compiler/optimizing/nodes.h - platform/art - Gitiles

 /*
  * Copyright (C) 2014 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #ifndef ART_COMPILER_OPTIMIZING_NODES_H_
 #define ART_COMPILER_OPTIMIZING_NODES_H_

 #include "base/arena_containers.h"
 #include "base/arena_object.h"
 #include "dex/compiler_enums.h"
 #include "entrypoints/quick/quick_entrypoints_enum.h"
 #include "handle.h"
 #include "handle_scope.h"
 #include "invoke_type.h"
 #include "locations.h"
 #include "mirror/class.h"
 #include "offsets.h"
 #include "primitive.h"
 #include "utils/arena_bit_vector.h"
 #include "utils/growable_array.h"

 namespace art {

 class GraphChecker;
 class HBasicBlock;
 class HCurrentMethod;
 class HDoubleConstant;
 class HEnvironment;
 class HFloatConstant;
 class HGraphBuilder;
 class HGraphVisitor;
 class HInstruction;
 class HIntConstant;
 class HInvoke;
 class HLongConstant;
 class HNullConstant;
 class HPhi;
 class HSuspendCheck;
 class LiveInterval;
 class LocationSummary;
 class SlowPathCode;
 class SsaBuilder;

 static const int kDefaultNumberOfBlocks = 8;
 static const int kDefaultNumberOfSuccessors = 2;
 static const int kDefaultNumberOfPredecessors = 2;
 static const int kDefaultNumberOfDominatedBlocks = 1;
 static const int kDefaultNumberOfBackEdges = 1;

 static constexpr uint32_t kMaxIntShiftValue = 0x1f;
 static constexpr uint64_t kMaxLongShiftValue = 0x3f;

 static constexpr uint32_t kUnknownFieldIndex = static_cast<uint32_t>(-1);

 static constexpr InvokeType kInvalidInvokeType = static_cast<InvokeType>(-1);

 enum IfCondition {
   kCondEQ,
   kCondNE,
   kCondLT,
   kCondLE,
   kCondGT,
   kCondGE,
 };

 class HInstructionList {
  public:
   HInstructionList() : first_instruction_(nullptr), last_instruction_(nullptr) {}

   void AddInstruction(HInstruction* instruction);
   void RemoveInstruction(HInstruction* instruction);

   // Insert `instruction` before/after an existing instruction `cursor`.
   void InsertInstructionBefore(HInstruction* instruction, HInstruction* cursor);
   void InsertInstructionAfter(HInstruction* instruction, HInstruction* cursor);

   // Return true if this list contains `instruction`.
   bool Contains(HInstruction* instruction) const;

   // Return true if `instruction1` is found before `instruction2` in
   // this instruction list and false otherwise.  Abort if none
   // of these instructions is found.
   bool FoundBefore(const HInstruction* instruction1,
                    const HInstruction* instruction2) const;

   bool IsEmpty() const { return first_instruction_ == nullptr; }
   void Clear() { first_instruction_ = last_instruction_ = nullptr; }

   // Update the block of all instructions to be `block`.
   void SetBlockOfInstructions(HBasicBlock* block) const;

   void AddAfter(HInstruction* cursor, const HInstructionList& instruction_list);
   void Add(const HInstructionList& instruction_list);

   // Return the number of instructions in the list. This is an expensive operation.
   size_t CountSize() const;

  private:
   HInstruction* first_instruction_;
   HInstruction* last_instruction_;

   friend class HBasicBlock;
   friend class HGraph;
   friend class HInstruction;
   friend class HInstructionIterator;
   friend class HBackwardInstructionIterator;

   DISALLOW_COPY_AND_ASSIGN(HInstructionList);
 };

 // Control-flow graph of a method. Contains a list of basic blocks.
 class HGraph : public ArenaObject<kArenaAllocMisc> {
  public:
   HGraph(ArenaAllocator* arena,
          const DexFile& dex_file,
          uint32_t method_idx,
          bool should_generate_constructor_barrier,
          InstructionSet instruction_set,
          InvokeType invoke_type = kInvalidInvokeType,
          bool debuggable = false,
          int start_instruction_id = 0)
       : arena_(arena),
         blocks_(arena, kDefaultNumberOfBlocks),
         reverse_post_order_(arena, kDefaultNumberOfBlocks),
         linear_order_(arena, kDefaultNumberOfBlocks),
         entry_block_(nullptr),
         exit_block_(nullptr),
         maximum_number_of_out_vregs_(0),
         number_of_vregs_(0),
         number_of_in_vregs_(0),
         temporaries_vreg_slots_(0),
         has_bounds_checks_(false),
         debuggable_(debuggable),
         current_instruction_id_(start_instruction_id),
         dex_file_(dex_file),
         method_idx_(method_idx),
         invoke_type_(invoke_type),
         in_ssa_form_(false),
         should_generate_constructor_barrier_(should_generate_constructor_barrier),
         instruction_set_(instruction_set),
         cached_null_constant_(nullptr),
         cached_int_constants_(std::less<int32_t>(), arena->Adapter()),
         cached_float_constants_(std::less<int32_t>(), arena->Adapter()),
         cached_long_constants_(std::less<int64_t>(), arena->Adapter()),
         cached_double_constants_(std::less<int64_t>(), arena->Adapter()),
         cached_current_method_(nullptr) {}

   ArenaAllocator* GetArena() const { return arena_; }
   const GrowableArray<HBasicBlock*>& GetBlocks() const { return blocks_; }
   HBasicBlock* GetBlock(size_t id) const { return blocks_.Get(id); }

   bool IsInSsaForm() const { return in_ssa_form_; }

   HBasicBlock* GetEntryBlock() const { return entry_block_; }
   HBasicBlock* GetExitBlock() const { return exit_block_; }
   bool HasExitBlock() const { return exit_block_ != nullptr; }

   void SetEntryBlock(HBasicBlock* block) { entry_block_ = block; }
   void SetExitBlock(HBasicBlock* block) { exit_block_ = block; }

   void AddBlock(HBasicBlock* block);

   // Try building the SSA form of this graph, with dominance computation and loop
   // recognition. Returns whether it was successful in doing all these steps.
   bool TryBuildingSsa() {
     BuildDominatorTree();
     // The SSA builder requires loops to all be natural. Specifically, the dead phi
     // elimination phase checks the consistency of the graph when doing a post-order
     // visit for eliminating dead phis: a dead phi can only have loop header phi
     // users remaining when being visited.
     if (!AnalyzeNaturalLoops()) return false;
     TransformToSsa();
     in_ssa_form_ = true;
     return true;
   }

   void ComputeDominanceInformation();
   void ClearDominanceInformation();

   void BuildDominatorTree();
   void TransformToSsa();
   void SimplifyCFG();

   // Analyze all natural loops in this graph. Returns false if one
   // loop is not natural, that is the header does not dominate the
   // back edge.
   bool AnalyzeNaturalLoops() const;

   // Inline this graph in `outer_graph`, replacing the given `invoke` instruction.
   void InlineInto(HGraph* outer_graph, HInvoke* invoke);

   // Need to add a couple of blocks to test if the loop body is entered and
   // put deoptimization instructions, etc.
   void TransformLoopHeaderForBCE(HBasicBlock* header);

   // Removes `block` from the graph.
   void DeleteDeadBlock(HBasicBlock* block);

   // Splits the edge between `block` and `successor` while preserving the
   // indices in the predecessor/successor lists. If there are multiple edges
   // between the blocks, the lowest indices are used.
   // Returns the new block which is empty and has the same dex pc as `successor`.
   HBasicBlock* SplitEdge(HBasicBlock* block, HBasicBlock* successor);

   void SplitCriticalEdge(HBasicBlock* block, HBasicBlock* successor);
   void SimplifyLoop(HBasicBlock* header);

   int32_t GetNextInstructionId() {
     DCHECK_NE(current_instruction_id_, INT32_MAX);
     return current_instruction_id_++;
   }

   int32_t GetCurrentInstructionId() const {
     return current_instruction_id_;
   }

   void SetCurrentInstructionId(int32_t id) {
     current_instruction_id_ = id;
   }

   uint16_t GetMaximumNumberOfOutVRegs() const {
     return maximum_number_of_out_vregs_;
   }

   void SetMaximumNumberOfOutVRegs(uint16_t new_value) {
     maximum_number_of_out_vregs_ = new_value;
   }

   void UpdateMaximumNumberOfOutVRegs(uint16_t other_value) {
     maximum_number_of_out_vregs_ = std::max(maximum_number_of_out_vregs_, other_value);
   }

   void UpdateTemporariesVRegSlots(size_t slots) {
     temporaries_vreg_slots_ = std::max(slots, temporaries_vreg_slots_);
   }

   size_t GetTemporariesVRegSlots() const {
     DCHECK(!in_ssa_form_);
     return temporaries_vreg_slots_;
   }

   void SetNumberOfVRegs(uint16_t number_of_vregs) {
     number_of_vregs_ = number_of_vregs;
   }

   uint16_t GetNumberOfVRegs() const {
     DCHECK(!in_ssa_form_);
     return number_of_vregs_;
   }

   void SetNumberOfInVRegs(uint16_t value) {
     number_of_in_vregs_ = value;
   }

   uint16_t GetNumberOfLocalVRegs() const {
     DCHECK(!in_ssa_form_);
     return number_of_vregs_ - number_of_in_vregs_;
   }

   const GrowableArray<HBasicBlock*>& GetReversePostOrder() const {
     return reverse_post_order_;
   }

   const GrowableArray<HBasicBlock*>& GetLinearOrder() const {
     return linear_order_;
   }

   bool HasBoundsChecks() const {
     return has_bounds_checks_;
   }

   void SetHasBoundsChecks(bool value) {
     has_bounds_checks_ = value;
   }

   bool ShouldGenerateConstructorBarrier() const {
     return should_generate_constructor_barrier_;
   }

   bool IsDebuggable() const { return debuggable_; }

   // Returns a constant of the given type and value. If it does not exist
   // already, it is created and inserted into the graph. This method is only for
   // integral types.
   HConstant* GetConstant(Primitive::Type type, int64_t value);
   HNullConstant* GetNullConstant();
   HIntConstant* GetIntConstant(int32_t value) {
     return CreateConstant(value, &cached_int_constants_);
   }
   HLongConstant* GetLongConstant(int64_t value) {
     return CreateConstant(value, &cached_long_constants_);
   }
   HFloatConstant* GetFloatConstant(float value) {
     return CreateConstant(bit_cast<int32_t, float>(value), &cached_float_constants_);
   }
   HDoubleConstant* GetDoubleConstant(double value) {
     return CreateConstant(bit_cast<int64_t, double>(value), &cached_double_constants_);
   }

   HCurrentMethod* GetCurrentMethod();

   HBasicBlock* FindCommonDominator(HBasicBlock* first, HBasicBlock* second) const;

   const DexFile& GetDexFile() const {
     return dex_file_;
   }

   uint32_t GetMethodIdx() const {
     return method_idx_;
   }

   InvokeType GetInvokeType() const {
     return invoke_type_;
   }

  private:
   void VisitBlockForDominatorTree(HBasicBlock* block,
                                   HBasicBlock* predecessor,
                                   GrowableArray<size_t>* visits);
   void FindBackEdges(ArenaBitVector* visited);
   void VisitBlockForBackEdges(HBasicBlock* block,
                               ArenaBitVector* visited,
                               ArenaBitVector* visiting);
   void RemoveInstructionsAsUsersFromDeadBlocks(const ArenaBitVector& visited) const;
   void RemoveDeadBlocks(const ArenaBitVector& visited);

   template <class InstructionType, typename ValueType>
   InstructionType* CreateConstant(ValueType value,
                                   ArenaSafeMap<ValueType, InstructionType*>* cache) {
     // Try to find an existing constant of the given value.
     InstructionType* constant = nullptr;
     auto cached_constant = cache->find(value);
     if (cached_constant != cache->end()) {
       constant = cached_constant->second;
     }

     // If not found or previously deleted, create and cache a new instruction.
     // Don't bother reviving a previously deleted instruction, for simplicity.
     if (constant == nullptr || constant->GetBlock() == nullptr) {
       constant = new (arena_) InstructionType(value);
       cache->Overwrite(value, constant);
       InsertConstant(constant);
     }
     return constant;
   }

   void InsertConstant(HConstant* instruction);

   // Cache a float constant into the graph. This method should only be
   // called by the SsaBuilder when creating "equivalent" instructions.
   void CacheFloatConstant(HFloatConstant* constant);

   // See CacheFloatConstant comment.
   void CacheDoubleConstant(HDoubleConstant* constant);

   ArenaAllocator* const arena_;

   // List of blocks in insertion order.
   GrowableArray<HBasicBlock*> blocks_;

   // List of blocks to perform a reverse post order tree traversal.
   GrowableArray<HBasicBlock*> reverse_post_order_;

   // List of blocks to perform a linear order tree traversal.
   GrowableArray<HBasicBlock*> linear_order_;

   HBasicBlock* entry_block_;
   HBasicBlock* exit_block_;

   // The maximum number of virtual registers arguments passed to a HInvoke in this graph.
   uint16_t maximum_number_of_out_vregs_;

   // The number of virtual registers in this method. Contains the parameters.
   uint16_t number_of_vregs_;

   // The number of virtual registers used by parameters of this method.
   uint16_t number_of_in_vregs_;

   // Number of vreg size slots that the temporaries use (used in baseline compiler).
   size_t temporaries_vreg_slots_;

   // Has bounds checks. We can totally skip BCE if it's false.
   bool has_bounds_checks_;

   // Indicates whether the graph should be compiled in a way that
   // ensures full debuggability. If false, we can apply more
   // aggressive optimizations that may limit the level of debugging.
   const bool debuggable_;

   // The current id to assign to a newly added instruction. See HInstruction.id_.
   int32_t current_instruction_id_;

   // The dex file from which the method is from.
   const DexFile& dex_file_;

   // The method index in the dex file.
   const uint32_t method_idx_;

   // If inlined, this encodes how the callee is being invoked.
   const InvokeType invoke_type_;

   // Whether the graph has been transformed to SSA form. Only used
   // in debug mode to ensure we are not using properties only valid
   // for non-SSA form (like the number of temporaries).
   bool in_ssa_form_;

   const bool should_generate_constructor_barrier_;

   const InstructionSet instruction_set_;

   // Cached constants.
   HNullConstant* cached_null_constant_;
   ArenaSafeMap<int32_t, HIntConstant*> cached_int_constants_;
   ArenaSafeMap<int32_t, HFloatConstant*> cached_float_constants_;
   ArenaSafeMap<int64_t, HLongConstant*> cached_long_constants_;
   ArenaSafeMap<int64_t, HDoubleConstant*> cached_double_constants_;

   HCurrentMethod* cached_current_method_;

   friend class SsaBuilder;           // For caching constants.
   friend class SsaLivenessAnalysis;  // For the linear order.
   ART_FRIEND_TEST(GraphTest, IfSuccessorSimpleJoinBlock1);
   DISALLOW_COPY_AND_ASSIGN(HGraph);
 };

 class HLoopInformation : public ArenaObject<kArenaAllocMisc> {
  public:
   HLoopInformation(HBasicBlock* header, HGraph* graph)
       : header_(header),
         suspend_check_(nullptr),
         back_edges_(graph->GetArena(), kDefaultNumberOfBackEdges),
         // Make bit vector growable, as the number of blocks may change.
         blocks_(graph->GetArena(), graph->GetBlocks().Size(), true) {}

   HBasicBlock* GetHeader() const {
     return header_;
   }

   void SetHeader(HBasicBlock* block) {
     header_ = block;
   }

   HSuspendCheck* GetSuspendCheck() const { return suspend_check_; }
   void SetSuspendCheck(HSuspendCheck* check) { suspend_check_ = check; }
   bool HasSuspendCheck() const { return suspend_check_ != nullptr; }

   void AddBackEdge(HBasicBlock* back_edge) {
     back_edges_.Add(back_edge);
   }

   void RemoveBackEdge(HBasicBlock* back_edge) {
     back_edges_.Delete(back_edge);
   }

   bool IsBackEdge(const HBasicBlock& block) const {
     for (size_t i = 0, e = back_edges_.Size(); i < e; ++i) {
       if (back_edges_.Get(i) == &block) return true;
     }
     return false;
   }

   size_t NumberOfBackEdges() const {
     return back_edges_.Size();
   }

   HBasicBlock* GetPreHeader() const;

   const GrowableArray<HBasicBlock*>& GetBackEdges() const {
     return back_edges_;
   }

   // Returns the lifetime position of the back edge that has the
   // greatest lifetime position.
   size_t GetLifetimeEnd() const;

   void ReplaceBackEdge(HBasicBlock* existing, HBasicBlock* new_back_edge) {
     for (size_t i = 0, e = back_edges_.Size(); i < e; ++i) {
       if (back_edges_.Get(i) == existing) {
         back_edges_.Put(i, new_back_edge);
         return;
       }
     }
     UNREACHABLE();
   }

   // Finds blocks that are part of this loop. Returns whether the loop is a natural loop,
   // that is the header dominates the back edge.
   bool Populate();

   // Reanalyzes the loop by removing loop info from its blocks and re-running
   // Populate(). If there are no back edges left, the loop info is completely
   // removed as well as its SuspendCheck instruction. It must be run on nested
   // inner loops first.
   void Update();

   // Returns whether this loop information contains `block`.
   // Note that this loop information *must* be populated before entering this function.
   bool Contains(const HBasicBlock& block) const;

   // Returns whether this loop information is an inner loop of `other`.
   // Note that `other` *must* be populated before entering this function.
   bool IsIn(const HLoopInformation& other) const;

   const ArenaBitVector& GetBlocks() const { return blocks_; }

   void Add(HBasicBlock* block);
   void Remove(HBasicBlock* block);

  private:
   // Internal recursive implementation of `Populate`.
   void PopulateRecursive(HBasicBlock* block);

   HBasicBlock* header_;
   HSuspendCheck* suspend_check_;
   GrowableArray<HBasicBlock*> back_edges_;
   ArenaBitVector blocks_;

   DISALLOW_COPY_AND_ASSIGN(HLoopInformation);
 };

 static constexpr size_t kNoLifetime = -1;
 static constexpr uint32_t kNoDexPc = -1;

 // A block in a method. Contains the list of instructions represented
 // as a double linked list. Each block knows its predecessors and
 // successors.

 class HBasicBlock : public ArenaObject<kArenaAllocMisc> {
  public:
   explicit HBasicBlock(HGraph* graph, uint32_t dex_pc = kNoDexPc)
       : graph_(graph),
         predecessors_(graph->GetArena(), kDefaultNumberOfPredecessors),
         successors_(graph->GetArena(), kDefaultNumberOfSuccessors),
         loop_information_(nullptr),
         dominator_(nullptr),
         dominated_blocks_(graph->GetArena(), kDefaultNumberOfDominatedBlocks),
         block_id_(-1),
         dex_pc_(dex_pc),
         lifetime_start_(kNoLifetime),
         lifetime_end_(kNoLifetime),
         is_catch_block_(false) {}

   const GrowableArray<HBasicBlock*>& GetPredecessors() const {
     return predecessors_;
   }

   const GrowableArray<HBasicBlock*>& GetSuccessors() const {
     return successors_;
   }

   const GrowableArray<HBasicBlock*>& GetDominatedBlocks() const {
     return dominated_blocks_;
   }

   bool IsEntryBlock() const {
     return graph_->GetEntryBlock() == this;
   }

   bool IsExitBlock() const {
     return graph_->GetExitBlock() == this;
   }

   bool IsSingleGoto() const;
   bool IsSingleTryBoundary() const;

   // Returns true if this block emits nothing but a jump.
   bool IsSingleJump() const {
     HLoopInformation* loop_info = GetLoopInformation();
     return (IsSingleGoto() || IsSingleTryBoundary())
            // Back edges generate a suspend check.
            && (loop_info == nullptr || !loop_info->IsBackEdge(*this));
   }

   void AddBackEdge(HBasicBlock* back_edge) {
     if (loop_information_ == nullptr) {
       loop_information_ = new (graph_->GetArena()) HLoopInformation(this, graph_);
     }
     DCHECK_EQ(loop_information_->GetHeader(), this);
     loop_information_->AddBackEdge(back_edge);
   }

   HGraph* GetGraph() const { return graph_; }
   void SetGraph(HGraph* graph) { graph_ = graph; }

   int GetBlockId() const { return block_id_; }
   void SetBlockId(int id) { block_id_ = id; }

   HBasicBlock* GetDominator() const { return dominator_; }
   void SetDominator(HBasicBlock* dominator) { dominator_ = dominator; }
   void AddDominatedBlock(HBasicBlock* block) { dominated_blocks_.Add(block); }
   void RemoveDominatedBlock(HBasicBlock* block) { dominated_blocks_.Delete(block); }
   void ReplaceDominatedBlock(HBasicBlock* existing, HBasicBlock* new_block) {
     for (size_t i = 0, e = dominated_blocks_.Size(); i < e; ++i) {
       if (dominated_blocks_.Get(i) == existing) {
         dominated_blocks_.Put(i, new_block);
         return;
       }
     }
     LOG(FATAL) << "Unreachable";
     UNREACHABLE();
   }
   void ClearDominanceInformation();

   int NumberOfBackEdges() const {
     return IsLoopHeader() ? loop_information_->NumberOfBackEdges() : 0;
   }

   HInstruction* GetFirstInstruction() const { return instructions_.first_instruction_; }
   HInstruction* GetLastInstruction() const { return instructions_.last_instruction_; }
   const HInstructionList& GetInstructions() const { return instructions_; }
   HInstruction* GetFirstPhi() const { return phis_.first_instruction_; }
   HInstruction* GetLastPhi() const { return phis_.last_instruction_; }
   const HInstructionList& GetPhis() const { return phis_; }

   void AddSuccessor(HBasicBlock* block) {
     successors_.Add(block);
     block->predecessors_.Add(this);
   }

   void ReplaceSuccessor(HBasicBlock* existing, HBasicBlock* new_block) {
     size_t successor_index = GetSuccessorIndexOf(existing);
     DCHECK_NE(successor_index, static_cast<size_t>(-1));
     existing->RemovePredecessor(this);
     new_block->predecessors_.Add(this);
     successors_.Put(successor_index, new_block);
   }

   void ReplacePredecessor(HBasicBlock* existing, HBasicBlock* new_block) {
     size_t predecessor_index = GetPredecessorIndexOf(existing);
     DCHECK_NE(predecessor_index, static_cast<size_t>(-1));
     existing->RemoveSuccessor(this);
     new_block->successors_.Add(this);
     predecessors_.Put(predecessor_index, new_block);
   }

   // Insert `this` between `predecessor` and `successor. This method
   // preserves the indicies, and will update the first edge found between
   // `predecessor` and `successor`.
   void InsertBetween(HBasicBlock* predecessor, HBasicBlock* successor) {
     size_t predecessor_index = successor->GetPredecessorIndexOf(predecessor);
     DCHECK_NE(predecessor_index, static_cast<size_t>(-1));
     size_t successor_index = predecessor->GetSuccessorIndexOf(successor);
     DCHECK_NE(successor_index, static_cast<size_t>(-1));
     successor->predecessors_.Put(predecessor_index, this);
     predecessor->successors_.Put(successor_index, this);
     successors_.Add(successor);
     predecessors_.Add(predecessor);
   }

   void RemovePredecessor(HBasicBlock* block) {
     predecessors_.Delete(block);
   }

   void RemoveSuccessor(HBasicBlock* block) {
     successors_.Delete(block);
   }

   void ClearAllPredecessors() {
     predecessors_.Reset();
   }

   void AddPredecessor(HBasicBlock* block) {
     predecessors_.Add(block);
     block->successors_.Add(this);
   }

   void SwapPredecessors() {
     DCHECK_EQ(predecessors_.Size(), 2u);
     HBasicBlock* temp = predecessors_.Get(0);
     predecessors_.Put(0, predecessors_.Get(1));
     predecessors_.Put(1, temp);
   }

   void SwapSuccessors() {
     DCHECK_EQ(successors_.Size(), 2u);
     HBasicBlock* temp = successors_.Get(0);
     successors_.Put(0, successors_.Get(1));
     successors_.Put(1, temp);
   }

   size_t GetPredecessorIndexOf(HBasicBlock* predecessor) const {
     for (size_t i = 0, e = predecessors_.Size(); i < e; ++i) {
       if (predecessors_.Get(i) == predecessor) {
         return i;
       }
     }
     return -1;
   }

   size_t GetSuccessorIndexOf(HBasicBlock* successor) const {
     for (size_t i = 0, e = successors_.Size(); i < e; ++i) {
       if (successors_.Get(i) == successor) {
         return i;
       }
     }
     return -1;
   }

   HBasicBlock* GetSinglePredecessor() const {
     DCHECK_EQ(GetPredecessors().Size(), 1u);
     return GetPredecessors().Get(0);
   }

   HBasicBlock* GetSingleSuccessor() const {
     DCHECK_EQ(GetSuccessors().Size(), 1u);
     return GetSuccessors().Get(0);
   }

   // Returns whether the first occurrence of `predecessor` in the list of
   // predecessors is at index `idx`.
   bool IsFirstIndexOfPredecessor(HBasicBlock* predecessor, size_t idx) const {
     DCHECK_EQ(GetPredecessors().Get(idx), predecessor);
     return GetPredecessorIndexOf(predecessor) == idx;
   }

   // Returns whether successor at index `idx` is an exception handler.
   bool IsExceptionalSuccessor(size_t idx) const;

   // Split the block into two blocks just before `cursor`. Returns the newly
   // created, latter block. Note that this method will add the block to the
   // graph, create a Goto at the end of the former block and will create an edge
   // between the blocks. It will not, however, update the reverse post order or
   // loop information.
   HBasicBlock* SplitBefore(HInstruction* cursor);

   // Split the block into two blocks just after `cursor`. Returns the newly
   // created block. Note that this method just updates raw block information,
   // like predecessors, successors, dominators, and instruction list. It does not
   // update the graph, reverse post order, loop information, nor make sure the
   // blocks are consistent (for example ending with a control flow instruction).
   HBasicBlock* SplitAfter(HInstruction* cursor);

   // Merge `other` at the end of `this`. Successors and dominated blocks of
   // `other` are changed to be successors and dominated blocks of `this`. Note
   // that this method does not update the graph, reverse post order, loop
   // information, nor make sure the blocks are consistent (for example ending
   // with a control flow instruction).
   void MergeWithInlined(HBasicBlock* other);

   // Replace `this` with `other`. Predecessors, successors, and dominated blocks
   // of `this` are moved to `other`.
   // Note that this method does not update the graph, reverse post order, loop
   // information, nor make sure the blocks are consistent (for example ending
   // with a control flow instruction).
   void ReplaceWith(HBasicBlock* other);

   // Merge `other` at the end of `this`. This method updates loops, reverse post
   // order, links to predecessors, successors, dominators and deletes the block
   // from the graph. The two blocks must be successive, i.e. `this` the only
   // predecessor of `other` and vice versa.
   void MergeWith(HBasicBlock* other);

   // Disconnects `this` from all its predecessors, successors and dominator,
   // removes it from all loops it is included in and eventually from the graph.
   // The block must not dominate any other block. Predecessors and successors
   // are safely updated.
   void DisconnectAndDelete();

   void AddInstruction(HInstruction* instruction);
   // Insert `instruction` before/after an existing instruction `cursor`.
   void InsertInstructionBefore(HInstruction* instruction, HInstruction* cursor);
   void InsertInstructionAfter(HInstruction* instruction, HInstruction* cursor);
   // Replace instruction `initial` with `replacement` within this block.
   void ReplaceAndRemoveInstructionWith(HInstruction* initial,
                                        HInstruction* replacement);
   void AddPhi(HPhi* phi);
   void InsertPhiAfter(HPhi* instruction, HPhi* cursor);
   // RemoveInstruction and RemovePhi delete a given instruction from the respective
   // instruction list. With 'ensure_safety' set to true, it verifies that the
   // instruction is not in use and removes it from the use lists of its inputs.
   void RemoveInstruction(HInstruction* instruction, bool ensure_safety = true);
   void RemovePhi(HPhi* phi, bool ensure_safety = true);
   void RemoveInstructionOrPhi(HInstruction* instruction, bool ensure_safety = true);

   bool IsLoopHeader() const {
     return IsInLoop() && (loop_information_->GetHeader() == this);
   }

   bool IsLoopPreHeaderFirstPredecessor() const {
     DCHECK(IsLoopHeader());
     DCHECK(!GetPredecessors().IsEmpty());
     return GetPredecessors().Get(0) == GetLoopInformation()->GetPreHeader();
   }

   HLoopInformation* GetLoopInformation() const {
     return loop_information_;
   }

   // Set the loop_information_ on this block. Overrides the current
   // loop_information if it is an outer loop of the passed loop information.
   // Note that this method is called while creating the loop information.
   void SetInLoop(HLoopInformation* info) {
     if (IsLoopHeader()) {
       // Nothing to do. This just means `info` is an outer loop.
     } else if (!IsInLoop()) {
       loop_information_ = info;
     } else if (loop_information_->Contains(*info->GetHeader())) {
       // Block is currently part of an outer loop. Make it part of this inner loop.
       // Note that a non loop header having a loop information means this loop information
       // has already been populated
       loop_information_ = info;
     } else {
       // Block is part of an inner loop. Do not update the loop information.
       // Note that we cannot do the check `info->Contains(loop_information_)->GetHeader()`
       // at this point, because this method is being called while populating `info`.
     }
   }

   // Raw update of the loop information.
   void SetLoopInformation(HLoopInformation* info) {
     loop_information_ = info;
   }

   bool IsInLoop() const { return loop_information_ != nullptr; }

   // Returns whether this block dominates the blocked passed as parameter.
   bool Dominates(HBasicBlock* block) const;

   size_t GetLifetimeStart() const { return lifetime_start_; }
   size_t GetLifetimeEnd() const { return lifetime_end_; }

   void SetLifetimeStart(size_t start) { lifetime_start_ = start; }
   void SetLifetimeEnd(size_t end) { lifetime_end_ = end; }

   uint32_t GetDexPc() const { return dex_pc_; }

   bool IsCatchBlock() const { return is_catch_block_; }
   void SetIsCatchBlock() { is_catch_block_ = true; }

   bool EndsWithControlFlowInstruction() const;
   bool EndsWithIf() const;
   bool HasSinglePhi() const;

  private:
   HGraph* graph_;
   GrowableArray<HBasicBlock*> predecessors_;
   GrowableArray<HBasicBlock*> successors_;
   HInstructionList instructions_;
   HInstructionList phis_;
   HLoopInformation* loop_information_;
   HBasicBlock* dominator_;
   GrowableArray<HBasicBlock*> dominated_blocks_;
   int block_id_;
   // The dex program counter of the first instruction of this block.
   const uint32_t dex_pc_;
   size_t lifetime_start_;
   size_t lifetime_end_;
   bool is_catch_block_;

   friend class HGraph;
   friend class HInstruction;

   DISALLOW_COPY_AND_ASSIGN(HBasicBlock);
 };

 // Iterates over the LoopInformation of all loops which contain 'block'
 // from the innermost to the outermost.
 class HLoopInformationOutwardIterator : public ValueObject {
  public:
   explicit HLoopInformationOutwardIterator(const HBasicBlock& block)
       : current_(block.GetLoopInformation()) {}

   bool Done() const { return current_ == nullptr; }

   void Advance() {
     DCHECK(!Done());
     current_ = current_->GetPreHeader()->GetLoopInformation();
   }

   HLoopInformation* Current() const {
     DCHECK(!Done());
     return current_;
   }

  private:
   HLoopInformation* current_;

   DISALLOW_COPY_AND_ASSIGN(HLoopInformationOutwardIterator);
 };

 #define FOR_EACH_CONCRETE_INSTRUCTION_COMMON(M)                         \
   M(Add, BinaryOperation)                                               \
   M(And, BinaryOperation)                                               \
   M(ArrayGet, Instruction)                                              \
   M(ArrayLength, Instruction)                                           \
   M(ArraySet, Instruction)                                              \
   M(BooleanNot, UnaryOperation)                                         \
   M(BoundsCheck, Instruction)                                           \
   M(BoundType, Instruction)                                             \
   M(CheckCast, Instruction)                                             \
   M(ClinitCheck, Instruction)                                           \
   M(Compare, BinaryOperation)                                           \
   M(Condition, BinaryOperation)                                         \
   M(CurrentMethod, Instruction)                                         \
   M(Deoptimize, Instruction)                                            \
   M(Div, BinaryOperation)                                               \
   M(DivZeroCheck, Instruction)                                          \
   M(DoubleConstant, Constant)                                           \
   M(Equal, Condition)                                                   \
   M(Exit, Instruction)                                                  \
   M(FloatConstant, Constant)                                            \
   M(Goto, Instruction)                                                  \
   M(GreaterThan, Condition)                                             \
   M(GreaterThanOrEqual, Condition)                                      \
   M(If, Instruction)                                                    \
   M(InstanceFieldGet, Instruction)                                      \
   M(InstanceFieldSet, Instruction)                                      \
   M(InstanceOf, Instruction)                                            \
   M(IntConstant, Constant)                                              \
   M(InvokeInterface, Invoke)                                            \
   M(InvokeStaticOrDirect, Invoke)                                       \
   M(InvokeVirtual, Invoke)                                              \
   M(LessThan, Condition)                                                \
   M(LessThanOrEqual, Condition)                                         \
   M(LoadClass, Instruction)                                             \
   M(LoadException, Instruction)                                         \
   M(LoadLocal, Instruction)                                             \
   M(LoadString, Instruction)                                            \
   M(Local, Instruction)                                                 \
   M(LongConstant, Constant)                                             \
   M(MemoryBarrier, Instruction)                                         \
   M(MonitorOperation, Instruction)                                      \
   M(Mul, BinaryOperation)                                               \
   M(Neg, UnaryOperation)                                                \
   M(NewArray, Instruction)                                              \
   M(NewInstance, Instruction)                                           \
   M(Not, UnaryOperation)                                                \
   M(NotEqual, Condition)                                                \
   M(NullConstant, Instruction)                                          \
   M(NullCheck, Instruction)                                             \
   M(Or, BinaryOperation)                                                \
   M(ParallelMove, Instruction)                                          \
   M(ParameterValue, Instruction)                                        \
   M(Phi, Instruction)                                                   \
   M(Rem, BinaryOperation)                                               \
   M(Return, Instruction)                                                \
   M(ReturnVoid, Instruction)                                            \
   M(Shl, BinaryOperation)                                               \
   M(Shr, BinaryOperation)                                               \
   M(StaticFieldGet, Instruction)                                        \
   M(StaticFieldSet, Instruction)                                        \
   M(StoreLocal, Instruction)                                            \
   M(Sub, BinaryOperation)                                               \
   M(SuspendCheck, Instruction)                                          \
   M(Temporary, Instruction)                                             \
   M(Throw, Instruction)                                                 \
   M(TryBoundary, Instruction)                                           \
   M(TypeConversion, Instruction)                                        \
   M(UShr, BinaryOperation)                                              \
   M(Xor, BinaryOperation)                                               \

 #define FOR_EACH_CONCRETE_INSTRUCTION_ARM(M)

 #define FOR_EACH_CONCRETE_INSTRUCTION_ARM64(M)

 #define FOR_EACH_CONCRETE_INSTRUCTION_MIPS64(M)

 #define FOR_EACH_CONCRETE_INSTRUCTION_X86(M)

 #define FOR_EACH_CONCRETE_INSTRUCTION_X86_64(M)

 #define FOR_EACH_CONCRETE_INSTRUCTION(M)                                \
   FOR_EACH_CONCRETE_INSTRUCTION_COMMON(M)                               \
   FOR_EACH_CONCRETE_INSTRUCTION_ARM(M)                                  \
   FOR_EACH_CONCRETE_INSTRUCTION_ARM64(M)                                \
   FOR_EACH_CONCRETE_INSTRUCTION_MIPS64(M)                               \
   FOR_EACH_CONCRETE_INSTRUCTION_X86(M)                                  \
   FOR_EACH_CONCRETE_INSTRUCTION_X86_64(M)

 #define FOR_EACH_INSTRUCTION(M)                                         \
   FOR_EACH_CONCRETE_INSTRUCTION(M)                                      \
   M(Constant, Instruction)                                              \
   M(UnaryOperation, Instruction)                                        \
   M(BinaryOperation, Instruction)                                       \
   M(Invoke, Instruction)

 #define FORWARD_DECLARATION(type, super) class H##type;
 FOR_EACH_INSTRUCTION(FORWARD_DECLARATION)
 #undef FORWARD_DECLARATION

 #define DECLARE_INSTRUCTION(type)                                       \
   InstructionKind GetKind() const OVERRIDE { return k##type; }          \
   const char* DebugName() const OVERRIDE { return #type; }              \
   const H##type* As##type() const OVERRIDE { return this; }             \
   H##type* As##type() OVERRIDE { return this; }                         \
   bool InstructionTypeEquals(HInstruction* other) const OVERRIDE {      \
     return other->Is##type();                                           \
   }                                                                     \
   void Accept(HGraphVisitor* visitor) OVERRIDE

 template <typename T> class HUseList;

 template <typename T>
 class HUseListNode : public ArenaObject<kArenaAllocMisc> {
  public:
   HUseListNode* GetPrevious() const { return prev_; }
   HUseListNode* GetNext() const { return next_; }
   T GetUser() const { return user_; }
   size_t GetIndex() const { return index_; }
   void SetIndex(size_t index) { index_ = index; }

  private:
   HUseListNode(T user, size_t index)
       : user_(user), index_(index), prev_(nullptr), next_(nullptr) {}

   T const user_;
   size_t index_;
   HUseListNode<T>* prev_;
   HUseListNode<T>* next_;

   friend class HUseList<T>;

   DISALLOW_COPY_AND_ASSIGN(HUseListNode);
 };

 template <typename T>
 class HUseList : public ValueObject {
  public:
   HUseList() : first_(nullptr) {}

   void Clear() {
     first_ = nullptr;
   }

   // Adds a new entry at the beginning of the use list and returns
   // the newly created node.
   HUseListNode<T>* AddUse(T user, size_t index, ArenaAllocator* arena) {
     HUseListNode<T>* new_node = new (arena) HUseListNode<T>(user, index);
     if (IsEmpty()) {
       first_ = new_node;
     } else {
       first_->prev_ = new_node;
       new_node->next_ = first_;
       first_ = new_node;
     }
     return new_node;
   }

   HUseListNode<T>* GetFirst() const {
     return first_;
   }

   void Remove(HUseListNode<T>* node) {
     DCHECK(node != nullptr);
     DCHECK(Contains(node));

     if (node->prev_ != nullptr) {
       node->prev_->next_ = node->next_;
     }
     if (node->next_ != nullptr) {
       node->next_->prev_ = node->prev_;
     }
     if (node == first_) {
       first_ = node->next_;
     }
   }

   bool Contains(const HUseListNode<T>* node) const {
     if (node == nullptr) {
       return false;
     }
     for (HUseListNode<T>* current = first_; current != nullptr; current = current->GetNext()) {
       if (current == node) {
         return true;
       }
     }
     return false;
   }

   bool IsEmpty() const {
     return first_ == nullptr;
   }

   bool HasOnlyOneUse() const {
     return first_ != nullptr && first_->next_ == nullptr;
   }

   size_t SizeSlow() const {
     size_t count = 0;
     for (HUseListNode<T>* current = first_; current != nullptr; current = current->GetNext()) {
       ++count;
     }
     return count;
   }

  private:
   HUseListNode<T>* first_;
 };

 template<typename T>
 class HUseIterator : public ValueObject {
  public:
   explicit HUseIterator(const HUseList<T>& uses) : current_(uses.GetFirst()) {}

   bool Done() const { return current_ == nullptr; }

   void Advance() {
     DCHECK(!Done());
     current_ = current_->GetNext();
   }

   HUseListNode<T>* Current() const {
     DCHECK(!Done());
     return current_;
   }

  private:
   HUseListNode<T>* current_;

   friend class HValue;
 };

 // This class is used by HEnvironment and HInstruction classes to record the
 // instructions they use and pointers to the corresponding HUseListNodes kept
 // by the used instructions.
 template <typename T>
 class HUserRecord : public ValueObject {
  public:
   HUserRecord() : instruction_(nullptr), use_node_(nullptr) {}
   explicit HUserRecord(HInstruction* instruction) : instruction_(instruction), use_node_(nullptr) {}

   HUserRecord(const HUserRecord<T>& old_record, HUseListNode<T>* use_node)
     : instruction_(old_record.instruction_), use_node_(use_node) {
     DCHECK(instruction_ != nullptr);
     DCHECK(use_node_ != nullptr);
     DCHECK(old_record.use_node_ == nullptr);
   }

   HInstruction* GetInstruction() const { return instruction_; }
   HUseListNode<T>* GetUseNode() const { return use_node_; }

  private:
   // Instruction used by the user.
   HInstruction* instruction_;

   // Corresponding entry in the use list kept by 'instruction_'.
   HUseListNode<T>* use_node_;
 };

 // TODO: Add better documentation to this class and maybe refactor with more suggestive names.
 // - Has(All)SideEffects suggests that all the side effects are present but only ChangesSomething
 //   flag is consider.
 // - DependsOn suggests that there is a real dependency between side effects but it only
 //   checks DependendsOnSomething flag.
 //
 // Represents the side effects an instruction may have.
 class SideEffects : public ValueObject {
  public:
   SideEffects() : flags_(0) {}

   static SideEffects None() {
     return SideEffects(0);
   }

   static SideEffects All() {
     return SideEffects(ChangesSomething().flags_ | DependsOnSomething().flags_);
   }

   static SideEffects ChangesSomething() {
     return SideEffects((1 << kFlagChangesCount) - 1);
   }

   static SideEffects DependsOnSomething() {
     int count = kFlagDependsOnCount - kFlagChangesCount;
     return SideEffects(((1 << count) - 1) << kFlagChangesCount);
   }

   SideEffects Union(SideEffects other) const {
     return SideEffects(flags_ | other.flags_);
   }

   bool HasSideEffects() const {
     size_t all_bits_set = (1 << kFlagChangesCount) - 1;
     return (flags_ & all_bits_set) != 0;
   }

   bool HasAllSideEffects() const {
     size_t all_bits_set = (1 << kFlagChangesCount) - 1;
     return all_bits_set == (flags_ & all_bits_set);
   }

   bool DependsOn(SideEffects other) const {
     size_t depends_flags = other.ComputeDependsFlags();
     return (flags_ & depends_flags) != 0;
   }

   bool HasDependencies() const {
     int count = kFlagDependsOnCount - kFlagChangesCount;
     size_t all_bits_set = (1 << count) - 1;
     return ((flags_ >> kFlagChangesCount) & all_bits_set) != 0;
   }

  private:
   static constexpr int kFlagChangesSomething = 0;
   static constexpr int kFlagChangesCount = kFlagChangesSomething + 1;

   static constexpr int kFlagDependsOnSomething = kFlagChangesCount;
   static constexpr int kFlagDependsOnCount = kFlagDependsOnSomething + 1;

   explicit SideEffects(size_t flags) : flags_(flags) {}

   size_t ComputeDependsFlags() const {
     return flags_ << kFlagChangesCount;
   }

   size_t flags_;
 };

 // A HEnvironment object contains the values of virtual registers at a given location.
 class HEnvironment : public ArenaObject<kArenaAllocMisc> {
  public:
   HEnvironment(ArenaAllocator* arena,
                size_t number_of_vregs,
                const DexFile& dex_file,
                uint32_t method_idx,
                uint32_t dex_pc,
                InvokeType invoke_type,
                HInstruction* holder)
      : vregs_(arena, number_of_vregs),
        locations_(arena, number_of_vregs),
        parent_(nullptr),
        dex_file_(dex_file),
        method_idx_(method_idx),
        dex_pc_(dex_pc),
        invoke_type_(invoke_type),
        holder_(holder) {
     vregs_.SetSize(number_of_vregs);
     for (size_t i = 0; i < number_of_vregs; i++) {
       vregs_.Put(i, HUserRecord<HEnvironment*>());
     }

     locations_.SetSize(number_of_vregs);
     for (size_t i = 0; i < number_of_vregs; ++i) {
       locations_.Put(i, Location());
     }
   }

   HEnvironment(ArenaAllocator* arena, const HEnvironment& to_copy, HInstruction* holder)
       : HEnvironment(arena,
                      to_copy.Size(),
                      to_copy.GetDexFile(),
                      to_copy.GetMethodIdx(),
                      to_copy.GetDexPc(),
                      to_copy.GetInvokeType(),
                      holder) {}

   void SetAndCopyParentChain(ArenaAllocator* allocator, HEnvironment* parent) {
     if (parent_ != nullptr) {
       parent_->SetAndCopyParentChain(allocator, parent);
     } else {
       parent_ = new (allocator) HEnvironment(allocator, *parent, holder_);
       parent_->CopyFrom(parent);
       if (parent->GetParent() != nullptr) {
         parent_->SetAndCopyParentChain(allocator, parent->GetParent());
       }
     }
   }

   void CopyFrom(const GrowableArray<HInstruction*>& locals);
   void CopyFrom(HEnvironment* environment);

   // Copy from `env`. If it's a loop phi for `loop_header`, copy the first
   // input to the loop phi instead. This is for inserting instructions that
   // require an environment (like HDeoptimization) in the loop pre-header.
   void CopyFromWithLoopPhiAdjustment(HEnvironment* env, HBasicBlock* loop_header);

   void SetRawEnvAt(size_t index, HInstruction* instruction) {
     vregs_.Put(index, HUserRecord<HEnvironment*>(instruction));
   }

   HInstruction* GetInstructionAt(size_t index) const {
     return vregs_.Get(index).GetInstruction();
   }

   void RemoveAsUserOfInput(size_t index) const;

   size_t Size() const { return vregs_.Size(); }

   HEnvironment* GetParent() const { return parent_; }

   void SetLocationAt(size_t index, Location location) {
     locations_.Put(index, location);
   }

   Location GetLocationAt(size_t index) const {
     return locations_.Get(index);
   }

   uint32_t GetDexPc() const {
     return dex_pc_;
   }

   uint32_t GetMethodIdx() const {
     return method_idx_;
   }

   InvokeType GetInvokeType() const {
     return invoke_type_;
   }

   const DexFile& GetDexFile() const {
     return dex_file_;
   }

   HInstruction* GetHolder() const {
     return holder_;
   }

  private:
   // Record instructions' use entries of this environment for constant-time removal.
   // It should only be called by HInstruction when a new environment use is added.
   void RecordEnvUse(HUseListNode<HEnvironment*>* env_use) {
     DCHECK(env_use->GetUser() == this);
     size_t index = env_use->GetIndex();
     vregs_.Put(index, HUserRecord<HEnvironment*>(vregs_.Get(index), env_use));
   }

   GrowableArray<HUserRecord<HEnvironment*> > vregs_;
   GrowableArray<Location> locations_;
   HEnvironment* parent_;
   const DexFile& dex_file_;
   const uint32_t method_idx_;
   const uint32_t dex_pc_;
   const InvokeType invoke_type_;

   // The instruction that holds this environment. Only used in debug mode
   // to ensure the graph is consistent.
   HInstruction* const holder_;

   friend class HInstruction;

   DISALLOW_COPY_AND_ASSIGN(HEnvironment);
 };

 class ReferenceTypeInfo : ValueObject {
  public:
   typedef Handle<mirror::Class> TypeHandle;

   static ReferenceTypeInfo Create(TypeHandle type_handle, bool is_exact)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     if (type_handle->IsObjectClass()) {
       // Override the type handle to be consistent with the case when we get to
       // Top but don't have the Object class available. It avoids having to guess
       // what value the type_handle has when it's Top.
       return ReferenceTypeInfo(TypeHandle(), is_exact, true);
     } else {
       return ReferenceTypeInfo(type_handle, is_exact, false);
     }
   }

   static ReferenceTypeInfo CreateTop(bool is_exact) {
     return ReferenceTypeInfo(TypeHandle(), is_exact, true);
   }

   bool IsExact() const { return is_exact_; }
   bool IsTop() const { return is_top_; }
   bool IsInterface() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     return !IsTop() && GetTypeHandle()->IsInterface();
   }

   Handle<mirror::Class> GetTypeHandle() const { return type_handle_; }

   bool IsSupertypeOf(ReferenceTypeInfo rti) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     if (IsTop()) {
       // Top (equivalent for java.lang.Object) is supertype of anything.
       return true;
     }
     if (rti.IsTop()) {
       // If we get here `this` is not Top() so it can't be a supertype.
       return false;
     }
     return GetTypeHandle()->IsAssignableFrom(rti.GetTypeHandle().Get());
   }

   // Returns true if the type information provide the same amount of details.
   // Note that it does not mean that the instructions have the same actual type
   // (e.g. tops are equal but they can be the result of a merge).
   bool IsEqual(ReferenceTypeInfo rti) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     if (IsExact() != rti.IsExact()) {
       return false;
     }
     if (IsTop() && rti.IsTop()) {
       // `Top` means java.lang.Object, so the types are equivalent.
       return true;
     }
     if (IsTop() || rti.IsTop()) {
       // If only one is top or object than they are not equivalent.
       // NB: We need this extra check because the type_handle of `Top` is invalid
       // and we cannot inspect its reference.
       return false;
     }

     // Finally check the types.
     return GetTypeHandle().Get() == rti.GetTypeHandle().Get();
   }

  private:
   ReferenceTypeInfo() : ReferenceTypeInfo(TypeHandle(), false, true) {}
   ReferenceTypeInfo(TypeHandle type_handle, bool is_exact, bool is_top)
       : type_handle_(type_handle), is_exact_(is_exact), is_top_(is_top) {}

   // The class of the object.
   TypeHandle type_handle_;
   // Whether or not the type is exact or a superclass of the actual type.
   // Whether or not we have any information about this type.
   bool is_exact_;
   // A true value here means that the object type should be java.lang.Object.
   // We don't have access to the corresponding mirror object every time so this
   // flag acts as a substitute. When true, the TypeHandle refers to a null
   // pointer and should not be used.
   bool is_top_;
 };

 std::ostream& operator<<(std::ostream& os, const ReferenceTypeInfo& rhs);

 class HInstruction : public ArenaObject<kArenaAllocMisc> {
  public:
   explicit HInstruction(SideEffects side_effects)
       : previous_(nullptr),
         next_(nullptr),
         block_(nullptr),
         id_(-1),
         ssa_index_(-1),
         environment_(nullptr),
         locations_(nullptr),
         live_interval_(nullptr),
         lifetime_position_(kNoLifetime),
         side_effects_(side_effects),
         reference_type_info_(ReferenceTypeInfo::CreateTop(/* is_exact */ false)) {}

   virtual ~HInstruction() {}

 #define DECLARE_KIND(type, super) k##type,
   enum InstructionKind {
     FOR_EACH_INSTRUCTION(DECLARE_KIND)
   };
 #undef DECLARE_KIND

   HInstruction* GetNext() const { return next_; }
   HInstruction* GetPrevious() const { return previous_; }

   HInstruction* GetNextDisregardingMoves() const;
   HInstruction* GetPreviousDisregardingMoves() const;

   HBasicBlock* GetBlock() const { return block_; }
   void SetBlock(HBasicBlock* block) { block_ = block; }
   bool IsInBlock() const { return block_ != nullptr; }
   bool IsInLoop() const { return block_->IsInLoop(); }
   bool IsLoopHeaderPhi() { return IsPhi() && block_->IsLoopHeader(); }

   virtual size_t InputCount() const = 0;
   HInstruction* InputAt(size_t i) const { return InputRecordAt(i).GetInstruction(); }

   virtual void Accept(HGraphVisitor* visitor) = 0;
   virtual const char* DebugName() const = 0;

   virtual Primitive::Type GetType() const { return Primitive::kPrimVoid; }
   void SetRawInputAt(size_t index, HInstruction* input) {
     SetRawInputRecordAt(index, HUserRecord<HInstruction*>(input));
   }

   virtual bool NeedsEnvironment() const { return false; }
   virtual uint32_t GetDexPc() const {
     LOG(FATAL) << "GetDexPc() cannot be called on an instruction that"
                   " does not need an environment";
     UNREACHABLE();
   }
   virtual bool IsControlFlow() const { return false; }
   virtual bool CanThrow() const { return false; }
   bool HasSideEffects() const { return side_effects_.HasSideEffects(); }

   // Does not apply for all instructions, but having this at top level greatly
   // simplifies the null check elimination.
   virtual bool CanBeNull() const {
     DCHECK_EQ(GetType(), Primitive::kPrimNot) << "CanBeNull only applies to reference types";
     return true;
   }

   virtual bool CanDoImplicitNullCheckOn(HInstruction* obj) const {
     UNUSED(obj);
     return false;
   }

   void SetReferenceTypeInfo(ReferenceTypeInfo reference_type_info) {
     DCHECK_EQ(GetType(), Primitive::kPrimNot);
     reference_type_info_ = reference_type_info;
   }

   ReferenceTypeInfo GetReferenceTypeInfo() const {
     DCHECK_EQ(GetType(), Primitive::kPrimNot);
     return reference_type_info_;
   }

   void AddUseAt(HInstruction* user, size_t index) {
     DCHECK(user != nullptr);
     HUseListNode<HInstruction*>* use =
         uses_.AddUse(user, index, GetBlock()->GetGraph()->GetArena());
     user->SetRawInputRecordAt(index, HUserRecord<HInstruction*>(user->InputRecordAt(index), use));
   }

   void AddEnvUseAt(HEnvironment* user, size_t index) {
     DCHECK(user != nullptr);
     HUseListNode<HEnvironment*>* env_use =
         env_uses_.AddUse(user, index, GetBlock()->GetGraph()->GetArena());
     user->RecordEnvUse(env_use);
   }

   void RemoveAsUserOfInput(size_t input) {
     HUserRecord<HInstruction*> input_use = InputRecordAt(input);
     input_use.GetInstruction()->uses_.Remove(input_use.GetUseNode());
   }

   const HUseList<HInstruction*>& GetUses() const { return uses_; }
   const HUseList<HEnvironment*>& GetEnvUses() const { return env_uses_; }

   bool HasUses() const { return !uses_.IsEmpty() || !env_uses_.IsEmpty(); }
   bool HasEnvironmentUses() const { return !env_uses_.IsEmpty(); }
   bool HasNonEnvironmentUses() const { return !uses_.IsEmpty(); }
   bool HasOnlyOneNonEnvironmentUse() const {
     return !HasEnvironmentUses() && GetUses().HasOnlyOneUse();
   }

   // Does this instruction strictly dominate `other_instruction`?
   // Returns false if this instruction and `other_instruction` are the same.
   // Aborts if this instruction and `other_instruction` are both phis.
   bool StrictlyDominates(HInstruction* other_instruction) const;

   int GetId() const { return id_; }
   void SetId(int id) { id_ = id; }

   int GetSsaIndex() const { return ssa_index_; }
   void SetSsaIndex(int ssa_index) { ssa_index_ = ssa_index; }
   bool HasSsaIndex() const { return ssa_index_ != -1; }

   bool HasEnvironment() const { return environment_ != nullptr; }
   HEnvironment* GetEnvironment() const { return environment_; }
   // Set the `environment_` field. Raw because this method does not
   // update the uses lists.
   void SetRawEnvironment(HEnvironment* environment) {
     DCHECK(environment_ == nullptr);
     DCHECK_EQ(environment->GetHolder(), this);
     environment_ = environment;
   }

   // Set the environment of this instruction, copying it from `environment`. While
   // copying, the uses lists are being updated.
   void CopyEnvironmentFrom(HEnvironment* environment) {
     DCHECK(environment_ == nullptr);
     ArenaAllocator* allocator = GetBlock()->GetGraph()->GetArena();
     environment_ = new (allocator) HEnvironment(allocator, *environment, this);
     environment_->CopyFrom(environment);
     if (environment->GetParent() != nullptr) {
       environment_->SetAndCopyParentChain(allocator, environment->GetParent());
     }
   }

   void CopyEnvironmentFromWithLoopPhiAdjustment(HEnvironment* environment,
                                                 HBasicBlock* block) {
     DCHECK(environment_ == nullptr);
     ArenaAllocator* allocator = GetBlock()->GetGraph()->GetArena();
     environment_ = new (allocator) HEnvironment(allocator, *environment, this);
     environment_->CopyFromWithLoopPhiAdjustment(environment, block);
     if (environment->GetParent() != nullptr) {
       environment_->SetAndCopyParentChain(allocator, environment->GetParent());
     }
   }

   // Returns the number of entries in the environment. Typically, that is the
   // number of dex registers in a method. It could be more in case of inlining.
   size_t EnvironmentSize() const;

   LocationSummary* GetLocations() const { return locations_; }
   void SetLocations(LocationSummary* locations) { locations_ = locations; }

   void ReplaceWith(HInstruction* instruction);
   void ReplaceInput(HInstruction* replacement, size_t index);

   // This is almost the same as doing `ReplaceWith()`. But in this helper, the
   // uses of this instruction by `other` are *not* updated.
   void ReplaceWithExceptInReplacementAtIndex(HInstruction* other, size_t use_index) {
     ReplaceWith(other);
     other->ReplaceInput(this, use_index);
   }

   // Move `this` instruction before `cursor`.
   void MoveBefore(HInstruction* cursor);

 #define INSTRUCTION_TYPE_CHECK(type, super)                                    \
   bool Is##type() const { return (As##type() != nullptr); }                    \
   virtual const H##type* As##type() const { return nullptr; }                  \
   virtual H##type* As##type() { return nullptr; }

   FOR_EACH_INSTRUCTION(INSTRUCTION_TYPE_CHECK)
 #undef INSTRUCTION_TYPE_CHECK

   // Returns whether the instruction can be moved within the graph.
   virtual bool CanBeMoved() const { return false; }

   // Returns whether the two instructions are of the same kind.
   virtual bool InstructionTypeEquals(HInstruction* other) const {
     UNUSED(other);
     return false;
   }

   // Returns whether any data encoded in the two instructions is equal.
   // This method does not look at the inputs. Both instructions must be
   // of the same type, otherwise the method has undefined behavior.
   virtual bool InstructionDataEquals(HInstruction* other) const {
     UNUSED(other);
     return false;
   }

   // Returns whether two instructions are equal, that is:
   // 1) They have the same type and contain the same data (InstructionDataEquals).
   // 2) Their inputs are identical.
   bool Equals(HInstruction* other) const;

   virtual InstructionKind GetKind() const = 0;

   virtual size_t ComputeHashCode() const {
     size_t result = GetKind();
     for (size_t i = 0, e = InputCount(); i < e; ++i) {
       result = (result * 31) + InputAt(i)->GetId();
     }
     return result;
   }

   SideEffects GetSideEffects() const { return side_effects_; }

   size_t GetLifetimePosition() const { return lifetime_position_; }
   void SetLifetimePosition(size_t position) { lifetime_position_ = position; }
   LiveInterval* GetLiveInterval() const { return live_interval_; }
   void SetLiveInterval(LiveInterval* interval) { live_interval_ = interval; }
   bool HasLiveInterval() const { return live_interval_ != nullptr; }

   bool IsSuspendCheckEntry() const { return IsSuspendCheck() && GetBlock()->IsEntryBlock(); }

   // Returns whether the code generation of the instruction will require to have access
   // to the current method. Such instructions are:
   // (1): Instructions that require an environment, as calling the runtime requires
   //      to walk the stack and have the current method stored at a specific stack address.
   // (2): Object literals like classes and strings, that are loaded from the dex cache
   //      fields of the current method.
   bool NeedsCurrentMethod() const {
     return NeedsEnvironment() || IsLoadClass() || IsLoadString();
   }

   virtual bool NeedsDexCache() const { return false; }

  protected:
   virtual const HUserRecord<HInstruction*> InputRecordAt(size_t i) const = 0;
   virtual void SetRawInputRecordAt(size_t index, const HUserRecord<HInstruction*>& input) = 0;

  private:
   void RemoveEnvironmentUser(HUseListNode<HEnvironment*>* use_node) { env_uses_.Remove(use_node); }

   HInstruction* previous_;
   HInstruction* next_;
   HBasicBlock* block_;

   // An instruction gets an id when it is added to the graph.
   // It reflects creation order. A negative id means the instruction
   // has not been added to the graph.
   int id_;

   // When doing liveness analysis, instructions that have uses get an SSA index.
   int ssa_index_;

   // List of instructions that have this instruction as input.
   HUseList<HInstruction*> uses_;

   // List of environments that contain this instruction.
   HUseList<HEnvironment*> env_uses_;

   // The environment associated with this instruction. Not null if the instruction
   // might jump out of the method.
   HEnvironment* environment_;

   // Set by the code generator.
   LocationSummary* locations_;

   // Set by the liveness analysis.
   LiveInterval* live_interval_;

   // Set by the liveness analysis, this is the position in a linear
   // order of blocks where this instruction's live interval start.
   size_t lifetime_position_;

   const SideEffects side_effects_;

   // TODO: for primitive types this should be marked as invalid.
   ReferenceTypeInfo reference_type_info_;

   friend class GraphChecker;
   friend class HBasicBlock;
   friend class HEnvironment;
   friend class HGraph;
   friend class HInstructionList;

   DISALLOW_COPY_AND_ASSIGN(HInstruction);
 };
 std::ostream& operator<<(std::ostream& os, const HInstruction::InstructionKind& rhs);

 class HInputIterator : public ValueObject {
  public:
   explicit HInputIterator(HInstruction* instruction) : instruction_(instruction), index_(0) {}

   bool Done() const { return index_ == instruction_->InputCount(); }
   HInstruction* Current() const { return instruction_->InputAt(index_); }
   void Advance() { index_++; }

  private:
   HInstruction* instruction_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HInputIterator);
 };

 class HInstructionIterator : public ValueObject {
  public:
   explicit HInstructionIterator(const HInstructionList& instructions)
       : instruction_(instructions.first_instruction_) {
     next_ = Done() ? nullptr : instruction_->GetNext();
   }

   bool Done() const { return instruction_ == nullptr; }
   HInstruction* Current() const { return instruction_; }
   void Advance() {
     instruction_ = next_;
     next_ = Done() ? nullptr : instruction_->GetNext();
   }

  private:
   HInstruction* instruction_;
   HInstruction* next_;

   DISALLOW_COPY_AND_ASSIGN(HInstructionIterator);
 };

 class HBackwardInstructionIterator : public ValueObject {
  public:
   explicit HBackwardInstructionIterator(const HInstructionList& instructions)
       : instruction_(instructions.last_instruction_) {
     next_ = Done() ? nullptr : instruction_->GetPrevious();
   }

   bool Done() const { return instruction_ == nullptr; }
   HInstruction* Current() const { return instruction_; }
   void Advance() {
     instruction_ = next_;
     next_ = Done() ? nullptr : instruction_->GetPrevious();
   }

  private:
   HInstruction* instruction_;
   HInstruction* next_;

   DISALLOW_COPY_AND_ASSIGN(HBackwardInstructionIterator);
 };

 // An embedded container with N elements of type T.  Used (with partial
 // specialization for N=0) because embedded arrays cannot have size 0.
 template<typename T, intptr_t N>
 class EmbeddedArray {
  public:
   EmbeddedArray() : elements_() {}

   intptr_t GetLength() const { return N; }

   const T& operator[](intptr_t i) const {
     DCHECK_LT(i, GetLength());
     return elements_[i];
   }

   T& operator[](intptr_t i) {
     DCHECK_LT(i, GetLength());
     return elements_[i];
   }

   const T& At(intptr_t i) const {
     return (*this)[i];
   }

   void SetAt(intptr_t i, const T& val) {
     (*this)[i] = val;
   }

  private:
   T elements_[N];
 };

 template<typename T>
 class EmbeddedArray<T, 0> {
  public:
   intptr_t length() const { return 0; }
   const T& operator[](intptr_t i) const {
     UNUSED(i);
     LOG(FATAL) << "Unreachable";
     UNREACHABLE();
   }
   T& operator[](intptr_t i) {
     UNUSED(i);
     LOG(FATAL) << "Unreachable";
     UNREACHABLE();
   }
 };

 template<intptr_t N>
 class HTemplateInstruction: public HInstruction {
  public:
   HTemplateInstruction<N>(SideEffects side_effects)
       : HInstruction(side_effects), inputs_() {}
   virtual ~HTemplateInstruction() {}

   size_t InputCount() const OVERRIDE { return N; }

  protected:
   const HUserRecord<HInstruction*> InputRecordAt(size_t i) const OVERRIDE { return inputs_[i]; }

   void SetRawInputRecordAt(size_t i, const HUserRecord<HInstruction*>& input) OVERRIDE {
     inputs_[i] = input;
   }

  private:
   EmbeddedArray<HUserRecord<HInstruction*>, N> inputs_;

   friend class SsaBuilder;
 };

 template<intptr_t N>
 class HExpression : public HTemplateInstruction<N> {
  public:
   HExpression<N>(Primitive::Type type, SideEffects side_effects)
       : HTemplateInstruction<N>(side_effects), type_(type) {}
   virtual ~HExpression() {}

   Primitive::Type GetType() const OVERRIDE { return type_; }

  protected:
   Primitive::Type type_;
 };

 // Represents dex's RETURN_VOID opcode. A HReturnVoid is a control flow
 // instruction that branches to the exit block.
 class HReturnVoid : public HTemplateInstruction<0> {
  public:
   HReturnVoid() : HTemplateInstruction(SideEffects::None()) {}

   bool IsControlFlow() const OVERRIDE { return true; }

   DECLARE_INSTRUCTION(ReturnVoid);

  private:
   DISALLOW_COPY_AND_ASSIGN(HReturnVoid);
 };

 // Represents dex's RETURN opcodes. A HReturn is a control flow
 // instruction that branches to the exit block.
 class HReturn : public HTemplateInstruction<1> {
  public:
   explicit HReturn(HInstruction* value) : HTemplateInstruction(SideEffects::None()) {
     SetRawInputAt(0, value);
   }

   bool IsControlFlow() const OVERRIDE { return true; }

   DECLARE_INSTRUCTION(Return);

  private:
   DISALLOW_COPY_AND_ASSIGN(HReturn);
 };

 // The exit instruction is the only instruction of the exit block.
 // Instructions aborting the method (HThrow and HReturn) must branch to the
 // exit block.
 class HExit : public HTemplateInstruction<0> {
  public:
   HExit() : HTemplateInstruction(SideEffects::None()) {}

   bool IsControlFlow() const OVERRIDE { return true; }

   DECLARE_INSTRUCTION(Exit);

  private:
   DISALLOW_COPY_AND_ASSIGN(HExit);
 };

 // Jumps from one block to another.
 class HGoto : public HTemplateInstruction<0> {
  public:
   HGoto() : HTemplateInstruction(SideEffects::None()) {}

   bool IsControlFlow() const OVERRIDE { return true; }

   HBasicBlock* GetSuccessor() const {
     return GetBlock()->GetSingleSuccessor();
   }

   DECLARE_INSTRUCTION(Goto);

  private:
   DISALLOW_COPY_AND_ASSIGN(HGoto);
 };


 // Conditional branch. A block ending with an HIf instruction must have
 // two successors.
 class HIf : public HTemplateInstruction<1> {
  public:
   explicit HIf(HInstruction* input) : HTemplateInstruction(SideEffects::None()) {
     SetRawInputAt(0, input);
   }

   bool IsControlFlow() const OVERRIDE { return true; }

   HBasicBlock* IfTrueSuccessor() const {
     return GetBlock()->GetSuccessors().Get(0);
   }

   HBasicBlock* IfFalseSuccessor() const {
     return GetBlock()->GetSuccessors().Get(1);
   }

   DECLARE_INSTRUCTION(If);

  private:
   DISALLOW_COPY_AND_ASSIGN(HIf);
 };


 // Abstract instruction which marks the beginning and/or end of a try block and
 // links it to the respective exception handlers. Behaves the same as a Goto in
 // non-exceptional control flow.
 // Normal-flow successor is stored at index zero, exception handlers under
 // higher indices in no particular order.
 class HTryBoundary : public HTemplateInstruction<0> {
  public:
   enum BoundaryKind {
     kEntry,
     kExit,
   };

   explicit HTryBoundary(BoundaryKind kind)
       : HTemplateInstruction(SideEffects::None()), kind_(kind) {}

   bool IsControlFlow() const OVERRIDE { return true; }

   // Returns the block's non-exceptional successor (index zero).
   HBasicBlock* GetNormalFlowSuccessor() const { return GetBlock()->GetSuccessors().Get(0); }

   // Returns whether `handler` is among its exception handlers (non-zero index
   // successors).
   bool HasExceptionHandler(HBasicBlock* handler) const {
     DCHECK(handler->IsCatchBlock());
     return GetBlock()->GetSuccessors().Contains(handler, /* start_from */ 1);
   }

   // Returns whether successor at index `idx` is an exception handler.
   bool IsExceptionalSuccessor(size_t idx) const {
     DCHECK_LT(idx, GetBlock()->GetSuccessors().Size());
     bool is_handler = (idx != 0);
     DCHECK(!is_handler || GetBlock()->GetSuccessors().Get(idx)->IsCatchBlock());
     return is_handler;
   }

   // If not present already, adds `handler` to its block's list of exception
   // handlers.
   void AddExceptionHandler(HBasicBlock* handler) {
     if (!HasExceptionHandler(handler)) {
       GetBlock()->AddSuccessor(handler);
     }
   }

   bool IsEntry() const { return kind_ == BoundaryKind::kEntry; }

   DECLARE_INSTRUCTION(TryBoundary);

  private:
   const BoundaryKind kind_;

   DISALLOW_COPY_AND_ASSIGN(HTryBoundary);
 };


 // Deoptimize to interpreter, upon checking a condition.
 class HDeoptimize : public HTemplateInstruction<1> {
  public:
   HDeoptimize(HInstruction* cond, uint32_t dex_pc)
       : HTemplateInstruction(SideEffects::None()),
         dex_pc_(dex_pc) {
     SetRawInputAt(0, cond);
   }

   bool NeedsEnvironment() const OVERRIDE { return true; }
   bool CanThrow() const OVERRIDE { return true; }
   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(Deoptimize);

  private:
   uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HDeoptimize);
 };

 // Represents the ArtMethod that was passed as a first argument to
 // the method. It is used by instructions that depend on it, like
 // instructions that work with the dex cache.
 class HCurrentMethod : public HExpression<0> {
  public:
   explicit HCurrentMethod(Primitive::Type type) : HExpression(type, SideEffects::None()) {}

   DECLARE_INSTRUCTION(CurrentMethod);

  private:
   DISALLOW_COPY_AND_ASSIGN(HCurrentMethod);
 };

 class HUnaryOperation : public HExpression<1> {
  public:
   HUnaryOperation(Primitive::Type result_type, HInstruction* input)
       : HExpression(result_type, SideEffects::None()) {
     SetRawInputAt(0, input);
   }

   HInstruction* GetInput() const { return InputAt(0); }
   Primitive::Type GetResultType() const { return GetType(); }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   // Try to statically evaluate `operation` and return a HConstant
   // containing the result of this evaluation.  If `operation` cannot
   // be evaluated as a constant, return null.
   HConstant* TryStaticEvaluation() const;

   // Apply this operation to `x`.
   virtual int32_t Evaluate(int32_t x) const = 0;
   virtual int64_t Evaluate(int64_t x) const = 0;

   DECLARE_INSTRUCTION(UnaryOperation);

  private:
   DISALLOW_COPY_AND_ASSIGN(HUnaryOperation);
 };

 class HBinaryOperation : public HExpression<2> {
  public:
   HBinaryOperation(Primitive::Type result_type,
                    HInstruction* left,
                    HInstruction* right) : HExpression(result_type, SideEffects::None()) {
     SetRawInputAt(0, left);
     SetRawInputAt(1, right);
   }

   HInstruction* GetLeft() const { return InputAt(0); }
   HInstruction* GetRight() const { return InputAt(1); }
   Primitive::Type GetResultType() const { return GetType(); }

   virtual bool IsCommutative() const { return false; }

   // Put constant on the right.
   // Returns whether order is changed.
   bool OrderInputsWithConstantOnTheRight() {
     HInstruction* left = InputAt(0);
     HInstruction* right = InputAt(1);
     if (left->IsConstant() && !right->IsConstant()) {
       ReplaceInput(right, 0);
       ReplaceInput(left, 1);
       return true;
     }
     return false;
   }

   // Order inputs by instruction id, but favor constant on the right side.
   // This helps GVN for commutative ops.
   void OrderInputs() {
     DCHECK(IsCommutative());
     HInstruction* left = InputAt(0);
     HInstruction* right = InputAt(1);
     if (left == right || (!left->IsConstant() && right->IsConstant())) {
       return;
     }
     if (OrderInputsWithConstantOnTheRight()) {
       return;
     }
     // Order according to instruction id.
     if (left->GetId() > right->GetId()) {
       ReplaceInput(right, 0);
       ReplaceInput(left, 1);
     }
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   // Try to statically evaluate `operation` and return a HConstant
   // containing the result of this evaluation.  If `operation` cannot
   // be evaluated as a constant, return null.
   HConstant* TryStaticEvaluation() const;

   // Apply this operation to `x` and `y`.
   virtual int32_t Evaluate(int32_t x, int32_t y) const = 0;
   virtual int64_t Evaluate(int64_t x, int64_t y) const = 0;

   // Returns an input that can legally be used as the right input and is
   // constant, or null.
   HConstant* GetConstantRight() const;

   // If `GetConstantRight()` returns one of the input, this returns the other
   // one. Otherwise it returns null.
   HInstruction* GetLeastConstantLeft() const;

   DECLARE_INSTRUCTION(BinaryOperation);

  private:
   DISALLOW_COPY_AND_ASSIGN(HBinaryOperation);
 };

 class HCondition : public HBinaryOperation {
  public:
   HCondition(HInstruction* first, HInstruction* second)
       : HBinaryOperation(Primitive::kPrimBoolean, first, second),
         needs_materialization_(true) {}

   bool NeedsMaterialization() const { return needs_materialization_; }
   void ClearNeedsMaterialization() { needs_materialization_ = false; }

   // For code generation purposes, returns whether this instruction is just before
   // `instruction`, and disregard moves in between.
   bool IsBeforeWhenDisregardMoves(HInstruction* instruction) const;

   DECLARE_INSTRUCTION(Condition);

   virtual IfCondition GetCondition() const = 0;

  private:
   // For register allocation purposes, returns whether this instruction needs to be
   // materialized (that is, not just be in the processor flags).
   bool needs_materialization_;

   DISALLOW_COPY_AND_ASSIGN(HCondition);
 };

 // Instruction to check if two inputs are equal to each other.
 class HEqual : public HCondition {
  public:
   HEqual(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x == y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x == y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(Equal);

   IfCondition GetCondition() const OVERRIDE {
     return kCondEQ;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HEqual);
 };

 class HNotEqual : public HCondition {
  public:
   HNotEqual(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x != y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x != y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(NotEqual);

   IfCondition GetCondition() const OVERRIDE {
     return kCondNE;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HNotEqual);
 };

 class HLessThan : public HCondition {
  public:
   HLessThan(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x < y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x < y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(LessThan);

   IfCondition GetCondition() const OVERRIDE {
     return kCondLT;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HLessThan);
 };

 class HLessThanOrEqual : public HCondition {
  public:
   HLessThanOrEqual(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x <= y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x <= y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(LessThanOrEqual);

   IfCondition GetCondition() const OVERRIDE {
     return kCondLE;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HLessThanOrEqual);
 };

 class HGreaterThan : public HCondition {
  public:
   HGreaterThan(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x > y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x > y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(GreaterThan);

   IfCondition GetCondition() const OVERRIDE {
     return kCondGT;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HGreaterThan);
 };

 class HGreaterThanOrEqual : public HCondition {
  public:
   HGreaterThanOrEqual(HInstruction* first, HInstruction* second)
       : HCondition(first, second) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x >= y ? 1 : 0;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x >= y ? 1 : 0;
   }

   DECLARE_INSTRUCTION(GreaterThanOrEqual);

   IfCondition GetCondition() const OVERRIDE {
     return kCondGE;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(HGreaterThanOrEqual);
 };


 // Instruction to check how two inputs compare to each other.
 // Result is 0 if input0 == input1, 1 if input0 > input1, or -1 if input0 < input1.
 class HCompare : public HBinaryOperation {
  public:
   // The bias applies for floating point operations and indicates how NaN
   // comparisons are treated:
   enum Bias {
     kNoBias,  // bias is not applicable (i.e. for long operation)
     kGtBias,  // return 1 for NaN comparisons
     kLtBias,  // return -1 for NaN comparisons
   };

   HCompare(Primitive::Type type,
            HInstruction* first,
            HInstruction* second,
            Bias bias,
            uint32_t dex_pc)
       : HBinaryOperation(Primitive::kPrimInt, first, second), bias_(bias), dex_pc_(dex_pc) {
     DCHECK_EQ(type, first->GetType());
     DCHECK_EQ(type, second->GetType());
   }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return
       x == y ? 0 :
       x > y ? 1 :
       -1;
   }

   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return
       x == y ? 0 :
       x > y ? 1 :
       -1;
   }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return bias_ == other->AsCompare()->bias_;
   }

   bool IsGtBias() { return bias_ == kGtBias; }

   uint32_t GetDexPc() const { return dex_pc_; }

   DECLARE_INSTRUCTION(Compare);

  private:
   const Bias bias_;
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HCompare);
 };

 // A local in the graph. Corresponds to a Dex register.
 class HLocal : public HTemplateInstruction<0> {
  public:
   explicit HLocal(uint16_t reg_number)
       : HTemplateInstruction(SideEffects::None()), reg_number_(reg_number) {}

   DECLARE_INSTRUCTION(Local);

   uint16_t GetRegNumber() const { return reg_number_; }

  private:
   // The Dex register number.
   const uint16_t reg_number_;

   DISALLOW_COPY_AND_ASSIGN(HLocal);
 };

 // Load a given local. The local is an input of this instruction.
 class HLoadLocal : public HExpression<1> {
  public:
   HLoadLocal(HLocal* local, Primitive::Type type)
       : HExpression(type, SideEffects::None()) {
     SetRawInputAt(0, local);
   }

   HLocal* GetLocal() const { return reinterpret_cast<HLocal*>(InputAt(0)); }

   DECLARE_INSTRUCTION(LoadLocal);

  private:
   DISALLOW_COPY_AND_ASSIGN(HLoadLocal);
 };

 // Store a value in a given local. This instruction has two inputs: the value
 // and the local.
 class HStoreLocal : public HTemplateInstruction<2> {
  public:
   HStoreLocal(HLocal* local, HInstruction* value) : HTemplateInstruction(SideEffects::None()) {
     SetRawInputAt(0, local);
     SetRawInputAt(1, value);
   }

   HLocal* GetLocal() const { return reinterpret_cast<HLocal*>(InputAt(0)); }

   DECLARE_INSTRUCTION(StoreLocal);

  private:
   DISALLOW_COPY_AND_ASSIGN(HStoreLocal);
 };

 class HConstant : public HExpression<0> {
  public:
   explicit HConstant(Primitive::Type type) : HExpression(type, SideEffects::None()) {}

   bool CanBeMoved() const OVERRIDE { return true; }

   virtual bool IsMinusOne() const { return false; }
   virtual bool IsZero() const { return false; }
   virtual bool IsOne() const { return false; }

   DECLARE_INSTRUCTION(Constant);

  private:
   DISALLOW_COPY_AND_ASSIGN(HConstant);
 };

 class HFloatConstant : public HConstant {
  public:
   float GetValue() const { return value_; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return bit_cast<uint32_t, float>(other->AsFloatConstant()->value_) ==
         bit_cast<uint32_t, float>(value_);
   }

   size_t ComputeHashCode() const OVERRIDE { return static_cast<size_t>(GetValue()); }

   bool IsMinusOne() const OVERRIDE {
     return bit_cast<uint32_t, float>(value_) == bit_cast<uint32_t, float>((-1.0f));
   }
   bool IsZero() const OVERRIDE {
     return value_ == 0.0f;
   }
   bool IsOne() const OVERRIDE {
     return bit_cast<uint32_t, float>(value_) == bit_cast<uint32_t, float>(1.0f);
   }
   bool IsNaN() const {
     return std::isnan(value_);
   }

   DECLARE_INSTRUCTION(FloatConstant);

  private:
   explicit HFloatConstant(float value) : HConstant(Primitive::kPrimFloat), value_(value) {}
   explicit HFloatConstant(int32_t value)
       : HConstant(Primitive::kPrimFloat), value_(bit_cast<float, int32_t>(value)) {}

   const float value_;

   // Only the SsaBuilder and HGraph can create floating-point constants.
   friend class SsaBuilder;
   friend class HGraph;
   DISALLOW_COPY_AND_ASSIGN(HFloatConstant);
 };

 class HDoubleConstant : public HConstant {
  public:
   double GetValue() const { return value_; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return bit_cast<uint64_t, double>(other->AsDoubleConstant()->value_) ==
         bit_cast<uint64_t, double>(value_);
   }

   size_t ComputeHashCode() const OVERRIDE { return static_cast<size_t>(GetValue()); }

   bool IsMinusOne() const OVERRIDE {
     return bit_cast<uint64_t, double>(value_) == bit_cast<uint64_t, double>((-1.0));
   }
   bool IsZero() const OVERRIDE {
     return value_ == 0.0;
   }
   bool IsOne() const OVERRIDE {
     return bit_cast<uint64_t, double>(value_) == bit_cast<uint64_t, double>(1.0);
   }
   bool IsNaN() const {
     return std::isnan(value_);
   }

   DECLARE_INSTRUCTION(DoubleConstant);

  private:
   explicit HDoubleConstant(double value) : HConstant(Primitive::kPrimDouble), value_(value) {}
   explicit HDoubleConstant(int64_t value)
       : HConstant(Primitive::kPrimDouble), value_(bit_cast<double, int64_t>(value)) {}

   const double value_;

   // Only the SsaBuilder and HGraph can create floating-point constants.
   friend class SsaBuilder;
   friend class HGraph;
   DISALLOW_COPY_AND_ASSIGN(HDoubleConstant);
 };

 class HNullConstant : public HConstant {
  public:
   bool InstructionDataEquals(HInstruction* other ATTRIBUTE_UNUSED) const OVERRIDE {
     return true;
   }

   size_t ComputeHashCode() const OVERRIDE { return 0; }

   DECLARE_INSTRUCTION(NullConstant);

  private:
   HNullConstant() : HConstant(Primitive::kPrimNot) {}

   friend class HGraph;
   DISALLOW_COPY_AND_ASSIGN(HNullConstant);
 };

 // Constants of the type int. Those can be from Dex instructions, or
 // synthesized (for example with the if-eqz instruction).
 class HIntConstant : public HConstant {
  public:
   int32_t GetValue() const { return value_; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return other->AsIntConstant()->value_ == value_;
   }

   size_t ComputeHashCode() const OVERRIDE { return GetValue(); }

   bool IsMinusOne() const OVERRIDE { return GetValue() == -1; }
   bool IsZero() const OVERRIDE { return GetValue() == 0; }
   bool IsOne() const OVERRIDE { return GetValue() == 1; }

   DECLARE_INSTRUCTION(IntConstant);

  private:
   explicit HIntConstant(int32_t value) : HConstant(Primitive::kPrimInt), value_(value) {}

   const int32_t value_;

   friend class HGraph;
   ART_FRIEND_TEST(GraphTest, InsertInstructionBefore);
   ART_FRIEND_TYPED_TEST(ParallelMoveTest, ConstantLast);
   DISALLOW_COPY_AND_ASSIGN(HIntConstant);
 };

 class HLongConstant : public HConstant {
  public:
   int64_t GetValue() const { return value_; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return other->AsLongConstant()->value_ == value_;
   }

   size_t ComputeHashCode() const OVERRIDE { return static_cast<size_t>(GetValue()); }

   bool IsMinusOne() const OVERRIDE { return GetValue() == -1; }
   bool IsZero() const OVERRIDE { return GetValue() == 0; }
   bool IsOne() const OVERRIDE { return GetValue() == 1; }

   DECLARE_INSTRUCTION(LongConstant);

  private:
   explicit HLongConstant(int64_t value) : HConstant(Primitive::kPrimLong), value_(value) {}

   const int64_t value_;

   friend class HGraph;
   DISALLOW_COPY_AND_ASSIGN(HLongConstant);
 };

 enum class Intrinsics {
 #define OPTIMIZING_INTRINSICS(Name, IsStatic) k ## Name,
 #include "intrinsics_list.h"
   kNone,
   INTRINSICS_LIST(OPTIMIZING_INTRINSICS)
 #undef INTRINSICS_LIST
 #undef OPTIMIZING_INTRINSICS
 };
 std::ostream& operator<<(std::ostream& os, const Intrinsics& intrinsic);

 class HInvoke : public HInstruction {
  public:
   size_t InputCount() const OVERRIDE { return inputs_.Size(); }

   // Runtime needs to walk the stack, so Dex -> Dex calls need to
   // know their environment.
   bool NeedsEnvironment() const OVERRIDE { return true; }

   void SetArgumentAt(size_t index, HInstruction* argument) {
     SetRawInputAt(index, argument);
   }

   // Return the number of arguments.  This number can be lower than
   // the number of inputs returned by InputCount(), as some invoke
   // instructions (e.g. HInvokeStaticOrDirect) can have non-argument
   // inputs at the end of their list of inputs.
   uint32_t GetNumberOfArguments() const { return number_of_arguments_; }

   Primitive::Type GetType() const OVERRIDE { return return_type_; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   uint32_t GetDexMethodIndex() const { return dex_method_index_; }
   const DexFile& GetDexFile() const { return GetEnvironment()->GetDexFile(); }

   InvokeType GetOriginalInvokeType() const { return original_invoke_type_; }

   Intrinsics GetIntrinsic() const {
     return intrinsic_;
   }

   void SetIntrinsic(Intrinsics intrinsic) {
     intrinsic_ = intrinsic;
   }

   bool IsFromInlinedInvoke() const {
     return GetEnvironment()->GetParent() != nullptr;
   }

   bool CanThrow() const OVERRIDE { return true; }

   DECLARE_INSTRUCTION(Invoke);

  protected:
   HInvoke(ArenaAllocator* arena,
           uint32_t number_of_arguments,
           uint32_t number_of_other_inputs,
           Primitive::Type return_type,
           uint32_t dex_pc,
           uint32_t dex_method_index,
           InvokeType original_invoke_type)
     : HInstruction(SideEffects::All()),
       number_of_arguments_(number_of_arguments),
       inputs_(arena, number_of_arguments),
       return_type_(return_type),
       dex_pc_(dex_pc),
       dex_method_index_(dex_method_index),
       original_invoke_type_(original_invoke_type),
       intrinsic_(Intrinsics::kNone) {
     uint32_t number_of_inputs = number_of_arguments + number_of_other_inputs;
     inputs_.SetSize(number_of_inputs);
   }

   const HUserRecord<HInstruction*> InputRecordAt(size_t i) const OVERRIDE { return inputs_.Get(i); }
   void SetRawInputRecordAt(size_t index, const HUserRecord<HInstruction*>& input) OVERRIDE {
     inputs_.Put(index, input);
   }

   uint32_t number_of_arguments_;
   GrowableArray<HUserRecord<HInstruction*> > inputs_;
   const Primitive::Type return_type_;
   const uint32_t dex_pc_;
   const uint32_t dex_method_index_;
   const InvokeType original_invoke_type_;
   Intrinsics intrinsic_;

  private:
   DISALLOW_COPY_AND_ASSIGN(HInvoke);
 };

 class HInvokeStaticOrDirect : public HInvoke {
  public:
   // Requirements of this method call regarding the class
   // initialization (clinit) check of its declaring class.
   enum class ClinitCheckRequirement {
     kNone,      // Class already initialized.
     kExplicit,  // Static call having explicit clinit check as last input.
     kImplicit,  // Static call implicitly requiring a clinit check.
   };

   HInvokeStaticOrDirect(ArenaAllocator* arena,
                         uint32_t number_of_arguments,
                         Primitive::Type return_type,
                         uint32_t dex_pc,
                         uint32_t dex_method_index,
                         bool is_recursive,
                         int32_t string_init_offset,
                         InvokeType original_invoke_type,
                         InvokeType invoke_type,
                         ClinitCheckRequirement clinit_check_requirement)
       : HInvoke(arena,
                 number_of_arguments,
                 // There is one extra argument for the  HCurrentMethod node, and
                 // potentially one other if the clinit check is explicit.
                 clinit_check_requirement == ClinitCheckRequirement::kExplicit ? 2u : 1u,
                 return_type,
                 dex_pc,
                 dex_method_index,
                 original_invoke_type),
         invoke_type_(invoke_type),
         is_recursive_(is_recursive),
         clinit_check_requirement_(clinit_check_requirement),
         string_init_offset_(string_init_offset) {}

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     UNUSED(obj);
     // We access the method via the dex cache so we can't do an implicit null check.
     // TODO: for intrinsics we can generate implicit null checks.
     return false;
   }

   InvokeType GetInvokeType() const { return invoke_type_; }
   bool IsRecursive() const { return is_recursive_; }
   bool NeedsDexCache() const OVERRIDE { return !IsRecursive(); }
   bool IsStringInit() const { return string_init_offset_ != 0; }
   int32_t GetStringInitOffset() const { return string_init_offset_; }
   uint32_t GetCurrentMethodInputIndex() const { return GetNumberOfArguments(); }

   // Is this instruction a call to a static method?
   bool IsStatic() const {
     return GetInvokeType() == kStatic;
   }

   // Remove the art::HLoadClass instruction set as last input by
   // art::PrepareForRegisterAllocation::VisitClinitCheck in lieu of
   // the initial art::HClinitCheck instruction (only relevant for
   // static calls with explicit clinit check).
   void RemoveLoadClassAsLastInput() {
     DCHECK(IsStaticWithExplicitClinitCheck());
     size_t last_input_index = InputCount() - 1;
     HInstruction* last_input = InputAt(last_input_index);
     DCHECK(last_input != nullptr);
     DCHECK(last_input->IsLoadClass()) << last_input->DebugName();
     RemoveAsUserOfInput(last_input_index);
     inputs_.DeleteAt(last_input_index);
     clinit_check_requirement_ = ClinitCheckRequirement::kImplicit;
     DCHECK(IsStaticWithImplicitClinitCheck());
   }

   // Is this a call to a static method whose declaring class has an
   // explicit intialization check in the graph?
   bool IsStaticWithExplicitClinitCheck() const {
     return IsStatic() && (clinit_check_requirement_ == ClinitCheckRequirement::kExplicit);
   }

   // Is this a call to a static method whose declaring class has an
   // implicit intialization check requirement?
   bool IsStaticWithImplicitClinitCheck() const {
     return IsStatic() && (clinit_check_requirement_ == ClinitCheckRequirement::kImplicit);
   }

   DECLARE_INSTRUCTION(InvokeStaticOrDirect);

  protected:
   const HUserRecord<HInstruction*> InputRecordAt(size_t i) const OVERRIDE {
     const HUserRecord<HInstruction*> input_record = HInvoke::InputRecordAt(i);
     if (kIsDebugBuild && IsStaticWithExplicitClinitCheck() && (i == InputCount() - 1)) {
       HInstruction* input = input_record.GetInstruction();
       // `input` is the last input of a static invoke marked as having
       // an explicit clinit check. It must either be:
       // - an art::HClinitCheck instruction, set by art::HGraphBuilder; or
       // - an art::HLoadClass instruction, set by art::PrepareForRegisterAllocation.
       DCHECK(input != nullptr);
       DCHECK(input->IsClinitCheck() || input->IsLoadClass()) << input->DebugName();
     }
     return input_record;
   }

  private:
   const InvokeType invoke_type_;
   const bool is_recursive_;
   ClinitCheckRequirement clinit_check_requirement_;
   // Thread entrypoint offset for string init method if this is a string init invoke.
   // Note that there are multiple string init methods, each having its own offset.
   int32_t string_init_offset_;

   DISALLOW_COPY_AND_ASSIGN(HInvokeStaticOrDirect);
 };

 class HInvokeVirtual : public HInvoke {
  public:
   HInvokeVirtual(ArenaAllocator* arena,
                  uint32_t number_of_arguments,
                  Primitive::Type return_type,
                  uint32_t dex_pc,
                  uint32_t dex_method_index,
                  uint32_t vtable_index)
       : HInvoke(arena, number_of_arguments, 0u, return_type, dex_pc, dex_method_index, kVirtual),
         vtable_index_(vtable_index) {}

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     // TODO: Add implicit null checks in intrinsics.
     return (obj == InputAt(0)) && !GetLocations()->Intrinsified();
   }

   uint32_t GetVTableIndex() const { return vtable_index_; }

   DECLARE_INSTRUCTION(InvokeVirtual);

  private:
   const uint32_t vtable_index_;

   DISALLOW_COPY_AND_ASSIGN(HInvokeVirtual);
 };

 class HInvokeInterface : public HInvoke {
  public:
   HInvokeInterface(ArenaAllocator* arena,
                    uint32_t number_of_arguments,
                    Primitive::Type return_type,
                    uint32_t dex_pc,
                    uint32_t dex_method_index,
                    uint32_t imt_index)
       : HInvoke(arena, number_of_arguments, 0u, return_type, dex_pc, dex_method_index, kInterface),
         imt_index_(imt_index) {}

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     // TODO: Add implicit null checks in intrinsics.
     return (obj == InputAt(0)) && !GetLocations()->Intrinsified();
   }

   uint32_t GetImtIndex() const { return imt_index_; }
   uint32_t GetDexMethodIndex() const { return dex_method_index_; }

   DECLARE_INSTRUCTION(InvokeInterface);

  private:
   const uint32_t imt_index_;

   DISALLOW_COPY_AND_ASSIGN(HInvokeInterface);
 };

 class HNewInstance : public HExpression<1> {
  public:
   HNewInstance(HCurrentMethod* current_method,
                uint32_t dex_pc,
                uint16_t type_index,
                const DexFile& dex_file,
                QuickEntrypointEnum entrypoint)
       : HExpression(Primitive::kPrimNot, SideEffects::None()),
         dex_pc_(dex_pc),
         type_index_(type_index),
         dex_file_(dex_file),
         entrypoint_(entrypoint) {
     SetRawInputAt(0, current_method);
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }
   uint16_t GetTypeIndex() const { return type_index_; }
   const DexFile& GetDexFile() const { return dex_file_; }

   // Calls runtime so needs an environment.
   bool NeedsEnvironment() const OVERRIDE { return true; }
   // It may throw when called on:
   //   - interfaces
   //   - abstract/innaccessible/unknown classes
   // TODO: optimize when possible.
   bool CanThrow() const OVERRIDE { return true; }

   bool CanBeNull() const OVERRIDE { return false; }

   QuickEntrypointEnum GetEntrypoint() const { return entrypoint_; }

   DECLARE_INSTRUCTION(NewInstance);

  private:
   const uint32_t dex_pc_;
   const uint16_t type_index_;
   const DexFile& dex_file_;
   const QuickEntrypointEnum entrypoint_;

   DISALLOW_COPY_AND_ASSIGN(HNewInstance);
 };

 class HNeg : public HUnaryOperation {
  public:
   explicit HNeg(Primitive::Type result_type, HInstruction* input)
       : HUnaryOperation(result_type, input) {}

   int32_t Evaluate(int32_t x) const OVERRIDE { return -x; }
   int64_t Evaluate(int64_t x) const OVERRIDE { return -x; }

   DECLARE_INSTRUCTION(Neg);

  private:
   DISALLOW_COPY_AND_ASSIGN(HNeg);
 };

 class HNewArray : public HExpression<2> {
  public:
   HNewArray(HInstruction* length,
             HCurrentMethod* current_method,
             uint32_t dex_pc,
             uint16_t type_index,
             const DexFile& dex_file,
             QuickEntrypointEnum entrypoint)
       : HExpression(Primitive::kPrimNot, SideEffects::None()),
         dex_pc_(dex_pc),
         type_index_(type_index),
         dex_file_(dex_file),
         entrypoint_(entrypoint) {
     SetRawInputAt(0, length);
     SetRawInputAt(1, current_method);
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }
   uint16_t GetTypeIndex() const { return type_index_; }
   const DexFile& GetDexFile() const { return dex_file_; }

   // Calls runtime so needs an environment.
   bool NeedsEnvironment() const OVERRIDE { return true; }

   // May throw NegativeArraySizeException, OutOfMemoryError, etc.
   bool CanThrow() const OVERRIDE { return true; }

   bool CanBeNull() const OVERRIDE { return false; }

   QuickEntrypointEnum GetEntrypoint() const { return entrypoint_; }

   DECLARE_INSTRUCTION(NewArray);

  private:
   const uint32_t dex_pc_;
   const uint16_t type_index_;
   const DexFile& dex_file_;
   const QuickEntrypointEnum entrypoint_;

   DISALLOW_COPY_AND_ASSIGN(HNewArray);
 };

 class HAdd : public HBinaryOperation {
  public:
   HAdd(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x + y;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x + y;
   }

   DECLARE_INSTRUCTION(Add);

  private:
   DISALLOW_COPY_AND_ASSIGN(HAdd);
 };

 class HSub : public HBinaryOperation {
  public:
   HSub(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     return x - y;
   }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     return x - y;
   }

   DECLARE_INSTRUCTION(Sub);

  private:
   DISALLOW_COPY_AND_ASSIGN(HSub);
 };

 class HMul : public HBinaryOperation {
  public:
   HMul(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x * y; }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x * y; }

   DECLARE_INSTRUCTION(Mul);

  private:
   DISALLOW_COPY_AND_ASSIGN(HMul);
 };

 class HDiv : public HBinaryOperation {
  public:
   HDiv(Primitive::Type result_type, HInstruction* left, HInstruction* right, uint32_t dex_pc)
       : HBinaryOperation(result_type, left, right), dex_pc_(dex_pc) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     // Our graph structure ensures we never have 0 for `y` during constant folding.
     DCHECK_NE(y, 0);
     // Special case -1 to avoid getting a SIGFPE on x86(_64).
     return (y == -1) ? -x : x / y;
   }

   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     DCHECK_NE(y, 0);
     // Special case -1 to avoid getting a SIGFPE on x86(_64).
     return (y == -1) ? -x : x / y;
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(Div);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HDiv);
 };

 class HRem : public HBinaryOperation {
  public:
   HRem(Primitive::Type result_type, HInstruction* left, HInstruction* right, uint32_t dex_pc)
       : HBinaryOperation(result_type, left, right), dex_pc_(dex_pc) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     DCHECK_NE(y, 0);
     // Special case -1 to avoid getting a SIGFPE on x86(_64).
     return (y == -1) ? 0 : x % y;
   }

   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     DCHECK_NE(y, 0);
     // Special case -1 to avoid getting a SIGFPE on x86(_64).
     return (y == -1) ? 0 : x % y;
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(Rem);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HRem);
 };

 class HDivZeroCheck : public HExpression<1> {
  public:
   HDivZeroCheck(HInstruction* value, uint32_t dex_pc)
       : HExpression(value->GetType(), SideEffects::None()), dex_pc_(dex_pc) {
     SetRawInputAt(0, value);
   }

   bool CanBeMoved() const OVERRIDE { return true; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE { return true; }
   bool CanThrow() const OVERRIDE { return true; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(DivZeroCheck);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HDivZeroCheck);
 };

 class HShl : public HBinaryOperation {
  public:
   HShl(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x << (y & kMaxIntShiftValue); }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x << (y & kMaxLongShiftValue); }

   DECLARE_INSTRUCTION(Shl);

  private:
   DISALLOW_COPY_AND_ASSIGN(HShl);
 };

 class HShr : public HBinaryOperation {
  public:
   HShr(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x >> (y & kMaxIntShiftValue); }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x >> (y & kMaxLongShiftValue); }

   DECLARE_INSTRUCTION(Shr);

  private:
   DISALLOW_COPY_AND_ASSIGN(HShr);
 };

 class HUShr : public HBinaryOperation {
  public:
   HUShr(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE {
     uint32_t ux = static_cast<uint32_t>(x);
     uint32_t uy = static_cast<uint32_t>(y) & kMaxIntShiftValue;
     return static_cast<int32_t>(ux >> uy);
   }

   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE {
     uint64_t ux = static_cast<uint64_t>(x);
     uint64_t uy = static_cast<uint64_t>(y) & kMaxLongShiftValue;
     return static_cast<int64_t>(ux >> uy);
   }

   DECLARE_INSTRUCTION(UShr);

  private:
   DISALLOW_COPY_AND_ASSIGN(HUShr);
 };

 class HAnd : public HBinaryOperation {
  public:
   HAnd(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x & y; }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x & y; }

   DECLARE_INSTRUCTION(And);

  private:
   DISALLOW_COPY_AND_ASSIGN(HAnd);
 };

 class HOr : public HBinaryOperation {
  public:
   HOr(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x | y; }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x | y; }

   DECLARE_INSTRUCTION(Or);

  private:
   DISALLOW_COPY_AND_ASSIGN(HOr);
 };

 class HXor : public HBinaryOperation {
  public:
   HXor(Primitive::Type result_type, HInstruction* left, HInstruction* right)
       : HBinaryOperation(result_type, left, right) {}

   bool IsCommutative() const OVERRIDE { return true; }

   int32_t Evaluate(int32_t x, int32_t y) const OVERRIDE { return x ^ y; }
   int64_t Evaluate(int64_t x, int64_t y) const OVERRIDE { return x ^ y; }

   DECLARE_INSTRUCTION(Xor);

  private:
   DISALLOW_COPY_AND_ASSIGN(HXor);
 };

 // The value of a parameter in this method. Its location depends on
 // the calling convention.
 class HParameterValue : public HExpression<0> {
  public:
   HParameterValue(uint8_t index, Primitive::Type parameter_type, bool is_this = false)
       : HExpression(parameter_type, SideEffects::None()), index_(index), is_this_(is_this) {}

   uint8_t GetIndex() const { return index_; }

   bool CanBeNull() const OVERRIDE { return !is_this_; }

   bool IsThis() const { return is_this_; }

   DECLARE_INSTRUCTION(ParameterValue);

  private:
   // The index of this parameter in the parameters list. Must be less
   // than HGraph::number_of_in_vregs_.
   const uint8_t index_;

   // Whether or not the parameter value corresponds to 'this' argument.
   const bool is_this_;

   DISALLOW_COPY_AND_ASSIGN(HParameterValue);
 };

 class HNot : public HUnaryOperation {
  public:
   explicit HNot(Primitive::Type result_type, HInstruction* input)
       : HUnaryOperation(result_type, input) {}

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   int32_t Evaluate(int32_t x) const OVERRIDE { return ~x; }
   int64_t Evaluate(int64_t x) const OVERRIDE { return ~x; }

   DECLARE_INSTRUCTION(Not);

  private:
   DISALLOW_COPY_AND_ASSIGN(HNot);
 };

 class HBooleanNot : public HUnaryOperation {
  public:
   explicit HBooleanNot(HInstruction* input)
       : HUnaryOperation(Primitive::Type::kPrimBoolean, input) {}

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   int32_t Evaluate(int32_t x) const OVERRIDE {
     DCHECK(IsUint<1>(x));
     return !x;
   }

   int64_t Evaluate(int64_t x ATTRIBUTE_UNUSED) const OVERRIDE {
     LOG(FATAL) << DebugName() << " cannot be used with 64-bit values";
     UNREACHABLE();
   }

   DECLARE_INSTRUCTION(BooleanNot);

  private:
   DISALLOW_COPY_AND_ASSIGN(HBooleanNot);
 };

 class HTypeConversion : public HExpression<1> {
  public:
   // Instantiate a type conversion of `input` to `result_type`.
   HTypeConversion(Primitive::Type result_type, HInstruction* input, uint32_t dex_pc)
       : HExpression(result_type, SideEffects::None()), dex_pc_(dex_pc) {
     SetRawInputAt(0, input);
     DCHECK_NE(input->GetType(), result_type);
   }

   HInstruction* GetInput() const { return InputAt(0); }
   Primitive::Type GetInputType() const { return GetInput()->GetType(); }
   Primitive::Type GetResultType() const { return GetType(); }

   // Required by the x86 and ARM code generators when producing calls
   // to the runtime.
   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other ATTRIBUTE_UNUSED) const OVERRIDE { return true; }

   // Try to statically evaluate the conversion and return a HConstant
   // containing the result.  If the input cannot be converted, return nullptr.
   HConstant* TryStaticEvaluation() const;

   DECLARE_INSTRUCTION(TypeConversion);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HTypeConversion);
 };

 static constexpr uint32_t kNoRegNumber = -1;

 class HPhi : public HInstruction {
  public:
   HPhi(ArenaAllocator* arena, uint32_t reg_number, size_t number_of_inputs, Primitive::Type type)
       : HInstruction(SideEffects::None()),
         inputs_(arena, number_of_inputs),
         reg_number_(reg_number),
         type_(type),
         is_live_(false),
         can_be_null_(true) {
     inputs_.SetSize(number_of_inputs);
   }

   // Returns a type equivalent to the given `type`, but that a `HPhi` can hold.
   static Primitive::Type ToPhiType(Primitive::Type type) {
     switch (type) {
       case Primitive::kPrimBoolean:
       case Primitive::kPrimByte:
       case Primitive::kPrimShort:
       case Primitive::kPrimChar:
         return Primitive::kPrimInt;
       default:
         return type;
     }
   }

   size_t InputCount() const OVERRIDE { return inputs_.Size(); }

   void AddInput(HInstruction* input);
   void RemoveInputAt(size_t index);

   Primitive::Type GetType() const OVERRIDE { return type_; }
   void SetType(Primitive::Type type) { type_ = type; }

   bool CanBeNull() const OVERRIDE { return can_be_null_; }
   void SetCanBeNull(bool can_be_null) { can_be_null_ = can_be_null; }

   uint32_t GetRegNumber() const { return reg_number_; }

   void SetDead() { is_live_ = false; }
   void SetLive() { is_live_ = true; }
   bool IsDead() const { return !is_live_; }
   bool IsLive() const { return is_live_; }

   // Returns the next equivalent phi (starting from the current one) or null if there is none.
   // An equivalent phi is a phi having the same dex register and type.
   // It assumes that phis with the same dex register are adjacent.
   HPhi* GetNextEquivalentPhiWithSameType() {
     HInstruction* next = GetNext();
     while (next != nullptr && next->AsPhi()->GetRegNumber() == reg_number_) {
       if (next->GetType() == GetType()) {
         return next->AsPhi();
       }
       next = next->GetNext();
     }
     return nullptr;
   }

   DECLARE_INSTRUCTION(Phi);

  protected:
   const HUserRecord<HInstruction*> InputRecordAt(size_t i) const OVERRIDE { return inputs_.Get(i); }

   void SetRawInputRecordAt(size_t index, const HUserRecord<HInstruction*>& input) OVERRIDE {
     inputs_.Put(index, input);
   }

  private:
   GrowableArray<HUserRecord<HInstruction*> > inputs_;
   const uint32_t reg_number_;
   Primitive::Type type_;
   bool is_live_;
   bool can_be_null_;

   DISALLOW_COPY_AND_ASSIGN(HPhi);
 };

 class HNullCheck : public HExpression<1> {
  public:
   HNullCheck(HInstruction* value, uint32_t dex_pc)
       : HExpression(value->GetType(), SideEffects::None()), dex_pc_(dex_pc) {
     SetRawInputAt(0, value);
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE { return true; }

   bool CanThrow() const OVERRIDE { return true; }

   bool CanBeNull() const OVERRIDE { return false; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(NullCheck);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HNullCheck);
 };

 class FieldInfo : public ValueObject {
  public:
   FieldInfo(MemberOffset field_offset,
             Primitive::Type field_type,
             bool is_volatile,
             uint32_t index,
             const DexFile& dex_file)
       : field_offset_(field_offset),
         field_type_(field_type),
         is_volatile_(is_volatile),
         index_(index),
         dex_file_(dex_file) {}

   MemberOffset GetFieldOffset() const { return field_offset_; }
   Primitive::Type GetFieldType() const { return field_type_; }
   uint32_t GetFieldIndex() const { return index_; }
   const DexFile& GetDexFile() const { return dex_file_; }
   bool IsVolatile() const { return is_volatile_; }

  private:
   const MemberOffset field_offset_;
   const Primitive::Type field_type_;
   const bool is_volatile_;
   uint32_t index_;
   const DexFile& dex_file_;
 };

 class HInstanceFieldGet : public HExpression<1> {
  public:
   HInstanceFieldGet(HInstruction* value,
                     Primitive::Type field_type,
                     MemberOffset field_offset,
                     bool is_volatile,
                     uint32_t field_idx,
                     const DexFile& dex_file)
       : HExpression(field_type, SideEffects::DependsOnSomething()),
         field_info_(field_offset, field_type, is_volatile, field_idx, dex_file) {
     SetRawInputAt(0, value);
   }

   bool CanBeMoved() const OVERRIDE { return !IsVolatile(); }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     HInstanceFieldGet* other_get = other->AsInstanceFieldGet();
     return GetFieldOffset().SizeValue() == other_get->GetFieldOffset().SizeValue();
   }

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     return (obj == InputAt(0)) && GetFieldOffset().Uint32Value() < kPageSize;
   }

   size_t ComputeHashCode() const OVERRIDE {
     return (HInstruction::ComputeHashCode() << 7) | GetFieldOffset().SizeValue();
   }

   const FieldInfo& GetFieldInfo() const { return field_info_; }
   MemberOffset GetFieldOffset() const { return field_info_.GetFieldOffset(); }
   Primitive::Type GetFieldType() const { return field_info_.GetFieldType(); }
   bool IsVolatile() const { return field_info_.IsVolatile(); }

   DECLARE_INSTRUCTION(InstanceFieldGet);

  private:
   const FieldInfo field_info_;

   DISALLOW_COPY_AND_ASSIGN(HInstanceFieldGet);
 };

 class HInstanceFieldSet : public HTemplateInstruction<2> {
  public:
   HInstanceFieldSet(HInstruction* object,
                     HInstruction* value,
                     Primitive::Type field_type,
                     MemberOffset field_offset,
                     bool is_volatile,
                     uint32_t field_idx,
                     const DexFile& dex_file)
       : HTemplateInstruction(SideEffects::ChangesSomething()),
         field_info_(field_offset, field_type, is_volatile, field_idx, dex_file),
         value_can_be_null_(true) {
     SetRawInputAt(0, object);
     SetRawInputAt(1, value);
   }

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     return (obj == InputAt(0)) && GetFieldOffset().Uint32Value() < kPageSize;
   }

   const FieldInfo& GetFieldInfo() const { return field_info_; }
   MemberOffset GetFieldOffset() const { return field_info_.GetFieldOffset(); }
   Primitive::Type GetFieldType() const { return field_info_.GetFieldType(); }
   bool IsVolatile() const { return field_info_.IsVolatile(); }
   HInstruction* GetValue() const { return InputAt(1); }
   bool GetValueCanBeNull() const { return value_can_be_null_; }
   void ClearValueCanBeNull() { value_can_be_null_ = false; }

   DECLARE_INSTRUCTION(InstanceFieldSet);

  private:
   const FieldInfo field_info_;
   bool value_can_be_null_;

   DISALLOW_COPY_AND_ASSIGN(HInstanceFieldSet);
 };

 class HArrayGet : public HExpression<2> {
  public:
   HArrayGet(HInstruction* array, HInstruction* index, Primitive::Type type)
       : HExpression(type, SideEffects::DependsOnSomething()) {
     SetRawInputAt(0, array);
     SetRawInputAt(1, index);
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }
   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     UNUSED(obj);
     // TODO: We can be smarter here.
     // Currently, the array access is always preceded by an ArrayLength or a NullCheck
     // which generates the implicit null check. There are cases when these can be removed
     // to produce better code. If we ever add optimizations to do so we should allow an
     // implicit check here (as long as the address falls in the first page).
     return false;
   }

   void SetType(Primitive::Type type) { type_ = type; }

   HInstruction* GetArray() const { return InputAt(0); }
   HInstruction* GetIndex() const { return InputAt(1); }

   DECLARE_INSTRUCTION(ArrayGet);

  private:
   DISALLOW_COPY_AND_ASSIGN(HArrayGet);
 };

 class HArraySet : public HTemplateInstruction<3> {
  public:
   HArraySet(HInstruction* array,
             HInstruction* index,
             HInstruction* value,
             Primitive::Type expected_component_type,
             uint32_t dex_pc)
       : HTemplateInstruction(SideEffects::ChangesSomething()),
         dex_pc_(dex_pc),
         expected_component_type_(expected_component_type),
         needs_type_check_(value->GetType() == Primitive::kPrimNot),
         value_can_be_null_(true) {
     SetRawInputAt(0, array);
     SetRawInputAt(1, index);
     SetRawInputAt(2, value);
   }

   bool NeedsEnvironment() const OVERRIDE {
     // We currently always call a runtime method to catch array store
     // exceptions.
     return needs_type_check_;
   }

   // Can throw ArrayStoreException.
   bool CanThrow() const OVERRIDE { return needs_type_check_; }

   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     UNUSED(obj);
     // TODO: Same as for ArrayGet.
     return false;
   }

   void ClearNeedsTypeCheck() {
     needs_type_check_ = false;
   }

   void ClearValueCanBeNull() {
     value_can_be_null_ = false;
   }

   bool GetValueCanBeNull() const { return value_can_be_null_; }
   bool NeedsTypeCheck() const { return needs_type_check_; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   HInstruction* GetArray() const { return InputAt(0); }
   HInstruction* GetIndex() const { return InputAt(1); }
   HInstruction* GetValue() const { return InputAt(2); }

   Primitive::Type GetComponentType() const {
     // The Dex format does not type floating point index operations. Since the
     // `expected_component_type_` is set during building and can therefore not
     // be correct, we also check what is the value type. If it is a floating
     // point type, we must use that type.
     Primitive::Type value_type = GetValue()->GetType();
     return ((value_type == Primitive::kPrimFloat) || (value_type == Primitive::kPrimDouble))
         ? value_type
         : expected_component_type_;
   }

   DECLARE_INSTRUCTION(ArraySet);

  private:
   const uint32_t dex_pc_;
   const Primitive::Type expected_component_type_;
   bool needs_type_check_;
   bool value_can_be_null_;

   DISALLOW_COPY_AND_ASSIGN(HArraySet);
 };

 class HArrayLength : public HExpression<1> {
  public:
   explicit HArrayLength(HInstruction* array)
       : HExpression(Primitive::kPrimInt, SideEffects::None()) {
     // Note that arrays do not change length, so the instruction does not
     // depend on any write.
     SetRawInputAt(0, array);
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }
   bool CanDoImplicitNullCheckOn(HInstruction* obj) const OVERRIDE {
     return obj == InputAt(0);
   }

   DECLARE_INSTRUCTION(ArrayLength);

  private:
   DISALLOW_COPY_AND_ASSIGN(HArrayLength);
 };

 class HBoundsCheck : public HExpression<2> {
  public:
   HBoundsCheck(HInstruction* index, HInstruction* length, uint32_t dex_pc)
       : HExpression(index->GetType(), SideEffects::None()), dex_pc_(dex_pc) {
     DCHECK(index->GetType() == Primitive::kPrimInt);
     SetRawInputAt(0, index);
     SetRawInputAt(1, length);
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE { return true; }

   bool CanThrow() const OVERRIDE { return true; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(BoundsCheck);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HBoundsCheck);
 };

 /**
  * Some DEX instructions are folded into multiple HInstructions that need
  * to stay live until the last HInstruction. This class
  * is used as a marker for the baseline compiler to ensure its preceding
  * HInstruction stays live. `index` represents the stack location index of the
  * instruction (the actual offset is computed as index * vreg_size).
  */
 class HTemporary : public HTemplateInstruction<0> {
  public:
   explicit HTemporary(size_t index) : HTemplateInstruction(SideEffects::None()), index_(index) {}

   size_t GetIndex() const { return index_; }

   Primitive::Type GetType() const OVERRIDE {
     // The previous instruction is the one that will be stored in the temporary location.
     DCHECK(GetPrevious() != nullptr);
     return GetPrevious()->GetType();
   }

   DECLARE_INSTRUCTION(Temporary);

  private:
   const size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HTemporary);
 };

 class HSuspendCheck : public HTemplateInstruction<0> {
  public:
   explicit HSuspendCheck(uint32_t dex_pc)
       : HTemplateInstruction(SideEffects::None()), dex_pc_(dex_pc), slow_path_(nullptr) {}

   bool NeedsEnvironment() const OVERRIDE {
     return true;
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }
   void SetSlowPath(SlowPathCode* slow_path) { slow_path_ = slow_path; }
   SlowPathCode* GetSlowPath() const { return slow_path_; }

   DECLARE_INSTRUCTION(SuspendCheck);

  private:
   const uint32_t dex_pc_;

   // Only used for code generation, in order to share the same slow path between back edges
   // of a same loop.
   SlowPathCode* slow_path_;

   DISALLOW_COPY_AND_ASSIGN(HSuspendCheck);
 };

 /**
  * Instruction to load a Class object.
  */
 class HLoadClass : public HExpression<1> {
  public:
   HLoadClass(HCurrentMethod* current_method,
              uint16_t type_index,
              const DexFile& dex_file,
              bool is_referrers_class,
              uint32_t dex_pc)
       : HExpression(Primitive::kPrimNot, SideEffects::None()),
         type_index_(type_index),
         dex_file_(dex_file),
         is_referrers_class_(is_referrers_class),
         dex_pc_(dex_pc),
         generate_clinit_check_(false),
         loaded_class_rti_(ReferenceTypeInfo::CreateTop(/* is_exact */ false)) {
     SetRawInputAt(0, current_method);
   }

   bool CanBeMoved() const OVERRIDE { return true; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return other->AsLoadClass()->type_index_ == type_index_;
   }

   size_t ComputeHashCode() const OVERRIDE { return type_index_; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }
   uint16_t GetTypeIndex() const { return type_index_; }
   bool IsReferrersClass() const { return is_referrers_class_; }

   bool NeedsEnvironment() const OVERRIDE {
     // Will call runtime and load the class if the class is not loaded yet.
     // TODO: finer grain decision.
     return !is_referrers_class_;
   }

   bool MustGenerateClinitCheck() const {
     return generate_clinit_check_;
   }

   void SetMustGenerateClinitCheck(bool generate_clinit_check) {
     generate_clinit_check_ = generate_clinit_check;
   }

   bool CanCallRuntime() const {
     return MustGenerateClinitCheck() || !is_referrers_class_;
   }

   bool CanThrow() const OVERRIDE {
     // May call runtime and and therefore can throw.
     // TODO: finer grain decision.
     return CanCallRuntime();
   }

   ReferenceTypeInfo GetLoadedClassRTI() {
     return loaded_class_rti_;
   }

   void SetLoadedClassRTI(ReferenceTypeInfo rti) {
     // Make sure we only set exact types (the loaded class should never be merged).
     DCHECK(rti.IsExact());
     loaded_class_rti_ = rti;
   }

   bool IsResolved() {
     return loaded_class_rti_.IsExact();
   }

   const DexFile& GetDexFile() { return dex_file_; }

   bool NeedsDexCache() const OVERRIDE { return !is_referrers_class_; }

   DECLARE_INSTRUCTION(LoadClass);

  private:
   const uint16_t type_index_;
   const DexFile& dex_file_;
   const bool is_referrers_class_;
   const uint32_t dex_pc_;
   // Whether this instruction must generate the initialization check.
   // Used for code generation.
   bool generate_clinit_check_;

   ReferenceTypeInfo loaded_class_rti_;

   DISALLOW_COPY_AND_ASSIGN(HLoadClass);
 };

 class HLoadString : public HExpression<1> {
  public:
   HLoadString(HCurrentMethod* current_method, uint32_t string_index, uint32_t dex_pc)
       : HExpression(Primitive::kPrimNot, SideEffects::None()),
         string_index_(string_index),
         dex_pc_(dex_pc) {
     SetRawInputAt(0, current_method);
   }

   bool CanBeMoved() const OVERRIDE { return true; }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     return other->AsLoadString()->string_index_ == string_index_;
   }

   size_t ComputeHashCode() const OVERRIDE { return string_index_; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }
   uint32_t GetStringIndex() const { return string_index_; }

   // TODO: Can we deopt or debug when we resolve a string?
   bool NeedsEnvironment() const OVERRIDE { return false; }
   bool NeedsDexCache() const OVERRIDE { return true; }

   DECLARE_INSTRUCTION(LoadString);

  private:
   const uint32_t string_index_;
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HLoadString);
 };

 /**
  * Performs an initialization check on its Class object input.
  */
 class HClinitCheck : public HExpression<1> {
  public:
   explicit HClinitCheck(HLoadClass* constant, uint32_t dex_pc)
       : HExpression(Primitive::kPrimNot, SideEffects::ChangesSomething()),
         dex_pc_(dex_pc) {
     SetRawInputAt(0, constant);
   }

   bool CanBeMoved() const OVERRIDE { return true; }
   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     UNUSED(other);
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE {
     // May call runtime to initialize the class.
     return true;
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   HLoadClass* GetLoadClass() const { return InputAt(0)->AsLoadClass(); }

   DECLARE_INSTRUCTION(ClinitCheck);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HClinitCheck);
 };

 class HStaticFieldGet : public HExpression<1> {
  public:
   HStaticFieldGet(HInstruction* cls,
                   Primitive::Type field_type,
                   MemberOffset field_offset,
                   bool is_volatile,
                   uint32_t field_idx,
                   const DexFile& dex_file)
       : HExpression(field_type, SideEffects::DependsOnSomething()),
         field_info_(field_offset, field_type, is_volatile, field_idx, dex_file) {
     SetRawInputAt(0, cls);
   }


   bool CanBeMoved() const OVERRIDE { return !IsVolatile(); }

   bool InstructionDataEquals(HInstruction* other) const OVERRIDE {
     HStaticFieldGet* other_get = other->AsStaticFieldGet();
     return GetFieldOffset().SizeValue() == other_get->GetFieldOffset().SizeValue();
   }

   size_t ComputeHashCode() const OVERRIDE {
     return (HInstruction::ComputeHashCode() << 7) | GetFieldOffset().SizeValue();
   }

   const FieldInfo& GetFieldInfo() const { return field_info_; }
   MemberOffset GetFieldOffset() const { return field_info_.GetFieldOffset(); }
   Primitive::Type GetFieldType() const { return field_info_.GetFieldType(); }
   bool IsVolatile() const { return field_info_.IsVolatile(); }

   DECLARE_INSTRUCTION(StaticFieldGet);

  private:
   const FieldInfo field_info_;

   DISALLOW_COPY_AND_ASSIGN(HStaticFieldGet);
 };

 class HStaticFieldSet : public HTemplateInstruction<2> {
  public:
   HStaticFieldSet(HInstruction* cls,
                   HInstruction* value,
                   Primitive::Type field_type,
                   MemberOffset field_offset,
                   bool is_volatile,
                   uint32_t field_idx,
                   const DexFile& dex_file)
       : HTemplateInstruction(SideEffects::ChangesSomething()),
         field_info_(field_offset, field_type, is_volatile, field_idx, dex_file),
         value_can_be_null_(true) {
     SetRawInputAt(0, cls);
     SetRawInputAt(1, value);
   }

   const FieldInfo& GetFieldInfo() const { return field_info_; }
   MemberOffset GetFieldOffset() const { return field_info_.GetFieldOffset(); }
   Primitive::Type GetFieldType() const { return field_info_.GetFieldType(); }
   bool IsVolatile() const { return field_info_.IsVolatile(); }

   HInstruction* GetValue() const { return InputAt(1); }
   bool GetValueCanBeNull() const { return value_can_be_null_; }
   void ClearValueCanBeNull() { value_can_be_null_ = false; }

   DECLARE_INSTRUCTION(StaticFieldSet);

  private:
   const FieldInfo field_info_;
   bool value_can_be_null_;

   DISALLOW_COPY_AND_ASSIGN(HStaticFieldSet);
 };

 // Implement the move-exception DEX instruction.
 class HLoadException : public HExpression<0> {
  public:
   HLoadException() : HExpression(Primitive::kPrimNot, SideEffects::None()) {}

   DECLARE_INSTRUCTION(LoadException);

  private:
   DISALLOW_COPY_AND_ASSIGN(HLoadException);
 };

 class HThrow : public HTemplateInstruction<1> {
  public:
   HThrow(HInstruction* exception, uint32_t dex_pc)
       : HTemplateInstruction(SideEffects::None()), dex_pc_(dex_pc) {
     SetRawInputAt(0, exception);
   }

   bool IsControlFlow() const OVERRIDE { return true; }

   bool NeedsEnvironment() const OVERRIDE { return true; }

   bool CanThrow() const OVERRIDE { return true; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   DECLARE_INSTRUCTION(Throw);

  private:
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HThrow);
 };

 class HInstanceOf : public HExpression<2> {
  public:
   HInstanceOf(HInstruction* object,
               HLoadClass* constant,
               bool class_is_final,
               uint32_t dex_pc)
       : HExpression(Primitive::kPrimBoolean, SideEffects::None()),
         class_is_final_(class_is_final),
         must_do_null_check_(true),
         dex_pc_(dex_pc) {
     SetRawInputAt(0, object);
     SetRawInputAt(1, constant);
   }

   bool CanBeMoved() const OVERRIDE { return true; }

   bool InstructionDataEquals(HInstruction* other ATTRIBUTE_UNUSED) const OVERRIDE {
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE {
     return false;
   }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   bool IsClassFinal() const { return class_is_final_; }

   // Used only in code generation.
   bool MustDoNullCheck() const { return must_do_null_check_; }
   void ClearMustDoNullCheck() { must_do_null_check_ = false; }

   DECLARE_INSTRUCTION(InstanceOf);

  private:
   const bool class_is_final_;
   bool must_do_null_check_;
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HInstanceOf);
 };

 class HBoundType : public HExpression<1> {
  public:
   HBoundType(HInstruction* input, ReferenceTypeInfo bound_type)
       : HExpression(Primitive::kPrimNot, SideEffects::None()),
         bound_type_(bound_type) {
     DCHECK_EQ(input->GetType(), Primitive::kPrimNot);
     SetRawInputAt(0, input);
   }

   const ReferenceTypeInfo& GetBoundType() const { return bound_type_; }

   bool CanBeNull() const OVERRIDE {
     // `null instanceof ClassX` always return false so we can't be null.
     return false;
   }

   DECLARE_INSTRUCTION(BoundType);

  private:
   // Encodes the most upper class that this instruction can have. In other words
   // it is always the case that GetBoundType().IsSupertypeOf(GetReferenceType()).
   // It is used to bound the type in cases like `if (x instanceof ClassX) {}`
   const ReferenceTypeInfo bound_type_;

   DISALLOW_COPY_AND_ASSIGN(HBoundType);
 };

 class HCheckCast : public HTemplateInstruction<2> {
  public:
   HCheckCast(HInstruction* object,
              HLoadClass* constant,
              bool class_is_final,
              uint32_t dex_pc)
       : HTemplateInstruction(SideEffects::None()),
         class_is_final_(class_is_final),
         must_do_null_check_(true),
         dex_pc_(dex_pc) {
     SetRawInputAt(0, object);
     SetRawInputAt(1, constant);
   }

   bool CanBeMoved() const OVERRIDE { return true; }

   bool InstructionDataEquals(HInstruction* other ATTRIBUTE_UNUSED) const OVERRIDE {
     return true;
   }

   bool NeedsEnvironment() const OVERRIDE {
     // Instruction may throw a CheckCastError.
     return true;
   }

   bool CanThrow() const OVERRIDE { return true; }

   bool MustDoNullCheck() const { return must_do_null_check_; }
   void ClearMustDoNullCheck() { must_do_null_check_ = false; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   bool IsClassFinal() const { return class_is_final_; }

   DECLARE_INSTRUCTION(CheckCast);

  private:
   const bool class_is_final_;
   bool must_do_null_check_;
   const uint32_t dex_pc_;

   DISALLOW_COPY_AND_ASSIGN(HCheckCast);
 };

 class HMemoryBarrier : public HTemplateInstruction<0> {
  public:
   explicit HMemoryBarrier(MemBarrierKind barrier_kind)
       : HTemplateInstruction(SideEffects::None()),
         barrier_kind_(barrier_kind) {}

   MemBarrierKind GetBarrierKind() { return barrier_kind_; }

   DECLARE_INSTRUCTION(MemoryBarrier);

  private:
   const MemBarrierKind barrier_kind_;

   DISALLOW_COPY_AND_ASSIGN(HMemoryBarrier);
 };

 class HMonitorOperation : public HTemplateInstruction<1> {
  public:
   enum OperationKind {
     kEnter,
     kExit,
   };

   HMonitorOperation(HInstruction* object, OperationKind kind, uint32_t dex_pc)
     : HTemplateInstruction(SideEffects::None()), kind_(kind), dex_pc_(dex_pc) {
     SetRawInputAt(0, object);
   }

   // Instruction may throw a Java exception, so we need an environment.
   bool NeedsEnvironment() const OVERRIDE { return true; }
   bool CanThrow() const OVERRIDE { return true; }

   uint32_t GetDexPc() const OVERRIDE { return dex_pc_; }

   bool IsEnter() const { return kind_ == kEnter; }

   DECLARE_INSTRUCTION(MonitorOperation);

  private:
   const OperationKind kind_;
   const uint32_t dex_pc_;

  private:
   DISALLOW_COPY_AND_ASSIGN(HMonitorOperation);
 };

 class MoveOperands : public ArenaObject<kArenaAllocMisc> {
  public:
   MoveOperands(Location source,
                Location destination,
                Primitive::Type type,
                HInstruction* instruction)
       : source_(source), destination_(destination), type_(type), instruction_(instruction) {}

   Location GetSource() const { return source_; }
   Location GetDestination() const { return destination_; }

   void SetSource(Location value) { source_ = value; }
   void SetDestination(Location value) { destination_ = value; }

   // The parallel move resolver marks moves as "in-progress" by clearing the
   // destination (but not the source).
   Location MarkPending() {
     DCHECK(!IsPending());
     Location dest = destination_;
     destination_ = Location::NoLocation();
     return dest;
   }

   void ClearPending(Location dest) {
     DCHECK(IsPending());
     destination_ = dest;
   }

   bool IsPending() const {
     DCHECK(!source_.IsInvalid() || destination_.IsInvalid());
     return destination_.IsInvalid() && !source_.IsInvalid();
   }

   // True if this blocks a move from the given location.
   bool Blocks(Location loc) const {
     return !IsEliminated() && source_.OverlapsWith(loc);
   }

   // A move is redundant if it's been eliminated, if its source and
   // destination are the same, or if its destination is unneeded.
   bool IsRedundant() const {
     return IsEliminated() || destination_.IsInvalid() || source_.Equals(destination_);
   }

   // We clear both operands to indicate move that's been eliminated.
   void Eliminate() {
     source_ = destination_ = Location::NoLocation();
   }

   bool IsEliminated() const {
     DCHECK(!source_.IsInvalid() || destination_.IsInvalid());
     return source_.IsInvalid();
   }

   Primitive::Type GetType() const { return type_; }

   bool Is64BitMove() const {
     return Primitive::Is64BitType(type_);
   }

   HInstruction* GetInstruction() const { return instruction_; }

  private:
   Location source_;
   Location destination_;
   // The type this move is for.
   Primitive::Type type_;
   // The instruction this move is assocatied with. Null when this move is
   // for moving an input in the expected locations of user (including a phi user).
   // This is only used in debug mode, to ensure we do not connect interval siblings
   // in the same parallel move.
   HInstruction* instruction_;
 };

 static constexpr size_t kDefaultNumberOfMoves = 4;

 class HParallelMove : public HTemplateInstruction<0> {
  public:
   explicit HParallelMove(ArenaAllocator* arena)
       : HTemplateInstruction(SideEffects::None()), moves_(arena, kDefaultNumberOfMoves) {}

   void AddMove(Location source,
                Location destination,
                Primitive::Type type,
                HInstruction* instruction) {
     DCHECK(source.IsValid());
     DCHECK(destination.IsValid());
     if (kIsDebugBuild) {
       if (instruction != nullptr) {
         for (size_t i = 0, e = moves_.Size(); i < e; ++i) {
           if (moves_.Get(i).GetInstruction() == instruction) {
             // Special case the situation where the move is for the spill slot
             // of the instruction.
             if ((GetPrevious() == instruction)
                 || ((GetPrevious() == nullptr)
                     && instruction->IsPhi()
                     && instruction->GetBlock() == GetBlock())) {
               DCHECK_NE(destination.GetKind(), moves_.Get(i).GetDestination().GetKind())
                   << "Doing parallel moves for the same instruction.";
             } else {
               DCHECK(false) << "Doing parallel moves for the same instruction.";
             }
           }
         }
       }
       for (size_t i = 0, e = moves_.Size(); i < e; ++i) {
         DCHECK(!destination.OverlapsWith(moves_.Get(i).GetDestination()))
             << "Overlapped destination for two moves in a parallel move: "
             << moves_.Get(i).GetSource() << " ==> " << moves_.Get(i).GetDestination() << " and "
             << source << " ==> " << destination;
       }
     }
     moves_.Add(MoveOperands(source, destination, type, instruction));
   }

   MoveOperands* MoveOperandsAt(size_t index) const {
     return moves_.GetRawStorage() + index;
   }

   size_t NumMoves() const { return moves_.Size(); }

   DECLARE_INSTRUCTION(ParallelMove);

  private:
   GrowableArray<MoveOperands> moves_;

   DISALLOW_COPY_AND_ASSIGN(HParallelMove);
 };

 class HGraphVisitor : public ValueObject {
  public:
   explicit HGraphVisitor(HGraph* graph) : graph_(graph) {}
   virtual ~HGraphVisitor() {}

   virtual void VisitInstruction(HInstruction* instruction) { UNUSED(instruction); }
   virtual void VisitBasicBlock(HBasicBlock* block);

   // Visit the graph following basic block insertion order.
   void VisitInsertionOrder();

   // Visit the graph following dominator tree reverse post-order.
   void VisitReversePostOrder();

   HGraph* GetGraph() const { return graph_; }

   // Visit functions for instruction classes.
 #define DECLARE_VISIT_INSTRUCTION(name, super)                                        \
   virtual void Visit##name(H##name* instr) { VisitInstruction(instr); }

   FOR_EACH_INSTRUCTION(DECLARE_VISIT_INSTRUCTION)

 #undef DECLARE_VISIT_INSTRUCTION

  private:
   HGraph* const graph_;

   DISALLOW_COPY_AND_ASSIGN(HGraphVisitor);
 };

 class HGraphDelegateVisitor : public HGraphVisitor {
  public:
   explicit HGraphDelegateVisitor(HGraph* graph) : HGraphVisitor(graph) {}
   virtual ~HGraphDelegateVisitor() {}

   // Visit functions that delegate to to super class.
 #define DECLARE_VISIT_INSTRUCTION(name, super)                                        \
   void Visit##name(H##name* instr) OVERRIDE { Visit##super(instr); }

   FOR_EACH_INSTRUCTION(DECLARE_VISIT_INSTRUCTION)

 #undef DECLARE_VISIT_INSTRUCTION

  private:
   DISALLOW_COPY_AND_ASSIGN(HGraphDelegateVisitor);
 };

 class HInsertionOrderIterator : public ValueObject {
  public:
   explicit HInsertionOrderIterator(const HGraph& graph) : graph_(graph), index_(0) {}

   bool Done() const { return index_ == graph_.GetBlocks().Size(); }
   HBasicBlock* Current() const { return graph_.GetBlocks().Get(index_); }
   void Advance() { ++index_; }

  private:
   const HGraph& graph_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HInsertionOrderIterator);
 };

 class HReversePostOrderIterator : public ValueObject {
  public:
   explicit HReversePostOrderIterator(const HGraph& graph) : graph_(graph), index_(0) {
     // Check that reverse post order of the graph has been built.
     DCHECK(!graph.GetReversePostOrder().IsEmpty());
   }

   bool Done() const { return index_ == graph_.GetReversePostOrder().Size(); }
   HBasicBlock* Current() const { return graph_.GetReversePostOrder().Get(index_); }
   void Advance() { ++index_; }

  private:
   const HGraph& graph_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HReversePostOrderIterator);
 };

 class HPostOrderIterator : public ValueObject {
  public:
   explicit HPostOrderIterator(const HGraph& graph)
       : graph_(graph), index_(graph_.GetReversePostOrder().Size()) {
     // Check that reverse post order of the graph has been built.
     DCHECK(!graph.GetReversePostOrder().IsEmpty());
   }

   bool Done() const { return index_ == 0; }
   HBasicBlock* Current() const { return graph_.GetReversePostOrder().Get(index_ - 1); }
   void Advance() { --index_; }

  private:
   const HGraph& graph_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HPostOrderIterator);
 };

 class HLinearPostOrderIterator : public ValueObject {
  public:
   explicit HLinearPostOrderIterator(const HGraph& graph)
       : order_(graph.GetLinearOrder()), index_(graph.GetLinearOrder().Size()) {}

   bool Done() const { return index_ == 0; }

   HBasicBlock* Current() const { return order_.Get(index_ -1); }

   void Advance() {
     --index_;
     DCHECK_GE(index_, 0U);
   }

  private:
   const GrowableArray<HBasicBlock*>& order_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HLinearPostOrderIterator);
 };

 class HLinearOrderIterator : public ValueObject {
  public:
   explicit HLinearOrderIterator(const HGraph& graph)
       : order_(graph.GetLinearOrder()), index_(0) {}

   bool Done() const { return index_ == order_.Size(); }
   HBasicBlock* Current() const { return order_.Get(index_); }
   void Advance() { ++index_; }

  private:
   const GrowableArray<HBasicBlock*>& order_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HLinearOrderIterator);
 };

 // Iterator over the blocks that art part of the loop. Includes blocks part
 // of an inner loop. The order in which the blocks are iterated is on their
 // block id.
 class HBlocksInLoopIterator : public ValueObject {
  public:
   explicit HBlocksInLoopIterator(const HLoopInformation& info)
       : blocks_in_loop_(info.GetBlocks()),
         blocks_(info.GetHeader()->GetGraph()->GetBlocks()),
         index_(0) {
     if (!blocks_in_loop_.IsBitSet(index_)) {
       Advance();
     }
   }

   bool Done() const { return index_ == blocks_.Size(); }
   HBasicBlock* Current() const { return blocks_.Get(index_); }
   void Advance() {
     ++index_;
     for (size_t e = blocks_.Size(); index_ < e; ++index_) {
       if (blocks_in_loop_.IsBitSet(index_)) {
         break;
       }
     }
   }

  private:
   const BitVector& blocks_in_loop_;
   const GrowableArray<HBasicBlock*>& blocks_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HBlocksInLoopIterator);
 };

 // Iterator over the blocks that art part of the loop. Includes blocks part
 // of an inner loop. The order in which the blocks are iterated is reverse
 // post order.
 class HBlocksInLoopReversePostOrderIterator : public ValueObject {
  public:
   explicit HBlocksInLoopReversePostOrderIterator(const HLoopInformation& info)
       : blocks_in_loop_(info.GetBlocks()),
         blocks_(info.GetHeader()->GetGraph()->GetReversePostOrder()),
         index_(0) {
     if (!blocks_in_loop_.IsBitSet(blocks_.Get(index_)->GetBlockId())) {
       Advance();
     }
   }

   bool Done() const { return index_ == blocks_.Size(); }
   HBasicBlock* Current() const { return blocks_.Get(index_); }
   void Advance() {
     ++index_;
     for (size_t e = blocks_.Size(); index_ < e; ++index_) {
       if (blocks_in_loop_.IsBitSet(blocks_.Get(index_)->GetBlockId())) {
         break;
       }
     }
   }

  private:
   const BitVector& blocks_in_loop_;
   const GrowableArray<HBasicBlock*>& blocks_;
   size_t index_;

   DISALLOW_COPY_AND_ASSIGN(HBlocksInLoopReversePostOrderIterator);
 };

 inline int64_t Int64FromConstant(HConstant* constant) {
   DCHECK(constant->IsIntConstant() || constant->IsLongConstant());
   return constant->IsIntConstant() ? constant->AsIntConstant()->GetValue()
                                    : constant->AsLongConstant()->GetValue();
 }

 }  // namespace art

 #endif  // ART_COMPILER_OPTIMIZING_NODES_H_