xref: /external/v8/src/compiler/backend/register-allocator.cc

// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/compiler/backend/register-allocator.h"

#include <iomanip>

#include "src/base/iterator.h"
#include "src/base/small-vector.h"
#include "src/codegen/assembler-inl.h"
#include "src/codegen/tick-counter.h"
#include "src/compiler/backend/spill-placer.h"
#include "src/compiler/linkage.h"
#include "src/strings/string-stream.h"
#include "src/utils/vector.h"

namespace v8 {
namespace internal {
namespace compiler {

#define TRACE_COND(cond, ...)      \
  do {                             \
    if (cond) PrintF(__VA_ARGS__); \
  } while (false)

#define TRACE(...) TRACE_COND(data()->is_trace_alloc(), __VA_ARGS__)

namespace {

static constexpr int kFloat32Bit =
    RepresentationBit(MachineRepresentation::kFloat32);
static constexpr int kSimd128Bit =
    RepresentationBit(MachineRepresentation::kSimd128);


const InstructionBlock* GetContainingLoop(const InstructionSequence* sequence,
                                          const InstructionBlock* block) {
  RpoNumber index = block->loop_header();
  if (!index.IsValid()) return nullptr;
  return sequence->InstructionBlockAt(index);
}

const InstructionBlock* GetInstructionBlock(const InstructionSequence* code,
                                            LifetimePosition pos) {
  return code->GetInstructionBlock(pos.ToInstructionIndex());
}

Instruction* GetLastInstruction(InstructionSequence* code,
                                const InstructionBlock* block) {
  return code->InstructionAt(block->last_instruction_index());
}

}  // namespace

void LiveRangeBoundArray::Initialize(Zone* zone, TopLevelLiveRange* range) {
  size_t max_child_count = range->GetMaxChildCount();

  start_ = zone->NewArray<LiveRangeBound>(max_child_count);
  length_ = 0;
  LiveRangeBound* curr = start_;
  // The primary loop in ResolveControlFlow is not responsible for inserting
  // connecting moves for spilled ranges.
  for (LiveRange* i = range; i != nullptr; i = i->next(), ++curr, ++length_) {
    new (curr) LiveRangeBound(i, i->spilled());
  }
}

LiveRangeBound* LiveRangeBoundArray::Find(
    const LifetimePosition position) const {
  size_t left_index = 0;
  size_t right_index = length_;
  while (true) {
    size_t current_index = left_index + (right_index - left_index) / 2;
    DCHECK(right_index > current_index);
    LiveRangeBound* bound = &start_[current_index];
    if (bound->start_ <= position) {
      if (position < bound->end_) return bound;
      DCHECK(left_index < current_index);
      left_index = current_index;
    } else {
      right_index = current_index;
    }
  }
}

LiveRangeBound* LiveRangeBoundArray::FindPred(const InstructionBlock* pred) {
  LifetimePosition pred_end = LifetimePosition::InstructionFromInstructionIndex(
      pred->last_instruction_index());
  return Find(pred_end);
}

LiveRangeBound* LiveRangeBoundArray::FindSucc(const InstructionBlock* succ) {
  LifetimePosition succ_start = LifetimePosition::GapFromInstructionIndex(
      succ->first_instruction_index());
  return Find(succ_start);
}

bool LiveRangeBoundArray::FindConnectableSubranges(
    const InstructionBlock* block, const InstructionBlock* pred,
    FindResult* result) const {
  LifetimePosition pred_end = LifetimePosition::InstructionFromInstructionIndex(
      pred->last_instruction_index());
  LiveRangeBound* bound = Find(pred_end);
  result->pred_cover_ = bound->range_;
  LifetimePosition cur_start = LifetimePosition::GapFromInstructionIndex(
      block->first_instruction_index());

  if (bound->CanCover(cur_start)) {
    // Both blocks are covered by the same range, so there is nothing to
    // connect.
    return false;
  }
  bound = Find(cur_start);
  if (bound->skip_) {
    return false;
  }
  result->cur_cover_ = bound->range_;
  DCHECK(result->pred_cover_ != nullptr && result->cur_cover_ != nullptr);
  return (result->cur_cover_ != result->pred_cover_);
}

LiveRangeFinder::LiveRangeFinder(const TopTierRegisterAllocationData* data,
                                 Zone* zone)
    : data_(data),
      bounds_length_(static_cast<int>(data_->live_ranges().size())),
      bounds_(zone->NewArray<LiveRangeBoundArray>(bounds_length_)),
      zone_(zone) {
  for (int i = 0; i < bounds_length_; ++i) {
    new (&bounds_[i]) LiveRangeBoundArray();
  }
}

LiveRangeBoundArray* LiveRangeFinder::ArrayFor(int operand_index) {
  DCHECK(operand_index < bounds_length_);
  TopLevelLiveRange* range = data_->live_ranges()[operand_index];
  DCHECK(range != nullptr && !range->IsEmpty());
  LiveRangeBoundArray* array = &bounds_[operand_index];
  if (array->ShouldInitialize()) {
    array->Initialize(zone_, range);
  }
  return array;
}

using DelayedInsertionMapKey = std::pair<ParallelMove*, InstructionOperand>;

struct DelayedInsertionMapCompare {
  bool operator()(const DelayedInsertionMapKey& a,
                  const DelayedInsertionMapKey& b) const {
    if (a.first == b.first) {
      return a.second.Compare(b.second);
    }
    return a.first < b.first;
  }
};

using DelayedInsertionMap = ZoneMap<DelayedInsertionMapKey, InstructionOperand,
                                    DelayedInsertionMapCompare>;

UsePosition::UsePosition(LifetimePosition pos, InstructionOperand* operand,
                         void* hint, UsePositionHintType hint_type)
    : operand_(operand), hint_(hint), next_(nullptr), pos_(pos), flags_(0) {
  DCHECK_IMPLIES(hint == nullptr, hint_type == UsePositionHintType::kNone);
  bool register_beneficial = true;
  UsePositionType type = UsePositionType::kRegisterOrSlot;
  if (operand_ != nullptr && operand_->IsUnallocated()) {
    const UnallocatedOperand* unalloc = UnallocatedOperand::cast(operand_);
    if (unalloc->HasRegisterPolicy()) {
      type = UsePositionType::kRequiresRegister;
    } else if (unalloc->HasSlotPolicy()) {
      type = UsePositionType::kRequiresSlot;
      register_beneficial = false;
    } else if (unalloc->HasRegisterOrSlotOrConstantPolicy()) {
      type = UsePositionType::kRegisterOrSlotOrConstant;
      register_beneficial = false;
    } else {
      register_beneficial = !unalloc->HasRegisterOrSlotPolicy();
    }
  }
  flags_ = TypeField::encode(type) | HintTypeField::encode(hint_type) |
           RegisterBeneficialField::encode(register_beneficial) |
           AssignedRegisterField::encode(kUnassignedRegister);
  DCHECK(pos_.IsValid());
}

bool UsePosition::HasHint() const {
  int hint_register;
  return HintRegister(&hint_register);
}

bool UsePosition::HintRegister(int* register_code) const {
  if (hint_ == nullptr) return false;
  switch (HintTypeField::decode(flags_)) {
    case UsePositionHintType::kNone:
    case UsePositionHintType::kUnresolved:
      return false;
    case UsePositionHintType::kUsePos: {
      UsePosition* use_pos = reinterpret_cast<UsePosition*>(hint_);
      int assigned_register = AssignedRegisterField::decode(use_pos->flags_);
      if (assigned_register == kUnassignedRegister) return false;
      *register_code = assigned_register;
      return true;
    }
    case UsePositionHintType::kOperand: {
      InstructionOperand* operand =
          reinterpret_cast<InstructionOperand*>(hint_);
      *register_code = LocationOperand::cast(operand)->register_code();
      return true;
    }
    case UsePositionHintType::kPhi: {
      TopTierRegisterAllocationData::PhiMapValue* phi =
          reinterpret_cast<TopTierRegisterAllocationData::PhiMapValue*>(hint_);
      int assigned_register = phi->assigned_register();
      if (assigned_register == kUnassignedRegister) return false;
      *register_code = assigned_register;
      return true;
    }
  }
  UNREACHABLE();
}

UsePositionHintType UsePosition::HintTypeForOperand(
    const InstructionOperand& op) {
  switch (op.kind()) {
    case InstructionOperand::CONSTANT:
    case InstructionOperand::IMMEDIATE:
      return UsePositionHintType::kNone;
    case InstructionOperand::UNALLOCATED:
      return UsePositionHintType::kUnresolved;
    case InstructionOperand::ALLOCATED:
      if (op.IsRegister() || op.IsFPRegister()) {
        return UsePositionHintType::kOperand;
      } else {
        DCHECK(op.IsStackSlot() || op.IsFPStackSlot());
        return UsePositionHintType::kNone;
      }
    case InstructionOperand::PENDING:
    case InstructionOperand::INVALID:
      break;
  }
  UNREACHABLE();
}

void UsePosition::SetHint(UsePosition* use_pos) {
  DCHECK_NOT_NULL(use_pos);
  hint_ = use_pos;
  flags_ = HintTypeField::update(flags_, UsePositionHintType::kUsePos);
}

void UsePosition::ResolveHint(UsePosition* use_pos) {
  DCHECK_NOT_NULL(use_pos);
  if (HintTypeField::decode(flags_) != UsePositionHintType::kUnresolved) return;
  hint_ = use_pos;
  flags_ = HintTypeField::update(flags_, UsePositionHintType::kUsePos);
}

void UsePosition::set_type(UsePositionType type, bool register_beneficial) {
  DCHECK_IMPLIES(type == UsePositionType::kRequiresSlot, !register_beneficial);
  DCHECK_EQ(kUnassignedRegister, AssignedRegisterField::decode(flags_));
  flags_ = TypeField::encode(type) |
           RegisterBeneficialField::encode(register_beneficial) |
           HintTypeField::encode(HintTypeField::decode(flags_)) |
           AssignedRegisterField::encode(kUnassignedRegister);
}

UseInterval* UseInterval::SplitAt(LifetimePosition pos, Zone* zone) {
  DCHECK(Contains(pos) && pos != start());
  UseInterval* after = zone->New<UseInterval>(pos, end_);
  after->next_ = next_;
  next_ = nullptr;
  end_ = pos;
  return after;
}

void LifetimePosition::Print() const { StdoutStream{} << *this << std::endl; }

std::ostream& operator<<(std::ostream& os, const LifetimePosition pos) {
  os << '@' << pos.ToInstructionIndex();
  if (pos.IsGapPosition()) {
    os << 'g';
  } else {
    os << 'i';
  }
  if (pos.IsStart()) {
    os << 's';
  } else {
    os << 'e';
  }
  return os;
}

LiveRange::LiveRange(int relative_id, MachineRepresentation rep,
                     TopLevelLiveRange* top_level)
    : relative_id_(relative_id),
      bits_(0),
      last_interval_(nullptr),
      first_interval_(nullptr),
      first_pos_(nullptr),
      top_level_(top_level),
      next_(nullptr),
      current_interval_(nullptr),
      last_processed_use_(nullptr),
      current_hint_position_(nullptr) {
  DCHECK(AllocatedOperand::IsSupportedRepresentation(rep));
  bits_ = AssignedRegisterField::encode(kUnassignedRegister) |
          RepresentationField::encode(rep) |
          ControlFlowRegisterHint::encode(kUnassignedRegister);
}

void LiveRange::VerifyPositions() const {
  // Walk the positions, verifying that each is in an interval.
  UseInterval* interval = first_interval_;
  for (UsePosition* pos = first_pos_; pos != nullptr; pos = pos->next()) {
    CHECK(Start() <= pos->pos());
    CHECK(pos->pos() <= End());
    CHECK_NOT_NULL(interval);
    while (!interval->Contains(pos->pos()) && interval->end() != pos->pos()) {
      interval = interval->next();
      CHECK_NOT_NULL(interval);
    }
  }
}

void LiveRange::VerifyIntervals() const {
  DCHECK(first_interval()->start() == Start());
  LifetimePosition last_end = first_interval()->end();
  for (UseInterval* interval = first_interval()->next(); interval != nullptr;
       interval = interval->next()) {
    DCHECK(last_end <= interval->start());
    last_end = interval->end();
  }
  DCHECK(last_end == End());
}

void LiveRange::set_assigned_register(int reg) {
  DCHECK(!HasRegisterAssigned() && !spilled());
  bits_ = AssignedRegisterField::update(bits_, reg);
}

void LiveRange::UnsetAssignedRegister() {
  DCHECK(HasRegisterAssigned() && !spilled());
  bits_ = AssignedRegisterField::update(bits_, kUnassignedRegister);
}

void LiveRange::AttachToNext() {
  DCHECK_NOT_NULL(next_);
  DCHECK_NE(TopLevel()->last_child_covers_, next_);
  last_interval_->set_next(next_->first_interval());
  next_->first_interval_ = nullptr;
  last_interval_ = next_->last_interval_;
  next_->last_interval_ = nullptr;
  if (first_pos() == nullptr) {
    first_pos_ = next_->first_pos();
  } else {
    UsePosition* ptr = first_pos_;
    while (ptr->next() != nullptr) {
      ptr = ptr->next();
    }
    ptr->set_next(next_->first_pos());
  }
  next_->first_pos_ = nullptr;
  LiveRange* old_next = next_;
  next_ = next_->next_;
  old_next->next_ = nullptr;
}

void LiveRange::Unspill() {
  DCHECK(spilled());
  set_spilled(false);
  bits_ = AssignedRegisterField::update(bits_, kUnassignedRegister);
}

void LiveRange::Spill() {
  DCHECK(!spilled());
  DCHECK(!TopLevel()->HasNoSpillType());
  set_spilled(true);
  bits_ = AssignedRegisterField::update(bits_, kUnassignedRegister);
}

RegisterKind LiveRange::kind() const {
  return IsFloatingPoint(representation()) ? RegisterKind::kDouble
                                           : RegisterKind::kGeneral;
}

UsePosition* LiveRange::FirstHintPosition(int* register_index) {
  if (!first_pos_) return nullptr;
  if (current_hint_position_) {
    if (current_hint_position_->pos() < first_pos_->pos()) {
      current_hint_position_ = first_pos_;
    }
    if (current_hint_position_->pos() > End()) {
      current_hint_position_ = nullptr;
    }
  }
  bool needs_revisit = false;
  UsePosition* pos = current_hint_position_;
  for (; pos != nullptr; pos = pos->next()) {
    if (pos->HintRegister(register_index)) {
      break;
    }
    // Phi and use position hints can be assigned during allocation which
    // would invalidate the cached hint position. Make sure we revisit them.
    needs_revisit = needs_revisit ||
                    pos->hint_type() == UsePositionHintType::kPhi ||
                    pos->hint_type() == UsePositionHintType::kUsePos;
  }
  if (!needs_revisit) {
    current_hint_position_ = pos;
  }
#ifdef DEBUG
  UsePosition* pos_check = first_pos_;
  for (; pos_check != nullptr; pos_check = pos_check->next()) {
    if (pos_check->HasHint()) {
      break;
    }
  }
  CHECK_EQ(pos, pos_check);
#endif
  return pos;
}

UsePosition* LiveRange::NextUsePosition(LifetimePosition start) const {
  UsePosition* use_pos = last_processed_use_;
  if (use_pos == nullptr || use_pos->pos() > start) {
    use_pos = first_pos();
  }
  while (use_pos != nullptr && use_pos->pos() < start) {
    use_pos = use_pos->next();
  }
  last_processed_use_ = use_pos;
  return use_pos;
}

UsePosition* LiveRange::NextUsePositionRegisterIsBeneficial(
    LifetimePosition start) const {
  UsePosition* pos = NextUsePosition(start);
  while (pos != nullptr && !pos->RegisterIsBeneficial()) {
    pos = pos->next();
  }
  return pos;
}

LifetimePosition LiveRange::NextLifetimePositionRegisterIsBeneficial(
    const LifetimePosition& start) const {
  UsePosition* next_use = NextUsePositionRegisterIsBeneficial(start);
  if (next_use == nullptr) return End();
  return next_use->pos();
}

UsePosition* LiveRange::PreviousUsePositionRegisterIsBeneficial(
    LifetimePosition start) const {
  UsePosition* pos = first_pos();
  UsePosition* prev = nullptr;
  while (pos != nullptr && pos->pos() < start) {
    if (pos->RegisterIsBeneficial()) prev = pos;
    pos = pos->next();
  }
  return prev;
}

UsePosition* LiveRange::NextUsePositionSpillDetrimental(
    LifetimePosition start) const {
  UsePosition* pos = NextUsePosition(start);
  while (pos != nullptr && pos->type() != UsePositionType::kRequiresRegister &&
         !pos->SpillDetrimental()) {
    pos = pos->next();
  }
  return pos;
}

UsePosition* LiveRange::NextRegisterPosition(LifetimePosition start) const {
  UsePosition* pos = NextUsePosition(start);
  while (pos != nullptr && pos->type() != UsePositionType::kRequiresRegister) {
    pos = pos->next();
  }
  return pos;
}

UsePosition* LiveRange::NextSlotPosition(LifetimePosition start) const {
  for (UsePosition* pos = NextUsePosition(start); pos != nullptr;
       pos = pos->next()) {
    if (pos->type() != UsePositionType::kRequiresSlot) continue;
    return pos;
  }
  return nullptr;
}

bool LiveRange::CanBeSpilled(LifetimePosition pos) const {
  // We cannot spill a live range that has a use requiring a register
  // at the current or the immediate next position.
  UsePosition* use_pos = NextRegisterPosition(pos);
  if (use_pos == nullptr) return true;
  return use_pos->pos() > pos.NextStart().End();
}

bool LiveRange::IsTopLevel() const { return top_level_ == this; }

InstructionOperand LiveRange::GetAssignedOperand() const {
  DCHECK(!IsEmpty());
  if (HasRegisterAssigned()) {
    DCHECK(!spilled());
    return AllocatedOperand(LocationOperand::REGISTER, representation(),
                            assigned_register());
  }
  DCHECK(spilled());
  DCHECK(!HasRegisterAssigned());
  if (TopLevel()->HasSpillOperand()) {
    InstructionOperand* op = TopLevel()->GetSpillOperand();
    DCHECK(!op->IsUnallocated());
    return *op;
  }
  return TopLevel()->GetSpillRangeOperand();
}

UseInterval* LiveRange::FirstSearchIntervalForPosition(
    LifetimePosition position) const {
  if (current_interval_ == nullptr) return first_interval_;
  if (current_interval_->start() > position) {
    current_interval_ = nullptr;
    return first_interval_;
  }
  return current_interval_;
}

void LiveRange::AdvanceLastProcessedMarker(
    UseInterval* to_start_of, LifetimePosition but_not_past) const {
  if (to_start_of == nullptr) return;
  if (to_start_of->start() > but_not_past) return;
  LifetimePosition start = current_interval_ == nullptr
                               ? LifetimePosition::Invalid()
                               : current_interval_->start();
  if (to_start_of->start() > start) {
    current_interval_ = to_start_of;
  }
}

LiveRange* LiveRange::SplitAt(LifetimePosition position, Zone* zone) {
  int new_id = TopLevel()->GetNextChildId();
  LiveRange* child = zone->New<LiveRange>(new_id, representation(), TopLevel());
  child->set_bundle(bundle_);
  // If we split, we do so because we're about to switch registers or move
  // to/from a slot, so there's no value in connecting hints.
  DetachAt(position, child, zone, DoNotConnectHints);

  child->top_level_ = TopLevel();
  child->next_ = next_;
  next_ = child;
  return child;
}

UsePosition* LiveRange::DetachAt(LifetimePosition position, LiveRange* result,
                                 Zone* zone,
                                 HintConnectionOption connect_hints) {
  DCHECK(Start() < position);
  DCHECK(End() > position);
  DCHECK(result->IsEmpty());
  // Find the last interval that ends before the position. If the
  // position is contained in one of the intervals in the chain, we
  // split that interval and use the first part.
  UseInterval* current = FirstSearchIntervalForPosition(position);

  // If the split position coincides with the beginning of a use interval
  // we need to split use positons in a special way.
  bool split_at_start = false;

  if (current->start() == position) {
    // When splitting at start we need to locate the previous use interval.
    current = first_interval_;
  }

  UseInterval* after = nullptr;
  while (current != nullptr) {
    if (current->Contains(position)) {
      after = current->SplitAt(position, zone);
      break;
    }
    UseInterval* next = current->next();
    if (next->start() >= position) {
      split_at_start = (next->start() == position);
      after = next;
      current->set_next(nullptr);
      break;
    }
    current = next;
  }
  DCHECK_NOT_NULL(after);

  // Partition original use intervals to the two live ranges.
  UseInterval* before = current;
  result->last_interval_ =
      (last_interval_ == before)
          ? after            // Only interval in the range after split.
          : last_interval_;  // Last interval of the original range.
  result->first_interval_ = after;
  last_interval_ = before;

  // Find the last use position before the split and the first use
  // position after it.
  UsePosition* use_after = first_pos();
  UsePosition* use_before = nullptr;
  if (split_at_start) {
    // The split position coincides with the beginning of a use interval (the
    // end of a lifetime hole). Use at this position should be attributed to
    // the split child because split child owns use interval covering it.
    while (use_after != nullptr && use_after->pos() < position) {
      use_before = use_after;
      use_after = use_after->next();
    }
  } else {
    while (use_after != nullptr && use_after->pos() <= position) {
      use_before = use_after;
      use_after = use_after->next();
    }
  }

  // Partition original use positions to the two live ranges.
  if (use_before != nullptr) {
    use_before->set_next(nullptr);
  } else {
    first_pos_ = nullptr;
  }
  result->first_pos_ = use_after;
  result->current_hint_position_ = current_hint_position_;

  // Discard cached iteration state. It might be pointing
  // to the use that no longer belongs to this live range.
  last_processed_use_ = nullptr;
  current_interval_ = nullptr;

  if (connect_hints == ConnectHints && use_before != nullptr &&
      use_after != nullptr) {
    use_after->SetHint(use_before);
    result->current_hint_position_ = use_after;
  }
#ifdef DEBUG
  VerifyChildStructure();
  result->VerifyChildStructure();
#endif
  return use_before;
}

void LiveRange::UpdateParentForAllChildren(TopLevelLiveRange* new_top_level) {
  LiveRange* child = this;
  for (; child != nullptr; child = child->next()) {
    child->top_level_ = new_top_level;
  }
}

void LiveRange::ConvertUsesToOperand(const InstructionOperand& op,
                                     const InstructionOperand& spill_op) {
  for (UsePosition* pos = first_pos(); pos != nullptr; pos = pos->next()) {
    DCHECK(Start() <= pos->pos() && pos->pos() <= End());
    if (!pos->HasOperand()) continue;
    switch (pos->type()) {
      case UsePositionType::kRequiresSlot:
        DCHECK(spill_op.IsStackSlot() || spill_op.IsFPStackSlot());
        InstructionOperand::ReplaceWith(pos->operand(), &spill_op);
        break;
      case UsePositionType::kRequiresRegister:
        DCHECK(op.IsRegister() || op.IsFPRegister());
        V8_FALLTHROUGH;
      case UsePositionType::kRegisterOrSlot:
      case UsePositionType::kRegisterOrSlotOrConstant:
        InstructionOperand::ReplaceWith(pos->operand(), &op);
        break;
    }
  }
}

// This implements an ordering on live ranges so that they are ordered by their
// start positions.  This is needed for the correctness of the register
// allocation algorithm.  If two live ranges start at the same offset then there
// is a tie breaker based on where the value is first used.  This part of the
// ordering is merely a heuristic.
bool LiveRange::ShouldBeAllocatedBefore(const LiveRange* other) const {
  LifetimePosition start = Start();
  LifetimePosition other_start = other->Start();
  if (start == other_start) {
    // Prefer register that has a controlflow hint to make sure it gets
    // allocated first. This allows the control flow aware alloction to
    // just put ranges back into the queue without other ranges interfering.
    if (controlflow_hint() < other->controlflow_hint()) {
      return true;
    }
    // The other has a smaller hint.
    if (controlflow_hint() > other->controlflow_hint()) {
      return false;
    }
    // Both have the same hint or no hint at all. Use first use position.
    UsePosition* pos = first_pos();
    UsePosition* other_pos = other->first_pos();
    // To make the order total, handle the case where both positions are null.
    if (pos == other_pos) return TopLevel()->vreg() < other->TopLevel()->vreg();
    if (pos == nullptr) return false;
    if (other_pos == nullptr) return true;
    // To make the order total, handle the case where both positions are equal.
    if (pos->pos() == other_pos->pos())
      return TopLevel()->vreg() < other->TopLevel()->vreg();
    return pos->pos() < other_pos->pos();
  }
  return start < other_start;
}

void LiveRange::SetUseHints(int register_index) {
  for (UsePosition* pos = first_pos(); pos != nullptr; pos = pos->next()) {
    if (!pos->HasOperand()) continue;
    switch (pos->type()) {
      case UsePositionType::kRequiresSlot:
        break;
      case UsePositionType::kRequiresRegister:
      case UsePositionType::kRegisterOrSlot:
      case UsePositionType::kRegisterOrSlotOrConstant:
        pos->set_assigned_register(register_index);
        break;
    }
  }
}

bool LiveRange::CanCover(LifetimePosition position) const {
  if (IsEmpty()) return false;
  return Start() <= position && position < End();
}

bool LiveRange::Covers(LifetimePosition position) const {
  if (!CanCover(position)) return false;
  UseInterval* start_search = FirstSearchIntervalForPosition(position);
  for (UseInterval* interval = start_search; interval != nullptr;
       interval = interval->next()) {
    DCHECK(interval->next() == nullptr ||
           interval->next()->start() >= interval->start());
    AdvanceLastProcessedMarker(interval, position);
    if (interval->Contains(position)) return true;
    if (interval->start() > position) return false;
  }
  return false;
}

LifetimePosition LiveRange::NextEndAfter(LifetimePosition position) const {
  UseInterval* start_search = FirstSearchIntervalForPosition(position);
  while (start_search->end() < position) {
    start_search = start_search->next();
  }
  return start_search->end();
}

LifetimePosition LiveRange::NextStartAfter(LifetimePosition position) {
  UseInterval* start_search = FirstSearchIntervalForPosition(position);
  while (start_search->start() < position) {
    start_search = start_search->next();
  }
  next_start_ = start_search->start();
  return next_start_;
}

LifetimePosition LiveRange::FirstIntersection(LiveRange* other) const {
  UseInterval* b = other->first_interval();
  if (b == nullptr) return LifetimePosition::Invalid();
  LifetimePosition advance_last_processed_up_to = b->start();
  UseInterval* a = FirstSearchIntervalForPosition(b->start());
  while (a != nullptr && b != nullptr) {
    if (a->start() > other->End()) break;
    if (b->start() > End()) break;
    LifetimePosition cur_intersection = a->Intersect(b);
    if (cur_intersection.IsValid()) {
      return cur_intersection;
    }
    if (a->start() < b->start()) {
      a = a->next();
      if (a == nullptr || a->start() > other->End()) break;
      AdvanceLastProcessedMarker(a, advance_last_processed_up_to);
    } else {
      b = b->next();
    }
  }
  return LifetimePosition::Invalid();
}

void LiveRange::Print(const RegisterConfiguration* config,
                      bool with_children) const {
  StdoutStream os;
  PrintableLiveRange wrapper;
  wrapper.register_configuration_ = config;
  for (const LiveRange* i = this; i != nullptr; i = i->next()) {
    wrapper.range_ = i;
    os << wrapper << std::endl;
    if (!with_children) break;
  }
}

void LiveRange::Print(bool with_children) const {
  Print(RegisterConfiguration::Default(), with_children);
}

bool LiveRange::RegisterFromBundle(int* hint) const {
  if (bundle_ == nullptr || bundle_->reg() == kUnassignedRegister) return false;
  *hint = bundle_->reg();
  return true;
}

void LiveRange::UpdateBundleRegister(int reg) const {
  if (bundle_ == nullptr || bundle_->reg() != kUnassignedRegister) return;
  bundle_->set_reg(reg);
}

struct TopLevelLiveRange::SpillMoveInsertionList : ZoneObject {
  SpillMoveInsertionList(int gap_index, InstructionOperand* operand,
                         SpillMoveInsertionList* next)
      : gap_index(gap_index), operand(operand), next(next) {}
  const int gap_index;
  InstructionOperand* const operand;
  SpillMoveInsertionList* next;
};

TopLevelLiveRange::TopLevelLiveRange(int vreg, MachineRepresentation rep)
    : LiveRange(0, rep, this),
      vreg_(vreg),
      last_child_id_(0),
      spill_operand_(nullptr),
      spill_move_insertion_locations_(nullptr),
      spilled_in_deferred_blocks_(false),
      has_preassigned_slot_(false),
      spill_start_index_(kMaxInt),
      last_pos_(nullptr),
      last_child_covers_(this) {
  bits_ |= SpillTypeField::encode(SpillType::kNoSpillType);
}

void TopLevelLiveRange::RecordSpillLocation(Zone* zone, int gap_index,
                                            InstructionOperand* operand) {
  DCHECK(HasNoSpillType());
  spill_move_insertion_locations_ = zone->New<SpillMoveInsertionList>(
      gap_index, operand, spill_move_insertion_locations_);
}

void TopLevelLiveRange::CommitSpillMoves(TopTierRegisterAllocationData* data,
                                         const InstructionOperand& op) {
  DCHECK_IMPLIES(op.IsConstant(),
                 GetSpillMoveInsertionLocations(data) == nullptr);

  if (HasGeneralSpillRange()) {
    SetLateSpillingSelected(false);
  }

  InstructionSequence* sequence = data->code();
  Zone* zone = sequence->zone();

  for (SpillMoveInsertionList* to_spill = GetSpillMoveInsertionLocations(data);
       to_spill != nullptr; to_spill = to_spill->next) {
    Instruction* instr = sequence->InstructionAt(to_spill->gap_index);
    ParallelMove* move =
        instr->GetOrCreateParallelMove(Instruction::START, zone);
    move->AddMove(*to_spill->operand, op);
    instr->block()->mark_needs_frame();
  }
}

void TopLevelLiveRange::FilterSpillMoves(TopTierRegisterAllocationData* data,
                                         const InstructionOperand& op) {
  DCHECK_IMPLIES(op.IsConstant(),
                 GetSpillMoveInsertionLocations(data) == nullptr);
  bool might_be_duplicated = has_slot_use() || spilled();
  InstructionSequence* sequence = data->code();

  SpillMoveInsertionList* previous = nullptr;
  for (SpillMoveInsertionList* to_spill = GetSpillMoveInsertionLocations(data);
       to_spill != nullptr; previous = to_spill, to_spill = to_spill->next) {
    Instruction* instr = sequence->InstructionAt(to_spill->gap_index);
    ParallelMove* move = instr->GetParallelMove(Instruction::START);
    // Skip insertion if it's possible that the move exists already as a
    // constraint move from a fixed output register to a slot.
    bool found = false;
    if (move != nullptr && (might_be_duplicated || has_preassigned_slot())) {
      for (MoveOperands* move_op : *move) {
        if (move_op->IsEliminated()) continue;
        if (move_op->source().Equals(*to_spill->operand) &&
            move_op->destination().Equals(op)) {
          found = true;
          if (has_preassigned_slot()) move_op->Eliminate();
          break;
        }
      }
    }
    if (found || has_preassigned_slot()) {
      // Remove the item from the list.
      if (previous == nullptr) {
        spill_move_insertion_locations_ = to_spill->next;
      } else {
        previous->next = to_spill->next;
      }
      // Even though this location doesn't need a spill instruction, the
      // block does require a frame.
      instr->block()->mark_needs_frame();
    }
  }
}

void TopLevelLiveRange::SetSpillOperand(InstructionOperand* operand) {
  DCHECK(HasNoSpillType());
  DCHECK(!operand->IsUnallocated() && !operand->IsImmediate());
  set_spill_type(SpillType::kSpillOperand);
  spill_operand_ = operand;
}

void TopLevelLiveRange::SetSpillRange(SpillRange* spill_range) {
  DCHECK(!HasSpillOperand());
  DCHECK(spill_range);
  spill_range_ = spill_range;
}

AllocatedOperand TopLevelLiveRange::GetSpillRangeOperand() const {
  SpillRange* spill_range = GetSpillRange();
  int index = spill_range->assigned_slot();
  return AllocatedOperand(LocationOperand::STACK_SLOT, representation(), index);
}

void TopLevelLiveRange::VerifyChildrenInOrder() const {
  LifetimePosition last_end = End();
  for (const LiveRange* child = this->next(); child != nullptr;
       child = child->next()) {
    DCHECK(last_end <= child->Start());
    last_end = child->End();
  }
}

LiveRange* TopLevelLiveRange::GetChildCovers(LifetimePosition pos) {
  LiveRange* child = last_child_covers_;
  DCHECK_NE(child, nullptr);
  if (pos < child->Start()) {
    // Cached value has advanced too far; start from the top.
    child = this;
  }
  LiveRange* previous_child = nullptr;
  while (child != nullptr && child->End() <= pos) {
    previous_child = child;
    child = child->next();
  }

  // If we've walked past the end, cache the last child instead. This allows
  // future calls that are also past the end to be fast, since they will know
  // that there is no need to reset the search to the beginning.
  last_child_covers_ = child == nullptr ? previous_child : child;

  return !child || !child->Covers(pos) ? nullptr : child;
}

void TopLevelLiveRange::Verify() const {
  VerifyChildrenInOrder();
  for (const LiveRange* child = this; child != nullptr; child = child->next()) {
    VerifyChildStructure();
  }
}

void TopLevelLiveRange::ShortenTo(LifetimePosition start, bool trace_alloc) {
  TRACE_COND(trace_alloc, "Shorten live range %d to [%d\n", vreg(),
             start.value());
  DCHECK_NOT_NULL(first_interval_);
  DCHECK(first_interval_->start() <= start);
  DCHECK(start < first_interval_->end());
  first_interval_->set_start(start);
}

void TopLevelLiveRange::EnsureInterval(LifetimePosition start,
                                       LifetimePosition end, Zone* zone,
                                       bool trace_alloc) {
  TRACE_COND(trace_alloc, "Ensure live range %d in interval [%d %d[\n", vreg(),
             start.value(), end.value());
  LifetimePosition new_end = end;
  while (first_interval_ != nullptr && first_interval_->start() <= end) {
    if (first_interval_->end() > end) {
      new_end = first_interval_->end();
    }
    first_interval_ = first_interval_->next();
  }

  UseInterval* new_interval = zone->New<UseInterval>(start, new_end);
  new_interval->set_next(first_interval_);
  first_interval_ = new_interval;
  if (new_interval->next() == nullptr) {
    last_interval_ = new_interval;
  }
}

void TopLevelLiveRange::AddUseInterval(LifetimePosition start,
                                       LifetimePosition end, Zone* zone,
                                       bool trace_alloc) {
  TRACE_COND(trace_alloc, "Add to live range %d interval [%d %d[\n", vreg(),
             start.value(), end.value());
  if (first_interval_ == nullptr) {
    UseInterval* interval = zone->New<UseInterval>(start, end);
    first_interval_ = interval;
    last_interval_ = interval;
  } else {
    if (end == first_interval_->start()) {
      first_interval_->set_start(start);
    } else if (end < first_interval_->start()) {
      UseInterval* interval = zone->New<UseInterval>(start, end);
      interval->set_next(first_interval_);
      first_interval_ = interval;
    } else {
      // Order of instruction's processing (see ProcessInstructions) guarantees
      // that each new use interval either precedes, intersects with or touches
      // the last added interval.
      DCHECK(start <= first_interval_->end());
      first_interval_->set_start(std::min(start, first_interval_->start()));
      first_interval_->set_end(std::max(end, first_interval_->end()));
    }
  }
}

void TopLevelLiveRange::AddUsePosition(UsePosition* use_pos, bool trace_alloc) {
  LifetimePosition pos = use_pos->pos();
  TRACE_COND(trace_alloc, "Add to live range %d use position %d\n", vreg(),
             pos.value());
  UsePosition* prev_hint = nullptr;
  UsePosition* prev = nullptr;
  UsePosition* current = first_pos_;
  while (current != nullptr && current->pos() < pos) {
    prev_hint = current->HasHint() ? current : prev_hint;
    prev = current;
    current = current->next();
  }

  if (prev == nullptr) {
    use_pos->set_next(first_pos_);
    first_pos_ = use_pos;
  } else {
    use_pos->set_next(prev->next());
    prev->set_next(use_pos);
  }

  if (prev_hint == nullptr && use_pos->HasHint()) {
    current_hint_position_ = use_pos;
  }
}

static bool AreUseIntervalsIntersecting(UseInterval* interval1,
                                        UseInterval* interval2) {
  while (interval1 != nullptr && interval2 != nullptr) {
    if (interval1->start() < interval2->start()) {
      if (interval1->end() > interval2->start()) {
        return true;
      }
      interval1 = interval1->next();
    } else {
      if (interval2->end() > interval1->start()) {
        return true;
      }
      interval2 = interval2->next();
    }
  }
  return false;
}

std::ostream& operator<<(std::ostream& os,
                         const PrintableLiveRange& printable_range) {
  const LiveRange* range = printable_range.range_;
  os << "Range: " << range->TopLevel()->vreg() << ":" << range->relative_id()
     << " ";
  if (range->TopLevel()->is_phi()) os << "phi ";
  if (range->TopLevel()->is_non_loop_phi()) os << "nlphi ";

  os << "{" << std::endl;
  UseInterval* interval = range->first_interval();
  UsePosition* use_pos = range->first_pos();
  while (use_pos != nullptr) {
    if (use_pos->HasOperand()) {
      os << *use_pos->operand() << use_pos->pos() << " ";
    }
    use_pos = use_pos->next();
  }
  os << std::endl;

  while (interval != nullptr) {
    os << '[' << interval->start() << ", " << interval->end() << ')'
       << std::endl;
    interval = interval->next();
  }
  os << "}";
  return os;
}

namespace {
void PrintBlockRow(std::ostream& os, const InstructionBlocks& blocks) {
  os << "     ";
  for (auto block : blocks) {
    LifetimePosition start_pos = LifetimePosition::GapFromInstructionIndex(
        block->first_instruction_index());
    LifetimePosition end_pos = LifetimePosition::GapFromInstructionIndex(
                                   block->last_instruction_index())
                                   .NextFullStart();
    int length = end_pos.value() - start_pos.value();
    constexpr int kMaxPrefixLength = 32;
    char buffer[kMaxPrefixLength];
    int rpo_number = block->rpo_number().ToInt();
    const char* deferred_marker = block->IsDeferred() ? "(deferred)" : "";
    int max_prefix_length = std::min(length, kMaxPrefixLength);
    int prefix = snprintf(buffer, max_prefix_length, "[-B%d-%s", rpo_number,
                          deferred_marker);
    os << buffer;
    int remaining = length - std::min(prefix, max_prefix_length) - 1;
    for (int i = 0; i < remaining; ++i) os << '-';
    os << ']';
  }
  os << '\n';
}
}  // namespace

void LinearScanAllocator::PrintRangeRow(std::ostream& os,
                                        const TopLevelLiveRange* toplevel) {
  int position = 0;
  os << std::setw(3) << toplevel->vreg() << ": ";

  const char* kind_string;
  switch (toplevel->spill_type()) {
    case TopLevelLiveRange::SpillType::kSpillRange:
      kind_string = "ss";
      break;
    case TopLevelLiveRange::SpillType::kDeferredSpillRange:
      kind_string = "sd";
      break;
    case TopLevelLiveRange::SpillType::kSpillOperand:
      kind_string = "so";
      break;
    default:
      kind_string = "s?";
  }

  for (const LiveRange* range = toplevel; range != nullptr;
       range = range->next()) {
    for (UseInterval* interval = range->first_interval(); interval != nullptr;
         interval = interval->next()) {
      LifetimePosition start = interval->start();
      LifetimePosition end = interval->end();
      CHECK_GE(start.value(), position);
      for (; start.value() > position; position++) {
        os << ' ';
      }
      int length = end.value() - start.value();
      constexpr int kMaxPrefixLength = 32;
      char buffer[kMaxPrefixLength];
      int max_prefix_length = std::min(length + 1, kMaxPrefixLength);
      int prefix;
      if (range->spilled()) {
        prefix = snprintf(buffer, max_prefix_length, "|%s", kind_string);
      } else {
        prefix = snprintf(buffer, max_prefix_length, "|%s",
                          RegisterName(range->assigned_register()));
      }
      os << buffer;
      position += std::min(prefix, max_prefix_length - 1);
      CHECK_GE(end.value(), position);
      const char line_style = range->spilled() ? '-' : '=';
      for (; end.value() > position; position++) {
        os << line_style;
      }
    }
  }
  os << '\n';
}

void LinearScanAllocator::PrintRangeOverview(std::ostream& os) {
  PrintBlockRow(os, code()->instruction_blocks());
  for (auto const toplevel : data()->fixed_live_ranges()) {
    if (toplevel == nullptr) continue;
    PrintRangeRow(os, toplevel);
  }
  int rowcount = 0;
  for (auto toplevel : data()->live_ranges()) {
    if (!CanProcessRange(toplevel)) continue;
    if (rowcount++ % 10 == 0) PrintBlockRow(os, code()->instruction_blocks());
    PrintRangeRow(os, toplevel);
  }
}

SpillRange::SpillRange(TopLevelLiveRange* parent, Zone* zone)
    : live_ranges_(zone),
      assigned_slot_(kUnassignedSlot),
      byte_width_(ByteWidthForStackSlot(parent->representation())) {
  // Spill ranges are created for top level. This is so that, when merging
  // decisions are made, we consider the full extent of the virtual register,
  // and avoid clobbering it.
  UseInterval* result = nullptr;
  UseInterval* node = nullptr;
  // Copy the intervals for all ranges.
  for (LiveRange* range = parent; range != nullptr; range = range->next()) {
    UseInterval* src = range->first_interval();
    while (src != nullptr) {
      UseInterval* new_node = zone->New<UseInterval>(src->start(), src->end());
      if (result == nullptr) {
        result = new_node;
      } else {
        node->set_next(new_node);
      }
      node = new_node;
      src = src->next();
    }
  }
  use_interval_ = result;
  live_ranges().push_back(parent);
  end_position_ = node->end();
  parent->SetSpillRange(this);
}

bool SpillRange::IsIntersectingWith(SpillRange* other) const {
  if (this->use_interval_ == nullptr || other->use_interval_ == nullptr ||
      this->End() <= other->use_interval_->start() ||
      other->End() <= this->use_interval_->start()) {
    return false;
  }
  return AreUseIntervalsIntersecting(use_interval_, other->use_interval_);
}

bool SpillRange::TryMerge(SpillRange* other) {
  if (HasSlot() || other->HasSlot()) return false;
  if (byte_width() != other->byte_width() || IsIntersectingWith(other))
    return false;

  LifetimePosition max = LifetimePosition::MaxPosition();
  if (End() < other->End() && other->End() != max) {
    end_position_ = other->End();
  }
  other->end_position_ = max;

  MergeDisjointIntervals(other->use_interval_);
  other->use_interval_ = nullptr;

  for (TopLevelLiveRange* range : other->live_ranges()) {
    DCHECK(range->GetSpillRange() == other);
    range->SetSpillRange(this);
  }

  live_ranges().insert(live_ranges().end(), other->live_ranges().begin(),
                       other->live_ranges().end());
  other->live_ranges().clear();

  return true;
}

void SpillRange::MergeDisjointIntervals(UseInterval* other) {
  UseInterval* tail = nullptr;
  UseInterval* current = use_interval_;
  while (other != nullptr) {
    // Make sure the 'current' list starts first
    if (current == nullptr || current->start() > other->start()) {
      std::swap(current, other);
    }
    // Check disjointness
    DCHECK(other == nullptr || current->end() <= other->start());
    // Append the 'current' node to the result accumulator and move forward
    if (tail == nullptr) {
      use_interval_ = current;
    } else {
      tail->set_next(current);
    }
    tail = current;
    current = current->next();
  }
  // Other list is empty => we are done
}

void SpillRange::Print() const {
  StdoutStream os;
  os << "{" << std::endl;
  for (TopLevelLiveRange* range : live_ranges()) {
    os << range->vreg() << " ";
  }
  os << std::endl;

  for (UseInterval* i = interval(); i != nullptr; i = i->next()) {
    os << '[' << i->start() << ", " << i->end() << ')' << std::endl;
  }
  os << "}" << std::endl;
}

TopTierRegisterAllocationData::PhiMapValue::PhiMapValue(
    PhiInstruction* phi, const InstructionBlock* block, Zone* zone)
    : phi_(phi),
      block_(block),
      incoming_operands_(zone),
      assigned_register_(kUnassignedRegister) {
  incoming_operands_.reserve(phi->operands().size());
}

void TopTierRegisterAllocationData::PhiMapValue::AddOperand(
    InstructionOperand* operand) {
  incoming_operands_.push_back(operand);
}

void TopTierRegisterAllocationData::PhiMapValue::CommitAssignment(
    const InstructionOperand& assigned) {
  for (InstructionOperand* operand : incoming_operands_) {
    InstructionOperand::ReplaceWith(operand, &assigned);
  }
}

TopTierRegisterAllocationData::TopTierRegisterAllocationData(
    const RegisterConfiguration* config, Zone* zone, Frame* frame,
    InstructionSequence* code, RegisterAllocationFlags flags,
    TickCounter* tick_counter, const char* debug_name)
    : RegisterAllocationData(Type::kTopTier),
      allocation_zone_(zone),
      frame_(frame),
      code_(code),
      debug_name_(debug_name),
      config_(config),
      phi_map_(allocation_zone()),
      live_in_sets_(code->InstructionBlockCount(), nullptr, allocation_zone()),
      live_out_sets_(code->InstructionBlockCount(), nullptr, allocation_zone()),
      live_ranges_(code->VirtualRegisterCount() * 2, nullptr,
                   allocation_zone()),
      fixed_live_ranges_(kNumberOfFixedRangesPerRegister *
                             this->config()->num_general_registers(),
                         nullptr, allocation_zone()),
      fixed_float_live_ranges_(allocation_zone()),
      fixed_double_live_ranges_(kNumberOfFixedRangesPerRegister *
                                    this->config()->num_double_registers(),
                                nullptr, allocation_zone()),
      fixed_simd128_live_ranges_(allocation_zone()),
      spill_ranges_(code->VirtualRegisterCount(), nullptr, allocation_zone()),
      delayed_references_(allocation_zone()),
      assigned_registers_(nullptr),
      assigned_double_registers_(nullptr),
      virtual_register_count_(code->VirtualRegisterCount()),
      preassigned_slot_ranges_(zone),
      spill_state_(code->InstructionBlockCount(), ZoneVector<LiveRange*>(zone),
                   zone),
      flags_(flags),
      tick_counter_(tick_counter) {
  if (!kSimpleFPAliasing) {
    fixed_float_live_ranges_.resize(
        kNumberOfFixedRangesPerRegister * this->config()->num_float_registers(),
        nullptr);
    fixed_simd128_live_ranges_.resize(
        kNumberOfFixedRangesPerRegister *
            this->config()->num_simd128_registers(),
        nullptr);
  }

  assigned_registers_ = code_zone()->New<BitVector>(
      this->config()->num_general_registers(), code_zone());
  assigned_double_registers_ = code_zone()->New<BitVector>(
      this->config()->num_double_registers(), code_zone());
  fixed_register_use_ = code_zone()->New<BitVector>(
      this->config()->num_general_registers(), code_zone());
  fixed_fp_register_use_ = code_zone()->New<BitVector>(
      this->config()->num_double_registers(), code_zone());

  this->frame()->SetAllocatedRegisters(assigned_registers_);
  this->frame()->SetAllocatedDoubleRegisters(assigned_double_registers_);
}

MoveOperands* TopTierRegisterAllocationData::AddGapMove(
    int index, Instruction::GapPosition position,
    const InstructionOperand& from, const InstructionOperand& to) {
  Instruction* instr = code()->InstructionAt(index);
  ParallelMove* moves = instr->GetOrCreateParallelMove(position, code_zone());
  return moves->AddMove(from, to);
}

MachineRepresentation TopTierRegisterAllocationData::RepresentationFor(
    int virtual_register) {
  DCHECK_LT(virtual_register, code()->VirtualRegisterCount());
  return code()->GetRepresentation(virtual_register);
}

TopLevelLiveRange* TopTierRegisterAllocationData::GetOrCreateLiveRangeFor(
    int index) {
  if (index >= static_cast<int>(live_ranges().size())) {
    live_ranges().resize(index + 1, nullptr);
  }
  TopLevelLiveRange* result = live_ranges()[index];
  if (result == nullptr) {
    result = NewLiveRange(index, RepresentationFor(index));
    live_ranges()[index] = result;
  }
  return result;
}

TopLevelLiveRange* TopTierRegisterAllocationData::NewLiveRange(
    int index, MachineRepresentation rep) {
  return allocation_zone()->New<TopLevelLiveRange>(index, rep);
}

int TopTierRegisterAllocationData::GetNextLiveRangeId() {
  int vreg = virtual_register_count_++;
  if (vreg >= static_cast<int>(live_ranges().size())) {
    live_ranges().resize(vreg + 1, nullptr);
  }
  return vreg;
}

TopLevelLiveRange* TopTierRegisterAllocationData::NextLiveRange(
    MachineRepresentation rep) {
  int vreg = GetNextLiveRangeId();
  TopLevelLiveRange* ret = NewLiveRange(vreg, rep);
  return ret;
}

TopTierRegisterAllocationData::PhiMapValue*
TopTierRegisterAllocationData::InitializePhiMap(const InstructionBlock* block,
                                                PhiInstruction* phi) {
  TopTierRegisterAllocationData::PhiMapValue* map_value =
      allocation_zone()->New<TopTierRegisterAllocationData::PhiMapValue>(
          phi, block, allocation_zone());
  auto res =
      phi_map_.insert(std::make_pair(phi->virtual_register(), map_value));
  DCHECK(res.second);
  USE(res);
  return map_value;
}

TopTierRegisterAllocationData::PhiMapValue*
TopTierRegisterAllocationData::GetPhiMapValueFor(int virtual_register) {
  auto it = phi_map_.find(virtual_register);
  DCHECK(it != phi_map_.end());
  return it->second;
}

TopTierRegisterAllocationData::PhiMapValue*
TopTierRegisterAllocationData::GetPhiMapValueFor(TopLevelLiveRange* top_range) {
  return GetPhiMapValueFor(top_range->vreg());
}

bool TopTierRegisterAllocationData::ExistsUseWithoutDefinition() {
  bool found = false;
  BitVector::Iterator iterator(live_in_sets()[0]);
  while (!iterator.Done()) {
    found = true;
    int operand_index = iterator.Current();
    PrintF("Register allocator error: live v%d reached first block.\n",
           operand_index);
    LiveRange* range = GetOrCreateLiveRangeFor(operand_index);
    PrintF("  (first use is at %d)\n", range->first_pos()->pos().value());
    if (debug_name() == nullptr) {
      PrintF("\n");
    } else {
      PrintF("  (function: %s)\n", debug_name());
    }
    iterator.Advance();
  }
  return found;
}

// If a range is defined in a deferred block, we can expect all the range
// to only cover positions in deferred blocks. Otherwise, a block on the
// hot path would be dominated by a deferred block, meaning it is unreachable
// without passing through the deferred block, which is contradictory.
// In particular, when such a range contributes a result back on the hot
// path, it will be as one of the inputs of a phi. In that case, the value
// will be transferred via a move in the Gap::END's of the last instruction
// of a deferred block.
bool TopTierRegisterAllocationData::RangesDefinedInDeferredStayInDeferred() {
  const size_t live_ranges_size = live_ranges().size();
  for (const TopLevelLiveRange* range : live_ranges()) {
    CHECK_EQ(live_ranges_size,
             live_ranges().size());  // TODO(neis): crbug.com/831822
    if (range == nullptr || range->IsEmpty() ||
        !code()
             ->GetInstructionBlock(range->Start().ToInstructionIndex())
             ->IsDeferred()) {
      continue;
    }
    for (const UseInterval* i = range->first_interval(); i != nullptr;
         i = i->next()) {
      int first = i->FirstGapIndex();
      int last = i->LastGapIndex();
      for (int instr = first; instr <= last;) {
        const InstructionBlock* block = code()->GetInstructionBlock(instr);
        if (!block->IsDeferred()) return false;
        instr = block->last_instruction_index() + 1;
      }
    }
  }
  return true;
}

SpillRange* TopTierRegisterAllocationData::AssignSpillRangeToLiveRange(
    TopLevelLiveRange* range, SpillMode spill_mode) {
  using SpillType = TopLevelLiveRange::SpillType;
  DCHECK(!range->HasSpillOperand());

  SpillRange* spill_range = range->GetAllocatedSpillRange();
  if (spill_range == nullptr) {
    spill_range = allocation_zone()->New<SpillRange>(range, allocation_zone());
  }
  if (spill_mode == SpillMode::kSpillDeferred &&
      (range->spill_type() != SpillType::kSpillRange)) {
    range->set_spill_type(SpillType::kDeferredSpillRange);
  } else {
    range->set_spill_type(SpillType::kSpillRange);
  }

  spill_ranges()[range->vreg()] = spill_range;
  return spill_range;
}

void TopTierRegisterAllocationData::MarkFixedUse(MachineRepresentation rep,
                                                 int index) {
  switch (rep) {
    case MachineRepresentation::kFloat32:
    case MachineRepresentation::kSimd128:
      if (kSimpleFPAliasing) {
        fixed_fp_register_use_->Add(index);
      } else {
        int alias_base_index = -1;
        int aliases = config()->GetAliases(
            rep, index, MachineRepresentation::kFloat64, &alias_base_index);
        DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
        while (aliases--) {
          int aliased_reg = alias_base_index + aliases;
          fixed_fp_register_use_->Add(aliased_reg);
        }
      }
      break;
    case MachineRepresentation::kFloat64:
      fixed_fp_register_use_->Add(index);
      break;
    default:
      DCHECK(!IsFloatingPoint(rep));
      fixed_register_use_->Add(index);
      break;
  }
}

bool TopTierRegisterAllocationData::HasFixedUse(MachineRepresentation rep,
                                                int index) {
  switch (rep) {
    case MachineRepresentation::kFloat32:
    case MachineRepresentation::kSimd128:
      if (kSimpleFPAliasing) {
        return fixed_fp_register_use_->Contains(index);
      } else {
        int alias_base_index = -1;
        int aliases = config()->GetAliases(
            rep, index, MachineRepresentation::kFloat64, &alias_base_index);
        DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
        bool result = false;
        while (aliases-- && !result) {
          int aliased_reg = alias_base_index + aliases;
          result |= fixed_fp_register_use_->Contains(aliased_reg);
        }
        return result;
      }
      break;
    case MachineRepresentation::kFloat64:
      return fixed_fp_register_use_->Contains(index);
      break;
    default:
      DCHECK(!IsFloatingPoint(rep));
      return fixed_register_use_->Contains(index);
      break;
  }
}

void TopTierRegisterAllocationData::MarkAllocated(MachineRepresentation rep,
                                                  int index) {
  switch (rep) {
    case MachineRepresentation::kFloat32:
    case MachineRepresentation::kSimd128:
      if (kSimpleFPAliasing) {
        assigned_double_registers_->Add(index);
      } else {
        int alias_base_index = -1;
        int aliases = config()->GetAliases(
            rep, index, MachineRepresentation::kFloat64, &alias_base_index);
        DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
        while (aliases--) {
          int aliased_reg = alias_base_index + aliases;
          assigned_double_registers_->Add(aliased_reg);
        }
      }
      break;
    case MachineRepresentation::kFloat64:
      assigned_double_registers_->Add(index);
      break;
    default:
      DCHECK(!IsFloatingPoint(rep));
      assigned_registers_->Add(index);
      break;
  }
}

bool TopTierRegisterAllocationData::IsBlockBoundary(
    LifetimePosition pos) const {
  return pos.IsFullStart() &&
         (static_cast<size_t>(pos.ToInstructionIndex()) ==
              code()->instructions().size() ||
          code()->GetInstructionBlock(pos.ToInstructionIndex())->code_start() ==
              pos.ToInstructionIndex());
}

ConstraintBuilder::ConstraintBuilder(TopTierRegisterAllocationData* data)
    : data_(data) {}

InstructionOperand* ConstraintBuilder::AllocateFixed(
    UnallocatedOperand* operand, int pos, bool is_tagged, bool is_input) {
  TRACE("Allocating fixed reg for op %d\n", operand->virtual_register());
  DCHECK(operand->HasFixedPolicy());
  InstructionOperand allocated;
  MachineRepresentation rep = InstructionSequence::DefaultRepresentation();
  int virtual_register = operand->virtual_register();
  if (virtual_register != InstructionOperand::kInvalidVirtualRegister) {
    rep = data()->RepresentationFor(virtual_register);
  }
  if (operand->HasFixedSlotPolicy()) {
    allocated = AllocatedOperand(AllocatedOperand::STACK_SLOT, rep,
                                 operand->fixed_slot_index());
  } else if (operand->HasFixedRegisterPolicy()) {
    DCHECK(!IsFloatingPoint(rep));
    DCHECK(data()->config()->IsAllocatableGeneralCode(
        operand->fixed_register_index()));
    allocated = AllocatedOperand(AllocatedOperand::REGISTER, rep,
                                 operand->fixed_register_index());
  } else if (operand->HasFixedFPRegisterPolicy()) {
    DCHECK(IsFloatingPoint(rep));
    DCHECK_NE(InstructionOperand::kInvalidVirtualRegister, virtual_register);
    allocated = AllocatedOperand(AllocatedOperand::REGISTER, rep,
                                 operand->fixed_register_index());
  } else {
    UNREACHABLE();
  }
  if (is_input && allocated.IsAnyRegister()) {
    data()->MarkFixedUse(rep, operand->fixed_register_index());
  }
  InstructionOperand::ReplaceWith(operand, &allocated);
  if (is_tagged) {
    TRACE("Fixed reg is tagged at %d\n", pos);
    Instruction* instr = code()->InstructionAt(pos);
    if (instr->HasReferenceMap()) {
      instr->reference_map()->RecordReference(*AllocatedOperand::cast(operand));
    }
  }
  return operand;
}

void ConstraintBuilder::MeetRegisterConstraints() {
  for (InstructionBlock* block : code()->instruction_blocks()) {
    data_->tick_counter()->TickAndMaybeEnterSafepoint();
    MeetRegisterConstraints(block);
  }
}

void ConstraintBuilder::MeetRegisterConstraints(const InstructionBlock* block) {
  int start = block->first_instruction_index();
  int end = block->last_instruction_index();
  DCHECK_NE(-1, start);
  for (int i = start; i <= end; ++i) {
    MeetConstraintsBefore(i);
    if (i != end) MeetConstraintsAfter(i);
  }
  // Meet register constraints for the instruction in the end.
  MeetRegisterConstraintsForLastInstructionInBlock(block);
}

void ConstraintBuilder::MeetRegisterConstraintsForLastInstructionInBlock(
    const InstructionBlock* block) {
  int end = block->last_instruction_index();
  Instruction* last_instruction = code()->InstructionAt(end);
  for (size_t i = 0; i < last_instruction->OutputCount(); i++) {
    InstructionOperand* output_operand = last_instruction->OutputAt(i);
    DCHECK(!output_operand->IsConstant());
    UnallocatedOperand* output = UnallocatedOperand::cast(output_operand);
    int output_vreg = output->virtual_register();
    TopLevelLiveRange* range = data()->GetOrCreateLiveRangeFor(output_vreg);
    bool assigned = false;
    if (output->HasFixedPolicy()) {
      AllocateFixed(output, -1, false, false);
      // This value is produced on the stack, we never need to spill it.
      if (output->IsStackSlot()) {
        DCHECK(LocationOperand::cast(output)->index() <
               data()->frame()->GetSpillSlotCount());
        range->SetSpillOperand(LocationOperand::cast(output));
        range->SetSpillStartIndex(end);
        assigned = true;
      }

      for (const RpoNumber& succ : block->successors()) {
        const InstructionBlock* successor = code()->InstructionBlockAt(succ);
        DCHECK_EQ(1, successor->PredecessorCount());
        int gap_index = successor->first_instruction_index();
        // Create an unconstrained operand for the same virtual register
        // and insert a gap move from the fixed output to the operand.
        UnallocatedOperand output_copy(UnallocatedOperand::REGISTER_OR_SLOT,
                                       output_vreg);
        data()->AddGapMove(gap_index, Instruction::START, *output, output_copy);
      }
    }

    if (!assigned) {
      for (const RpoNumber& succ : block->successors()) {
        const InstructionBlock* successor = code()->InstructionBlockAt(succ);
        DCHECK_EQ(1, successor->PredecessorCount());
        int gap_index = successor->first_instruction_index();
        range->RecordSpillLocation(allocation_zone(), gap_index, output);
        range->SetSpillStartIndex(gap_index);
      }
    }
  }
}

void ConstraintBuilder::MeetConstraintsAfter(int instr_index) {
  Instruction* first = code()->InstructionAt(instr_index);
  // Handle fixed temporaries.
  for (size_t i = 0; i < first->TempCount(); i++) {
    UnallocatedOperand* temp = UnallocatedOperand::cast(first->TempAt(i));
    if (temp->HasFixedPolicy()) AllocateFixed(temp, instr_index, false, false);
  }
  // Handle constant/fixed output operands.
  for (size_t i = 0; i < first->OutputCount(); i++) {
    InstructionOperand* output = first->OutputAt(i);
    if (output->IsConstant()) {
      int output_vreg = ConstantOperand::cast(output)->virtual_register();
      TopLevelLiveRange* range = data()->GetOrCreateLiveRangeFor(output_vreg);
      range->SetSpillStartIndex(instr_index + 1);
      range->SetSpillOperand(output);
      continue;
    }
    UnallocatedOperand* first_output = UnallocatedOperand::cast(output);
    TopLevelLiveRange* range =
        data()->GetOrCreateLiveRangeFor(first_output->virtual_register());
    bool assigned = false;
    if (first_output->HasFixedPolicy()) {
      int output_vreg = first_output->virtual_register();
      UnallocatedOperand output_copy(UnallocatedOperand::REGISTER_OR_SLOT,
                                     output_vreg);
      bool is_tagged = code()->IsReference(output_vreg);
      if (first_output->HasSecondaryStorage()) {
        range->MarkHasPreassignedSlot();
        data()->preassigned_slot_ranges().push_back(
            std::make_pair(range, first_output->GetSecondaryStorage()));
      }
      AllocateFixed(first_output, instr_index, is_tagged, false);

      // This value is produced on the stack, we never need to spill it.
      if (first_output->IsStackSlot()) {
        DCHECK(LocationOperand::cast(first_output)->index() <
               data()->frame()->GetTotalFrameSlotCount());
        range->SetSpillOperand(LocationOperand::cast(first_output));
        range->SetSpillStartIndex(instr_index + 1);
        assigned = true;
      }
      data()->AddGapMove(instr_index + 1, Instruction::START, *first_output,
                         output_copy);
    }
    // Make sure we add a gap move for spilling (if we have not done
    // so already).
    if (!assigned) {
      range->RecordSpillLocation(allocation_zone(), instr_index + 1,
                                 first_output);
      range->SetSpillStartIndex(instr_index + 1);
    }
  }
}

void ConstraintBuilder::MeetConstraintsBefore(int instr_index) {
  Instruction* second = code()->InstructionAt(instr_index);
  // Handle fixed input operands of second instruction.
  for (size_t i = 0; i < second->InputCount(); i++) {
    InstructionOperand* input = second->InputAt(i);
    if (input->IsImmediate()) {
      continue;  // Ignore immediates.
    }
    UnallocatedOperand* cur_input = UnallocatedOperand::cast(input);
    if (cur_input->HasFixedPolicy()) {
      int input_vreg = cur_input->virtual_register();
      UnallocatedOperand input_copy(UnallocatedOperand::REGISTER_OR_SLOT,
                                    input_vreg);
      bool is_tagged = code()->IsReference(input_vreg);
      AllocateFixed(cur_input, instr_index, is_tagged, true);
      data()->AddGapMove(instr_index, Instruction::END, input_copy, *cur_input);
    }
  }
  // Handle "output same as input" for second instruction.
  for (size_t i = 0; i < second->OutputCount(); i++) {
    InstructionOperand* output = second->OutputAt(i);
    if (!output->IsUnallocated()) continue;
    UnallocatedOperand* second_output = UnallocatedOperand::cast(output);
    if (!second_output->HasSameAsInputPolicy()) continue;
    DCHECK_EQ(0, i);  // Only valid for first output.
    UnallocatedOperand* cur_input =
        UnallocatedOperand::cast(second->InputAt(0));
    int output_vreg = second_output->virtual_register();
    int input_vreg = cur_input->virtual_register();
    UnallocatedOperand input_copy(UnallocatedOperand::REGISTER_OR_SLOT,
                                  input_vreg);
    *cur_input =
        UnallocatedOperand(*cur_input, second_output->virtual_register());
    MoveOperands* gap_move = data()->AddGapMove(instr_index, Instruction::END,
                                                input_copy, *cur_input);
    DCHECK_NOT_NULL(gap_move);
    if (code()->IsReference(input_vreg) && !code()->IsReference(output_vreg)) {
      if (second->HasReferenceMap()) {
        TopTierRegisterAllocationData::DelayedReference delayed_reference = {
            second->reference_map(), &gap_move->source()};
        data()->delayed_references().push_back(delayed_reference);
      }
    }
  }
}

void ConstraintBuilder::ResolvePhis() {
  // Process the blocks in reverse order.
  for (InstructionBlock* block : base::Reversed(code()->instruction_blocks())) {
    data_->tick_counter()->TickAndMaybeEnterSafepoint();
    ResolvePhis(block);
  }
}

void ConstraintBuilder::ResolvePhis(const InstructionBlock* block) {
  for (PhiInstruction* phi : block->phis()) {
    int phi_vreg = phi->virtual_register();
    TopTierRegisterAllocationData::PhiMapValue* map_value =
        data()->InitializePhiMap(block, phi);
    InstructionOperand& output = phi->output();
    // Map the destination operands, so the commitment phase can find them.
    for (size_t i = 0; i < phi->operands().size(); ++i) {
      InstructionBlock* cur_block =
          code()->InstructionBlockAt(block->predecessors()[i]);
      UnallocatedOperand input(UnallocatedOperand::REGISTER_OR_SLOT,
                               phi->operands()[i]);
      MoveOperands* move = data()->AddGapMove(
          cur_block->last_instruction_index(), Instruction::END, input, output);
      map_value->AddOperand(&move->destination());
      DCHECK(!code()
                  ->InstructionAt(cur_block->last_instruction_index())
                  ->HasReferenceMap());
    }
    TopLevelLiveRange* live_range = data()->GetOrCreateLiveRangeFor(phi_vreg);
    int gap_index = block->first_instruction_index();
    live_range->RecordSpillLocation(allocation_zone(), gap_index, &output);
    live_range->SetSpillStartIndex(gap_index);
    // We use the phi-ness of some nodes in some later heuristics.
    live_range->set_is_phi(true);
    live_range->set_is_non_loop_phi(!block->IsLoopHeader());
  }
}

LiveRangeBuilder::LiveRangeBuilder(TopTierRegisterAllocationData* data,
                                   Zone* local_zone)
    : data_(data), phi_hints_(local_zone) {}

BitVector* LiveRangeBuilder::ComputeLiveOut(
    const InstructionBlock* block, TopTierRegisterAllocationData* data) {
  size_t block_index = block->rpo_number().ToSize();
  BitVector* live_out = data->live_out_sets()[block_index];
  if (live_out == nullptr) {
    // Compute live out for the given block, except not including backward
    // successor edges.
    Zone* zone = data->allocation_zone();
    const InstructionSequence* code = data->code();

    live_out = zone->New<BitVector>(code->VirtualRegisterCount(), zone);

    // Process all successor blocks.
    for (const RpoNumber& succ : block->successors()) {
      // Add values live on entry to the successor.
      if (succ <= block->rpo_number()) continue;
      BitVector* live_in = data->live_in_sets()[succ.ToSize()];
      if (live_in != nullptr) live_out->Union(*live_in);

      // All phi input operands corresponding to this successor edge are live
      // out from this block.
      const InstructionBlock* successor = code->InstructionBlockAt(succ);
      size_t index = successor->PredecessorIndexOf(block->rpo_number());
      DCHECK(index < successor->PredecessorCount());
      for (PhiInstruction* phi : successor->phis()) {
        live_out->Add(phi->operands()[index]);
      }
    }
    data->live_out_sets()[block_index] = live_out;
  }
  return live_out;
}

void LiveRangeBuilder::AddInitialIntervals(const InstructionBlock* block,
                                           BitVector* live_out) {
  // Add an interval that includes the entire block to the live range for
  // each live_out value.
  LifetimePosition start = LifetimePosition::GapFromInstructionIndex(
      block->first_instruction_index());
  LifetimePosition end = LifetimePosition::InstructionFromInstructionIndex(
                             block->last_instruction_index())
                             .NextStart();
  BitVector::Iterator iterator(live_out);
  while (!iterator.Done()) {
    int operand_index = iterator.Current();
    TopLevelLiveRange* range = data()->GetOrCreateLiveRangeFor(operand_index);
    range->AddUseInterval(start, end, allocation_zone(),
                          data()->is_trace_alloc());
    iterator.Advance();
  }
}

int LiveRangeBuilder::FixedFPLiveRangeID(int index, MachineRepresentation rep) {
  int result = -index - 1;
  switch (rep) {
    case MachineRepresentation::kSimd128:
      result -=
          kNumberOfFixedRangesPerRegister * config()->num_float_registers();
      V8_FALLTHROUGH;
    case MachineRepresentation::kFloat32:
      result -=
          kNumberOfFixedRangesPerRegister * config()->num_double_registers();
      V8_FALLTHROUGH;
    case MachineRepresentation::kFloat64:
      result -=
          kNumberOfFixedRangesPerRegister * config()->num_general_registers();
      break;
    default:
      UNREACHABLE();
  }
  return result;
}

TopLevelLiveRange* LiveRangeBuilder::FixedLiveRangeFor(int index,
                                                       SpillMode spill_mode) {
  int offset = spill_mode == SpillMode::kSpillAtDefinition
                   ? 0
                   : config()->num_general_registers();
  DCHECK(index < config()->num_general_registers());
  TopLevelLiveRange* result = data()->fixed_live_ranges()[offset + index];
  if (result == nullptr) {
    MachineRepresentation rep = InstructionSequence::DefaultRepresentation();
    result = data()->NewLiveRange(FixedLiveRangeID(offset + index), rep);
    DCHECK(result->IsFixed());
    result->set_assigned_register(index);
    data()->MarkAllocated(rep, index);
    if (spill_mode == SpillMode::kSpillDeferred) {
      result->set_deferred_fixed();
    }
    data()->fixed_live_ranges()[offset + index] = result;
  }
  return result;
}

TopLevelLiveRange* LiveRangeBuilder::FixedFPLiveRangeFor(
    int index, MachineRepresentation rep, SpillMode spill_mode) {
  int num_regs = config()->num_double_registers();
  ZoneVector<TopLevelLiveRange*>* live_ranges =
      &data()->fixed_double_live_ranges();
  if (!kSimpleFPAliasing) {
    switch (rep) {
      case MachineRepresentation::kFloat32:
        num_regs = config()->num_float_registers();
        live_ranges = &data()->fixed_float_live_ranges();
        break;
      case MachineRepresentation::kSimd128:
        num_regs = config()->num_simd128_registers();
        live_ranges = &data()->fixed_simd128_live_ranges();
        break;
      default:
        break;
    }
  }

  int offset = spill_mode == SpillMode::kSpillAtDefinition ? 0 : num_regs;

  DCHECK(index < num_regs);
  USE(num_regs);
  TopLevelLiveRange* result = (*live_ranges)[offset + index];
  if (result == nullptr) {
    result = data()->NewLiveRange(FixedFPLiveRangeID(offset + index, rep), rep);
    DCHECK(result->IsFixed());
    result->set_assigned_register(index);
    data()->MarkAllocated(rep, index);
    if (spill_mode == SpillMode::kSpillDeferred) {
      result->set_deferred_fixed();
    }
    (*live_ranges)[offset + index] = result;
  }
  return result;
}

TopLevelLiveRange* LiveRangeBuilder::LiveRangeFor(InstructionOperand* operand,
                                                  SpillMode spill_mode) {
  if (operand->IsUnallocated()) {
    return data()->GetOrCreateLiveRangeFor(
        UnallocatedOperand::cast(operand)->virtual_register());
  } else if (operand->IsConstant()) {
    return data()->GetOrCreateLiveRangeFor(
        ConstantOperand::cast(operand)->virtual_register());
  } else if (operand->IsRegister()) {
    return FixedLiveRangeFor(
        LocationOperand::cast(operand)->GetRegister().code(), spill_mode);
  } else if (operand->IsFPRegister()) {
    LocationOperand* op = LocationOperand::cast(operand);
    return FixedFPLiveRangeFor(op->register_code(), op->representation(),
                               spill_mode);
  } else {
    return nullptr;
  }
}

UsePosition* LiveRangeBuilder::NewUsePosition(LifetimePosition pos,
                                              InstructionOperand* operand,
                                              void* hint,
                                              UsePositionHintType hint_type) {
  return allocation_zone()->New<UsePosition>(pos, operand, hint, hint_type);
}

UsePosition* LiveRangeBuilder::Define(LifetimePosition position,
                                      InstructionOperand* operand, void* hint,
                                      UsePositionHintType hint_type,
                                      SpillMode spill_mode) {
  TopLevelLiveRange* range = LiveRangeFor(operand, spill_mode);
  if (range == nullptr) return nullptr;

  if (range->IsEmpty() || range->Start() > position) {
    // Can happen if there is a definition without use.
    range->AddUseInterval(position, position.NextStart(), allocation_zone(),
                          data()->is_trace_alloc());
    range->AddUsePosition(NewUsePosition(position.NextStart()),
                          data()->is_trace_alloc());
  } else {
    range->ShortenTo(position, data()->is_trace_alloc());
  }
  if (!operand->IsUnallocated()) return nullptr;
  UnallocatedOperand* unalloc_operand = UnallocatedOperand::cast(operand);
  UsePosition* use_pos =
      NewUsePosition(position, unalloc_operand, hint, hint_type);
  range->AddUsePosition(use_pos, data()->is_trace_alloc());
  return use_pos;
}

UsePosition* LiveRangeBuilder::Use(LifetimePosition block_start,
                                   LifetimePosition position,
                                   InstructionOperand* operand, void* hint,
                                   UsePositionHintType hint_type,
                                   SpillMode spill_mode) {
  TopLevelLiveRange* range = LiveRangeFor(operand, spill_mode);
  if (range == nullptr) return nullptr;
  UsePosition* use_pos = nullptr;
  if (operand->IsUnallocated()) {
    UnallocatedOperand* unalloc_operand = UnallocatedOperand::cast(operand);
    use_pos = NewUsePosition(position, unalloc_operand, hint, hint_type);
    range->AddUsePosition(use_pos, data()->is_trace_alloc());
  }
  range->AddUseInterval(block_start, position, allocation_zone(),
                        data()->is_trace_alloc());
  return use_pos;
}

void LiveRangeBuilder::ProcessInstructions(const InstructionBlock* block,
                                           BitVector* live) {
  int block_start = block->first_instruction_index();
  LifetimePosition block_start_position =
      LifetimePosition::GapFromInstructionIndex(block_start);
  bool fixed_float_live_ranges = false;
  bool fixed_simd128_live_ranges = false;
  if (!kSimpleFPAliasing) {
    int mask = data()->code()->representation_mask();
    fixed_float_live_ranges = (mask & kFloat32Bit) != 0;
    fixed_simd128_live_ranges = (mask & kSimd128Bit) != 0;
  }
  SpillMode spill_mode = SpillModeForBlock(block);

  for (int index = block->last_instruction_index(); index >= block_start;
       index--) {
    LifetimePosition curr_position =
        LifetimePosition::InstructionFromInstructionIndex(index);
    Instruction* instr = code()->InstructionAt(index);
    DCHECK_NOT_NULL(instr);
    DCHECK(curr_position.IsInstructionPosition());
    // Process output, inputs, and temps of this instruction.
    for (size_t i = 0; i < instr->OutputCount(); i++) {
      InstructionOperand* output = instr->OutputAt(i);
      if (output->IsUnallocated()) {
        // Unsupported.
        DCHECK(!UnallocatedOperand::cast(output)->HasSlotPolicy());
        int out_vreg = UnallocatedOperand::cast(output)->virtual_register();
        live->Remove(out_vreg);
      } else if (output->IsConstant()) {
        int out_vreg = ConstantOperand::cast(output)->virtual_register();
        live->Remove(out_vreg);
      }
      if (block->IsHandler() && index == block_start && output->IsAllocated() &&
          output->IsRegister() &&
          AllocatedOperand::cast(output)->GetRegister() ==
              v8::internal::kReturnRegister0) {
        // The register defined here is blocked from gap start - it is the
        // exception value.
        // TODO(mtrofin): should we explore an explicit opcode for
        // the first instruction in the handler?
        Define(LifetimePosition::GapFromInstructionIndex(index), output,
               spill_mode);
      } else {
        Define(curr_position, output, spill_mode);
      }
    }

    if (instr->ClobbersRegisters()) {
      for (int i = 0; i < config()->num_allocatable_general_registers(); ++i) {
        // Create a UseInterval at this instruction for all fixed registers,
        // (including the instruction outputs). Adding another UseInterval here
        // is OK because AddUseInterval will just merge it with the existing
        // one at the end of the range.
        int code = config()->GetAllocatableGeneralCode(i);
        TopLevelLiveRange* range = FixedLiveRangeFor(code, spill_mode);
        range->AddUseInterval(curr_position, curr_position.End(),
                              allocation_zone(), data()->is_trace_alloc());
      }
    }

    if (instr->ClobbersDoubleRegisters()) {
      for (int i = 0; i < config()->num_allocatable_double_registers(); ++i) {
        // Add a UseInterval for all DoubleRegisters. See comment above for
        // general registers.
        int code = config()->GetAllocatableDoubleCode(i);
        TopLevelLiveRange* range = FixedFPLiveRangeFor(
            code, MachineRepresentation::kFloat64, spill_mode);
        range->AddUseInterval(curr_position, curr_position.End(),
                              allocation_zone(), data()->is_trace_alloc());
      }
      // Clobber fixed float registers on archs with non-simple aliasing.
      if (!kSimpleFPAliasing) {
        if (fixed_float_live_ranges) {
          for (int i = 0; i < config()->num_allocatable_float_registers();
               ++i) {
            // Add a UseInterval for all FloatRegisters. See comment above for
            // general registers.
            int code = config()->GetAllocatableFloatCode(i);
            TopLevelLiveRange* range = FixedFPLiveRangeFor(
                code, MachineRepresentation::kFloat32, spill_mode);
            range->AddUseInterval(curr_position, curr_position.End(),
                                  allocation_zone(), data()->is_trace_alloc());
          }
        }
        if (fixed_simd128_live_ranges) {
          for (int i = 0; i < config()->num_allocatable_simd128_registers();
               ++i) {
            int code = config()->GetAllocatableSimd128Code(i);
            TopLevelLiveRange* range = FixedFPLiveRangeFor(
                code, MachineRepresentation::kSimd128, spill_mode);
            range->AddUseInterval(curr_position, curr_position.End(),
                                  allocation_zone(), data()->is_trace_alloc());
          }
        }
      }
    }

    for (size_t i = 0; i < instr->InputCount(); i++) {
      InstructionOperand* input = instr->InputAt(i);
      if (input->IsImmediate()) {
        continue;  // Ignore immediates.
      }
      LifetimePosition use_pos;
      if (input->IsUnallocated() &&
          UnallocatedOperand::cast(input)->IsUsedAtStart()) {
        use_pos = curr_position;
      } else {
        use_pos = curr_position.End();
      }

      if (input->IsUnallocated()) {
        UnallocatedOperand* unalloc = UnallocatedOperand::cast(input);
        int vreg = unalloc->virtual_register();
        live->Add(vreg);
        if (unalloc->HasSlotPolicy()) {
          data()->GetOrCreateLiveRangeFor(vreg)->register_slot_use(
              block->IsDeferred()
                  ? TopLevelLiveRange::SlotUseKind::kDeferredSlotUse
                  : TopLevelLiveRange::SlotUseKind::kGeneralSlotUse);
        }
      }
      Use(block_start_position, use_pos, input, spill_mode);
    }

    for (size_t i = 0; i < instr->TempCount(); i++) {
      InstructionOperand* temp = instr->TempAt(i);
      // Unsupported.
      DCHECK_IMPLIES(temp->IsUnallocated(),
                     !UnallocatedOperand::cast(temp)->HasSlotPolicy());
      if (instr->ClobbersTemps()) {
        if (temp->IsRegister()) continue;
        if (temp->IsUnallocated()) {
          UnallocatedOperand* temp_unalloc = UnallocatedOperand::cast(temp);
          if (temp_unalloc->HasFixedPolicy()) {
            continue;
          }
        }
      }
      Use(block_start_position, curr_position.End(), temp, spill_mode);
      Define(curr_position, temp, spill_mode);
    }

    // Process the moves of the instruction's gaps, making their sources live.
    const Instruction::GapPosition kPositions[] = {Instruction::END,
                                                   Instruction::START};
    curr_position = curr_position.PrevStart();
    DCHECK(curr_position.IsGapPosition());
    for (const Instruction::GapPosition& position : kPositions) {
      ParallelMove* move = instr->GetParallelMove(position);
      if (move == nullptr) continue;
      if (position == Instruction::END) {
        curr_position = curr_position.End();
      } else {
        curr_position = curr_position.Start();
      }
      for (MoveOperands* cur : *move) {
        InstructionOperand& from = cur->source();
        InstructionOperand& to = cur->destination();
        void* hint = &to;
        UsePositionHintType hint_type = UsePosition::HintTypeForOperand(to);
        UsePosition* to_use = nullptr;
        int phi_vreg = -1;
        if (to.IsUnallocated()) {
          int to_vreg = UnallocatedOperand::cast(to).virtual_register();
          TopLevelLiveRange* to_range =
              data()->GetOrCreateLiveRangeFor(to_vreg);
          if (to_range->is_phi()) {
            phi_vreg = to_vreg;
            if (to_range->is_non_loop_phi()) {
              hint = to_range->current_hint_position();
              hint_type = hint == nullptr ? UsePositionHintType::kNone
                                          : UsePositionHintType::kUsePos;
            } else {
              hint_type = UsePositionHintType::kPhi;
              hint = data()->GetPhiMapValueFor(to_vreg);
            }
          } else {
            if (live->Contains(to_vreg)) {
              to_use =
                  Define(curr_position, &to, &from,
                         UsePosition::HintTypeForOperand(from), spill_mode);
              live->Remove(to_vreg);
            } else {
              cur->Eliminate();
              continue;
            }
          }
        } else {
          Define(curr_position, &to, spill_mode);
        }
        UsePosition* from_use = Use(block_start_position, curr_position, &from,
                                    hint, hint_type, spill_mode);
        // Mark range live.
        if (from.IsUnallocated()) {
          live->Add(UnallocatedOperand::cast(from).virtual_register());
        }
        // When the value is moved to a register to meet input constraints,
        // we should consider this value use similar as a register use in the
        // backward spilling heuristics, even though this value use is not
        // register benefical at the AllocateBlockedReg stage.
        if (to.IsAnyRegister() ||
            (to.IsUnallocated() &&
             UnallocatedOperand::cast(&to)->HasRegisterPolicy())) {
          from_use->set_spill_detrimental();
        }
        // Resolve use position hints just created.
        if (to_use != nullptr && from_use != nullptr) {
          to_use->ResolveHint(from_use);
          from_use->ResolveHint(to_use);
        }
        DCHECK_IMPLIES(to_use != nullptr, to_use->IsResolved());
        DCHECK_IMPLIES(from_use != nullptr, from_use->IsResolved());
        // Potentially resolve phi hint.
        if (phi_vreg != -1) ResolvePhiHint(&from, from_use);
      }
    }
  }
}

void LiveRangeBuilder::ProcessPhis(const InstructionBlock* block,
                                   BitVector* live) {
  for (PhiInstruction* phi : block->phis()) {
    // The live range interval already ends at the first instruction of the
    // block.
    int phi_vreg = phi->virtual_register();
    live->Remove(phi_vreg);
    // Select a hint from a predecessor block that precedes this block in the
    // rpo order. In order of priority:
    // - Avoid hints from deferred blocks.
    // - Prefer hints from allocated (or explicit) operands.
    // - Prefer hints from empty blocks (containing just parallel moves and a
    //   jump). In these cases, if we can elide the moves, the jump threader
    //   is likely to be able to elide the jump.
    // The enforcement of hinting in rpo order is required because hint
    // resolution that happens later in the compiler pipeline visits
    // instructions in reverse rpo order, relying on the fact that phis are
    // encountered before their hints.
    InstructionOperand* hint = nullptr;
    int hint_preference = 0;

    // The cost of hinting increases with the number of predecessors. At the
    // same time, the typical benefit decreases, since this hinting only
    // optimises the execution path through one predecessor. A limit of 2 is
    // sufficient to hit the common if/else pattern.
    int predecessor_limit = 2;

    for (RpoNumber predecessor : block->predecessors()) {
      const InstructionBlock* predecessor_block =
          code()->InstructionBlockAt(predecessor);
      DCHECK_EQ(predecessor_block->rpo_number(), predecessor);

      // Only take hints from earlier rpo numbers.
      if (predecessor >= block->rpo_number()) continue;

      // Look up the predecessor instruction.
      const Instruction* predecessor_instr =
          GetLastInstruction(code(), predecessor_block);
      InstructionOperand* predecessor_hint = nullptr;
      // Phis are assigned in the END position of the last instruction in each
      // predecessor block.
      for (MoveOperands* move :
           *predecessor_instr->GetParallelMove(Instruction::END)) {
        InstructionOperand& to = move->destination();
        if (to.IsUnallocated() &&
            UnallocatedOperand::cast(to).virtual_register() == phi_vreg) {
          predecessor_hint = &move->source();
          break;
        }
      }
      DCHECK_NOT_NULL(predecessor_hint);

      // For each predecessor, generate a score according to the priorities
      // described above, and pick the best one. Flags in higher-order bits have
      // a higher priority than those in lower-order bits.
      int predecessor_hint_preference = 0;
      const int kNotDeferredBlockPreference = (1 << 2);
      const int kMoveIsAllocatedPreference = (1 << 1);
      const int kBlockIsEmptyPreference = (1 << 0);

      // - Avoid hints from deferred blocks.
      if (!predecessor_block->IsDeferred()) {
        predecessor_hint_preference |= kNotDeferredBlockPreference;
      }

      // - Prefer hints from allocated operands.
      //
      // Already-allocated operands are typically assigned using the parallel
      // moves on the last instruction. For example:
      //
      //      gap (v101 = [x0|R|w32]) (v100 = v101)
      //      ArchJmp
      //    ...
      //    phi: v100 = v101 v102
      //
      // We have already found the END move, so look for a matching START move
      // from an allocated operand.
      //
      // Note that we cannot simply look up data()->live_ranges()[vreg] here
      // because the live ranges are still being built when this function is
      // called.
      // TODO(v8): Find a way to separate hinting from live range analysis in
      // BuildLiveRanges so that we can use the O(1) live-range look-up.
      auto moves = predecessor_instr->GetParallelMove(Instruction::START);
      if (moves != nullptr) {
        for (MoveOperands* move : *moves) {
          InstructionOperand& to = move->destination();
          if (predecessor_hint->Equals(to)) {
            if (move->source().IsAllocated()) {
              predecessor_hint_preference |= kMoveIsAllocatedPreference;
            }
            break;
          }
        }
      }

      // - Prefer hints from empty blocks.
      if (predecessor_block->last_instruction_index() ==
          predecessor_block->first_instruction_index()) {
        predecessor_hint_preference |= kBlockIsEmptyPreference;
      }

      if ((hint == nullptr) ||
          (predecessor_hint_preference > hint_preference)) {
        // Take the hint from this predecessor.
        hint = predecessor_hint;
        hint_preference = predecessor_hint_preference;
      }

      if (--predecessor_limit <= 0) break;
    }
    DCHECK_NOT_NULL(hint);

    LifetimePosition block_start = LifetimePosition::GapFromInstructionIndex(
        block->first_instruction_index());
    UsePosition* use_pos = Define(block_start, &phi->output(), hint,
                                  UsePosition::HintTypeForOperand(*hint),
                                  SpillModeForBlock(block));
    MapPhiHint(hint, use_pos);
  }
}

void LiveRangeBuilder::ProcessLoopHeader(const InstructionBlock* block,
                                         BitVector* live) {
  DCHECK(block->IsLoopHeader());
  // Add a live range stretching from the first loop instruction to the last
  // for each value live on entry to the header.
  BitVector::Iterator iterator(live);
  LifetimePosition start = LifetimePosition::GapFromInstructionIndex(
      block->first_instruction_index());
  LifetimePosition end = LifetimePosition::GapFromInstructionIndex(
                             code()->LastLoopInstructionIndex(block))
                             .NextFullStart();
  while (!iterator.Done()) {
    int operand_index = iterator.Current();
    TopLevelLiveRange* range = data()->GetOrCreateLiveRangeFor(operand_index);
    range->EnsureInterval(start, end, allocation_zone(),
                          data()->is_trace_alloc());
    iterator.Advance();
  }
  // Insert all values into the live in sets of all blocks in the loop.
  for (int i = block->rpo_number().ToInt() + 1; i < block->loop_end().ToInt();
       ++i) {
    live_in_sets()[i]->Union(*live);
  }
}

void LiveRangeBuilder::BuildLiveRanges() {
  // Process the blocks in reverse order.
  for (int block_id = code()->InstructionBlockCount() - 1; block_id >= 0;
       --block_id) {
    data_->tick_counter()->TickAndMaybeEnterSafepoint();
    InstructionBlock* block =
        code()->InstructionBlockAt(RpoNumber::FromInt(block_id));
    BitVector* live = ComputeLiveOut(block, data());
    // Initially consider all live_out values live for the entire block. We
    // will shorten these intervals if necessary.
    AddInitialIntervals(block, live);
    // Process the instructions in reverse order, generating and killing
    // live values.
    ProcessInstructions(block, live);
    // All phi output operands are killed by this block.
    ProcessPhis(block, live);
    // Now live is live_in for this block except not including values live
    // out on backward successor edges.
    if (block->IsLoopHeader()) ProcessLoopHeader(block, live);
    live_in_sets()[block_id] = live;
  }
  // Postprocess the ranges.
  const size_t live_ranges_size = data()->live_ranges().size();
  for (TopLevelLiveRange* range : data()->live_ranges()) {
    data_->tick_counter()->TickAndMaybeEnterSafepoint();
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (range == nullptr) continue;
    // Give slots to all ranges with a non fixed slot use.
    if (range->has_slot_use() && range->HasNoSpillType()) {
      SpillMode spill_mode =
          range->slot_use_kind() ==
                  TopLevelLiveRange::SlotUseKind::kDeferredSlotUse
              ? SpillMode::kSpillDeferred
              : SpillMode::kSpillAtDefinition;
      data()->AssignSpillRangeToLiveRange(range, spill_mode);
    }
    // TODO(bmeurer): This is a horrible hack to make sure that for constant
    // live ranges, every use requires the constant to be in a register.
    // Without this hack, all uses with "any" policy would get the constant
    // operand assigned.
    if (range->HasSpillOperand() && range->GetSpillOperand()->IsConstant()) {
      for (UsePosition* pos = range->first_pos(); pos != nullptr;
           pos = pos->next()) {
        if (pos->type() == UsePositionType::kRequiresSlot ||
            pos->type() == UsePositionType::kRegisterOrSlotOrConstant) {
          continue;
        }
        UsePositionType new_type = UsePositionType::kRegisterOrSlot;
        // Can't mark phis as needing a register.
        if (!pos->pos().IsGapPosition()) {
          new_type = UsePositionType::kRequiresRegister;
        }
        pos->set_type(new_type, true);
      }
    }
    range->ResetCurrentHintPosition();
  }
  for (auto preassigned : data()->preassigned_slot_ranges()) {
    TopLevelLiveRange* range = preassigned.first;
    int slot_id = preassigned.second;
    SpillRange* spill = range->HasSpillRange()
                            ? range->GetSpillRange()
                            : data()->AssignSpillRangeToLiveRange(
                                  range, SpillMode::kSpillAtDefinition);
    spill->set_assigned_slot(slot_id);
  }
#ifdef DEBUG
  Verify();
#endif
}

void LiveRangeBuilder::MapPhiHint(InstructionOperand* operand,
                                  UsePosition* use_pos) {
  DCHECK(!use_pos->IsResolved());
  auto res = phi_hints_.insert(std::make_pair(operand, use_pos));
  DCHECK(res.second);
  USE(res);
}

void LiveRangeBuilder::ResolvePhiHint(InstructionOperand* operand,
                                      UsePosition* use_pos) {
  auto it = phi_hints_.find(operand);
  if (it == phi_hints_.end()) return;
  DCHECK(!it->second->IsResolved());
  it->second->ResolveHint(use_pos);
}

void LiveRangeBuilder::Verify() const {
  for (auto& hint : phi_hints_) {
    CHECK(hint.second->IsResolved());
  }
  for (const TopLevelLiveRange* current : data()->live_ranges()) {
    if (current != nullptr && !current->IsEmpty()) {
      // New LiveRanges should not be split.
      CHECK_NULL(current->next());
      // General integrity check.
      current->Verify();
      const UseInterval* first = current->first_interval();
      if (first->next() == nullptr) continue;

      // Consecutive intervals should not end and start in the same block,
      // otherwise the intervals should have been joined, because the
      // variable is live throughout that block.
      CHECK(NextIntervalStartsInDifferentBlocks(first));

      for (const UseInterval* i = first->next(); i != nullptr; i = i->next()) {
        // Except for the first interval, the other intevals must start at
        // a block boundary, otherwise data wouldn't flow to them.
        CHECK(IntervalStartsAtBlockBoundary(i));
        // The last instruction of the predecessors of the block the interval
        // starts must be covered by the range.
        CHECK(IntervalPredecessorsCoveredByRange(i, current));
        if (i->next() != nullptr) {
          // Check the consecutive intervals property, except for the last
          // interval, where it doesn't apply.
          CHECK(NextIntervalStartsInDifferentBlocks(i));
        }
      }
    }
  }
}

bool LiveRangeBuilder::IntervalStartsAtBlockBoundary(
    const UseInterval* interval) const {
  LifetimePosition start = interval->start();
  if (!start.IsFullStart()) return false;
  int instruction_index = start.ToInstructionIndex();
  const InstructionBlock* block =
      data()->code()->GetInstructionBlock(instruction_index);
  return block->first_instruction_index() == instruction_index;
}

bool LiveRangeBuilder::IntervalPredecessorsCoveredByRange(
    const UseInterval* interval, const TopLevelLiveRange* range) const {
  LifetimePosition start = interval->start();
  int instruction_index = start.ToInstructionIndex();
  const InstructionBlock* block =
      data()->code()->GetInstructionBlock(instruction_index);
  for (RpoNumber pred_index : block->predecessors()) {
    const InstructionBlock* predecessor =
        data()->code()->InstructionBlockAt(pred_index);
    LifetimePosition last_pos = LifetimePosition::GapFromInstructionIndex(
        predecessor->last_instruction_index());
    last_pos = last_pos.NextStart().End();
    if (!range->Covers(last_pos)) return false;
  }
  return true;
}

bool LiveRangeBuilder::NextIntervalStartsInDifferentBlocks(
    const UseInterval* interval) const {
  DCHECK_NOT_NULL(interval->next());
  LifetimePosition end = interval->end();
  LifetimePosition next_start = interval->next()->start();
  // Since end is not covered, but the previous position is, move back a
  // position
  end = end.IsStart() ? end.PrevStart().End() : end.Start();
  int last_covered_index = end.ToInstructionIndex();
  const InstructionBlock* block =
      data()->code()->GetInstructionBlock(last_covered_index);
  const InstructionBlock* next_block =
      data()->code()->GetInstructionBlock(next_start.ToInstructionIndex());
  return block->rpo_number() < next_block->rpo_number();
}

void BundleBuilder::BuildBundles() {
  TRACE("Build bundles\n");
  // Process the blocks in reverse order.
  for (int block_id = code()->InstructionBlockCount() - 1; block_id >= 0;
       --block_id) {
    InstructionBlock* block =
        code()->InstructionBlockAt(RpoNumber::FromInt(block_id));
    TRACE("Block B%d\n", block_id);
    for (auto phi : block->phis()) {
      LiveRange* out_range =
          data()->GetOrCreateLiveRangeFor(phi->virtual_register());
      LiveRangeBundle* out = out_range->get_bundle();
      if (out == nullptr) {
        out = data()->allocation_zone()->New<LiveRangeBundle>(
            data()->allocation_zone(), next_bundle_id_++);
        out->TryAddRange(out_range);
      }
      TRACE("Processing phi for v%d with %d:%d\n", phi->virtual_register(),
            out_range->TopLevel()->vreg(), out_range->relative_id());
      bool phi_interferes_with_backedge_input = false;
      for (auto input : phi->operands()) {
        LiveRange* input_range = data()->GetOrCreateLiveRangeFor(input);
        TRACE("Input value v%d with range %d:%d\n", input,
              input_range->TopLevel()->vreg(), input_range->relative_id());
        LiveRangeBundle* input_bundle = input_range->get_bundle();
        if (input_bundle != nullptr) {
          TRACE("Merge\n");
          if (out->TryMerge(input_bundle, data()->is_trace_alloc())) {
            TRACE("Merged %d and %d to %d\n", phi->virtual_register(), input,
                  out->id());
          } else if (input_range->Start() > out_range->Start()) {
            // We are only interested in values defined after the phi, because
            // those are values that will go over a back-edge.
            phi_interferes_with_backedge_input = true;
          }
        } else {
          TRACE("Add\n");
          if (out->TryAddRange(input_range)) {
            TRACE("Added %d and %d to %d\n", phi->virtual_register(), input,
                  out->id());
          } else if (input_range->Start() > out_range->Start()) {
            // We are only interested in values defined after the phi, because
            // those are values that will go over a back-edge.
            phi_interferes_with_backedge_input = true;
          }
        }
      }
      // Spilling the phi at the loop header is not beneficial if there is
      // a back-edge with an input for the phi that interferes with the phi's
      // value, because in case that input gets spilled it might introduce
      // a stack-to-stack move at the back-edge.
      if (phi_interferes_with_backedge_input)
        out_range->TopLevel()->set_spilling_at_loop_header_not_beneficial();
    }
    TRACE("Done block B%d\n", block_id);
  }
}

bool LiveRangeBundle::TryAddRange(LiveRange* range) {
  DCHECK_NULL(range->get_bundle());
  // We may only add a new live range if its use intervals do not
  // overlap with existing intervals in the bundle.
  if (UsesOverlap(range->first_interval())) return false;
  ranges_.insert(range);
  range->set_bundle(this);
  InsertUses(range->first_interval());
  return true;
}
bool LiveRangeBundle::TryMerge(LiveRangeBundle* other, bool trace_alloc) {
  if (other == this) return true;

  auto iter1 = uses_.begin();
  auto iter2 = other->uses_.begin();

  while (iter1 != uses_.end() && iter2 != other->uses_.end()) {
    if (iter1->start >= iter2->end) {
      ++iter2;
    } else if (iter2->start >= iter1->end) {
      ++iter1;
    } else {
      TRACE_COND(trace_alloc, "No merge %d:%d %d:%d\n", iter1->start,
                 iter1->end, iter2->start, iter2->end);
      return false;
    }
  }
  // Uses are disjoint, merging is possible.
  for (auto it = other->ranges_.begin(); it != other->ranges_.end(); ++it) {
    (*it)->set_bundle(this);
    InsertUses((*it)->first_interval());
  }
  ranges_.insert(other->ranges_.begin(), other->ranges_.end());
  other->ranges_.clear();

  return true;
}

void LiveRangeBundle::MergeSpillRanges() {
  SpillRange* target = nullptr;
  for (auto range : ranges_) {
    if (range->TopLevel()->HasSpillRange()) {
      SpillRange* current = range->TopLevel()->GetSpillRange();
      if (target == nullptr) {
        target = current;
      } else if (target != current) {
        target->TryMerge(current);
      }
    }
  }
}

RegisterAllocator::RegisterAllocator(TopTierRegisterAllocationData* data,
                                     RegisterKind kind)
    : data_(data),
      mode_(kind),
      num_registers_(GetRegisterCount(data->config(), kind)),
      num_allocatable_registers_(
          GetAllocatableRegisterCount(data->config(), kind)),
      allocatable_register_codes_(
          GetAllocatableRegisterCodes(data->config(), kind)),
      check_fp_aliasing_(false) {
  if (!kSimpleFPAliasing && kind == RegisterKind::kDouble) {
    check_fp_aliasing_ = (data->code()->representation_mask() &
                          (kFloat32Bit | kSimd128Bit)) != 0;
  }
}

LifetimePosition RegisterAllocator::GetSplitPositionForInstruction(
    const LiveRange* range, int instruction_index) {
  LifetimePosition ret = LifetimePosition::Invalid();

  ret = LifetimePosition::GapFromInstructionIndex(instruction_index);
  if (range->Start() >= ret || ret >= range->End()) {
    return LifetimePosition::Invalid();
  }
  return ret;
}

void RegisterAllocator::SplitAndSpillRangesDefinedByMemoryOperand() {
  size_t initial_range_count = data()->live_ranges().size();
  for (size_t i = 0; i < initial_range_count; ++i) {
    CHECK_EQ(initial_range_count,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    TopLevelLiveRange* range = data()->live_ranges()[i];
    if (!CanProcessRange(range)) continue;
    // Only assume defined by memory operand if we are guaranteed to spill it or
    // it has a spill operand.
    if (range->HasNoSpillType() ||
        (range->HasSpillRange() && !range->has_non_deferred_slot_use())) {
      continue;
    }
    LifetimePosition start = range->Start();
    TRACE("Live range %d:%d is defined by a spill operand.\n",
          range->TopLevel()->vreg(), range->relative_id());
    LifetimePosition next_pos = start;
    if (next_pos.IsGapPosition()) {
      next_pos = next_pos.NextStart();
    }

    UsePosition* pos = range->NextUsePositionRegisterIsBeneficial(next_pos);
    // If the range already has a spill operand and it doesn't need a
    // register immediately, split it and spill the first part of the range.
    if (pos == nullptr) {
      Spill(range, SpillMode::kSpillAtDefinition);
    } else if (pos->pos() > range->Start().NextStart()) {
      // Do not spill live range eagerly if use position that can benefit from
      // the register is too close to the start of live range.
      LifetimePosition split_pos = GetSplitPositionForInstruction(
          range, pos->pos().ToInstructionIndex());
      // There is no place to split, so we can't split and spill.
      if (!split_pos.IsValid()) continue;

      split_pos =
          FindOptimalSplitPos(range->Start().NextFullStart(), split_pos);

      SplitRangeAt(range, split_pos);
      Spill(range, SpillMode::kSpillAtDefinition);
    }
  }
}

LiveRange* RegisterAllocator::SplitRangeAt(LiveRange* range,
                                           LifetimePosition pos) {
  DCHECK(!range->TopLevel()->IsFixed());
  TRACE("Splitting live range %d:%d at %d\n", range->TopLevel()->vreg(),
        range->relative_id(), pos.value());

  if (pos <= range->Start()) return range;

  // We can't properly connect liveranges if splitting occurred at the end
  // a block.
  DCHECK(pos.IsStart() || pos.IsGapPosition() ||
         (GetInstructionBlock(code(), pos)->last_instruction_index() !=
          pos.ToInstructionIndex()));

  LiveRange* result = range->SplitAt(pos, allocation_zone());
  return result;
}

LiveRange* RegisterAllocator::SplitBetween(LiveRange* range,
                                           LifetimePosition start,
                                           LifetimePosition end) {
  DCHECK(!range->TopLevel()->IsFixed());
  TRACE("Splitting live range %d:%d in position between [%d, %d]\n",
        range->TopLevel()->vreg(), range->relative_id(), start.value(),
        end.value());

  LifetimePosition split_pos = FindOptimalSplitPos(start, end);
  DCHECK(split_pos >= start);
  return SplitRangeAt(range, split_pos);
}

LifetimePosition RegisterAllocator::FindOptimalSplitPos(LifetimePosition start,
                                                        LifetimePosition end) {
  int start_instr = start.ToInstructionIndex();
  int end_instr = end.ToInstructionIndex();
  DCHECK_LE(start_instr, end_instr);

  // We have no choice
  if (start_instr == end_instr) return end;

  const InstructionBlock* start_block = GetInstructionBlock(code(), start);
  const InstructionBlock* end_block = GetInstructionBlock(code(), end);

  if (end_block == start_block) {
    // The interval is split in the same basic block. Split at the latest
    // possible position.
    return end;
  }

  const InstructionBlock* block = end_block;
  // Find header of outermost loop.
  do {
    const InstructionBlock* loop = GetContainingLoop(code(), block);
    if (loop == nullptr ||
        loop->rpo_number().ToInt() <= start_block->rpo_number().ToInt()) {
      // No more loops or loop starts before the lifetime start.
      break;
    }
    block = loop;
  } while (true);

  // We did not find any suitable outer loop. Split at the latest possible
  // position unless end_block is a loop header itself.
  if (block == end_block && !end_block->IsLoopHeader()) return end;

  return LifetimePosition::GapFromInstructionIndex(
      block->first_instruction_index());
}

LifetimePosition RegisterAllocator::FindOptimalSpillingPos(
    LiveRange* range, LifetimePosition pos, SpillMode spill_mode,
    LiveRange** begin_spill_out) {
  *begin_spill_out = range;
  // TODO(herhut): Be more clever here as long as we do not move pos out of
  // deferred code.
  if (spill_mode == SpillMode::kSpillDeferred) return pos;
  const InstructionBlock* block = GetInstructionBlock(code(), pos.Start());
  const InstructionBlock* loop_header =
      block->IsLoopHeader() ? block : GetContainingLoop(code(), block);
  if (loop_header == nullptr) return pos;

  while (loop_header != nullptr) {
    // We are going to spill live range inside the loop.
    // If possible try to move spilling position backwards to loop header.
    // This will reduce number of memory moves on the back edge.
    LifetimePosition loop_start = LifetimePosition::GapFromInstructionIndex(
        loop_header->first_instruction_index());
    // Stop if we moved to a loop header before the value is defined or
    // at the define position that is not beneficial to spill.
    if (range->TopLevel()->Start() > loop_start ||
        (range->TopLevel()->Start() == loop_start &&
         range->TopLevel()->SpillAtLoopHeaderNotBeneficial()))
      return pos;

    LiveRange* live_at_header = range->TopLevel()->GetChildCovers(loop_start);

    if (live_at_header != nullptr && !live_at_header->spilled()) {
      for (LiveRange* check_use = live_at_header;
           check_use != nullptr && check_use->Start() < pos;
           check_use = check_use->next()) {
        // If we find a use for which spilling is detrimental, don't spill
        // at the loop header
        UsePosition* next_use =
            check_use->NextUsePositionSpillDetrimental(loop_start);
        // UsePosition at the end of a UseInterval may
        // have the same value as the start of next range.
        if (next_use != nullptr && next_use->pos() <= pos) {
          return pos;
        }
      }
      // No register beneficial use inside the loop before the pos.
      *begin_spill_out = live_at_header;
      pos = loop_start;
    }

    // Try hoisting out to an outer loop.
    loop_header = GetContainingLoop(code(), loop_header);
  }
  return pos;
}

void RegisterAllocator::Spill(LiveRange* range, SpillMode spill_mode) {
  DCHECK(!range->spilled());
  DCHECK(spill_mode == SpillMode::kSpillAtDefinition ||
         GetInstructionBlock(code(), range->Start())->IsDeferred());
  TopLevelLiveRange* first = range->TopLevel();
  TRACE("Spilling live range %d:%d mode %d\n", first->vreg(),
        range->relative_id(), spill_mode);

  TRACE("Starting spill type is %d\n", static_cast<int>(first->spill_type()));
  if (first->HasNoSpillType()) {
    TRACE("New spill range needed");
    data()->AssignSpillRangeToLiveRange(first, spill_mode);
  }
  // Upgrade the spillmode, in case this was only spilled in deferred code so
  // far.
  if ((spill_mode == SpillMode::kSpillAtDefinition) &&
      (first->spill_type() ==
       TopLevelLiveRange::SpillType::kDeferredSpillRange)) {
    TRACE("Upgrading\n");
    first->set_spill_type(TopLevelLiveRange::SpillType::kSpillRange);
  }
  TRACE("Final spill type is %d\n", static_cast<int>(first->spill_type()));
  range->Spill();
}

const char* RegisterAllocator::RegisterName(int register_code) const {
  if (register_code == kUnassignedRegister) return "unassigned";
  return mode() == RegisterKind::kGeneral
             ? i::RegisterName(Register::from_code(register_code))
             : i::RegisterName(DoubleRegister::from_code(register_code));
}

LinearScanAllocator::LinearScanAllocator(TopTierRegisterAllocationData* data,
                                         RegisterKind kind, Zone* local_zone)
    : RegisterAllocator(data, kind),
      unhandled_live_ranges_(local_zone),
      active_live_ranges_(local_zone),
      inactive_live_ranges_(num_registers(), InactiveLiveRangeQueue(local_zone),
                            local_zone),
      next_active_ranges_change_(LifetimePosition::Invalid()),
      next_inactive_ranges_change_(LifetimePosition::Invalid()) {
  active_live_ranges().reserve(8);
}

void LinearScanAllocator::MaybeSpillPreviousRanges(LiveRange* begin_range,
                                                   LifetimePosition begin_pos,
                                                   LiveRange* end_range) {
  // Spill begin_range after begin_pos, then spill every live range of this
  // virtual register until but excluding end_range.
  DCHECK(begin_range->Covers(begin_pos));
  DCHECK_EQ(begin_range->TopLevel(), end_range->TopLevel());

  if (begin_range != end_range) {
    DCHECK_LE(begin_range->End(), end_range->Start());
    if (!begin_range->spilled()) {
      SpillAfter(begin_range, begin_pos, SpillMode::kSpillAtDefinition);
    }
    for (LiveRange* range = begin_range->next(); range != end_range;
         range = range->next()) {
      if (!range->spilled()) {
        range->Spill();
      }
    }
  }
}

void LinearScanAllocator::MaybeUndoPreviousSplit(LiveRange* range) {
  if (range->next() != nullptr && range->next()->ShouldRecombine()) {
    LiveRange* to_remove = range->next();
    TRACE("Recombining %d:%d with %d\n", range->TopLevel()->vreg(),
          range->relative_id(), to_remove->relative_id());

    // Remove the range from unhandled, as attaching it will change its
    // state and hence ordering in the unhandled set.
    auto removed_cnt = unhandled_live_ranges().erase(to_remove);
    DCHECK_EQ(removed_cnt, 1);
    USE(removed_cnt);

    range->AttachToNext();
  } else if (range->next() != nullptr) {
    TRACE("No recombine for %d:%d to %d\n", range->TopLevel()->vreg(),
          range->relative_id(), range->next()->relative_id());
  }
}

void LinearScanAllocator::SpillNotLiveRanges(RangeWithRegisterSet* to_be_live,
                                             LifetimePosition position,
                                             SpillMode spill_mode) {
  for (auto it = active_live_ranges().begin();
       it != active_live_ranges().end();) {
    LiveRange* active_range = *it;
    TopLevelLiveRange* toplevel = (*it)->TopLevel();
    auto found = to_be_live->find({toplevel, kUnassignedRegister});
    if (found == to_be_live->end()) {
      // Is not contained in {to_be_live}, spill it.
      // Fixed registers are exempt from this. They might have been
      // added from inactive at the block boundary but we know that
      // they cannot conflict as they are built before register
      // allocation starts. It would be algorithmically fine to split
      // them and reschedule but the code does not allow to do this.
      if (toplevel->IsFixed()) {
        TRACE("Keeping reactivated fixed range for %s\n",
              RegisterName(toplevel->assigned_register()));
        ++it;
      } else {
        // When spilling a previously spilled/reloaded range, we add back the
        // tail that we might have split off when we reloaded/spilled it
        // previously. Otherwise we might keep generating small split-offs.
        MaybeUndoPreviousSplit(active_range);
        TRACE("Putting back %d:%d\n", toplevel->vreg(),
              active_range->relative_id());
        LiveRange* split = SplitRangeAt(active_range, position);
        DCHECK_NE(split, active_range);

        // Make sure we revisit this range once it has a use that requires
        // a register.
        UsePosition* next_use = split->NextRegisterPosition(position);
        if (next_use != nullptr) {
          // Move to the start of the gap before use so that we have a space
          // to perform the potential reload. Otherwise, do not spill but add
          // to unhandled for reallocation.
          LifetimePosition revisit_at = next_use->pos().FullStart();
          TRACE("Next use at %d\n", revisit_at.value());
          if (!data()->IsBlockBoundary(revisit_at)) {
            // Leave some space so we have enough gap room.
            revisit_at = revisit_at.PrevStart().FullStart();
          }
          // If this range became life right at the block boundary that we are
          // currently processing, we do not need to split it. Instead move it
          // to unhandled right away.
          if (position < revisit_at) {
            LiveRange* third_part = SplitRangeAt(split, revisit_at);
            DCHECK_NE(split, third_part);
            Spill(split, spill_mode);
            TRACE("Marking %d:%d to recombine\n", toplevel->vreg(),
                  third_part->relative_id());
            third_part->SetRecombine();
            AddToUnhandled(third_part);
          } else {
            AddToUnhandled(split);
          }
        } else {
          Spill(split, spill_mode);
        }
        it = ActiveToHandled(it);
      }
    } else {
      // This range is contained in {to_be_live}, so we can keep it.
      int expected_register = (*found).expected_register;
      to_be_live->erase(found);
      if (expected_register == active_range->assigned_register()) {
        // Was life and in correct register, simply pass through.
        TRACE("Keeping %d:%d in %s\n", toplevel->vreg(),
              active_range->relative_id(),
              RegisterName(active_range->assigned_register()));
        ++it;
      } else {
        // Was life but wrong register. Split and schedule for
        // allocation.
        TRACE("Scheduling %d:%d\n", toplevel->vreg(),
              active_range->relative_id());
        LiveRange* split = SplitRangeAt(active_range, position);
        split->set_controlflow_hint(expected_register);
        AddToUnhandled(split);
        it = ActiveToHandled(it);
      }
    }
  }
}

LiveRange* LinearScanAllocator::AssignRegisterOnReload(LiveRange* range,
                                                       int reg) {
  // We know the register is currently free but it might be in
  // use by a currently inactive range. So we might not be able
  // to reload for the full distance. In such case, split here.
  // TODO(herhut):
  // It might be better if we could use the normal unhandled queue and
  // give reloading registers pecedence. That way we would compute the
  // intersection for the entire future.
  LifetimePosition new_end = range->End();
  for (int cur_reg = 0; cur_reg < num_registers(); ++cur_reg) {
    if ((kSimpleFPAliasing || !check_fp_aliasing()) && cur_reg != reg) {
      continue;
    }
    for (const LiveRange* cur_inactive : inactive_live_ranges(cur_reg)) {
      if (!kSimpleFPAliasing && check_fp_aliasing() &&
          !data()->config()->AreAliases(cur_inactive->representation(), cur_reg,
                                        range->representation(), reg)) {
        continue;
      }
      if (new_end <= cur_inactive->NextStart()) {
        // Inactive ranges are sorted by their next start, so the remaining
        // ranges cannot contribute to new_end.
        break;
      }
      auto next_intersection = cur_inactive->FirstIntersection(range);
      if (!next_intersection.IsValid()) continue;
      new_end = std::min(new_end, next_intersection);
    }
  }
  if (new_end != range->End()) {
    TRACE("Found new end for %d:%d at %d\n", range->TopLevel()->vreg(),
          range->relative_id(), new_end.value());
    LiveRange* tail = SplitRangeAt(range, new_end);
    AddToUnhandled(tail);
  }
  SetLiveRangeAssignedRegister(range, reg);
  return range;
}

void LinearScanAllocator::ReloadLiveRanges(
    RangeWithRegisterSet const& to_be_live, LifetimePosition position) {
  // Assumption: All ranges in {to_be_live} are currently spilled and there are
  // no conflicting registers in the active ranges.
  // The former is ensured by SpillNotLiveRanges, the latter is by construction
  // of the to_be_live set.
  for (RangeWithRegister range_with_register : to_be_live) {
    TopLevelLiveRange* range = range_with_register.range;
    int reg = range_with_register.expected_register;
    LiveRange* to_resurrect = range->GetChildCovers(position);
    if (to_resurrect == nullptr) {
      // While the range was life until the end of the predecessor block, it is
      // not live in this block. Either there is a lifetime gap or the range
      // died.
      TRACE("No candidate for %d at %d\n", range->vreg(), position.value());
    } else {
      // We might be resurrecting a range that we spilled until its next use
      // before. In such cases, we have to unsplit it before processing as
      // otherwise we might get register changes from one range to the other
      // in the middle of blocks.
      // If there is a gap between this range and the next, we can just keep
      // it as a register change won't hurt.
      MaybeUndoPreviousSplit(to_resurrect);
      if (to_resurrect->Start() == position) {
        // This range already starts at this block. It might have been spilled,
        // so we have to unspill it. Otherwise, it is already in the unhandled
        // queue waiting for processing.
        DCHECK(!to_resurrect->HasRegisterAssigned());
        TRACE("Reload %d:%d starting at %d itself\n", range->vreg(),
              to_resurrect->relative_id(), position.value());
        if (to_resurrect->spilled()) {
          to_resurrect->Unspill();
          to_resurrect->set_controlflow_hint(reg);
          AddToUnhandled(to_resurrect);
        } else {
          // Assign the preassigned register if we know. Otherwise, nothing to
          // do as already in unhandeled.
          if (reg != kUnassignedRegister) {
            auto erased_cnt = unhandled_live_ranges().erase(to_resurrect);
            DCHECK_EQ(erased_cnt, 1);
            USE(erased_cnt);
            // We know that there is no conflict with active ranges, so just
            // assign the register to the range.
            to_resurrect = AssignRegisterOnReload(to_resurrect, reg);
            AddToActive(to_resurrect);
          }
        }
      } else {
        // This range was spilled before. We have to split it and schedule the
        // second part for allocation (or assign the register if we know).
        DCHECK(to_resurrect->spilled());
        LiveRange* split = SplitRangeAt(to_resurrect, position);
        TRACE("Reload %d:%d starting at %d as %d\n", range->vreg(),
              to_resurrect->relative_id(), split->Start().value(),
              split->relative_id());
        DCHECK_NE(split, to_resurrect);
        if (reg != kUnassignedRegister) {
          // We know that there is no conflict with active ranges, so just
          // assign the register to the range.
          split = AssignRegisterOnReload(split, reg);
          AddToActive(split);
        } else {
          // Let normal register assignment find a suitable register.
          split->set_controlflow_hint(reg);
          AddToUnhandled(split);
        }
      }
    }
  }
}

RpoNumber LinearScanAllocator::ChooseOneOfTwoPredecessorStates(
    InstructionBlock* current_block, LifetimePosition boundary) {
  using SmallRangeVector =
      base::SmallVector<TopLevelLiveRange*,
                        RegisterConfiguration::kMaxRegisters>;
  // Pick the state that would generate the least spill/reloads.
  // Compute vectors of ranges with imminent use for both sides.
  // As GetChildCovers is cached, it is cheaper to repeatedly
  // call is rather than compute a shared set first.
  auto& left = data()->GetSpillState(current_block->predecessors()[0]);
  auto& right = data()->GetSpillState(current_block->predecessors()[1]);
  SmallRangeVector left_used;
  for (const auto item : left) {
    LiveRange* at_next_block = item->TopLevel()->GetChildCovers(boundary);
    if (at_next_block != nullptr &&
        at_next_block->NextUsePositionRegisterIsBeneficial(boundary) !=
            nullptr) {
      left_used.emplace_back(item->TopLevel());
    }
  }
  SmallRangeVector right_used;
  for (const auto item : right) {
    LiveRange* at_next_block = item->TopLevel()->GetChildCovers(boundary);
    if (at_next_block != nullptr &&
        at_next_block->NextUsePositionRegisterIsBeneficial(boundary) !=
            nullptr) {
      right_used.emplace_back(item->TopLevel());
    }
  }
  if (left_used.empty() && right_used.empty()) {
    // There are no beneficial register uses. Look at any use at
    // all. We do not account for all uses, like flowing into a phi.
    // So we just look at ranges still being live.
    TRACE("Looking at only uses\n");
    for (const auto item : left) {
      LiveRange* at_next_block = item->TopLevel()->GetChildCovers(boundary);
      if (at_next_block != nullptr &&
          at_next_block->NextUsePosition(boundary) != nullptr) {
        left_used.emplace_back(item->TopLevel());
      }
    }
    for (const auto item : right) {
      LiveRange* at_next_block = item->TopLevel()->GetChildCovers(boundary);
      if (at_next_block != nullptr &&
          at_next_block->NextUsePosition(boundary) != nullptr) {
        right_used.emplace_back(item->TopLevel());
      }
    }
  }
  // Now left_used and right_used contains those ranges that matter.
  // Count which side matches this most.
  TRACE("Vote went %zu vs %zu\n", left_used.size(), right_used.size());
  return left_used.size() > right_used.size()
             ? current_block->predecessors()[0]
             : current_block->predecessors()[1];
}

bool LinearScanAllocator::CheckConflict(MachineRepresentation rep, int reg,
                                        RangeWithRegisterSet* to_be_live) {
  for (RangeWithRegister range_with_reg : *to_be_live) {
    if (data()->config()->AreAliases(range_with_reg.range->representation(),
                                     range_with_reg.expected_register, rep,
                                     reg)) {
      return true;
    }
  }
  return false;
}

void LinearScanAllocator::ComputeStateFromManyPredecessors(
    InstructionBlock* current_block, RangeWithRegisterSet* to_be_live) {
  struct Vote {
    size_t count;
    int used_registers[RegisterConfiguration::kMaxRegisters];
  };
  struct TopLevelLiveRangeComparator {
    bool operator()(const TopLevelLiveRange* lhs,
                    const TopLevelLiveRange* rhs) const {
      return lhs->vreg() < rhs->vreg();
    }
  };
  ZoneMap<TopLevelLiveRange*, Vote, TopLevelLiveRangeComparator> counts(
      data()->allocation_zone());
  int deferred_blocks = 0;
  for (RpoNumber pred : current_block->predecessors()) {
    if (!ConsiderBlockForControlFlow(current_block, pred)) {
      // Back edges of a loop count as deferred here too.
      deferred_blocks++;
      continue;
    }
    const auto& pred_state = data()->GetSpillState(pred);
    for (LiveRange* range : pred_state) {
      // We might have spilled the register backwards, so the range we
      // stored might have lost its register. Ignore those.
      if (!range->HasRegisterAssigned()) continue;
      TopLevelLiveRange* toplevel = range->TopLevel();
      auto previous = counts.find(toplevel);
      if (previous == counts.end()) {
        auto result = counts.emplace(std::make_pair(toplevel, Vote{1, {0}}));
        CHECK(result.second);
        result.first->second.used_registers[range->assigned_register()]++;
      } else {
        previous->second.count++;
        previous->second.used_registers[range->assigned_register()]++;
      }
    }
  }

  // Choose the live ranges from the majority.
  const size_t majority =
      (current_block->PredecessorCount() + 2 - deferred_blocks) / 2;
  bool taken_registers[RegisterConfiguration::kMaxRegisters] = {false};
  auto assign_to_live = [this, counts, majority](
                            std::function<bool(TopLevelLiveRange*)> filter,
                            RangeWithRegisterSet* to_be_live,
                            bool* taken_registers) {
    bool check_aliasing = !kSimpleFPAliasing && check_fp_aliasing();
    for (const auto& val : counts) {
      if (!filter(val.first)) continue;
      if (val.second.count >= majority) {
        int register_max = 0;
        int reg = kUnassignedRegister;
        bool conflict = false;
        int num_regs = num_registers();
        int num_codes = num_allocatable_registers();
        const int* codes = allocatable_register_codes();
        MachineRepresentation rep = val.first->representation();
        if (check_aliasing && (rep == MachineRepresentation::kFloat32 ||
                               rep == MachineRepresentation::kSimd128))
          GetFPRegisterSet(rep, &num_regs, &num_codes, &codes);
        for (int idx = 0; idx < num_regs; idx++) {
          int uses = val.second.used_registers[idx];
          if (uses == 0) continue;
          if (uses > register_max || (conflict && uses == register_max)) {
            reg = idx;
            register_max = uses;
            conflict = check_aliasing ? CheckConflict(rep, reg, to_be_live)
                                      : taken_registers[reg];
          }
        }
        if (conflict) {
          reg = kUnassignedRegister;
        } else if (!check_aliasing) {
          taken_registers[reg] = true;
        }
        to_be_live->emplace(val.first, reg);
        TRACE("Reset %d as live due vote %zu in %s\n",
              val.first->TopLevel()->vreg(), val.second.count,
              RegisterName(reg));
      }
    }
  };
  // First round, process fixed registers, as these have precedence.
  // There is only one fixed range per register, so we cannot have
  // conflicts.
  assign_to_live([](TopLevelLiveRange* r) { return r->IsFixed(); }, to_be_live,
                 taken_registers);
  // Second round, process the rest.
  assign_to_live([](TopLevelLiveRange* r) { return !r->IsFixed(); }, to_be_live,
                 taken_registers);
}

bool LinearScanAllocator::ConsiderBlockForControlFlow(
    InstructionBlock* current_block, RpoNumber predecessor) {
  // We ignore predecessors on back edges when looking for control flow effects,
  // as those lie in the future of allocation and we have no data yet. Also,
  // deferred bocks are ignored on deferred to non-deferred boundaries, as we do
  // not want them to influence allocation of non deferred code.
  return (predecessor < current_block->rpo_number()) &&
         (current_block->IsDeferred() ||
          !code()->InstructionBlockAt(predecessor)->IsDeferred());
}

void LinearScanAllocator::UpdateDeferredFixedRanges(SpillMode spill_mode,
                                                    InstructionBlock* block) {
  if (spill_mode == SpillMode::kSpillDeferred) {
    LifetimePosition max = LifetimePosition::InstructionFromInstructionIndex(
        LastDeferredInstructionIndex(block));
    // Adds range back to inactive, resolving resulting conflicts.
    auto add_to_inactive = [this, max](LiveRange* range) {
      AddToInactive(range);
      // Splits other if it conflicts with range. Other is placed in unhandled
      // for later reallocation.
      auto split_conflicting = [this, max](LiveRange* range, LiveRange* other,
                                           std::function<void(LiveRange*)>
                                               update_caches) {
        if (other->TopLevel()->IsFixed()) return;
        int reg = range->assigned_register();
        if (kSimpleFPAliasing || !check_fp_aliasing()) {
          if (other->assigned_register() != reg) {
            return;
          }
        } else {
          if (!data()->config()->AreAliases(range->representation(), reg,
                                            other->representation(),
                                            other->assigned_register())) {
            return;
          }
        }
        // The inactive range might conflict, so check whether we need to
        // split and spill. We can look for the first intersection, as there
        // cannot be any intersections in the past, as those would have been a
        // conflict then.
        LifetimePosition next_start = range->FirstIntersection(other);
        if (!next_start.IsValid() || (next_start > max)) {
          // There is no conflict or the conflict is outside of the current
          // stretch of deferred code. In either case we can ignore the
          // inactive range.
          return;
        }
        // They overlap. So we need to split active and reschedule it
        // for allocation.
        TRACE("Resolving conflict of %d with deferred fixed for register %s\n",
              other->TopLevel()->vreg(),
              RegisterName(other->assigned_register()));
        LiveRange* split_off =
            other->SplitAt(next_start, data()->allocation_zone());
        // Try to get the same register after the deferred block.
        split_off->set_controlflow_hint(other->assigned_register());
        DCHECK_NE(split_off, other);
        AddToUnhandled(split_off);
        update_caches(other);
      };
      // Now check for conflicts in active and inactive ranges. We might have
      // conflicts in inactive, as we do not do this check on every block
      // boundary but only on deferred/non-deferred changes but inactive
      // live ranges might become live on any block boundary.
      for (auto active : active_live_ranges()) {
        split_conflicting(range, active, [this](LiveRange* updated) {
          next_active_ranges_change_ =
              std::min(updated->End(), next_active_ranges_change_);
        });
      }
      for (int reg = 0; reg < num_registers(); ++reg) {
        if ((kSimpleFPAliasing || !check_fp_aliasing()) &&
            reg != range->assigned_register()) {
          continue;
        }
        for (auto inactive : inactive_live_ranges(reg)) {
          split_conflicting(range, inactive, [this](LiveRange* updated) {
            next_inactive_ranges_change_ =
                std::min(updated->End(), next_inactive_ranges_change_);
          });
        }
      }
    };
    if (mode() == RegisterKind::kGeneral) {
      for (TopLevelLiveRange* current : data()->fixed_live_ranges()) {
        if (current != nullptr) {
          if (current->IsDeferredFixed()) {
            add_to_inactive(current);
          }
        }
      }
    } else {
      for (TopLevelLiveRange* current : data()->fixed_double_live_ranges()) {
        if (current != nullptr) {
          if (current->IsDeferredFixed()) {
            add_to_inactive(current);
          }
        }
      }
      if (!kSimpleFPAliasing && check_fp_aliasing()) {
        for (TopLevelLiveRange* current : data()->fixed_float_live_ranges()) {
          if (current != nullptr) {
            if (current->IsDeferredFixed()) {
              add_to_inactive(current);
            }
          }
        }
        for (TopLevelLiveRange* current : data()->fixed_simd128_live_ranges()) {
          if (current != nullptr) {
            if (current->IsDeferredFixed()) {
              add_to_inactive(current);
            }
          }
        }
      }
    }
  } else {
    // Remove all ranges.
    for (int reg = 0; reg < num_registers(); ++reg) {
      for (auto it = inactive_live_ranges(reg).begin();
           it != inactive_live_ranges(reg).end();) {
        if ((*it)->TopLevel()->IsDeferredFixed()) {
          it = inactive_live_ranges(reg).erase(it);
        } else {
          ++it;
        }
      }
    }
  }
}

bool LinearScanAllocator::BlockIsDeferredOrImmediatePredecessorIsNotDeferred(
    const InstructionBlock* block) {
  if (block->IsDeferred()) return true;
  if (block->PredecessorCount() == 0) return true;
  bool pred_is_deferred = false;
  for (auto pred : block->predecessors()) {
    if (pred.IsNext(block->rpo_number())) {
      pred_is_deferred = code()->InstructionBlockAt(pred)->IsDeferred();
      break;
    }
  }
  return !pred_is_deferred;
}

bool LinearScanAllocator::HasNonDeferredPredecessor(InstructionBlock* block) {
  for (auto pred : block->predecessors()) {
    InstructionBlock* pred_block = code()->InstructionBlockAt(pred);
    if (!pred_block->IsDeferred()) return true;
  }
  return false;
}

void LinearScanAllocator::AllocateRegisters() {
  DCHECK(unhandled_live_ranges().empty());
  DCHECK(active_live_ranges().empty());
  for (int reg = 0; reg < num_registers(); ++reg) {
    DCHECK(inactive_live_ranges(reg).empty());
  }

  SplitAndSpillRangesDefinedByMemoryOperand();
  data()->ResetSpillState();

  if (data()->is_trace_alloc()) {
    PrintRangeOverview(std::cout);
  }

  const size_t live_ranges_size = data()->live_ranges().size();
  for (TopLevelLiveRange* range : data()->live_ranges()) {
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (!CanProcessRange(range)) continue;
    for (LiveRange* to_add = range; to_add != nullptr;
         to_add = to_add->next()) {
      if (!to_add->spilled()) {
        AddToUnhandled(to_add);
      }
    }
  }

  if (mode() == RegisterKind::kGeneral) {
    for (TopLevelLiveRange* current : data()->fixed_live_ranges()) {
      if (current != nullptr) {
        if (current->IsDeferredFixed()) continue;
        AddToInactive(current);
      }
    }
  } else {
    for (TopLevelLiveRange* current : data()->fixed_double_live_ranges()) {
      if (current != nullptr) {
        if (current->IsDeferredFixed()) continue;
        AddToInactive(current);
      }
    }
    if (!kSimpleFPAliasing && check_fp_aliasing()) {
      for (TopLevelLiveRange* current : data()->fixed_float_live_ranges()) {
        if (current != nullptr) {
          if (current->IsDeferredFixed()) continue;
          AddToInactive(current);
        }
      }
      for (TopLevelLiveRange* current : data()->fixed_simd128_live_ranges()) {
        if (current != nullptr) {
          if (current->IsDeferredFixed()) continue;
          AddToInactive(current);
        }
      }
    }
  }

  RpoNumber last_block = RpoNumber::FromInt(0);
  RpoNumber max_blocks =
      RpoNumber::FromInt(code()->InstructionBlockCount() - 1);
  LifetimePosition next_block_boundary =
      LifetimePosition::InstructionFromInstructionIndex(
          data()
              ->code()
              ->InstructionBlockAt(last_block)
              ->last_instruction_index())
          .NextFullStart();
  SpillMode spill_mode = SpillMode::kSpillAtDefinition;

  // Process all ranges. We also need to ensure that we have seen all block
  // boundaries. Linear scan might have assigned and spilled ranges before
  // reaching the last block and hence we would ignore control flow effects for
  // those. Not only does this produce a potentially bad assignment, it also
  // breaks with the invariant that we undo spills that happen in deferred code
  // when crossing a deferred/non-deferred boundary.
  while (!unhandled_live_ranges().empty() || last_block < max_blocks) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    LiveRange* current = unhandled_live_ranges().empty()
                             ? nullptr
                             : *unhandled_live_ranges().begin();
    LifetimePosition position =
        current ? current->Start() : next_block_boundary;
#ifdef DEBUG
    allocation_finger_ = position;
#endif
    // Check whether we just moved across a block boundary. This will trigger
    // for the first range that is past the current boundary.
    if (position >= next_block_boundary) {
      TRACE("Processing boundary at %d leaving %d\n",
            next_block_boundary.value(), last_block.ToInt());

      // Forward state to before block boundary
      LifetimePosition end_of_block = next_block_boundary.PrevStart().End();
      ForwardStateTo(end_of_block);

      // Remember this state.
      InstructionBlock* current_block = data()->code()->GetInstructionBlock(
          next_block_boundary.ToInstructionIndex());

      // Store current spill state (as the state at end of block). For
      // simplicity, we store the active ranges, e.g., the live ranges that
      // are not spilled.
      data()->RememberSpillState(last_block, active_live_ranges());

      // Only reset the state if this was not a direct fallthrough. Otherwise
      // control flow resolution will get confused (it does not expect changes
      // across fallthrough edges.).
      bool fallthrough =
          (current_block->PredecessorCount() == 1) &&
          current_block->predecessors()[0].IsNext(current_block->rpo_number());

      // When crossing a deferred/non-deferred boundary, we have to load or
      // remove the deferred fixed ranges from inactive.
      if ((spill_mode == SpillMode::kSpillDeferred) !=
          current_block->IsDeferred()) {
        // Update spill mode.
        spill_mode = current_block->IsDeferred()
                         ? SpillMode::kSpillDeferred
                         : SpillMode::kSpillAtDefinition;

        ForwardStateTo(next_block_boundary);

#ifdef DEBUG
        // Allow allocation at current position.
        allocation_finger_ = next_block_boundary;
#endif
        UpdateDeferredFixedRanges(spill_mode, current_block);
      }

      // Allocation relies on the fact that each non-deferred block has at
      // least one non-deferred predecessor. Check this invariant here.
      DCHECK_IMPLIES(!current_block->IsDeferred(),
                     HasNonDeferredPredecessor(current_block));

      if (!fallthrough) {
#ifdef DEBUG
        // Allow allocation at current position.
        allocation_finger_ = next_block_boundary;
#endif

        // We are currently at next_block_boundary - 1. Move the state to the
        // actual block boundary position. In particular, we have to
        // reactivate inactive ranges so that they get rescheduled for
        // allocation if they were not live at the predecessors.
        ForwardStateTo(next_block_boundary);

        RangeWithRegisterSet to_be_live(data()->allocation_zone());

        // If we end up deciding to use the state of the immediate
        // predecessor, it is better not to perform a change. It would lead to
        // the same outcome anyway.
        // This may never happen on boundaries between deferred and
        // non-deferred code, as we rely on explicit respill to ensure we
        // spill at definition.
        bool no_change_required = false;

        auto pick_state_from = [this, current_block](
                                   RpoNumber pred,
                                   RangeWithRegisterSet* to_be_live) -> bool {
          TRACE("Using information from B%d\n", pred.ToInt());
          // If this is a fall-through that is not across a deferred
          // boundary, there is nothing to do.
          bool is_noop = pred.IsNext(current_block->rpo_number());
          if (!is_noop) {
            auto& spill_state = data()->GetSpillState(pred);
            TRACE("Not a fallthrough. Adding %zu elements...\n",
                  spill_state.size());
            LifetimePosition pred_end =
                LifetimePosition::GapFromInstructionIndex(
                    this->code()->InstructionBlockAt(pred)->code_end());
            for (const auto range : spill_state) {
              // Filter out ranges that were split or had their register
              // stolen by backwards working spill heuristics. These have
              // been spilled after the fact, so ignore them.
              if (range->End() < pred_end || !range->HasRegisterAssigned())
                continue;
              to_be_live->emplace(range);
            }
          }
          return is_noop;
        };

        // Multiple cases here:
        // 1) We have a single predecessor => this is a control flow split, so
        //     just restore the predecessor state.
        // 2) We have two predecessors => this is a conditional, so break ties
        //     based on what to do based on forward uses, trying to benefit
        //     the same branch if in doubt (make one path fast).
        // 3) We have many predecessors => this is a switch. Compute union
        //     based on majority, break ties by looking forward.
        if (current_block->PredecessorCount() == 1) {
          TRACE("Single predecessor for B%d\n",
                current_block->rpo_number().ToInt());
          no_change_required =
              pick_state_from(current_block->predecessors()[0], &to_be_live);
        } else if (current_block->PredecessorCount() == 2) {
          TRACE("Two predecessors for B%d\n",
                current_block->rpo_number().ToInt());
          // If one of the branches does not contribute any information,
          // e.g. because it is deferred or a back edge, we can short cut
          // here right away.
          RpoNumber chosen_predecessor = RpoNumber::Invalid();
          if (!ConsiderBlockForControlFlow(current_block,
                                           current_block->predecessors()[0])) {
            chosen_predecessor = current_block->predecessors()[1];
          } else if (!ConsiderBlockForControlFlow(
                         current_block, current_block->predecessors()[1])) {
            chosen_predecessor = current_block->predecessors()[0];
          } else {
            chosen_predecessor = ChooseOneOfTwoPredecessorStates(
                current_block, next_block_boundary);
          }
          no_change_required = pick_state_from(chosen_predecessor, &to_be_live);

        } else {
          // Merge at the end of, e.g., a switch.
          ComputeStateFromManyPredecessors(current_block, &to_be_live);
        }

        if (!no_change_required) {
          SpillNotLiveRanges(&to_be_live, next_block_boundary, spill_mode);
          ReloadLiveRanges(to_be_live, next_block_boundary);
        }
      }
      // Update block information
      last_block = current_block->rpo_number();
      next_block_boundary = LifetimePosition::InstructionFromInstructionIndex(
                                current_block->last_instruction_index())
                                .NextFullStart();

      // We might have created new unhandled live ranges, so cycle around the
      // loop to make sure we pick the top most range in unhandled for
      // processing.
      continue;
    }

    DCHECK_NOT_NULL(current);

    TRACE("Processing interval %d:%d start=%d\n", current->TopLevel()->vreg(),
          current->relative_id(), position.value());

    // Now we can erase current, as we are sure to process it.
    unhandled_live_ranges().erase(unhandled_live_ranges().begin());

    if (current->IsTopLevel() && TryReuseSpillForPhi(current->TopLevel()))
      continue;

    ForwardStateTo(position);

    DCHECK(!current->HasRegisterAssigned() && !current->spilled());

    ProcessCurrentRange(current, spill_mode);
  }

  if (data()->is_trace_alloc()) {
    PrintRangeOverview(std::cout);
  }
}

void LinearScanAllocator::SetLiveRangeAssignedRegister(LiveRange* range,
                                                       int reg) {
  data()->MarkAllocated(range->representation(), reg);
  range->set_assigned_register(reg);
  range->SetUseHints(reg);
  range->UpdateBundleRegister(reg);
  if (range->IsTopLevel() && range->TopLevel()->is_phi()) {
    data()->GetPhiMapValueFor(range->TopLevel())->set_assigned_register(reg);
  }
}

void LinearScanAllocator::AddToActive(LiveRange* range) {
  TRACE("Add live range %d:%d in %s to active\n", range->TopLevel()->vreg(),
        range->relative_id(), RegisterName(range->assigned_register()));
  active_live_ranges().push_back(range);
  next_active_ranges_change_ =
      std::min(next_active_ranges_change_, range->NextEndAfter(range->Start()));
}

void LinearScanAllocator::AddToInactive(LiveRange* range) {
  TRACE("Add live range %d:%d to inactive\n", range->TopLevel()->vreg(),
        range->relative_id());
  next_inactive_ranges_change_ = std::min(
      next_inactive_ranges_change_, range->NextStartAfter(range->Start()));
  DCHECK(range->HasRegisterAssigned());
  inactive_live_ranges(range->assigned_register()).insert(range);
}

void LinearScanAllocator::AddToUnhandled(LiveRange* range) {
  if (range == nullptr || range->IsEmpty()) return;
  DCHECK(!range->HasRegisterAssigned() && !range->spilled());
  DCHECK(allocation_finger_ <= range->Start());

  TRACE("Add live range %d:%d to unhandled\n", range->TopLevel()->vreg(),
        range->relative_id());
  unhandled_live_ranges().insert(range);
}

ZoneVector<LiveRange*>::iterator LinearScanAllocator::ActiveToHandled(
    const ZoneVector<LiveRange*>::iterator it) {
  TRACE("Moving live range %d:%d from active to handled\n",
        (*it)->TopLevel()->vreg(), (*it)->relative_id());
  return active_live_ranges().erase(it);
}

ZoneVector<LiveRange*>::iterator LinearScanAllocator::ActiveToInactive(
    const ZoneVector<LiveRange*>::iterator it, LifetimePosition position) {
  LiveRange* range = *it;
  TRACE("Moving live range %d:%d from active to inactive\n",
        (range)->TopLevel()->vreg(), range->relative_id());
  LifetimePosition next_active = range->NextStartAfter(position);
  next_inactive_ranges_change_ =
      std::min(next_inactive_ranges_change_, next_active);
  DCHECK(range->HasRegisterAssigned());
  inactive_live_ranges(range->assigned_register()).insert(range);
  return active_live_ranges().erase(it);
}

LinearScanAllocator::InactiveLiveRangeQueue::iterator
LinearScanAllocator::InactiveToHandled(InactiveLiveRangeQueue::iterator it) {
  LiveRange* range = *it;
  TRACE("Moving live range %d:%d from inactive to handled\n",
        range->TopLevel()->vreg(), range->relative_id());
  int reg = range->assigned_register();
  return inactive_live_ranges(reg).erase(it);
}

LinearScanAllocator::InactiveLiveRangeQueue::iterator
LinearScanAllocator::InactiveToActive(InactiveLiveRangeQueue::iterator it,
                                      LifetimePosition position) {
  LiveRange* range = *it;
  active_live_ranges().push_back(range);
  TRACE("Moving live range %d:%d from inactive to active\n",
        range->TopLevel()->vreg(), range->relative_id());
  next_active_ranges_change_ =
      std::min(next_active_ranges_change_, range->NextEndAfter(position));
  int reg = range->assigned_register();
  return inactive_live_ranges(reg).erase(it);
}

void LinearScanAllocator::ForwardStateTo(LifetimePosition position) {
  if (position >= next_active_ranges_change_) {
    next_active_ranges_change_ = LifetimePosition::MaxPosition();
    for (auto it = active_live_ranges().begin();
         it != active_live_ranges().end();) {
      LiveRange* cur_active = *it;
      if (cur_active->End() <= position) {
        it = ActiveToHandled(it);
      } else if (!cur_active->Covers(position)) {
        it = ActiveToInactive(it, position);
      } else {
        next_active_ranges_change_ = std::min(
            next_active_ranges_change_, cur_active->NextEndAfter(position));
        ++it;
      }
    }
  }

  if (position >= next_inactive_ranges_change_) {
    next_inactive_ranges_change_ = LifetimePosition::MaxPosition();
    for (int reg = 0; reg < num_registers(); ++reg) {
      ZoneVector<LiveRange*> reorder(data()->allocation_zone());
      for (auto it = inactive_live_ranges(reg).begin();
           it != inactive_live_ranges(reg).end();) {
        LiveRange* cur_inactive = *it;
        if (cur_inactive->End() <= position) {
          it = InactiveToHandled(it);
        } else if (cur_inactive->Covers(position)) {
          it = InactiveToActive(it, position);
        } else {
          next_inactive_ranges_change_ =
              std::min(next_inactive_ranges_change_,
                       cur_inactive->NextStartAfter(position));
          it = inactive_live_ranges(reg).erase(it);
          reorder.push_back(cur_inactive);
        }
      }
      for (LiveRange* range : reorder) {
        inactive_live_ranges(reg).insert(range);
      }
    }
  }
}

int LinearScanAllocator::LastDeferredInstructionIndex(InstructionBlock* start) {
  DCHECK(start->IsDeferred());
  RpoNumber last_block =
      RpoNumber::FromInt(code()->InstructionBlockCount() - 1);
  while ((start->rpo_number() < last_block)) {
    InstructionBlock* next =
        code()->InstructionBlockAt(start->rpo_number().Next());
    if (!next->IsDeferred()) break;
    start = next;
  }
  return start->last_instruction_index();
}

void LinearScanAllocator::GetFPRegisterSet(MachineRepresentation rep,
                                           int* num_regs, int* num_codes,
                                           const int** codes) const {
  DCHECK(!kSimpleFPAliasing);
  if (rep == MachineRepresentation::kFloat32) {
    *num_regs = data()->config()->num_float_registers();
    *num_codes = data()->config()->num_allocatable_float_registers();
    *codes = data()->config()->allocatable_float_codes();
  } else if (rep == MachineRepresentation::kSimd128) {
    *num_regs = data()->config()->num_simd128_registers();
    *num_codes = data()->config()->num_allocatable_simd128_registers();
    *codes = data()->config()->allocatable_simd128_codes();
  } else {
    UNREACHABLE();
  }
}

void LinearScanAllocator::FindFreeRegistersForRange(
    LiveRange* range, Vector<LifetimePosition> positions) {
  int num_regs = num_registers();
  int num_codes = num_allocatable_registers();
  const int* codes = allocatable_register_codes();
  MachineRepresentation rep = range->representation();
  if (!kSimpleFPAliasing && (rep == MachineRepresentation::kFloat32 ||
                             rep == MachineRepresentation::kSimd128))
    GetFPRegisterSet(rep, &num_regs, &num_codes, &codes);
  DCHECK_GE(positions.length(), num_regs);

  for (int i = 0; i < num_regs; ++i) {
    positions[i] = LifetimePosition::MaxPosition();
  }

  for (LiveRange* cur_active : active_live_ranges()) {
    int cur_reg = cur_active->assigned_register();
    if (kSimpleFPAliasing || !check_fp_aliasing()) {
      positions[cur_reg] = LifetimePosition::GapFromInstructionIndex(0);
      TRACE("Register %s is free until pos %d (1) due to %d\n",
            RegisterName(cur_reg),
            LifetimePosition::GapFromInstructionIndex(0).value(),
            cur_active->TopLevel()->vreg());
    } else {
      int alias_base_index = -1;
      int aliases = data()->config()->GetAliases(
          cur_active->representation(), cur_reg, rep, &alias_base_index);
      DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
      while (aliases--) {
        int aliased_reg = alias_base_index + aliases;
        positions[aliased_reg] = LifetimePosition::GapFromInstructionIndex(0);
      }
    }
  }

  for (int cur_reg = 0; cur_reg < num_regs; ++cur_reg) {
    for (LiveRange* cur_inactive : inactive_live_ranges(cur_reg)) {
      DCHECK_GT(cur_inactive->End(), range->Start());
      CHECK_EQ(cur_inactive->assigned_register(), cur_reg);
      // No need to carry out intersections, when this register won't be
      // interesting to this range anyway.
      // TODO(mtrofin): extend to aliased ranges, too.
      if ((kSimpleFPAliasing || !check_fp_aliasing()) &&
          positions[cur_reg] <= cur_inactive->NextStart()) {
        break;
      }
      LifetimePosition next_intersection =
          cur_inactive->FirstIntersection(range);
      if (!next_intersection.IsValid()) continue;
      if (kSimpleFPAliasing || !check_fp_aliasing()) {
        positions[cur_reg] = std::min(positions[cur_reg], next_intersection);
        TRACE("Register %s is free until pos %d (2)\n", RegisterName(cur_reg),
              positions[cur_reg].value());
      } else {
        int alias_base_index = -1;
        int aliases = data()->config()->GetAliases(
            cur_inactive->representation(), cur_reg, rep, &alias_base_index);
        DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
        while (aliases--) {
          int aliased_reg = alias_base_index + aliases;
          positions[aliased_reg] =
              std::min(positions[aliased_reg], next_intersection);
        }
      }
    }
  }
}

// High-level register allocation summary:
//
// We attempt to first allocate the preferred (hint) register. If that is not
// possible, we find a register that's free, and allocate that. If that's not
// possible, we search for a register to steal from a range that was allocated.
// The goal is to optimize for throughput by avoiding register-to-memory moves,
// which are expensive.
void LinearScanAllocator::ProcessCurrentRange(LiveRange* current,
                                              SpillMode spill_mode) {
  EmbeddedVector<LifetimePosition, RegisterConfiguration::kMaxRegisters>
      free_until_pos;
  FindFreeRegistersForRange(current, free_until_pos);
  if (!TryAllocatePreferredReg(current, free_until_pos)) {
    if (!TryAllocateFreeReg(current, free_until_pos)) {
      AllocateBlockedReg(current, spill_mode);
    }
  }
  if (current->HasRegisterAssigned()) {
    AddToActive(current);
  }
}

bool LinearScanAllocator::TryAllocatePreferredReg(
    LiveRange* current, const Vector<LifetimePosition>& free_until_pos) {
  int hint_register;
  if (current->RegisterFromControlFlow(&hint_register) ||
      current->FirstHintPosition(&hint_register) != nullptr ||
      current->RegisterFromBundle(&hint_register)) {
    TRACE(
        "Found reg hint %s (free until [%d) for live range %d:%d (end %d[).\n",
        RegisterName(hint_register), free_until_pos[hint_register].value(),
        current->TopLevel()->vreg(), current->relative_id(),
        current->End().value());

    // The desired register is free until the end of the current live range.
    if (free_until_pos[hint_register] >= current->End()) {
      TRACE("Assigning preferred reg %s to live range %d:%d\n",
            RegisterName(hint_register), current->TopLevel()->vreg(),
            current->relative_id());
      SetLiveRangeAssignedRegister(current, hint_register);
      return true;
    }
  }
  return false;
}

int LinearScanAllocator::PickRegisterThatIsAvailableLongest(
    LiveRange* current, int hint_reg,
    const Vector<LifetimePosition>& free_until_pos) {
  int num_regs = 0;  // used only for the call to GetFPRegisterSet.
  int num_codes = num_allocatable_registers();
  const int* codes = allocatable_register_codes();
  MachineRepresentation rep = current->representation();
  if (!kSimpleFPAliasing && (rep == MachineRepresentation::kFloat32 ||
                             rep == MachineRepresentation::kSimd128)) {
    GetFPRegisterSet(rep, &num_regs, &num_codes, &codes);
  }

  DCHECK_GE(free_until_pos.length(), num_codes);

  // Find the register which stays free for the longest time. Check for
  // the hinted register first, as we might want to use that one. Only
  // count full instructions for free ranges, as an instruction's internal
  // positions do not help but might shadow a hinted register. This is
  // typically the case for function calls, where all registered are
  // cloberred after the call except for the argument registers, which are
  // set before the call. Hence, the argument registers always get ignored,
  // as their available time is shorter.
  int reg = (hint_reg == kUnassignedRegister) ? codes[0] : hint_reg;
  int current_free = free_until_pos[reg].ToInstructionIndex();
  for (int i = 0; i < num_codes; ++i) {
    int code = codes[i];
    // Prefer registers that have no fixed uses to avoid blocking later hints.
    // We use the first register that has no fixed uses to ensure we use
    // byte addressable registers in ia32 first.
    int candidate_free = free_until_pos[code].ToInstructionIndex();
    TRACE("Register %s in free until %d\n", RegisterName(code), candidate_free);
    if ((candidate_free > current_free) ||
        (candidate_free == current_free && reg != hint_reg &&
         (data()->HasFixedUse(current->representation(), reg) &&
          !data()->HasFixedUse(current->representation(), code)))) {
      reg = code;
      current_free = candidate_free;
    }
  }

  return reg;
}

bool LinearScanAllocator::TryAllocateFreeReg(
    LiveRange* current, const Vector<LifetimePosition>& free_until_pos) {
  // Compute register hint, if such exists.
  int hint_reg = kUnassignedRegister;
  current->RegisterFromControlFlow(&hint_reg) ||
      current->FirstHintPosition(&hint_reg) != nullptr ||
      current->RegisterFromBundle(&hint_reg);

  int reg =
      PickRegisterThatIsAvailableLongest(current, hint_reg, free_until_pos);

  LifetimePosition pos = free_until_pos[reg];

  if (pos <= current->Start()) {
    // All registers are blocked.
    return false;
  }

  if (pos < current->End()) {
    // Register reg is available at the range start but becomes blocked before
    // the range end. Split current at position where it becomes blocked.
    LiveRange* tail = SplitRangeAt(current, pos);
    AddToUnhandled(tail);

    // Try to allocate preferred register once more.
    if (TryAllocatePreferredReg(current, free_until_pos)) return true;
  }

  // Register reg is available at the range start and is free until the range
  // end.
  DCHECK(pos >= current->End());
  TRACE("Assigning free reg %s to live range %d:%d\n", RegisterName(reg),
        current->TopLevel()->vreg(), current->relative_id());
  SetLiveRangeAssignedRegister(current, reg);

  return true;
}

void LinearScanAllocator::AllocateBlockedReg(LiveRange* current,
                                             SpillMode spill_mode) {
  UsePosition* register_use = current->NextRegisterPosition(current->Start());
  if (register_use == nullptr) {
    // There is no use in the current live range that requires a register.
    // We can just spill it.
    LiveRange* begin_spill = nullptr;
    LifetimePosition spill_pos = FindOptimalSpillingPos(
        current, current->Start(), spill_mode, &begin_spill);
    MaybeSpillPreviousRanges(begin_spill, spill_pos, current);
    Spill(current, spill_mode);
    return;
  }

  MachineRepresentation rep = current->representation();

  // use_pos keeps track of positions a register/alias is used at.
  // block_pos keeps track of positions where a register/alias is blocked
  // from.
  EmbeddedVector<LifetimePosition, RegisterConfiguration::kMaxRegisters>
      use_pos(LifetimePosition::MaxPosition());
  EmbeddedVector<LifetimePosition, RegisterConfiguration::kMaxRegisters>
      block_pos(LifetimePosition::MaxPosition());

  for (LiveRange* range : active_live_ranges()) {
    int cur_reg = range->assigned_register();
    bool is_fixed_or_cant_spill =
        range->TopLevel()->IsFixed() || !range->CanBeSpilled(current->Start());
    if (kSimpleFPAliasing || !check_fp_aliasing()) {
      if (is_fixed_or_cant_spill) {
        block_pos[cur_reg] = use_pos[cur_reg] =
            LifetimePosition::GapFromInstructionIndex(0);
      } else {
        DCHECK_NE(LifetimePosition::GapFromInstructionIndex(0),
                  block_pos[cur_reg]);
        use_pos[cur_reg] =
            range->NextLifetimePositionRegisterIsBeneficial(current->Start());
      }
    } else {
      int alias_base_index = -1;
      int aliases = data()->config()->GetAliases(
          range->representation(), cur_reg, rep, &alias_base_index);
      DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
      while (aliases--) {
        int aliased_reg = alias_base_index + aliases;
        if (is_fixed_or_cant_spill) {
          block_pos[aliased_reg] = use_pos[aliased_reg] =
              LifetimePosition::GapFromInstructionIndex(0);
        } else {
          use_pos[aliased_reg] =
              std::min(block_pos[aliased_reg],
                       range->NextLifetimePositionRegisterIsBeneficial(
                           current->Start()));
        }
      }
    }
  }

  for (int cur_reg = 0; cur_reg < num_registers(); ++cur_reg) {
    for (LiveRange* range : inactive_live_ranges(cur_reg)) {
      DCHECK(range->End() > current->Start());
      DCHECK_EQ(range->assigned_register(), cur_reg);
      bool is_fixed = range->TopLevel()->IsFixed();

      // Don't perform costly intersections if they are guaranteed to not update
      // block_pos or use_pos.
      // TODO(mtrofin): extend to aliased ranges, too.
      if ((kSimpleFPAliasing || !check_fp_aliasing())) {
        DCHECK_LE(use_pos[cur_reg], block_pos[cur_reg]);
        if (block_pos[cur_reg] <= range->NextStart()) break;
        if (!is_fixed && use_pos[cur_reg] <= range->NextStart()) continue;
      }

      LifetimePosition next_intersection = range->FirstIntersection(current);
      if (!next_intersection.IsValid()) continue;

      if (kSimpleFPAliasing || !check_fp_aliasing()) {
        if (is_fixed) {
          block_pos[cur_reg] = std::min(block_pos[cur_reg], next_intersection);
          use_pos[cur_reg] = std::min(block_pos[cur_reg], use_pos[cur_reg]);
        } else {
          use_pos[cur_reg] = std::min(use_pos[cur_reg], next_intersection);
        }
      } else {
        int alias_base_index = -1;
        int aliases = data()->config()->GetAliases(
            range->representation(), cur_reg, rep, &alias_base_index);
        DCHECK(aliases > 0 || (aliases == 0 && alias_base_index == -1));
        while (aliases--) {
          int aliased_reg = alias_base_index + aliases;
          if (is_fixed) {
            block_pos[aliased_reg] =
                std::min(block_pos[aliased_reg], next_intersection);
            use_pos[aliased_reg] =
                std::min(block_pos[aliased_reg], use_pos[aliased_reg]);
          } else {
            use_pos[aliased_reg] =
                std::min(use_pos[aliased_reg], next_intersection);
          }
        }
      }
    }
  }

  // Compute register hint if it exists.
  int hint_reg = kUnassignedRegister;
  current->RegisterFromControlFlow(&hint_reg) ||
      register_use->HintRegister(&hint_reg) ||
      current->RegisterFromBundle(&hint_reg);
  int reg = PickRegisterThatIsAvailableLongest(current, hint_reg, use_pos);

  if (use_pos[reg] < register_use->pos()) {
    // If there is a gap position before the next register use, we can
    // spill until there. The gap position will then fit the fill move.
    if (LifetimePosition::ExistsGapPositionBetween(current->Start(),
                                                   register_use->pos())) {
      SpillBetween(current, current->Start(), register_use->pos(), spill_mode);
      return;
    }
  }

  // When in deferred spilling mode avoid stealing registers beyond the current
  // deferred region. This is required as we otherwise might spill an inactive
  // range with a start outside of deferred code and that would not be reloaded.
  LifetimePosition new_end = current->End();
  if (spill_mode == SpillMode::kSpillDeferred) {
    InstructionBlock* deferred_block =
        code()->GetInstructionBlock(current->Start().ToInstructionIndex());
    new_end =
        std::min(new_end, LifetimePosition::GapFromInstructionIndex(
                              LastDeferredInstructionIndex(deferred_block)));
  }

  // We couldn't spill until the next register use. Split before the register
  // is blocked, if applicable.
  if (block_pos[reg] < new_end) {
    // Register becomes blocked before the current range end. Split before that
    // position.
    new_end = block_pos[reg].Start();
  }

  // If there is no register available at all, we can only spill this range.
  // Happens for instance on entry to deferred code where registers might
  // become blocked yet we aim to reload ranges.
  if (new_end == current->Start()) {
    SpillBetween(current, new_end, register_use->pos(), spill_mode);
    return;
  }

  // Split at the new end if we found one.
  if (new_end != current->End()) {
    LiveRange* tail = SplitBetween(current, current->Start(), new_end);
    AddToUnhandled(tail);
  }

  // Register reg is not blocked for the whole range.
  DCHECK(block_pos[reg] >= current->End());
  TRACE("Assigning blocked reg %s to live range %d:%d\n", RegisterName(reg),
        current->TopLevel()->vreg(), current->relative_id());
  SetLiveRangeAssignedRegister(current, reg);

  // This register was not free. Thus we need to find and spill
  // parts of active and inactive live regions that use the same register
  // at the same lifetime positions as current.
  SplitAndSpillIntersecting(current, spill_mode);
}

void LinearScanAllocator::SplitAndSpillIntersecting(LiveRange* current,
                                                    SpillMode spill_mode) {
  DCHECK(current->HasRegisterAssigned());
  int reg = current->assigned_register();
  LifetimePosition split_pos = current->Start();
  for (auto it = active_live_ranges().begin();
       it != active_live_ranges().end();) {
    LiveRange* range = *it;
    if (kSimpleFPAliasing || !check_fp_aliasing()) {
      if (range->assigned_register() != reg) {
        ++it;
        continue;
      }
    } else {
      if (!data()->config()->AreAliases(current->representation(), reg,
                                        range->representation(),
                                        range->assigned_register())) {
        ++it;
        continue;
      }
    }

    UsePosition* next_pos = range->NextRegisterPosition(current->Start());
    LiveRange* begin_spill = nullptr;
    LifetimePosition spill_pos =
        FindOptimalSpillingPos(range, split_pos, spill_mode, &begin_spill);
    MaybeSpillPreviousRanges(begin_spill, spill_pos, range);
    if (next_pos == nullptr) {
      SpillAfter(range, spill_pos, spill_mode);
    } else {
      // When spilling between spill_pos and next_pos ensure that the range
      // remains spilled at least until the start of the current live range.
      // This guarantees that we will not introduce new unhandled ranges that
      // start before the current range as this violates allocation invariants
      // and will lead to an inconsistent state of active and inactive
      // live-ranges: ranges are allocated in order of their start positions,
      // ranges are retired from active/inactive when the start of the
      // current live-range is larger than their end.
      DCHECK(LifetimePosition::ExistsGapPositionBetween(current->Start(),
                                                        next_pos->pos()));
      SpillBetweenUntil(range, spill_pos, current->Start(), next_pos->pos(),
                        spill_mode);
    }
    it = ActiveToHandled(it);
  }

  for (int cur_reg = 0; cur_reg < num_registers(); ++cur_reg) {
    if (kSimpleFPAliasing || !check_fp_aliasing()) {
      if (cur_reg != reg) continue;
    }
    for (auto it = inactive_live_ranges(cur_reg).begin();
         it != inactive_live_ranges(cur_reg).end();) {
      LiveRange* range = *it;
      if (!kSimpleFPAliasing && check_fp_aliasing() &&
          !data()->config()->AreAliases(current->representation(), reg,
                                        range->representation(), cur_reg)) {
        ++it;
        continue;
      }
      DCHECK(range->End() > current->Start());
      if (range->TopLevel()->IsFixed()) {
        ++it;
        continue;
      }

      LifetimePosition next_intersection = range->FirstIntersection(current);
      if (next_intersection.IsValid()) {
        UsePosition* next_pos = range->NextRegisterPosition(current->Start());
        if (next_pos == nullptr) {
          SpillAfter(range, split_pos, spill_mode);
        } else {
          next_intersection = std::min(next_intersection, next_pos->pos());
          SpillBetween(range, split_pos, next_intersection, spill_mode);
        }
        it = InactiveToHandled(it);
      } else {
        ++it;
      }
    }
  }
}

bool LinearScanAllocator::TryReuseSpillForPhi(TopLevelLiveRange* range) {
  if (!range->is_phi()) return false;

  DCHECK(!range->HasSpillOperand());
  // Check how many operands belong to the same bundle as the output.
  LiveRangeBundle* out_bundle = range->get_bundle();
  TopTierRegisterAllocationData::PhiMapValue* phi_map_value =
      data()->GetPhiMapValueFor(range);
  const PhiInstruction* phi = phi_map_value->phi();
  const InstructionBlock* block = phi_map_value->block();
  // Count the number of spilled operands.
  size_t spilled_count = 0;
  for (size_t i = 0; i < phi->operands().size(); i++) {
    int op = phi->operands()[i];
    LiveRange* op_range = data()->GetOrCreateLiveRangeFor(op);
    if (!op_range->TopLevel()->HasSpillRange()) continue;
    const InstructionBlock* pred =
        code()->InstructionBlockAt(block->predecessors()[i]);
    LifetimePosition pred_end =
        LifetimePosition::InstructionFromInstructionIndex(
            pred->last_instruction_index());
    while (op_range != nullptr && !op_range->CanCover(pred_end)) {
      op_range = op_range->next();
    }
    if (op_range != nullptr && op_range->spilled() &&
        op_range->get_bundle() == out_bundle) {
      spilled_count++;
    }
  }

  // Only continue if more than half of the operands are spilled to the same
  // slot (because part of same bundle).
  if (spilled_count * 2 <= phi->operands().size()) {
    return false;
  }

  // If the range does not need register soon, spill it to the merged
  // spill range.
  LifetimePosition next_pos = range->Start();
  if (next_pos.IsGapPosition()) next_pos = next_pos.NextStart();
  UsePosition* pos = range->NextUsePositionRegisterIsBeneficial(next_pos);
  if (pos == nullptr) {
    Spill(range, SpillMode::kSpillAtDefinition);
    return true;
  } else if (pos->pos() > range->Start().NextStart()) {
    SpillBetween(range, range->Start(), pos->pos(),
                 SpillMode::kSpillAtDefinition);
    return true;
  }
  return false;
}

void LinearScanAllocator::SpillAfter(LiveRange* range, LifetimePosition pos,
                                     SpillMode spill_mode) {
  LiveRange* second_part = SplitRangeAt(range, pos);
  Spill(second_part, spill_mode);
}

void LinearScanAllocator::SpillBetween(LiveRange* range, LifetimePosition start,
                                       LifetimePosition end,
                                       SpillMode spill_mode) {
  SpillBetweenUntil(range, start, start, end, spill_mode);
}

void LinearScanAllocator::SpillBetweenUntil(LiveRange* range,
                                            LifetimePosition start,
                                            LifetimePosition until,
                                            LifetimePosition end,
                                            SpillMode spill_mode) {
  CHECK(start < end);
  LiveRange* second_part = SplitRangeAt(range, start);

  if (second_part->Start() < end) {
    // The split result intersects with [start, end[.
    // Split it at position between ]start+1, end[, spill the middle part
    // and put the rest to unhandled.

    // Make sure that the third part always starts after the start of the
    // second part, as that likely is the current position of the register
    // allocator and we cannot add ranges to unhandled that start before
    // the current position.
    LifetimePosition split_start = std::max(second_part->Start().End(), until);

    // If end is an actual use (which it typically is) we have to split
    // so that there is a gap before so that we have space for moving the
    // value into its position.
    // However, if we have no choice, split right where asked.
    LifetimePosition third_part_end =
        std::max(split_start, end.PrevStart().End());
    // Instead of spliting right after or even before the block boundary,
    // split on the boumndary to avoid extra moves.
    if (data()->IsBlockBoundary(end.Start())) {
      third_part_end = std::max(split_start, end.Start());
    }

    LiveRange* third_part =
        SplitBetween(second_part, split_start, third_part_end);
    if (GetInstructionBlock(data()->code(), second_part->Start())
            ->IsDeferred()) {
      // Try to use the same register as before.
      TRACE("Setting control flow hint for %d:%d to %s\n",
            third_part->TopLevel()->vreg(), third_part->relative_id(),
            RegisterName(range->controlflow_hint()));
      third_part->set_controlflow_hint(range->controlflow_hint());
    }

    AddToUnhandled(third_part);
    // This can happen, even if we checked for start < end above, as we fiddle
    // with the end location. However, we are guaranteed to be after or at
    // until, so this is fine.
    if (third_part != second_part) {
      Spill(second_part, spill_mode);
    }
  } else {
    // The split result does not intersect with [start, end[.
    // Nothing to spill. Just put it to unhandled as whole.
    AddToUnhandled(second_part);
  }
}

OperandAssigner::OperandAssigner(TopTierRegisterAllocationData* data)
    : data_(data) {}

void OperandAssigner::DecideSpillingMode() {
  for (auto range : data()->live_ranges()) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    int max_blocks = data()->code()->InstructionBlockCount();
    if (range != nullptr && range->IsSpilledOnlyInDeferredBlocks(data())) {
      // If the range is spilled only in deferred blocks and starts in
      // a non-deferred block, we transition its representation here so
      // that the LiveRangeConnector processes them correctly. If,
      // however, they start in a deferred block, we uograde them to
      // spill at definition, as that definition is in a deferred block
      // anyway. While this is an optimization, the code in LiveRangeConnector
      // relies on it!
      if (GetInstructionBlock(data()->code(), range->Start())->IsDeferred()) {
        TRACE("Live range %d is spilled and alive in deferred code only\n",
              range->vreg());
        range->TransitionRangeToSpillAtDefinition();
      } else {
        TRACE("Live range %d is spilled deferred code only but alive outside\n",
              range->vreg());
        range->TransitionRangeToDeferredSpill(data()->allocation_zone(),
                                              max_blocks);
      }
    }
  }
}

void OperandAssigner::AssignSpillSlots() {
  for (auto range : data()->live_ranges()) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    if (range != nullptr && range->get_bundle() != nullptr) {
      range->get_bundle()->MergeSpillRanges();
    }
  }
  ZoneVector<SpillRange*>& spill_ranges = data()->spill_ranges();
  // Merge disjoint spill ranges
  for (size_t i = 0; i < spill_ranges.size(); ++i) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    SpillRange* range = spill_ranges[i];
    if (range == nullptr) continue;
    if (range->IsEmpty()) continue;
    for (size_t j = i + 1; j < spill_ranges.size(); ++j) {
      SpillRange* other = spill_ranges[j];
      if (other != nullptr && !other->IsEmpty()) {
        range->TryMerge(other);
      }
    }
  }
  // Allocate slots for the merged spill ranges.
  for (SpillRange* range : spill_ranges) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    if (range == nullptr || range->IsEmpty()) continue;
    // Allocate a new operand referring to the spill slot.
    if (!range->HasSlot()) {
      int index = data()->frame()->AllocateSpillSlot(range->byte_width());
      range->set_assigned_slot(index);
    }
  }
}

void OperandAssigner::CommitAssignment() {
  const size_t live_ranges_size = data()->live_ranges().size();
  for (TopLevelLiveRange* top_range : data()->live_ranges()) {
    data()->tick_counter()->TickAndMaybeEnterSafepoint();
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (top_range == nullptr || top_range->IsEmpty()) continue;
    InstructionOperand spill_operand;
    if (top_range->HasSpillOperand()) {
      spill_operand = *top_range->TopLevel()->GetSpillOperand();
    } else if (top_range->TopLevel()->HasSpillRange()) {
      spill_operand = top_range->TopLevel()->GetSpillRangeOperand();
    }
    if (top_range->is_phi()) {
      data()->GetPhiMapValueFor(top_range)->CommitAssignment(
          top_range->GetAssignedOperand());
    }
    for (LiveRange* range = top_range; range != nullptr;
         range = range->next()) {
      InstructionOperand assigned = range->GetAssignedOperand();
      DCHECK(!assigned.IsUnallocated());
      range->ConvertUsesToOperand(assigned, spill_operand);
    }

    if (!spill_operand.IsInvalid()) {
      // If this top level range has a child spilled in a deferred block, we use
      // the range and control flow connection mechanism instead of spilling at
      // definition. Refer to the ConnectLiveRanges and ResolveControlFlow
      // phases. Normally, when we spill at definition, we do not insert a
      // connecting move when a successor child range is spilled - because the
      // spilled range picks up its value from the slot which was assigned at
      // definition. For ranges that are determined to spill only in deferred
      // blocks, we let ConnectLiveRanges and ResolveControlFlow find the blocks
      // where a spill operand is expected, and then finalize by inserting the
      // spills in the deferred blocks dominators.
      if (!top_range->IsSpilledOnlyInDeferredBlocks(data()) &&
          !top_range->HasGeneralSpillRange()) {
        // Spill at definition if the range isn't spilled in a way that will be
        // handled later.
        top_range->FilterSpillMoves(data(), spill_operand);
        top_range->CommitSpillMoves(data(), spill_operand);
      }
    }
  }
}

ReferenceMapPopulator::ReferenceMapPopulator(
    TopTierRegisterAllocationData* data)
    : data_(data) {}

bool ReferenceMapPopulator::SafePointsAreInOrder() const {
  int safe_point = 0;
  for (ReferenceMap* map : *data()->code()->reference_maps()) {
    if (safe_point > map->instruction_position()) return false;
    safe_point = map->instruction_position();
  }
  return true;
}

void ReferenceMapPopulator::PopulateReferenceMaps() {
  DCHECK(SafePointsAreInOrder());
  // Map all delayed references.
  for (TopTierRegisterAllocationData::DelayedReference& delayed_reference :
       data()->delayed_references()) {
    delayed_reference.map->RecordReference(
        AllocatedOperand::cast(*delayed_reference.operand));
  }
  // Iterate over all safe point positions and record a pointer
  // for all spilled live ranges at this point.
  int last_range_start = 0;
  const ReferenceMapDeque* reference_maps = data()->code()->reference_maps();
  ReferenceMapDeque::const_iterator first_it = reference_maps->begin();
  const size_t live_ranges_size = data()->live_ranges().size();
  for (TopLevelLiveRange* range : data()->live_ranges()) {
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (range == nullptr) continue;
    // Skip non-reference values.
    if (!data()->code()->IsReference(range->vreg())) continue;
    // Skip empty live ranges.
    if (range->IsEmpty()) continue;
    if (range->has_preassigned_slot()) continue;

    // Find the extent of the range and its children.
    int start = range->Start().ToInstructionIndex();
    int end = 0;
    for (LiveRange* cur = range; cur != nullptr; cur = cur->next()) {
      LifetimePosition this_end = cur->End();
      if (this_end.ToInstructionIndex() > end)
        end = this_end.ToInstructionIndex();
      DCHECK(cur->Start().ToInstructionIndex() >= start);
    }

    // Most of the ranges are in order, but not all.  Keep an eye on when they
    // step backwards and reset the first_it so we don't miss any safe points.
    if (start < last_range_start) first_it = reference_maps->begin();
    last_range_start = start;

    // Step across all the safe points that are before the start of this range,
    // recording how far we step in order to save doing this for the next range.
    for (; first_it != reference_maps->end(); ++first_it) {
      ReferenceMap* map = *first_it;
      if (map->instruction_position() >= start) break;
    }

    InstructionOperand spill_operand;
    if (((range->HasSpillOperand() &&
          !range->GetSpillOperand()->IsConstant()) ||
         range->HasSpillRange())) {
      if (range->HasSpillOperand()) {
        spill_operand = *range->GetSpillOperand();
      } else {
        spill_operand = range->GetSpillRangeOperand();
      }
      DCHECK(spill_operand.IsStackSlot());
      DCHECK(CanBeTaggedOrCompressedPointer(
          AllocatedOperand::cast(spill_operand).representation()));
    }

    LiveRange* cur = range;
    // Step through the safe points to see whether they are in the range.
    for (auto it = first_it; it != reference_maps->end(); ++it) {
      ReferenceMap* map = *it;
      int safe_point = map->instruction_position();

      // The safe points are sorted so we can stop searching here.
      if (safe_point - 1 > end) break;

      // Advance to the next active range that covers the current
      // safe point position.
      LifetimePosition safe_point_pos =
          LifetimePosition::InstructionFromInstructionIndex(safe_point);

      // Search for the child range (cur) that covers safe_point_pos. If we
      // don't find it before the children pass safe_point_pos, keep cur at
      // the last child, because the next safe_point_pos may be covered by cur.
      // This may happen if cur has more than one interval, and the current
      // safe_point_pos is in between intervals.
      // For that reason, cur may be at most the last child.
      DCHECK_NOT_NULL(cur);
      DCHECK(safe_point_pos >= cur->Start() || range == cur);
      bool found = false;
      while (!found) {
        if (cur->Covers(safe_point_pos)) {
          found = true;
        } else {
          LiveRange* next = cur->next();
          if (next == nullptr || next->Start() > safe_point_pos) {
            break;
          }
          cur = next;
        }
      }

      if (!found) {
        continue;
      }

      // Check if the live range is spilled and the safe point is after
      // the spill position.
      int spill_index = range->IsSpilledOnlyInDeferredBlocks(data()) ||
                                range->LateSpillingSelected()
                            ? cur->Start().ToInstructionIndex()
                            : range->spill_start_index();

      if (!spill_operand.IsInvalid() && safe_point >= spill_index) {
        TRACE("Pointer for range %d (spilled at %d) at safe point %d\n",
              range->vreg(), spill_index, safe_point);
        map->RecordReference(AllocatedOperand::cast(spill_operand));
      }

      if (!cur->spilled()) {
        TRACE(
            "Pointer in register for range %d:%d (start at %d) "
            "at safe point %d\n",
            range->vreg(), cur->relative_id(), cur->Start().value(),
            safe_point);
        InstructionOperand operand = cur->GetAssignedOperand();
        DCHECK(!operand.IsStackSlot());
        DCHECK(CanBeTaggedOrCompressedPointer(
            AllocatedOperand::cast(operand).representation()));
        map->RecordReference(AllocatedOperand::cast(operand));
      }
    }
  }
}

LiveRangeConnector::LiveRangeConnector(TopTierRegisterAllocationData* data)
    : data_(data) {}

bool LiveRangeConnector::CanEagerlyResolveControlFlow(
    const InstructionBlock* block) const {
  if (block->PredecessorCount() != 1) return false;
  return block->predecessors()[0].IsNext(block->rpo_number());
}

void LiveRangeConnector::ResolveControlFlow(Zone* local_zone) {
  // Lazily linearize live ranges in memory for fast lookup.
  LiveRangeFinder finder(data(), local_zone);
  ZoneVector<BitVector*>& live_in_sets = data()->live_in_sets();
  for (const InstructionBlock* block : code()->instruction_blocks()) {
    if (CanEagerlyResolveControlFlow(block)) continue;
    BitVector* live = live_in_sets[block->rpo_number().ToInt()];
    BitVector::Iterator iterator(live);
    while (!iterator.Done()) {
      data()->tick_counter()->TickAndMaybeEnterSafepoint();
      int vreg = iterator.Current();
      LiveRangeBoundArray* array = finder.ArrayFor(vreg);
      for (const RpoNumber& pred : block->predecessors()) {
        FindResult result;
        const InstructionBlock* pred_block = code()->InstructionBlockAt(pred);
        if (!array->FindConnectableSubranges(block, pred_block, &result)) {
          continue;
        }
        InstructionOperand pred_op = result.pred_cover_->GetAssignedOperand();
        InstructionOperand cur_op = result.cur_cover_->GetAssignedOperand();
        if (pred_op.Equals(cur_op)) continue;
        if (!pred_op.IsAnyRegister() && cur_op.IsAnyRegister()) {
          // We're doing a reload.
          // We don't need to, if:
          // 1) there's no register use in this block, and
          // 2) the range ends before the block does, and
          // 3) we don't have a successor, or the successor is spilled.
          LifetimePosition block_start =
              LifetimePosition::GapFromInstructionIndex(block->code_start());
          LifetimePosition block_end =
              LifetimePosition::GapFromInstructionIndex(block->code_end());
          const LiveRange* current = result.cur_cover_;
          // Note that this is not the successor if we have control flow!
          // However, in the following condition, we only refer to it if it
          // begins in the current block, in which case we can safely declare it
          // to be the successor.
          const LiveRange* successor = current->next();
          if (current->End() < block_end &&
              (successor == nullptr || successor->spilled())) {
            // verify point 1: no register use. We can go to the end of the
            // range, since it's all within the block.

            bool uses_reg = false;
            for (const UsePosition* use = current->NextUsePosition(block_start);
                 use != nullptr; use = use->next()) {
              if (use->operand()->IsAnyRegister()) {
                uses_reg = true;
                break;
              }
            }
            if (!uses_reg) continue;
          }
          if (current->TopLevel()->IsSpilledOnlyInDeferredBlocks(data()) &&
              pred_block->IsDeferred()) {
            // The spill location should be defined in pred_block, so add
            // pred_block to the list of blocks requiring a spill operand.
            TRACE("Adding B%d to list of spill blocks for %d\n",
                  pred_block->rpo_number().ToInt(),
                  current->TopLevel()->vreg());
            current->TopLevel()
                ->GetListOfBlocksRequiringSpillOperands(data())
                ->Add(pred_block->rpo_number().ToInt());
          }
        }
        int move_loc = ResolveControlFlow(block, cur_op, pred_block, pred_op);
        USE(move_loc);
        DCHECK_IMPLIES(
            result.cur_cover_->TopLevel()->IsSpilledOnlyInDeferredBlocks(
                data()) &&
                !(pred_op.IsAnyRegister() && cur_op.IsAnyRegister()),
            code()->GetInstructionBlock(move_loc)->IsDeferred());
      }
      iterator.Advance();
    }
  }

  // At this stage, we collected blocks needing a spill operand due to reloads
  // from ConnectRanges and from ResolveControlFlow. Time to commit the spills
  // for deferred blocks. This is a convenient time to commit spills for general
  // spill ranges also, because they need to use the LiveRangeFinder.
  const size_t live_ranges_size = data()->live_ranges().size();
  SpillPlacer spill_placer(&finder, data(), local_zone);
  for (TopLevelLiveRange* top : data()->live_ranges()) {
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (top == nullptr || top->IsEmpty()) continue;
    if (top->IsSpilledOnlyInDeferredBlocks(data())) {
      CommitSpillsInDeferredBlocks(top, finder.ArrayFor(top->vreg()),
                                   local_zone);
    } else if (top->HasGeneralSpillRange()) {
      spill_placer.Add(top);
    }
  }
}

int LiveRangeConnector::ResolveControlFlow(const InstructionBlock* block,
                                           const InstructionOperand& cur_op,
                                           const InstructionBlock* pred,
                                           const InstructionOperand& pred_op) {
  DCHECK(!pred_op.Equals(cur_op));
  int gap_index;
  Instruction::GapPosition position;
  if (block->PredecessorCount() == 1) {
    gap_index = block->first_instruction_index();
    position = Instruction::START;
  } else {
    DCHECK_EQ(1, pred->SuccessorCount());
    DCHECK(!code()
                ->InstructionAt(pred->last_instruction_index())
                ->HasReferenceMap());
    gap_index = pred->last_instruction_index();
    position = Instruction::END;
  }
  data()->AddGapMove(gap_index, position, pred_op, cur_op);
  return gap_index;
}

void LiveRangeConnector::ConnectRanges(Zone* local_zone) {
  DelayedInsertionMap delayed_insertion_map(local_zone);
  const size_t live_ranges_size = data()->live_ranges().size();
  for (TopLevelLiveRange* top_range : data()->live_ranges()) {
    CHECK_EQ(live_ranges_size,
             data()->live_ranges().size());  // TODO(neis): crbug.com/831822
    if (top_range == nullptr) continue;
    bool connect_spilled = top_range->IsSpilledOnlyInDeferredBlocks(data());
    LiveRange* first_range = top_range;
    for (LiveRange *second_range = first_range->next(); second_range != nullptr;
         first_range = second_range, second_range = second_range->next()) {
      LifetimePosition pos = second_range->Start();
      // Add gap move if the two live ranges touch and there is no block
      // boundary.
      if (second_range->spilled()) continue;
      if (first_range->End() != pos) continue;
      if (data()->IsBlockBoundary(pos) &&
          !CanEagerlyResolveControlFlow(GetInstructionBlock(code(), pos))) {
        continue;
      }
      InstructionOperand prev_operand = first_range->GetAssignedOperand();
      InstructionOperand cur_operand = second_range->GetAssignedOperand();
      if (prev_operand.Equals(cur_operand)) continue;
      bool delay_insertion = false;
      Instruction::GapPosition gap_pos;
      int gap_index = pos.ToInstructionIndex();
      if (connect_spilled && !prev_operand.IsAnyRegister() &&
          cur_operand.IsAnyRegister()) {
        const InstructionBlock* block = code()->GetInstructionBlock(gap_index);
        DCHECK(block->IsDeferred());
        // Performing a reload in this block, meaning the spill operand must
        // be defined here.
        top_range->GetListOfBlocksRequiringSpillOperands(data())->Add(
            block->rpo_number().ToInt());
      }

      if (pos.IsGapPosition()) {
        gap_pos = pos.IsStart() ? Instruction::START : Instruction::END;
      } else {
        if (pos.IsStart()) {
          delay_insertion = true;
        } else {
          gap_index++;
        }
        gap_pos = delay_insertion ? Instruction::END : Instruction::START;
      }
      // Reloads or spills for spilled in deferred blocks ranges must happen
      // only in deferred blocks.
      DCHECK_IMPLIES(connect_spilled && !(prev_operand.IsAnyRegister() &&
                                          cur_operand.IsAnyRegister()),
                     code()->GetInstructionBlock(gap_index)->IsDeferred());

      ParallelMove* move =
          code()->InstructionAt(gap_index)->GetOrCreateParallelMove(
              gap_pos, code_zone());
      if (!delay_insertion) {
        move->AddMove(prev_operand, cur_operand);
      } else {
        delayed_insertion_map.insert(
            std::make_pair(std::make_pair(move, prev_operand), cur_operand));
      }
    }
  }
  if (delayed_insertion_map.empty()) return;
  // Insert all the moves which should occur after the stored move.
  ZoneVector<MoveOperands*> to_insert(local_zone);
  ZoneVector<MoveOperands*> to_eliminate(local_zone);
  to_insert.reserve(4);
  to_eliminate.reserve(4);
  ParallelMove* moves = delayed_insertion_map.begin()->first.first;
  for (auto it = delayed_insertion_map.begin();; ++it) {
    bool done = it == delayed_insertion_map.end();
    if (done || it->first.first != moves) {
      // Commit the MoveOperands for current ParallelMove.
      for (MoveOperands* move : to_eliminate) {
        move->Eliminate();
      }
      for (MoveOperands* move : to_insert) {
        moves->push_back(move);
      }
      if (done) break;
      // Reset state.
      to_eliminate.clear();
      to_insert.clear();
      moves = it->first.first;
    }
    // Gather all MoveOperands for a single ParallelMove.
    MoveOperands* move =
        code_zone()->New<MoveOperands>(it->first.second, it->second);
    moves->PrepareInsertAfter(move, &to_eliminate);
    to_insert.push_back(move);
  }
}

void LiveRangeConnector::CommitSpillsInDeferredBlocks(
    TopLevelLiveRange* range, LiveRangeBoundArray* array, Zone* temp_zone) {
  DCHECK(range->IsSpilledOnlyInDeferredBlocks(data()));
  DCHECK(!range->spilled());

  InstructionSequence* code = data()->code();
  InstructionOperand spill_operand = range->GetSpillRangeOperand();

  TRACE("Live Range %d will be spilled only in deferred blocks.\n",
        range->vreg());
  // If we have ranges that aren't spilled but require the operand on the stack,
  // make sure we insert the spill.
  for (const LiveRange* child = range; child != nullptr;
       child = child->next()) {
    for (const UsePosition* pos = child->first_pos(); pos != nullptr;
         pos = pos->next()) {
      if (pos->type() != UsePositionType::kRequiresSlot && !child->spilled())
        continue;
      range->AddBlockRequiringSpillOperand(
          code->GetInstructionBlock(pos->pos().ToInstructionIndex())
              ->rpo_number(),
          data());
    }
  }

  ZoneQueue<int> worklist(temp_zone);

  for (BitVector::Iterator iterator(
           range->GetListOfBlocksRequiringSpillOperands(data()));
       !iterator.Done(); iterator.Advance()) {
    worklist.push(iterator.Current());
  }

  ZoneSet<std::pair<RpoNumber, int>> done_moves(temp_zone);
  // Seek the deferred blocks that dominate locations requiring spill operands,
  // and spill there. We only need to spill at the start of such blocks.
  BitVector done_blocks(
      range->GetListOfBlocksRequiringSpillOperands(data())->length(),
      temp_zone);
  while (!worklist.empty()) {
    int block_id = worklist.front();
    worklist.pop();
    if (done_blocks.Contains(block_id)) continue;
    done_blocks.Add(block_id);
    InstructionBlock* spill_block =
        code->InstructionBlockAt(RpoNumber::FromInt(block_id));

    for (const RpoNumber& pred : spill_block->predecessors()) {
      const InstructionBlock* pred_block = code->InstructionBlockAt(pred);

      if (pred_block->IsDeferred()) {
        worklist.push(pred_block->rpo_number().ToInt());
      } else {
        LifetimePosition pred_end =
            LifetimePosition::InstructionFromInstructionIndex(
                pred_block->last_instruction_index());

        LiveRangeBound* bound = array->Find(pred_end);

        InstructionOperand pred_op = bound->range_->GetAssignedOperand();

        RpoNumber spill_block_number = spill_block->rpo_number();
        if (done_moves.find(std::make_pair(
                spill_block_number, range->vreg())) == done_moves.end()) {
          TRACE("Spilling deferred spill for range %d at B%d\n", range->vreg(),
                spill_block_number.ToInt());
          data()->AddGapMove(spill_block->first_instruction_index(),
                             Instruction::GapPosition::START, pred_op,
                             spill_operand);
          done_moves.insert(std::make_pair(spill_block_number, range->vreg()));
          spill_block->mark_needs_frame();
        }
      }
    }
  }
}

#undef TRACE
#undef TRACE_COND

}  // namespace compiler
}  // namespace internal
}  // namespace v8