end(); I != E; ) {
    MachineOperand &O = *I;
    ++I;
    if (Register::isPhysicalRegister(ToReg)) {
      O.substPhysReg(ToReg, *TRI);
    } else {
      O.setReg(ToReg);
    }
  }
}

/// getVRegDef - Return the machine instr that defines the specified virtual
/// register or null if none is found.  This assumes that the code is in SSA
/// form, so there should only be one definition.
MachineInstr *MachineRegisterInfo::getVRegDef(Register Reg) const {
  // Since we are in SSA form, we can use the first definition.
  def_instr_iterator I = def_instr_begin(Reg);
  assert((I.atEnd() || std::next(I) == def_instr_end()) &&
         "getVRegDef assumes a single definition or no definition");
  return !I.atEnd() ? &*I : nullptr;
}

/// getUniqueVRegDef - Return the unique machine instr that defines the
/// specified virtual register or null if none is found.  If there are
/// multiple definitions or no definition, return null.
MachineInstr *MachineRegisterInfo::getUniqueVRegDef(Register Reg) const {
  if (def_empty(Reg)) return nullptr;
  def_instr_iterator I = def_instr_begin(Reg);
  if (std::next(I) != def_instr_end())
    return nullptr;
  return &*I;
}

bool MachineRegisterInfo::hasOneNonDBGUse(Register RegNo) const {
  return hasSingleElement(use_nodbg_operands(RegNo));
}

bool MachineRegisterInfo::hasOneNonDBGUser(Register RegNo) const {
  return hasSingleElement(use_nodbg_instructions(RegNo));
}

/// clearKillFlags - Iterate over all the uses of the given register and
/// clear the kill flag from the MachineOperand. This function is used by
/// optimization passes which extend register lifetimes and need only
/// preserve conservative kill flag information.
void MachineRegisterInfo::clearKillFlags(Register Reg) const {
  for (MachineOperand &MO : use_operands(Reg))
    MO.setIsKill(false);
}

bool MachineRegisterInfo::isLiveIn(Register Reg) const {
  for (const std::pair<MCRegister, Register> &LI : liveins())
    if ((Register)LI.first == Reg || LI.second == Reg)
      return true;
  return false;
}

/// getLiveInPhysReg - If VReg is a live-in virtual register, return the
/// corresponding live-in physical register.
MCRegister MachineRegisterInfo::getLiveInPhysReg(Register VReg) const {
  for (const std::pair<MCRegister, Register> &LI : liveins())
    if (LI.second == VReg)
      return LI.first;
  return MCRegister();
}

/// getLiveInVirtReg - If PReg is a live-in physical register, return the
/// corresponding live-in physical register.
Register MachineRegisterInfo::getLiveInVirtReg(MCRegister PReg) const {
  for (const std::pair<MCRegister, Register> &LI : liveins())
    if (LI.first == PReg)
      return LI.second;
  return Register();
}

/// EmitLiveInCopies - Emit copies to initialize livein virtual registers
/// into the given entry block.
void
MachineRegisterInfo::EmitLiveInCopies(MachineBasicBlock *EntryMBB,
                                      const TargetRegisterInfo &TRI,
                                      const TargetInstrInfo &TII) {
  // Emit the copies into the top of the block.
  for (unsigned i = 0, e = LiveIns.size(); i != e; ++i)
    if (LiveIns[i].second) {
      if (use_nodbg_empty(LiveIns[i].second)) {
        // The livein has no non-dbg uses. Drop it.
        //
        // It would be preferable to have isel avoid creating live-in
        // records for unused arguments in the first place, but it's
        // complicated by the debug info code for arguments.
        LiveIns.erase(LiveIns.begin() + i);
        --i; --e;
      } else {
        // Emit a copy.
        BuildMI(*EntryMBB, EntryMBB->begin(), DebugLoc(),
                TII.get(TargetOpcode::COPY), LiveIns[i].second)
          .addReg(LiveIns[i].first);

        // Add the register to the entry block live-in set.
        EntryMBB->addLiveIn(LiveIns[i].first);
      }
    } else {
      // Add the register to the entry block live-in set.
      EntryMBB->addLiveIn(LiveIns[i].first);
    }
}

LaneBitmask MachineRegisterInfo::getMaxLaneMaskForVReg(Register Reg) const {
  // Lane masks are only defined for vregs.
  assert(Register::isVirtualRegister(Reg));
  const TargetRegisterClass &TRC = *getRegClass(Reg);
  return TRC.getLaneMask();
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MachineRegisterInfo::dumpUses(Register Reg) const {
  for (MachineInstr &I : use_instructions(Reg))
    I.dump();
}
#endif

void MachineRegisterInfo::freezeReservedRegs(const MachineFunction &MF) {
  ReservedRegs = getTargetRegisterInfo()->getReservedRegs(MF);
  assert(ReservedRegs.size() == getTargetRegisterInfo()->getNumRegs() &&
         "Invalid ReservedRegs vector from target");
}

bool MachineRegisterInfo::isConstantPhysReg(MCRegister PhysReg) const {
  assert(Register::isPhysicalRegister(PhysReg));

  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
  if (TRI->isConstantPhysReg(PhysReg))
    return true;

  // Check if any overlapping register is modified, or allocatable so it may be
  // used later.
  for (MCRegAliasIterator AI(PhysReg, TRI, true);
       AI.isValid(); ++AI)
    if (!def_empty(*AI) || isAllocatable(*AI))
      return false;
  return true;
}

/// markUsesInDebugValueAsUndef - Mark every DBG_VALUE referencing the
/// specified register as undefined which causes the DBG_VALUE to be
/// deleted during LiveDebugVariables analysis.
void MachineRegisterInfo::markUsesInDebugValueAsUndef(Register Reg) const {
  // Mark any DBG_VALUE* that uses Reg as undef (but don't delete it.)
  // We use make_early_inc_range because setReg invalidates the iterator.
  for (MachineInstr &UseMI : llvm::make_early_inc_range(use_instructions(Reg))) {
    if (UseMI.isDebugValue() && UseMI.hasDebugOperandForReg(Reg))
      UseMI.setDebugValueUndef();
  }
}

static const Function *getCalledFunction(const MachineInstr &MI) {
  for (const MachineOperand &MO : MI.operands()) {
    if (!MO.isGlobal())
      continue;
    const Function *Func = dyn_cast<Function>(MO.getGlobal());
    if (Func != nullptr)
      return Func;
  }
  return nullptr;
}

static bool isNoReturnDef(const MachineOperand &MO) {
  // Anything which is not a noreturn function is a real def.
  const MachineInstr &MI = *MO.getParent();
  if (!MI.isCall())
    return false;
  const MachineBasicBlock &MBB = *MI.getParent();
  if (!MBB.succ_empty())
    return false;
  const MachineFunction &MF = *MBB.getParent();
  // We need to keep correct unwind information even if the function will
  // not return, since the runtime may need it.
  if (MF.getFunction().hasFnAttribute(Attribute::UWTable))
    return false;
  const Function *Called = getCalledFunction(MI);
  return !(Called == nullptr || !Called->hasFnAttribute(Attribute::NoReturn) ||
           !Called->hasFnAttribute(Attribute::NoUnwind));
}

bool MachineRegisterInfo::isPhysRegModified(MCRegister PhysReg,
                                            bool SkipNoReturnDef) const {
  if (UsedPhysRegMask.test(PhysReg))
    return true;
  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
  for (MCRegAliasIterator AI(PhysReg, TRI, true); AI.isValid(); ++AI) {
    for (const MachineOperand &MO : make_range(def_begin(*AI), def_end())) {
      if (!SkipNoReturnDef && isNoReturnDef(MO))
        continue;
      return true;
    }
  }
  return false;
}

bool MachineRegisterInfo::isPhysRegUsed(MCRegister PhysReg,
                                        bool SkipRegMaskTest) const {
  if (!SkipRegMaskTest && UsedPhysRegMask.test(PhysReg))
    return true;
  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
  for (MCRegAliasIterator AliasReg(PhysReg, TRI, true); AliasReg.isValid();
       ++AliasReg) {
    if (!reg_nodbg_empty(*AliasReg))
      return true;
  }
  return false;
}

void MachineRegisterInfo::disableCalleeSavedRegister(MCRegister Reg) {

  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
  assert(Reg && (Reg < TRI->getNumRegs()) &&
         "Trying to disable an invalid register");

  if (!IsUpdatedCSRsInitialized) {
    const MCPhysReg *CSR = TRI->getCalleeSavedRegs(MF);
    for (const MCPhysReg *I = CSR; *I; ++I)
      UpdatedCSRs.push_back(*I);

    // Zero value represents the end of the register list
    // (no more registers should be pushed).
    UpdatedCSRs.push_back(0);

    IsUpdatedCSRsInitialized = true;
  }

  // Remove the register (and its aliases from the list).
  for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
    llvm::erase_value(UpdatedCSRs, *AI);
}

const MCPhysReg *MachineRegisterInfo::getCalleeSavedRegs() const {
  if (IsUpdatedCSRsInitialized)
    return UpdatedCSRs.data();

  return getTargetRegisterInfo()->getCalleeSavedRegs(MF);
}

void MachineRegisterInfo::setCalleeSavedRegs(ArrayRef<MCPhysReg> CSRs) {
  if (IsUpdatedCSRsInitialized)
    UpdatedCSRs.clear();

  append_range(UpdatedCSRs, CSRs);

  // Zero value represents the end of the register list
  // (no more registers should be pushed).
  UpdatedCSRs.push_back(0);
  IsUpdatedCSRsInitialized = true;
}

bool MachineRegisterInfo::isReservedRegUnit(unsigned Unit) const {
  const TargetRegisterInfo *TRI = getTargetRegisterInfo();
  for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
    bool IsRootReserved = true;
    for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
         Super.isValid(); ++Super) {
      MCRegister Reg = *Super;
      if (!isReserved(Reg)) {
        IsRootReserved = false;
        break;
      }
    }
    if (IsRootReserved)
      return true;
  }
  return false;
}