[turbofan] Separate LiveRange and TopLevelLiveRange concepts

src/compiler/register-allocator.h

Index: src/compiler/register-allocator.h
diff --git a/src/compiler/register-allocator.h b/src/compiler/register-allocator.h
index c537bbe7f93352720d659b87dc449843c16b3b27..ff4ddd0c741403528424b3afc66e259f6ff4acae 100644
--- a/src/compiler/register-allocator.h
+++ b/src/compiler/register-allocator.h
@@ -274,27 +274,26 @@ class UsePosition final : public ZoneObject {
 
 class SpillRange;
 class RegisterAllocationData;
+class TopLevelLiveRange;
 
 // Representation of SSA values' live ranges as a collection of (continuous)
 // intervals over the instruction ordering.
-class LiveRange final : public ZoneObject {
+class LiveRange : public ZoneObject {
  public:
-  explicit LiveRange(int id, MachineType machine_type);
-
   UseInterval* first_interval() const { return first_interval_; }
   UsePosition* first_pos() const { return first_pos_; }
-  LiveRange* parent() const { return parent_; }
-  LiveRange* TopLevel() { return (parent_ == nullptr) ? this : parent_; }
-  const LiveRange* TopLevel() const {
-    return (parent_ == nullptr) ? this : parent_;
-  }
+  TopLevelLiveRange* TopLevel() { return top_level_; }
+  const TopLevelLiveRange* TopLevel() const { return top_level_; }
+
+  bool IsTopLevel() const;
+
   LiveRange* next() const { return next_; }
-  bool IsChild() const { return parent() != nullptr; }
-  int id() const { return id_; }
-  bool IsFixed() const { return id_ < 0; }
+
+  int relative_id() const { return relative_id_; }
+
   bool IsEmpty() const { return first_interval() == nullptr; }
+
   InstructionOperand GetAssignedOperand() const;
-  int spill_start_index() const { return spill_start_index_; }
 
   MachineType machine_type() const { return MachineTypeField::decode(bits_); }
 
@@ -310,22 +309,6 @@ class LiveRange final : public ZoneObject {
 
   RegisterKind kind() const;
 
-  // Correct only for parent.
-  bool is_phi() const { return IsPhiField::decode(bits_); }
-  void set_is_phi(bool value) { bits_ = IsPhiField::update(bits_, value); }
-
-  // Correct only for parent.
-  bool is_non_loop_phi() const { return IsNonLoopPhiField::decode(bits_); }
-  void set_is_non_loop_phi(bool value) {
-    bits_ = IsNonLoopPhiField::update(bits_, value);
-  }
-
-  // Relevant only for parent.
-  bool has_slot_use() const { return HasSlotUseField::decode(bits_); }
-  void set_has_slot_use(bool value) {
-    bits_ = HasSlotUseField::update(bits_, value);
-  }
-
   // Returns use position in this live range that follows both start
   // and last processed use position.
   UsePosition* NextUsePosition(LifetimePosition start) const;
@@ -350,14 +333,18 @@ class LiveRange final : public ZoneObject {
   // Can this live range be spilled at this position.
   bool CanBeSpilled(LifetimePosition pos) const;
 
-  // Split this live range at the given position which must follow the start of
-  // the range.
+  // Splitting primitive used by both splitting and splintering members.
+  // Performs the split, but does not link the resulting ranges.
+  // The given position must follow the start of the range.
   // All uses following the given position will be moved from this
   // live range to the result live range.
-  void SplitAt(LifetimePosition position, LiveRange* result, Zone* zone);
-  void Splinter(LifetimePosition start, LifetimePosition end, LiveRange* result,
-                Zone* zone);
-  void Merge(LiveRange* other, RegisterAllocationData* data);
+  // The current range will terminate at position, while result will start from
+  // position.
+  void DetachAt(LifetimePosition position, LiveRange* result, Zone* zone);
+
+  // Detaches at position, and then links the resulting ranges. Returns the
+  // child, which starts at position.
+  LiveRange* SplitAt(LifetimePosition position, Zone* zone);
 
   // Returns nullptr when no register is hinted, otherwise sets register_index.
   UsePosition* FirstHintPosition(int* register_index) const;
@@ -381,7 +368,117 @@ class LiveRange final : public ZoneObject {
     return last_interval_->end();
   }
 
+  bool ShouldBeAllocatedBefore(const LiveRange* other) const;
+  bool CanCover(LifetimePosition position) const;
+  bool Covers(LifetimePosition position) const;
+  LifetimePosition FirstIntersection(LiveRange* other) const;
+
+  void Verify() const;
+
+  void ConvertUsesToOperand(const InstructionOperand& op,
+                            const InstructionOperand& spill_op);
+  void SetUseHints(int register_index);
+  void UnsetUseHints() { SetUseHints(kUnassignedRegister); }
+
+  // Used solely by the Greedy Allocator:
+  unsigned GetSize();
+  float weight() const { return weight_; }
+  void set_weight(float weight) { weight_ = weight; }
+
+  static const int kInvalidSize = -1;
+  static const float kInvalidWeight;
+  static const float kMaxWeight;
+
+ private:
+  friend class TopLevelLiveRange;
+  explicit LiveRange(int relative_id, MachineType machine_type,
+                     TopLevelLiveRange* top_level);
+
+  void AppendAsChild(TopLevelLiveRange* other);
+  void UpdateParentForAllChildren(TopLevelLiveRange* new_top_level);
+
+  void set_spilled(bool value) { bits_ = SpilledField::update(bits_, value); }
+
+  UseInterval* FirstSearchIntervalForPosition(LifetimePosition position) const;
+  void AdvanceLastProcessedMarker(UseInterval* to_start_of,
+                                  LifetimePosition but_not_past) const;
+
+  typedef BitField<bool, 0, 1> SpilledField;
+  typedef BitField<int32_t, 6, 6> AssignedRegisterField;
+  typedef BitField<MachineType, 12, 15> MachineTypeField;
+
+  int relative_id_;
+  uint32_t bits_;
+  UseInterval* last_interval_;
+  UseInterval* first_interval_;
+  UsePosition* first_pos_;
+  TopLevelLiveRange* top_level_;
+  LiveRange* next_;
+  // This is used as a cache, it doesn't affect correctness.
+  mutable UseInterval* current_interval_;
+  // This is used as a cache, it doesn't affect correctness.
+  mutable UsePosition* last_processed_use_;
+  // This is used as a cache, it's invalid outside of BuildLiveRanges.
+  mutable UsePosition* current_hint_position_;
+
+  // greedy: the number of LifetimePositions covered by this range. Used to
+  // prioritize selecting live ranges for register assignment, as well as
+  // in weight calculations.
+  int size_;
+
+  // greedy: a metric for resolving conflicts between ranges with an assigned
+  // register and ranges that intersect them and need a register.
+  float weight_;
+
+  DISALLOW_COPY_AND_ASSIGN(LiveRange);
+};
+
+
+class TopLevelLiveRange final : public LiveRange {
+ public:
+  explicit TopLevelLiveRange(int vreg, MachineType machine_type);
+  int spill_start_index() const { return spill_start_index_; }
+
+  bool IsFixed() const { return vreg_ < 0; }
+
+  bool is_phi() const { return IsPhiField::decode(bits_); }
+  void set_is_phi(bool value) { bits_ = IsPhiField::update(bits_, value); }
+
+  bool is_non_loop_phi() const { return IsNonLoopPhiField::decode(bits_); }
+  void set_is_non_loop_phi(bool value) {
+    bits_ = IsNonLoopPhiField::update(bits_, value);
+  }
+
+  bool has_slot_use() const { return HasSlotUseField::decode(bits_); }
+  void set_has_slot_use(bool value) {
+    bits_ = HasSlotUseField::update(bits_, value);
+  }
+
+  // Add a new interval or a new use position to this live range.
+  void EnsureInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
+  void AddUseInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
+  void AddUsePosition(UsePosition* pos);
+
+  // Shorten the most recently added interval by setting a new start.
+  void ShortenTo(LifetimePosition start);
+
+  // Detaches between start and end, and attributes the resulting range to
+  // result.
+  // The current range is pointed to as "splintered_from". No parent/child
+  // relationship is established between this and result.
+  void Splinter(LifetimePosition start, LifetimePosition end,
+                TopLevelLiveRange* result, Zone* zone);
+
+  // Assuming other was splintered from this range, embeds other and its
+  // children as part of the children sequence of this range.
+  void Merge(TopLevelLiveRange* other, RegisterAllocationData* data);
+
+  // Spill range management.
+  void SetSpillRange(SpillRange* spill_range);
   enum class SpillType { kNoSpillType, kSpillOperand, kSpillRange };
+  void set_spill_type(SpillType value) {
+    bits_ = SpillTypeField::update(bits_, value);
+  }
   SpillType spill_type() const { return SpillTypeField::decode(bits_); }
   InstructionOperand* GetSpillOperand() const {
     DCHECK(spill_type() == SpillType::kSpillOperand);
@@ -404,21 +501,21 @@ class LiveRange final : public ZoneObject {
     return spill_type() == SpillType::kSpillOperand;
   }
   bool HasSpillRange() const { return spill_type() == SpillType::kSpillRange; }
-  bool MayRequireSpillRange() const {
-    DCHECK(!IsChild() && !IsSplinter());
-    return !HasSpillOperand() && spill_range_ == nullptr;
-  }
 
   AllocatedOperand GetSpillRangeOperand() const;
 
   void SpillAtDefinition(Zone* zone, int gap_index,
                          InstructionOperand* operand);
   void SetSpillOperand(InstructionOperand* operand);
-  void SetSpillRange(SpillRange* spill_range);
+  void SetSpillStartIndex(int start) {
+    spill_start_index_ = Min(start, spill_start_index_);
+  }
+
+  void SetSplinteredFrom(TopLevelLiveRange* splinter_parent);
   void CommitSpillsAtDefinition(InstructionSequence* sequence,
                                 const InstructionOperand& operand,
                                 bool might_be_duplicated);
-  // This must be applied on top level ranges.
+
   // If all the children of this range are spilled in deferred blocks, and if
   // for any non-spilled child with a use position requiring a slot, that range
   // is contained in a deferred block, mark the range as
@@ -429,29 +526,19 @@ class LiveRange final : public ZoneObject {
   bool TryCommitSpillInDeferredBlock(InstructionSequence* code,
                                      const InstructionOperand& spill_operand);
 
-  void SetSpillStartIndex(int start) {
-    spill_start_index_ = Min(start, spill_start_index_);
+  TopLevelLiveRange* splintered_from() const { return splintered_from_; }
+  bool IsSplinter() const { return splintered_from_ != nullptr; }
+  bool MayRequireSpillRange() const {
+    DCHECK(!IsSplinter());
+    return !HasSpillOperand() && spill_range_ == nullptr;
   }
+  void UpdateSpillRangePostMerge(TopLevelLiveRange* merged);
+  int vreg() const { return vreg_; }
 
-  bool ShouldBeAllocatedBefore(const LiveRange* other) const;
-  bool CanCover(LifetimePosition position) const;
-  bool Covers(LifetimePosition position) const;
-  LifetimePosition FirstIntersection(LiveRange* other) const;
-
-  // Add a new interval or a new use position to this live range.
-  void EnsureInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
-  void AddUseInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
-  void AddUsePosition(UsePosition* pos);
-
-  // Shorten the most recently added interval by setting a new start.
-  void ShortenTo(LifetimePosition start);
-
-  void Verify() const;
-
-  void ConvertUsesToOperand(const InstructionOperand& op,
-                            const InstructionOperand& spill_op);
-  void SetUseHints(int register_index);
-  void UnsetUseHints() { SetUseHints(kUnassignedRegister); }
+  int GetNextChildId() { return ++last_child_id_; }
+  bool IsSpilledOnlyInDeferredBlocks() const {
+    return spilled_in_deferred_blocks_;
+  }
 
   struct SpillAtDefinitionList;
 
@@ -459,91 +546,29 @@ class LiveRange final : public ZoneObject {
     return spills_at_definition_;
   }
 
-  // Used solely by the Greedy Allocator:
-  unsigned GetSize();
-  float weight() const { return weight_; }
-  void set_weight(float weight) { weight_ = weight; }
-
-  bool IsSpilledOnlyInDeferredBlocks() const {
-    return spilled_in_deferred_block_;
-  }
-
-  static const int kInvalidSize = -1;
-  static const float kInvalidWeight;
-  static const float kMaxWeight;
-
-  LiveRange* splintered_from() const {
-    DCHECK(!IsChild());
-    return splintered_from_;
-  }
-  bool IsSplinter() const {
-    DCHECK(!IsChild());
-    return splintered_from_ != nullptr;
-  }
-
-  void set_spill_type(SpillType value) {
-    bits_ = SpillTypeField::update(bits_, value);
-  }
-
  private:
-  void AppendChild(LiveRange* other);
-  void UpdateParentForAllChildren(LiveRange* new_parent);
-  void UpdateSpillRangePostMerge(LiveRange* merged);
-
-  void SetSplinteredFrom(LiveRange* splinter_parent);
-
-
-  void set_spilled(bool value) { bits_ = SpilledField::update(bits_, value); }
-
-  UseInterval* FirstSearchIntervalForPosition(LifetimePosition position) const;
-  void AdvanceLastProcessedMarker(UseInterval* to_start_of,
-                                  LifetimePosition but_not_past) const;
-
-  LiveRange* GetLastChild();
-
-  typedef BitField<bool, 0, 1> SpilledField;
   typedef BitField<bool, 1, 1> HasSlotUseField;
   typedef BitField<bool, 2, 1> IsPhiField;
   typedef BitField<bool, 3, 1> IsNonLoopPhiField;
   typedef BitField<SpillType, 4, 2> SpillTypeField;
-  typedef BitField<int32_t, 6, 6> AssignedRegisterField;
-  typedef BitField<MachineType, 12, 15> MachineTypeField;
 
-  int id_;
-  int spill_start_index_;
-  uint32_t bits_;
-  UseInterval* last_interval_;
-  UseInterval* first_interval_;
-  UsePosition* first_pos_;
-  LiveRange* parent_;
-  LiveRange* next_;
-  LiveRange* splintered_from_;
+  LiveRange* GetLastChild();
+
+  int vreg_;
+  int last_child_id_;
+  TopLevelLiveRange* splintered_from_;
   union {
     // Correct value determined by spill_type()
     InstructionOperand* spill_operand_;
     SpillRange* spill_range_;
   };
   SpillAtDefinitionList* spills_at_definition_;
-  // This is used as a cache, it doesn't affect correctness.
-  mutable UseInterval* current_interval_;
-  // This is used as a cache, it doesn't affect correctness.
-  mutable UsePosition* last_processed_use_;
-  // This is used as a cache, it's invalid outside of BuildLiveRanges.
-  mutable UsePosition* current_hint_position_;
-
-  // greedy: the number of LifetimePositions covered by this range. Used to
-  // prioritize selecting live ranges for register assignment, as well as
-  // in weight calculations.
-  int size_;
-
-  // greedy: a metric for resolving conflicts between ranges with an assigned
-  // register and ranges that intersect them and need a register.
-  float weight_;
-
   // TODO(mtrofin): generalize spilling after definition, currently specialized
   // just for spill in a single deferred block.
-  bool spilled_in_deferred_block_;
-  DISALLOW_COPY_AND_ASSIGN(LiveRange);
+  bool spilled_in_deferred_blocks_;
+  int spill_start_index_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopLevelLiveRange);
 };
 
 
@@ -560,7 +585,7 @@ std::ostream& operator<<(std::ostream& os,
 class SpillRange final : public ZoneObject {
  public:
   static const int kUnassignedSlot = -1;
-  SpillRange(LiveRange* range, Zone* zone);
+  SpillRange(TopLevelLiveRange* range, Zone* zone);
 
   UseInterval* interval() const { return use_interval_; }
   // Currently, only 4 or 8 byte slots are supported.
@@ -576,8 +601,10 @@ class SpillRange final : public ZoneObject {
     DCHECK_NE(kUnassignedSlot, assigned_slot_);
     return assigned_slot_;
   }
-  const ZoneVector<LiveRange*>& live_ranges() const { return live_ranges_; }
-  ZoneVector<LiveRange*>& live_ranges() { return live_ranges_; }
+  const ZoneVector<TopLevelLiveRange*>& live_ranges() const {
+    return live_ranges_;
+  }
+  ZoneVector<TopLevelLiveRange*>& live_ranges() { return live_ranges_; }
   int byte_width() const { return byte_width_; }
   RegisterKind kind() const { return kind_; }
 
@@ -587,7 +614,7 @@ class SpillRange final : public ZoneObject {
   // Merge intervals, making sure the use intervals are sorted
   void MergeDisjointIntervals(UseInterval* other);
 
-  ZoneVector<LiveRange*> live_ranges_;
+  ZoneVector<TopLevelLiveRange*> live_ranges_;
   UseInterval* use_interval_;
   LifetimePosition end_position_;
   int assigned_slot_;
@@ -637,16 +664,20 @@ class RegisterAllocationData final : public ZoneObject {
                          InstructionSequence* code,
                          const char* debug_name = nullptr);
 
-  const ZoneVector<LiveRange*>& live_ranges() const { return live_ranges_; }
-  ZoneVector<LiveRange*>& live_ranges() { return live_ranges_; }
-  const ZoneVector<LiveRange*>& fixed_live_ranges() const {
+  const ZoneVector<TopLevelLiveRange*>& live_ranges() const {
+    return live_ranges_;
+  }
+  ZoneVector<TopLevelLiveRange*>& live_ranges() { return live_ranges_; }
+  const ZoneVector<TopLevelLiveRange*>& fixed_live_ranges() const {
     return fixed_live_ranges_;
   }
-  ZoneVector<LiveRange*>& fixed_live_ranges() { return fixed_live_ranges_; }
-  ZoneVector<LiveRange*>& fixed_double_live_ranges() {
+  ZoneVector<TopLevelLiveRange*>& fixed_live_ranges() {
+    return fixed_live_ranges_;
+  }
+  ZoneVector<TopLevelLiveRange*>& fixed_double_live_ranges() {
     return fixed_double_live_ranges_;
   }
-  const ZoneVector<LiveRange*>& fixed_double_live_ranges() const {
+  const ZoneVector<TopLevelLiveRange*>& fixed_double_live_ranges() const {
     return fixed_double_live_ranges_;
   }
   ZoneVector<BitVector*>& live_in_sets() { return live_in_sets_; }
@@ -665,21 +696,20 @@ class RegisterAllocationData final : public ZoneObject {
 
   MachineType MachineTypeFor(int virtual_register);
 
-  LiveRange* LiveRangeFor(int index);
+  TopLevelLiveRange* GetOrCreateLiveRangeFor(int index);
   // Creates a new live range.
-  LiveRange* NewLiveRange(int index, MachineType machine_type);
-  LiveRange* NextLiveRange(MachineType machine_type);
-  LiveRange* NewChildRangeFor(LiveRange* range);
+  TopLevelLiveRange* NewLiveRange(int index, MachineType machine_type);
+  TopLevelLiveRange* NextLiveRange(MachineType machine_type);
 
-  SpillRange* AssignSpillRangeToLiveRange(LiveRange* range);
-  SpillRange* CreateSpillRangeForLiveRange(LiveRange* range);
+  SpillRange* AssignSpillRangeToLiveRange(TopLevelLiveRange* range);
+  SpillRange* CreateSpillRangeForLiveRange(TopLevelLiveRange* range);
 
   MoveOperands* AddGapMove(int index, Instruction::GapPosition position,
                            const InstructionOperand& from,
                            const InstructionOperand& to);
 
-  bool IsReference(int virtual_register) const {
-    return code()->IsReference(virtual_register);
+  bool IsReference(TopLevelLiveRange* top_range) const {
+    return code()->IsReference(top_range->vreg());
   }
 
   bool ExistsUseWithoutDefinition();
@@ -688,6 +718,7 @@ class RegisterAllocationData final : public ZoneObject {
 
   PhiMapValue* InitializePhiMap(const InstructionBlock* block,
                                 PhiInstruction* phi);
+  PhiMapValue* GetPhiMapValueFor(TopLevelLiveRange* top_range);
   PhiMapValue* GetPhiMapValueFor(int virtual_register);
   bool IsBlockBoundary(LifetimePosition pos) const;
 
@@ -699,6 +730,8 @@ class RegisterAllocationData final : public ZoneObject {
   void Print(const SpillRange* spill_range);
 
  private:
+  int GetNextLiveRangeId();
+
   Zone* const allocation_zone_;
   Frame* const frame_;
   InstructionSequence* const code_;
@@ -706,9 +739,9 @@ class RegisterAllocationData final : public ZoneObject {
   const RegisterConfiguration* const config_;
   PhiMap phi_map_;
   ZoneVector<BitVector*> live_in_sets_;
-  ZoneVector<LiveRange*> live_ranges_;
-  ZoneVector<LiveRange*> fixed_live_ranges_;
-  ZoneVector<LiveRange*> fixed_double_live_ranges_;
+  ZoneVector<TopLevelLiveRange*> live_ranges_;
+  ZoneVector<TopLevelLiveRange*> fixed_live_ranges_;
+  ZoneVector<TopLevelLiveRange*> fixed_double_live_ranges_;
   ZoneSet<SpillRange*> spill_ranges_;
   DelayedReferences delayed_references_;
   BitVector* assigned_registers_;
@@ -735,12 +768,6 @@ class ConstraintBuilder final : public ZoneObject {
   InstructionSequence* code() const { return data()->code(); }
   Zone* allocation_zone() const { return data()->allocation_zone(); }
 
-  Instruction* InstructionAt(int index) { return code()->InstructionAt(index); }
-  bool IsReference(int virtual_register) const {
-    return data()->IsReference(virtual_register);
-  }
-  LiveRange* LiveRangeFor(int index) { return data()->LiveRangeFor(index); }
-
   InstructionOperand* AllocateFixed(UnallocatedOperand* operand, int pos,
                                     bool is_tagged);
   void MeetRegisterConstraints(const InstructionBlock* block);
@@ -775,8 +802,6 @@ class LiveRangeBuilder final : public ZoneObject {
     return data()->live_in_sets();
   }
 
-  LiveRange* LiveRangeFor(int index) { return data()->LiveRangeFor(index); }
-
   void Verify() const;
 
   // Liveness analysis support.
@@ -787,8 +812,8 @@ class LiveRangeBuilder final : public ZoneObject {
 
   static int FixedLiveRangeID(int index) { return -index - 1; }
   int FixedDoubleLiveRangeID(int index);
-  LiveRange* FixedLiveRangeFor(int index);
-  LiveRange* FixedDoubleLiveRangeFor(int index);
+  TopLevelLiveRange* FixedLiveRangeFor(int index);
+  TopLevelLiveRange* FixedDoubleLiveRangeFor(int index);
 
   void MapPhiHint(InstructionOperand* operand, UsePosition* use_pos);
   void ResolvePhiHint(InstructionOperand* operand, UsePosition* use_pos);
@@ -798,7 +823,7 @@ class LiveRangeBuilder final : public ZoneObject {
   UsePosition* NewUsePosition(LifetimePosition pos) {
     return NewUsePosition(pos, nullptr, nullptr, UsePositionHintType::kNone);
   }
-  LiveRange* LiveRangeFor(InstructionOperand* operand);
+  TopLevelLiveRange* LiveRangeFor(InstructionOperand* operand);
   // Helper methods for building intervals.
   UsePosition* Define(LifetimePosition position, InstructionOperand* operand,
                       void* hint, UsePositionHintType hint_type);
@@ -832,8 +857,6 @@ class RegisterAllocator : public ZoneObject {
 
   Zone* allocation_zone() const { return data()->allocation_zone(); }
 
-  LiveRange* LiveRangeFor(int index) { return data()->LiveRangeFor(index); }
-
   // Split the given range at the given position.
   // If range starts at or after the given position then the
   // original range is returned.
@@ -859,7 +882,7 @@ class RegisterAllocator : public ZoneObject {
   LifetimePosition FindOptimalSpillingPos(LiveRange* range,
                                           LifetimePosition pos);
 
-  const ZoneVector<LiveRange*>& GetFixedRegisters() const;
+  const ZoneVector<TopLevelLiveRange*>& GetFixedRegisters() const;
   const char* RegisterName(int allocation_index) const;
 
  private:
@@ -903,7 +926,7 @@ class LinearScanAllocator final : public RegisterAllocator {
   void InactiveToActive(LiveRange* range);
 
   // Helper methods for allocating registers.
-  bool TryReuseSpillForPhi(LiveRange* range);
+  bool TryReuseSpillForPhi(TopLevelLiveRange* range);
   bool TryAllocateFreeReg(LiveRange* range);
   void AllocateBlockedReg(LiveRange* range);