src/v8/src/interpreter/bytecode-generator.cc

// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/interpreter/bytecode-generator.h"

#include "src/api.h"
#include "src/ast/ast-source-ranges.h"
#include "src/ast/compile-time-value.h"
#include "src/ast/scopes.h"
#include "src/builtins/builtins-constructor.h"
#include "src/code-stubs.h"
#include "src/compilation-info.h"
#include "src/compiler.h"
#include "src/interpreter/bytecode-flags.h"
#include "src/interpreter/bytecode-jump-table.h"
#include "src/interpreter/bytecode-label.h"
#include "src/interpreter/bytecode-register-allocator.h"
#include "src/interpreter/control-flow-builders.h"
#include "src/objects-inl.h"
#include "src/objects/debug-objects.h"
#include "src/objects/literal-objects-inl.h"
#include "src/parsing/parse-info.h"
#include "src/parsing/token.h"

namespace v8 {
namespace internal {
namespace interpreter {

// Scoped class tracking context objects created by the visitor. Represents
// mutations of the context chain within the function body, allowing pushing and
// popping of the current {context_register} during visitation.
class BytecodeGenerator::ContextScope BASE_EMBEDDED {
 public:
  ContextScope(BytecodeGenerator* generator, Scope* scope)
      : generator_(generator),
        scope_(scope),
        outer_(generator_->execution_context()),
        register_(Register::current_context()),
        depth_(0) {
    DCHECK(scope->NeedsContext() || outer_ == nullptr);
    if (outer_) {
      depth_ = outer_->depth_ + 1;

      // Push the outer context into a new context register.
      Register outer_context_reg =
          generator_->register_allocator()->NewRegister();
      outer_->set_register(outer_context_reg);
      generator_->builder()->PushContext(outer_context_reg);
    }
    generator_->set_execution_context(this);
  }

  ~ContextScope() {
    if (outer_) {
      DCHECK_EQ(register_.index(), Register::current_context().index());
      generator_->builder()->PopContext(outer_->reg());
      outer_->set_register(register_);
    }
    generator_->set_execution_context(outer_);
  }

  // Returns the depth of the given |scope| for the current execution context.
  int ContextChainDepth(Scope* scope) {
    return scope_->ContextChainLength(scope);
  }

  // Returns the execution context at |depth| in the current context chain if it
  // is a function local execution context, otherwise returns nullptr.
  ContextScope* Previous(int depth) {
    if (depth > depth_) {
      return nullptr;
    }

    ContextScope* previous = this;
    for (int i = depth; i > 0; --i) {
      previous = previous->outer_;
    }
    return previous;
  }

  Register reg() const { return register_; }

 private:
  const BytecodeArrayBuilder* builder() const { return generator_->builder(); }

  void set_register(Register reg) { register_ = reg; }

  BytecodeGenerator* generator_;
  Scope* scope_;
  ContextScope* outer_;
  Register register_;
  int depth_;
};

// Scoped class for tracking control statements entered by the
// visitor. The pattern derives AstGraphBuilder::ControlScope.
class BytecodeGenerator::ControlScope BASE_EMBEDDED {
 public:
  explicit ControlScope(BytecodeGenerator* generator)
      : generator_(generator), outer_(generator->execution_control()),
        context_(generator->execution_context()) {
    generator_->set_execution_control(this);
  }
  virtual ~ControlScope() { generator_->set_execution_control(outer()); }

  void Break(Statement* stmt) {
    PerformCommand(CMD_BREAK, stmt, kNoSourcePosition);
  }
  void Continue(Statement* stmt) {
    PerformCommand(CMD_CONTINUE, stmt, kNoSourcePosition);
  }
  void ReturnAccumulator(int source_position = kNoSourcePosition) {
    PerformCommand(CMD_RETURN, nullptr, source_position);
  }
  void AsyncReturnAccumulator(int source_position = kNoSourcePosition) {
    PerformCommand(CMD_ASYNC_RETURN, nullptr, source_position);
  }

  class DeferredCommands;

 protected:
  enum Command {
    CMD_BREAK,
    CMD_CONTINUE,
    CMD_RETURN,
    CMD_ASYNC_RETURN,
    CMD_RETHROW
  };
  static constexpr bool CommandUsesAccumulator(Command command) {
    return command != CMD_BREAK && command != CMD_CONTINUE;
  }

  void PerformCommand(Command command, Statement* statement,
                      int source_position);
  virtual bool Execute(Command command, Statement* statement,
                       int source_position) = 0;

  // Helper to pop the context chain to a depth expected by this control scope.
  // Note that it is the responsibility of each individual {Execute} method to
  // trigger this when commands are handled and control-flow continues locally.
  void PopContextToExpectedDepth();

  BytecodeGenerator* generator() const { return generator_; }
  ControlScope* outer() const { return outer_; }
  ContextScope* context() const { return context_; }

 private:
  BytecodeGenerator* generator_;
  ControlScope* outer_;
  ContextScope* context_;

  DISALLOW_COPY_AND_ASSIGN(ControlScope);
};

// Helper class for a try-finally control scope. It can record intercepted
// control-flow commands that cause entry into a finally-block, and re-apply
// them after again leaving that block. Special tokens are used to identify
// paths going through the finally-block to dispatch after leaving the block.
class BytecodeGenerator::ControlScope::DeferredCommands final {
 public:
  DeferredCommands(BytecodeGenerator* generator, Register token_register,
                   Register result_register)
      : generator_(generator),
        deferred_(generator->zone()),
        token_register_(token_register),
        result_register_(result_register),
        return_token_(-1),
        async_return_token_(-1),
        rethrow_token_(-1) {}

  // One recorded control-flow command.
  struct Entry {
    Command command;       // The command type being applied on this path.
    Statement* statement;  // The target statement for the command or {nullptr}.
    int token;             // A token identifying this particular path.
  };

  // Records a control-flow command while entering the finally-block. This also
  // generates a new dispatch token that identifies one particular path. This
  // expects the result to be in the accumulator.
  void RecordCommand(Command command, Statement* statement) {
    int token = GetTokenForCommand(command, statement);

    DCHECK_LT(token, deferred_.size());
    DCHECK_EQ(deferred_[token].command, command);
    DCHECK_EQ(deferred_[token].statement, statement);
    DCHECK_EQ(deferred_[token].token, token);

    if (CommandUsesAccumulator(command)) {
      builder()->StoreAccumulatorInRegister(result_register_);
    }
    builder()->LoadLiteral(Smi::FromInt(token));
    builder()->StoreAccumulatorInRegister(token_register_);
    if (!CommandUsesAccumulator(command)) {
      // If we're not saving the accumulator in the result register, shove a
      // harmless value there instead so that it is still considered "killed" in
      // the liveness analysis. Normally we would LdaUndefined first, but the
      // Smi token value is just as good, and by reusing it we save a bytecode.
      builder()->StoreAccumulatorInRegister(result_register_);
    }
  }

  // Records the dispatch token to be used to identify the re-throw path when
  // the finally-block has been entered through the exception handler. This
  // expects the exception to be in the accumulator.
  void RecordHandlerReThrowPath() {
    // The accumulator contains the exception object.
    RecordCommand(CMD_RETHROW, nullptr);
  }

  // Records the dispatch token to be used to identify the implicit fall-through
  // path at the end of a try-block into the corresponding finally-block.
  void RecordFallThroughPath() {
    builder()->LoadLiteral(Smi::FromInt(-1));
    builder()->StoreAccumulatorInRegister(token_register_);
    // Since we're not saving the accumulator in the result register, shove a
    // harmless value there instead so that it is still considered "killed" in
    // the liveness analysis. Normally we would LdaUndefined first, but the Smi
    // token value is just as good, and by reusing it we save a bytecode.
    builder()->StoreAccumulatorInRegister(result_register_);
  }

  // Applies all recorded control-flow commands after the finally-block again.
  // This generates a dynamic dispatch on the token from the entry point.
  void ApplyDeferredCommands() {
    if (deferred_.size() == 0) return;

    BytecodeLabel fall_through;

    if (deferred_.size() == 1) {
      // For a single entry, just jump to the fallthrough if we don't match the
      // entry token.
      const Entry& entry = deferred_[0];

      builder()
          ->LoadLiteral(Smi::FromInt(entry.token))
          .CompareOperation(Token::EQ_STRICT, token_register_)
          .JumpIfFalse(ToBooleanMode::kAlreadyBoolean, &fall_through);

      if (CommandUsesAccumulator(entry.command)) {
        builder()->LoadAccumulatorWithRegister(result_register_);
      }
      execution_control()->PerformCommand(entry.command, entry.statement,
                                          kNoSourcePosition);
    } else {
      // For multiple entries, build a jump table and switch on the token,
      // jumping to the fallthrough if none of them match.

      BytecodeJumpTable* jump_table =
          builder()->AllocateJumpTable(static_cast<int>(deferred_.size()), 0);
      builder()
          ->LoadAccumulatorWithRegister(token_register_)
          .SwitchOnSmiNoFeedback(jump_table)
          .Jump(&fall_through);
      for (const Entry& entry : deferred_) {
        builder()->Bind(jump_table, entry.token);

        if (CommandUsesAccumulator(entry.command)) {
          builder()->LoadAccumulatorWithRegister(result_register_);
        }
        execution_control()->PerformCommand(entry.command, entry.statement,
                                            kNoSourcePosition);
      }
    }

    builder()->Bind(&fall_through);
  }

  BytecodeArrayBuilder* builder() { return generator_->builder(); }
  ControlScope* execution_control() { return generator_->execution_control(); }

 private:
  int GetTokenForCommand(Command command, Statement* statement) {
    switch (command) {
      case CMD_RETURN:
        return GetReturnToken();
      case CMD_ASYNC_RETURN:
        return GetAsyncReturnToken();
      case CMD_RETHROW:
        return GetRethrowToken();
      default:
        // TODO(leszeks): We could also search for entries with the same
        // command and statement.
        return GetNewTokenForCommand(command, statement);
    }
  }

  int GetReturnToken() {
    if (return_token_ == -1) {
      return_token_ = GetNewTokenForCommand(CMD_RETURN, nullptr);
    }
    return return_token_;
  }

  int GetAsyncReturnToken() {
    if (async_return_token_ == -1) {
      async_return_token_ = GetNewTokenForCommand(CMD_ASYNC_RETURN, nullptr);
    }
    return async_return_token_;
  }

  int GetRethrowToken() {
    if (rethrow_token_ == -1) {
      rethrow_token_ = GetNewTokenForCommand(CMD_RETHROW, nullptr);
    }
    return rethrow_token_;
  }

  int GetNewTokenForCommand(Command command, Statement* statement) {
    int token = static_cast<int>(deferred_.size());
    deferred_.push_back({command, statement, token});
    return token;
  }

  BytecodeGenerator* generator_;
  ZoneVector<Entry> deferred_;
  Register token_register_;
  Register result_register_;

  // Tokens for commands that don't need a statement.
  int return_token_;
  int async_return_token_;
  int rethrow_token_;
};

// Scoped class for dealing with control flow reaching the function level.
class BytecodeGenerator::ControlScopeForTopLevel final
    : public BytecodeGenerator::ControlScope {
 public:
  explicit ControlScopeForTopLevel(BytecodeGenerator* generator)
      : ControlScope(generator) {}

 protected:
  bool Execute(Command command, Statement* statement,
               int source_position) override {
    switch (command) {
      case CMD_BREAK:  // We should never see break/continue in top-level.
      case CMD_CONTINUE:
        UNREACHABLE();
      case CMD_RETURN:
        // No need to pop contexts, execution leaves the method body.
        generator()->BuildReturn(source_position);
        return true;
      case CMD_ASYNC_RETURN:
        // No need to pop contexts, execution leaves the method body.
        generator()->BuildAsyncReturn(source_position);
        return true;
      case CMD_RETHROW:
        // No need to pop contexts, execution leaves the method body.
        generator()->BuildReThrow();
        return true;
    }
    return false;
  }
};

// Scoped class for enabling break inside blocks and switch blocks.
class BytecodeGenerator::ControlScopeForBreakable final
    : public BytecodeGenerator::ControlScope {
 public:
  ControlScopeForBreakable(BytecodeGenerator* generator,
                           BreakableStatement* statement,
                           BreakableControlFlowBuilder* control_builder)
      : ControlScope(generator),
        statement_(statement),
        control_builder_(control_builder) {}

 protected:
  bool Execute(Command command, Statement* statement,
               int source_position) override {
    control_builder_->set_needs_continuation_counter();
    if (statement != statement_) return false;
    switch (command) {
      case CMD_BREAK:
        PopContextToExpectedDepth();
        control_builder_->Break();
        return true;
      case CMD_CONTINUE:
      case CMD_RETURN:
      case CMD_ASYNC_RETURN:
      case CMD_RETHROW:
        break;
    }
    return false;
  }

 private:
  Statement* statement_;
  BreakableControlFlowBuilder* control_builder_;
};

// Scoped class for enabling 'break' and 'continue' in iteration
// constructs, e.g. do...while, while..., for...
class BytecodeGenerator::ControlScopeForIteration final
    : public BytecodeGenerator::ControlScope {
 public:
  ControlScopeForIteration(BytecodeGenerator* generator,
                           IterationStatement* statement,
                           LoopBuilder* loop_builder)
      : ControlScope(generator),
        statement_(statement),
        loop_builder_(loop_builder) {
    generator->loop_depth_++;
  }
  ~ControlScopeForIteration() { generator()->loop_depth_--; }

 protected:
  bool Execute(Command command, Statement* statement,
               int source_position) override {
    if (statement != statement_) return false;
    switch (command) {
      case CMD_BREAK:
        PopContextToExpectedDepth();
        loop_builder_->Break();
        return true;
      case CMD_CONTINUE:
        PopContextToExpectedDepth();
        loop_builder_->Continue();
        return true;
      case CMD_RETURN:
      case CMD_ASYNC_RETURN:
      case CMD_RETHROW:
        break;
    }
    return false;
  }

 private:
  Statement* statement_;
  LoopBuilder* loop_builder_;
};

// Scoped class for enabling 'throw' in try-catch constructs.
class BytecodeGenerator::ControlScopeForTryCatch final
    : public BytecodeGenerator::ControlScope {
 public:
  ControlScopeForTryCatch(BytecodeGenerator* generator,
                          TryCatchBuilder* try_catch_builder)
      : ControlScope(generator) {}

 protected:
  bool Execute(Command command, Statement* statement,
               int source_position) override {
    switch (command) {
      case CMD_BREAK:
      case CMD_CONTINUE:
      case CMD_RETURN:
      case CMD_ASYNC_RETURN:
        break;
      case CMD_RETHROW:
        // No need to pop contexts, execution re-enters the method body via the
        // stack unwinding mechanism which itself restores contexts correctly.
        generator()->BuildReThrow();
        return true;
    }
    return false;
  }
};

// Scoped class for enabling control flow through try-finally constructs.
class BytecodeGenerator::ControlScopeForTryFinally final
    : public BytecodeGenerator::ControlScope {
 public:
  ControlScopeForTryFinally(BytecodeGenerator* generator,
                            TryFinallyBuilder* try_finally_builder,
                            DeferredCommands* commands)
      : ControlScope(generator),
        try_finally_builder_(try_finally_builder),
        commands_(commands) {}

 protected:
  bool Execute(Command command, Statement* statement,
               int source_position) override {
    switch (command) {
      case CMD_BREAK:
      case CMD_CONTINUE:
      case CMD_RETURN:
      case CMD_ASYNC_RETURN:
      case CMD_RETHROW:
        PopContextToExpectedDepth();
        // We don't record source_position here since we don't generate return
        // bytecode right here and will generate it later as part of finally
        // block. Each return bytecode generated in finally block will get own
        // return source position from corresponded return statement or we'll
        // use end of function if no return statement is presented.
        commands_->RecordCommand(command, statement);
        try_finally_builder_->LeaveTry();
        return true;
    }
    return false;
  }

 private:
  TryFinallyBuilder* try_finally_builder_;
  DeferredCommands* commands_;
};

// Allocate and fetch the coverage indices tracking NaryLogical Expressions.
class BytecodeGenerator::NaryCodeCoverageSlots {
 public:
  NaryCodeCoverageSlots(BytecodeGenerator* generator, NaryOperation* expr)
      : generator_(generator) {
    if (generator_->block_coverage_builder_ == nullptr) return;
    for (size_t i = 0; i < expr->subsequent_length(); i++) {
      coverage_slots_.push_back(
          generator_->AllocateNaryBlockCoverageSlotIfEnabled(expr, i));
    }
  }

  int GetSlotFor(size_t subsequent_expr_index) const {
    if (generator_->block_coverage_builder_ == nullptr) {
      return BlockCoverageBuilder::kNoCoverageArraySlot;
    }
    DCHECK(coverage_slots_.size() > subsequent_expr_index);
    return coverage_slots_[subsequent_expr_index];
  }

 private:
  BytecodeGenerator* generator_;
  std::vector<int> coverage_slots_;
};

void BytecodeGenerator::ControlScope::PerformCommand(Command command,
                                                     Statement* statement,
                                                     int source_position) {
  ControlScope* current = this;
  do {
    if (current->Execute(command, statement, source_position)) {
      return;
    }
    current = current->outer();
  } while (current != nullptr);
  UNREACHABLE();
}

void BytecodeGenerator::ControlScope::PopContextToExpectedDepth() {
  // Pop context to the expected depth. Note that this can in fact pop multiple
  // contexts at once because the {PopContext} bytecode takes a saved register.
  if (generator()->execution_context() != context()) {
    generator()->builder()->PopContext(context()->reg());
  }
}

class BytecodeGenerator::RegisterAllocationScope final {
 public:
  explicit RegisterAllocationScope(BytecodeGenerator* generator)
      : generator_(generator),
        outer_next_register_index_(
            generator->register_allocator()->next_register_index()) {}

  ~RegisterAllocationScope() {
    generator_->register_allocator()->ReleaseRegisters(
        outer_next_register_index_);
  }

 private:
  BytecodeGenerator* generator_;
  int outer_next_register_index_;

  DISALLOW_COPY_AND_ASSIGN(RegisterAllocationScope);
};

// Scoped base class for determining how the result of an expression will be
// used.
class BytecodeGenerator::ExpressionResultScope {
 public:
  ExpressionResultScope(BytecodeGenerator* generator, Expression::Context kind)
      : generator_(generator),
        outer_(generator->execution_result()),
        allocator_(generator),
        kind_(kind),
        type_hint_(TypeHint::kAny) {
    generator_->set_execution_result(this);
  }

  virtual ~ExpressionResultScope() {
    generator_->set_execution_result(outer_);
  }

  bool IsEffect() const { return kind_ == Expression::kEffect; }
  bool IsValue() const { return kind_ == Expression::kValue; }
  bool IsTest() const { return kind_ == Expression::kTest; }

  TestResultScope* AsTest() {
    DCHECK(IsTest());
    return reinterpret_cast<TestResultScope*>(this);
  }

  // Specify expression always returns a Boolean result value.
  void SetResultIsBoolean() {
    DCHECK_EQ(type_hint_, TypeHint::kAny);
    type_hint_ = TypeHint::kBoolean;
  }

  TypeHint type_hint() const { return type_hint_; }

 private:
  BytecodeGenerator* generator_;
  ExpressionResultScope* outer_;
  RegisterAllocationScope allocator_;
  Expression::Context kind_;
  TypeHint type_hint_;

  DISALLOW_COPY_AND_ASSIGN(ExpressionResultScope);
};

// Scoped class used when the result of the current expression is not
// expected to produce a result.
class BytecodeGenerator::EffectResultScope final
    : public ExpressionResultScope {
 public:
  explicit EffectResultScope(BytecodeGenerator* generator)
      : ExpressionResultScope(generator, Expression::kEffect) {}
};

// Scoped class used when the result of the current expression to be
// evaluated should go into the interpreter's accumulator.
class BytecodeGenerator::ValueResultScope final : public ExpressionResultScope {
 public:
  explicit ValueResultScope(BytecodeGenerator* generator)
      : ExpressionResultScope(generator, Expression::kValue) {}
};

// Scoped class used when the result of the current expression to be
// evaluated is only tested with jumps to two branches.
class BytecodeGenerator::TestResultScope final : public ExpressionResultScope {
 public:
  TestResultScope(BytecodeGenerator* generator, BytecodeLabels* then_labels,
                  BytecodeLabels* else_labels, TestFallthrough fallthrough)
      : ExpressionResultScope(generator, Expression::kTest),
        result_consumed_by_test_(false),
        fallthrough_(fallthrough),
        then_labels_(then_labels),
        else_labels_(else_labels) {}

  // Used when code special cases for TestResultScope and consumes any
  // possible value by testing and jumping to a then/else label.
  void SetResultConsumedByTest() {
    result_consumed_by_test_ = true;
  }
  bool result_consumed_by_test() { return result_consumed_by_test_; }

  // Inverts the control flow of the operation, swapping the then and else
  // labels and the fallthrough.
  void InvertControlFlow() {
    std::swap(then_labels_, else_labels_);
    fallthrough_ = inverted_fallthrough();
  }

  BytecodeLabel* NewThenLabel() { return then_labels_->New(); }
  BytecodeLabel* NewElseLabel() { return else_labels_->New(); }

  BytecodeLabels* then_labels() const { return then_labels_; }
  BytecodeLabels* else_labels() const { return else_labels_; }

  void set_then_labels(BytecodeLabels* then_labels) {
    then_labels_ = then_labels;
  }
  void set_else_labels(BytecodeLabels* else_labels) {
    else_labels_ = else_labels;
  }

  TestFallthrough fallthrough() const { return fallthrough_; }
  TestFallthrough inverted_fallthrough() const {
    switch (fallthrough_) {
      case TestFallthrough::kThen:
        return TestFallthrough::kElse;
      case TestFallthrough::kElse:
        return TestFallthrough::kThen;
      default:
        return TestFallthrough::kNone;
    }
  }
  void set_fallthrough(TestFallthrough fallthrough) {
    fallthrough_ = fallthrough;
  }

 private:
  bool result_consumed_by_test_;
  TestFallthrough fallthrough_;
  BytecodeLabels* then_labels_;
  BytecodeLabels* else_labels_;

  DISALLOW_COPY_AND_ASSIGN(TestResultScope);
};

// Used to build a list of global declaration initial value pairs.
class BytecodeGenerator::GlobalDeclarationsBuilder final : public ZoneObject {
 public:
  explicit GlobalDeclarationsBuilder(Zone* zone)
      : declarations_(0, zone),
        constant_pool_entry_(0),
        has_constant_pool_entry_(false) {}

  void AddFunctionDeclaration(const AstRawString* name, FeedbackSlot slot,
                              FeedbackSlot literal_slot,
                              FunctionLiteral* func) {
    DCHECK(!slot.IsInvalid());
    declarations_.push_back(Declaration(name, slot, literal_slot, func));
  }

  void AddUndefinedDeclaration(const AstRawString* name, FeedbackSlot slot) {
    DCHECK(!slot.IsInvalid());
    declarations_.push_back(Declaration(name, slot, nullptr));
  }

  Handle<FixedArray> AllocateDeclarations(CompilationInfo* info,
                                          Handle<Script> script,
                                          Isolate* isolate) {
    DCHECK(has_constant_pool_entry_);
    int array_index = 0;
    Handle<FixedArray> data = isolate->factory()->NewFixedArray(
        static_cast<int>(declarations_.size() * 4), TENURED);
    for (const Declaration& declaration : declarations_) {
      FunctionLiteral* func = declaration.func;
      Handle<Object> initial_value;
      if (func == nullptr) {
        initial_value = isolate->factory()->undefined_value();
      } else {
        initial_value = Compiler::GetSharedFunctionInfo(func, script, isolate);
      }

      // Return a null handle if any initial values can't be created. Caller
      // will set stack overflow.
      if (initial_value.is_null()) return Handle<FixedArray>();

      data->set(array_index++, *declaration.name->string());
      data->set(array_index++, Smi::FromInt(declaration.slot.ToInt()));
      Object* undefined_or_literal_slot;
      if (declaration.literal_slot.IsInvalid()) {
        undefined_or_literal_slot = isolate->heap()->undefined_value();
      } else {
        undefined_or_literal_slot =
            Smi::FromInt(declaration.literal_slot.ToInt());
      }
      data->set(array_index++, undefined_or_literal_slot);
      data->set(array_index++, *initial_value);
    }
    return data;
  }

  size_t constant_pool_entry() {
    DCHECK(has_constant_pool_entry_);
    return constant_pool_entry_;
  }

  void set_constant_pool_entry(size_t constant_pool_entry) {
    DCHECK(!empty());
    DCHECK(!has_constant_pool_entry_);
    constant_pool_entry_ = constant_pool_entry;
    has_constant_pool_entry_ = true;
  }

  bool empty() { return declarations_.empty(); }

 private:
  struct Declaration {
    Declaration() : slot(FeedbackSlot::Invalid()), func(nullptr) {}
    Declaration(const AstRawString* name, FeedbackSlot slot,
                FeedbackSlot literal_slot, FunctionLiteral* func)
        : name(name), slot(slot), literal_slot(literal_slot), func(func) {}
    Declaration(const AstRawString* name, FeedbackSlot slot,
                FunctionLiteral* func)
        : name(name),
          slot(slot),
          literal_slot(FeedbackSlot::Invalid()),
          func(func) {}

    const AstRawString* name;
    FeedbackSlot slot;
    FeedbackSlot literal_slot;
    FunctionLiteral* func;
  };
  ZoneVector<Declaration> declarations_;
  size_t constant_pool_entry_;
  bool has_constant_pool_entry_;
};

class BytecodeGenerator::CurrentScope final {
 public:
  CurrentScope(BytecodeGenerator* generator, Scope* scope)
      : generator_(generator), outer_scope_(generator->current_scope()) {
    if (scope != nullptr) {
      DCHECK_EQ(outer_scope_, scope->outer_scope());
      generator_->set_current_scope(scope);
    }
  }
  ~CurrentScope() {
    if (outer_scope_ != generator_->current_scope()) {
      generator_->set_current_scope(outer_scope_);
    }
  }

 private:
  BytecodeGenerator* generator_;
  Scope* outer_scope_;
};

class BytecodeGenerator::FeedbackSlotCache : public ZoneObject {
 public:
  typedef std::pair<TypeofMode, void*> Key;

  explicit FeedbackSlotCache(Zone* zone) : map_(zone) {}

  void Put(TypeofMode typeof_mode, Variable* variable, FeedbackSlot slot) {
    Key key = std::make_pair(typeof_mode, variable);
    auto entry = std::make_pair(key, slot);
    map_.insert(entry);
  }
  void Put(AstNode* node, FeedbackSlot slot) {
    Key key = std::make_pair(NOT_INSIDE_TYPEOF, node);
    auto entry = std::make_pair(key, slot);
    map_.insert(entry);
  }

  FeedbackSlot Get(TypeofMode typeof_mode, Variable* variable) const {
    Key key = std::make_pair(typeof_mode, variable);
    auto iter = map_.find(key);
    if (iter != map_.end()) {
      return iter->second;
    }
    return FeedbackSlot();
  }
  FeedbackSlot Get(AstNode* node) const {
    Key key = std::make_pair(NOT_INSIDE_TYPEOF, node);
    auto iter = map_.find(key);
    if (iter != map_.end()) {
      return iter->second;
    }
    return FeedbackSlot();
  }

 private:
  ZoneMap<Key, FeedbackSlot> map_;
};

class BytecodeGenerator::IteratorRecord final {
 public:
  IteratorRecord(Register object_register, Register next_register,
                 IteratorType type = IteratorType::kNormal)
      : type_(type), object_(object_register), next_(next_register) {
    DCHECK(object_.is_valid() && next_.is_valid());
  }

  inline IteratorType type() const { return type_; }
  inline Register object() const { return object_; }
  inline Register next() const { return next_; }

 private:
  IteratorType type_;
  Register object_;
  Register next_;
};

BytecodeGenerator::BytecodeGenerator(
    CompilationInfo* info, const AstStringConstants* ast_string_constants)
    : zone_(info->zone()),
      builder_(zone(), info->num_parameters_including_this(),
               info->scope()->num_stack_slots(), info->feedback_vector_spec(),
               info->SourcePositionRecordingMode()),
      info_(info),
      ast_string_constants_(ast_string_constants),
      closure_scope_(info->scope()),
      current_scope_(info->scope()),
      feedback_slot_cache_(new (zone()) FeedbackSlotCache(zone())),
      globals_builder_(new (zone()) GlobalDeclarationsBuilder(zone())),
      block_coverage_builder_(nullptr),
      global_declarations_(0, zone()),
      function_literals_(0, zone()),
      native_function_literals_(0, zone()),
      object_literals_(0, zone()),
      array_literals_(0, zone()),
      class_literals_(0, zone()),
      template_objects_(0, zone()),
      execution_control_(nullptr),
      execution_context_(nullptr),
      execution_result_(nullptr),
      incoming_new_target_or_generator_(),
      generator_jump_table_(nullptr),
      generator_state_(),
      loop_depth_(0),
      catch_prediction_(HandlerTable::UNCAUGHT) {
  DCHECK_EQ(closure_scope(), closure_scope()->GetClosureScope());
  if (info->has_source_range_map()) {
    block_coverage_builder_ = new (zone())
        BlockCoverageBuilder(zone(), builder(), info->source_range_map());
  }
}

Handle<BytecodeArray> BytecodeGenerator::FinalizeBytecode(
    Isolate* isolate, Handle<Script> script) {
  DCHECK(ThreadId::Current().Equals(isolate->thread_id()));

  AllocateDeferredConstants(isolate, script);

  if (block_coverage_builder_) {
    info()->set_coverage_info(
        isolate->factory()->NewCoverageInfo(block_coverage_builder_->slots()));
    if (FLAG_trace_block_coverage) {
      info()->coverage_info()->Print(info()->shared_info()->name());
    }
  }

  if (HasStackOverflow()) return Handle<BytecodeArray>();
  Handle<BytecodeArray> bytecode_array = builder()->ToBytecodeArray(isolate);

  if (incoming_new_target_or_generator_.is_valid()) {
    bytecode_array->set_incoming_new_target_or_generator_register(
        incoming_new_target_or_generator_);
  }

  return bytecode_array;
}

void BytecodeGenerator::AllocateDeferredConstants(Isolate* isolate,
                                                  Handle<Script> script) {
  // Build global declaration pair arrays.
  for (GlobalDeclarationsBuilder* globals_builder : global_declarations_) {
    Handle<FixedArray> declarations =
        globals_builder->AllocateDeclarations(info(), script, isolate);
    if (declarations.is_null()) return SetStackOverflow();
    builder()->SetDeferredConstantPoolEntry(
        globals_builder->constant_pool_entry(), declarations);
  }

  // Find or build shared function infos.
  for (std::pair<FunctionLiteral*, size_t> literal : function_literals_) {
    FunctionLiteral* expr = literal.first;
    Handle<SharedFunctionInfo> shared_info =
        Compiler::GetSharedFunctionInfo(expr, script, isolate);
    if (shared_info.is_null()) return SetStackOverflow();
    builder()->SetDeferredConstantPoolEntry(literal.second, shared_info);
  }

  // Find or build shared function infos for the native function templates.
  for (std::pair<NativeFunctionLiteral*, size_t> literal :
       native_function_literals_) {
    NativeFunctionLiteral* expr = literal.first;
    v8::Isolate* v8_isolate = reinterpret_cast<v8::Isolate*>(isolate);

    // Compute the function template for the native function.
    v8::Local<v8::FunctionTemplate> info =
        expr->extension()->GetNativeFunctionTemplate(
            v8_isolate, Utils::ToLocal(expr->name()));
    DCHECK(!info.IsEmpty());

    Handle<SharedFunctionInfo> shared_info =
        FunctionTemplateInfo::GetOrCreateSharedFunctionInfo(
            isolate, Utils::OpenHandle(*info), expr->name());
    DCHECK(!shared_info.is_null());
    builder()->SetDeferredConstantPoolEntry(literal.second, shared_info);
  }

  // Build object literal constant properties
  for (std::pair<ObjectLiteral*, size_t> literal : object_literals_) {
    ObjectLiteral* object_literal = literal.first;
    if (object_literal->properties_count() > 0) {
      // If constant properties is an empty fixed array, we've already added it
      // to the constant pool when visiting the object literal.
      Handle<BoilerplateDescription> constant_properties =
          object_literal->GetOrBuildConstantProperties(isolate);

      builder()->SetDeferredConstantPoolEntry(literal.second,
                                              constant_properties);
    }
  }

  // Build array literal constant elements
  for (std::pair<ArrayLiteral*, size_t> literal : array_literals_) {
    ArrayLiteral* array_literal = literal.first;
    Handle<ConstantElementsPair> constant_elements =
        array_literal->GetOrBuildConstantElements(isolate);
    builder()->SetDeferredConstantPoolEntry(literal.second, constant_elements);
  }

  // Build class literal boilerplates.
  for (std::pair<ClassLiteral*, size_t> literal : class_literals_) {
    ClassLiteral* class_literal = literal.first;
    Handle<ClassBoilerplate> class_boilerplate =
        ClassBoilerplate::BuildClassBoilerplate(isolate, class_literal);
    builder()->SetDeferredConstantPoolEntry(literal.second, class_boilerplate);
  }

  // Build template literals.
  for (std::pair<GetTemplateObject*, size_t> literal : template_objects_) {
    GetTemplateObject* get_template_object = literal.first;
    Handle<TemplateObjectDescription> description =
        get_template_object->GetOrBuildDescription(isolate);
    builder()->SetDeferredConstantPoolEntry(literal.second, description);
  }
}

void BytecodeGenerator::GenerateBytecode(uintptr_t stack_limit) {
  DisallowHeapAllocation no_allocation;
  DisallowHandleAllocation no_handles;
  DisallowHandleDereference no_deref;

  InitializeAstVisitor(stack_limit);

  // Initialize the incoming context.
  ContextScope incoming_context(this, closure_scope());

  // Initialize control scope.
  ControlScopeForTopLevel control(this);

  RegisterAllocationScope register_scope(this);

  AllocateTopLevelRegisters();

  if (info()->literal()->CanSuspend()) {
    BuildGeneratorPrologue();
  }

  if (closure_scope()->NeedsContext()) {
    // Push a new inner context scope for the function.
    BuildNewLocalActivationContext();
    ContextScope local_function_context(this, closure_scope());
    BuildLocalActivationContextInitialization();
    GenerateBytecodeBody();
  } else {
    GenerateBytecodeBody();
  }

  // Check that we are not falling off the end.
  DCHECK(!builder()->RequiresImplicitReturn());
}

void BytecodeGenerator::GenerateBytecodeBody() {
  // Build the arguments object if it is used.
  VisitArgumentsObject(closure_scope()->arguments());

  // Build rest arguments array if it is used.
  Variable* rest_parameter = closure_scope()->rest_parameter();
  VisitRestArgumentsArray(rest_parameter);

  // Build assignment to the function name or {.this_function}
  // variables if used.
  VisitThisFunctionVariable(closure_scope()->function_var());
  VisitThisFunctionVariable(closure_scope()->this_function_var());

  // Build assignment to {new.target} variable if it is used.
  VisitNewTargetVariable(closure_scope()->new_target_var());

  // Create a generator object if necessary and initialize the
  // {.generator_object} variable.
  if (info()->literal()->CanSuspend()) {
    BuildGeneratorObjectVariableInitialization();
  }

  // Emit tracing call if requested to do so.
  if (FLAG_trace) builder()->CallRuntime(Runtime::kTraceEnter);

  // Emit type profile call.
  if (info()->collect_type_profile()) {
    feedback_spec()->AddTypeProfileSlot();
    int num_parameters = closure_scope()->num_parameters();
    for (int i = 0; i < num_parameters; i++) {
      Register parameter(builder()->Parameter(i));
      builder()->LoadAccumulatorWithRegister(parameter).CollectTypeProfile(
          closure_scope()->parameter(i)->initializer_position());
    }
  }

  // Visit declarations within the function scope.
  VisitDeclarations(closure_scope()->declarations());

  // Emit initializing assignments for module namespace imports (if any).
  VisitModuleNamespaceImports();

  // Perform a stack-check before the body.
  builder()->StackCheck(info()->literal()->start_position());

  // The derived constructor case is handled in VisitCallSuper.
  if (IsBaseConstructor(function_kind()) &&
      info()->literal()->requires_instance_fields_initializer()) {
    BuildInstanceFieldInitialization(Register::function_closure(),
                                     builder()->Receiver());
  }

  // Visit statements in the function body.
  VisitStatements(info()->literal()->body());

  // Emit an implicit return instruction in case control flow can fall off the
  // end of the function without an explicit return being present on all paths.
  if (builder()->RequiresImplicitReturn()) {
    builder()->LoadUndefined();
    BuildReturn();
  }
}

void BytecodeGenerator::AllocateTopLevelRegisters() {
  if (info()->literal()->CanSuspend()) {
    // Allocate a register for generator_state_.
    generator_state_ = register_allocator()->NewRegister();
    // Either directly use generator_object_var or allocate a new register for
    // the incoming generator object.
    Variable* generator_object_var = closure_scope()->generator_object_var();
    if (generator_object_var->location() == VariableLocation::LOCAL) {
      incoming_new_target_or_generator_ =
          GetRegisterForLocalVariable(generator_object_var);
    } else {
      incoming_new_target_or_generator_ = register_allocator()->NewRegister();
    }
  } else if (closure_scope()->new_target_var()) {
    // Either directly use new_target_var or allocate a new register for
    // the incoming new target object.
    Variable* new_target_var = closure_scope()->new_target_var();
    if (new_target_var->location() == VariableLocation::LOCAL) {
      incoming_new_target_or_generator_ =
          GetRegisterForLocalVariable(new_target_var);
    } else {
      incoming_new_target_or_generator_ = register_allocator()->NewRegister();
    }
  }
}

void BytecodeGenerator::VisitIterationHeader(IterationStatement* stmt,
                                             LoopBuilder* loop_builder) {
  VisitIterationHeader(stmt->first_suspend_id(), stmt->suspend_count(),
                       loop_builder);
}

void BytecodeGenerator::VisitIterationHeader(int first_suspend_id,
                                             int suspend_count,
                                             LoopBuilder* loop_builder) {
  // Recall that suspend_count is always zero inside ordinary (i.e.
  // non-generator) functions.
  if (suspend_count == 0) {
    loop_builder->LoopHeader();
  } else {
    loop_builder->LoopHeaderInGenerator(&generator_jump_table_,
                                        first_suspend_id, suspend_count);

    // Perform state dispatch on the generator state, assuming this is a resume.
    builder()
        ->LoadAccumulatorWithRegister(generator_state_)
        .SwitchOnSmiNoFeedback(generator_jump_table_);

    // We fall through when the generator state is not in the jump table. If we
    // are not resuming, we want to fall through to the loop body.
    // TODO(leszeks): Only generate this test for debug builds, we can skip it
    // entirely in release assuming that the generator states is always valid.
    BytecodeLabel not_resuming;
    builder()
        ->LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
        .CompareOperation(Token::Value::EQ_STRICT, generator_state_)
        .JumpIfTrue(ToBooleanMode::kAlreadyBoolean, &not_resuming);

    // Otherwise this is an error.
    builder()->Abort(AbortReason::kInvalidJumpTableIndex);

    builder()->Bind(&not_resuming);
  }
}

void BytecodeGenerator::BuildGeneratorPrologue() {
  DCHECK_GT(info()->literal()->suspend_count(), 0);
  DCHECK(generator_state_.is_valid());
  DCHECK(generator_object().is_valid());
  generator_jump_table_ =
      builder()->AllocateJumpTable(info()->literal()->suspend_count(), 0);

  BytecodeLabel regular_call;
  builder()
      ->LoadAccumulatorWithRegister(generator_object())
      .JumpIfUndefined(&regular_call);

  // This is a resume call. Restore the current context and the registers,
  // then perform state dispatch.
  {
    RegisterAllocationScope register_scope(this);
    Register generator_context = register_allocator()->NewRegister();
    builder()
        ->CallRuntime(Runtime::kInlineGeneratorGetContext, generator_object())
        .PushContext(generator_context)
        .RestoreGeneratorState(generator_object())
        .StoreAccumulatorInRegister(generator_state_)
        .SwitchOnSmiNoFeedback(generator_jump_table_);
  }
  // We fall through when the generator state is not in the jump table.
  // TODO(leszeks): Only generate this for debug builds.
  builder()->Abort(AbortReason::kInvalidJumpTableIndex);

  // This is a regular call.
  builder()
      ->Bind(&regular_call)
      .LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
      .StoreAccumulatorInRegister(generator_state_);
  // Now fall through to the ordinary function prologue, after which we will run
  // into the generator object creation and other extra code inserted by the
  // parser.
}

void BytecodeGenerator::VisitBlock(Block* stmt) {
  // Visit declarations and statements.
  CurrentScope current_scope(this, stmt->scope());
  if (stmt->scope() != nullptr && stmt->scope()->NeedsContext()) {
    BuildNewLocalBlockContext(stmt->scope());
    ContextScope scope(this, stmt->scope());
    VisitBlockDeclarationsAndStatements(stmt);
  } else {
    VisitBlockDeclarationsAndStatements(stmt);
  }
}

void BytecodeGenerator::VisitBlockDeclarationsAndStatements(Block* stmt) {
  BlockBuilder block_builder(builder(), block_coverage_builder_, stmt);
  ControlScopeForBreakable execution_control(this, stmt, &block_builder);
  if (stmt->scope() != nullptr) {
    VisitDeclarations(stmt->scope()->declarations());
  }
  VisitStatements(stmt->statements());
}

void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
  Variable* variable = decl->proxy()->var();
  switch (variable->location()) {
    case VariableLocation::UNALLOCATED: {
      DCHECK(!variable->binding_needs_init());
      FeedbackSlot slot =
          GetCachedLoadGlobalICSlot(NOT_INSIDE_TYPEOF, variable);
      globals_builder()->AddUndefinedDeclaration(variable->raw_name(), slot);
      break;
    }
    case VariableLocation::LOCAL:
      if (variable->binding_needs_init()) {
        Register destination(builder()->Local(variable->index()));
        builder()->LoadTheHole().StoreAccumulatorInRegister(destination);
      }
      break;
    case VariableLocation::PARAMETER:
      if (variable->binding_needs_init()) {
        Register destination(builder()->Parameter(variable->index()));
        builder()->LoadTheHole().StoreAccumulatorInRegister(destination);
      }
      break;
    case VariableLocation::CONTEXT:
      if (variable->binding_needs_init()) {
        DCHECK_EQ(0, execution_context()->ContextChainDepth(variable->scope()));
        builder()->LoadTheHole().StoreContextSlot(execution_context()->reg(),
                                                  variable->index(), 0);
      }
      break;
    case VariableLocation::LOOKUP: {
      DCHECK_EQ(VAR, variable->mode());
      DCHECK(!variable->binding_needs_init());

      Register name = register_allocator()->NewRegister();

      builder()
          ->LoadLiteral(variable->raw_name())
          .StoreAccumulatorInRegister(name)
          .CallRuntime(Runtime::kDeclareEvalVar, name);
      break;
    }
    case VariableLocation::MODULE:
      if (variable->IsExport() && variable->binding_needs_init()) {
        builder()->LoadTheHole();
        BuildVariableAssignment(variable, Token::INIT, HoleCheckMode::kElided);
      }
      // Nothing to do for imports.
      break;
  }
}

void BytecodeGenerator::VisitFunctionDeclaration(FunctionDeclaration* decl) {
  Variable* variable = decl->proxy()->var();
  DCHECK(variable->mode() == LET || variable->mode() == VAR);
  switch (variable->location()) {
    case VariableLocation::UNALLOCATED: {
      FeedbackSlot slot =
          GetCachedLoadGlobalICSlot(NOT_INSIDE_TYPEOF, variable);
      FeedbackSlot literal_slot = GetCachedCreateClosureSlot(decl->fun());
      globals_builder()->AddFunctionDeclaration(variable->raw_name(), slot,
                                                literal_slot, decl->fun());
      break;
    }
    case VariableLocation::PARAMETER:
    case VariableLocation::LOCAL: {
      VisitForAccumulatorValue(decl->fun());
      BuildVariableAssignment(variable, Token::INIT, HoleCheckMode::kElided);
      break;
    }
    case VariableLocation::CONTEXT: {
      DCHECK_EQ(0, execution_context()->ContextChainDepth(variable->scope()));
      VisitForAccumulatorValue(decl->fun());
      builder()->StoreContextSlot(execution_context()->reg(), variable->index(),
                                  0);
      break;
    }
    case VariableLocation::LOOKUP: {
      RegisterList args = register_allocator()->NewRegisterList(2);
      builder()
          ->LoadLiteral(variable->raw_name())
          .StoreAccumulatorInRegister(args[0]);
      VisitForAccumulatorValue(decl->fun());
      builder()->StoreAccumulatorInRegister(args[1]).CallRuntime(
          Runtime::kDeclareEvalFunction, args);
      break;
    }
    case VariableLocation::MODULE:
      DCHECK_EQ(variable->mode(), LET);
      DCHECK(variable->IsExport());
      VisitForAccumulatorValue(decl->fun());
      BuildVariableAssignment(variable, Token::INIT, HoleCheckMode::kElided);
      break;
  }
}

void BytecodeGenerator::VisitModuleNamespaceImports() {
  if (!closure_scope()->is_module_scope()) return;

  RegisterAllocationScope register_scope(this);
  Register module_request = register_allocator()->NewRegister();

  ModuleDescriptor* descriptor = closure_scope()->AsModuleScope()->module();
  for (auto entry : descriptor->namespace_imports()) {
    builder()
        ->LoadLiteral(Smi::FromInt(entry->module_request))
        .StoreAccumulatorInRegister(module_request)
        .CallRuntime(Runtime::kGetModuleNamespace, module_request);
    Variable* var = closure_scope()->LookupLocal(entry->local_name);
    DCHECK_NOT_NULL(var);
    BuildVariableAssignment(var, Token::INIT, HoleCheckMode::kElided);
  }
}

void BytecodeGenerator::VisitDeclarations(Declaration::List* declarations) {
  RegisterAllocationScope register_scope(this);
  DCHECK(globals_builder()->empty());
  for (Declaration* decl : *declarations) {
    RegisterAllocationScope register_scope(this);
    Visit(decl);
  }
  if (globals_builder()->empty()) return;

  globals_builder()->set_constant_pool_entry(
      builder()->AllocateDeferredConstantPoolEntry());
  int encoded_flags = info()->GetDeclareGlobalsFlags();

  // Emit code to declare globals.
  RegisterList args = register_allocator()->NewRegisterList(3);
  builder()
      ->LoadConstantPoolEntry(globals_builder()->constant_pool_entry())
      .StoreAccumulatorInRegister(args[0])
      .LoadLiteral(Smi::FromInt(encoded_flags))
      .StoreAccumulatorInRegister(args[1])
      .MoveRegister(Register::function_closure(), args[2])
      .CallRuntime(Runtime::kDeclareGlobalsForInterpreter, args);

  // Push and reset globals builder.
  global_declarations_.push_back(globals_builder());
  globals_builder_ = new (zone()) GlobalDeclarationsBuilder(zone());
}

void BytecodeGenerator::VisitStatements(ZoneList<Statement*>* statements) {
  for (int i = 0; i < statements->length(); i++) {
    // Allocate an outer register allocations scope for the statement.
    RegisterAllocationScope allocation_scope(this);
    Statement* stmt = statements->at(i);
    Visit(stmt);
    if (stmt->IsJump()) break;
  }
}

void BytecodeGenerator::VisitExpressionStatement(ExpressionStatement* stmt) {
  builder()->SetStatementPosition(stmt);
  VisitForEffect(stmt->expression());
}

void BytecodeGenerator::VisitEmptyStatement(EmptyStatement* stmt) {
}

void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) {
  ConditionalControlFlowBuilder conditional_builder(
      builder(), block_coverage_builder_, stmt);
  builder()->SetStatementPosition(stmt);

  if (stmt->condition()->ToBooleanIsTrue()) {
    // Generate then block unconditionally as always true.
    conditional_builder.Then();
    Visit(stmt->then_statement());
  } else if (stmt->condition()->ToBooleanIsFalse()) {
    // Generate else block unconditionally if it exists.
    if (stmt->HasElseStatement()) {
      conditional_builder.Else();
      Visit(stmt->else_statement());
    }
  } else {
    // TODO(oth): If then statement is BreakStatement or
    // ContinueStatement we can reduce number of generated
    // jump/jump_ifs here. See BasicLoops test.
    VisitForTest(stmt->condition(), conditional_builder.then_labels(),
                 conditional_builder.else_labels(), TestFallthrough::kThen);

    conditional_builder.Then();
    Visit(stmt->then_statement());

    if (stmt->HasElseStatement()) {
      conditional_builder.JumpToEnd();
      conditional_builder.Else();
      Visit(stmt->else_statement());
    }
  }
}

void BytecodeGenerator::VisitSloppyBlockFunctionStatement(
    SloppyBlockFunctionStatement* stmt) {
  Visit(stmt->statement());
}

void BytecodeGenerator::VisitContinueStatement(ContinueStatement* stmt) {
  AllocateBlockCoverageSlotIfEnabled(stmt, SourceRangeKind::kContinuation);
  builder()->SetStatementPosition(stmt);
  execution_control()->Continue(stmt->target());
}

void BytecodeGenerator::VisitBreakStatement(BreakStatement* stmt) {
  AllocateBlockCoverageSlotIfEnabled(stmt, SourceRangeKind::kContinuation);
  builder()->SetStatementPosition(stmt);
  execution_control()->Break(stmt->target());
}

void BytecodeGenerator::VisitReturnStatement(ReturnStatement* stmt) {
  AllocateBlockCoverageSlotIfEnabled(stmt, SourceRangeKind::kContinuation);
  builder()->SetStatementPosition(stmt);
  VisitForAccumulatorValue(stmt->expression());
  if (stmt->is_async_return()) {
    execution_control()->AsyncReturnAccumulator(stmt->end_position());
  } else {
    execution_control()->ReturnAccumulator(stmt->end_position());
  }
}

void BytecodeGenerator::VisitWithStatement(WithStatement* stmt) {
  builder()->SetStatementPosition(stmt);
  VisitForAccumulatorValue(stmt->expression());
  BuildNewLocalWithContext(stmt->scope());
  VisitInScope(stmt->statement(), stmt->scope());
}

void BytecodeGenerator::VisitSwitchStatement(SwitchStatement* stmt) {
  // We need this scope because we visit for register values. We have to
  // maintain a execution result scope where registers can be allocated.
  ZoneList<CaseClause*>* clauses = stmt->cases();
  SwitchBuilder switch_builder(builder(), block_coverage_builder_, stmt,
                               clauses->length());
  ControlScopeForBreakable scope(this, stmt, &switch_builder);
  int default_index = -1;

  builder()->SetStatementPosition(stmt);

  // Keep the switch value in a register until a case matches.
  Register tag = VisitForRegisterValue(stmt->tag());
  FeedbackSlot slot = clauses->length() > 0
                          ? feedback_spec()->AddCompareICSlot()
                          : FeedbackSlot::Invalid();

  // Iterate over all cases and create nodes for label comparison.
  for (int i = 0; i < clauses->length(); i++) {
    CaseClause* clause = clauses->at(i);

    // The default is not a test, remember index.
    if (clause->is_default()) {
      default_index = i;
      continue;
    }

    // Perform label comparison as if via '===' with tag.
    VisitForAccumulatorValue(clause->label());
    builder()->CompareOperation(Token::Value::EQ_STRICT, tag,
                                feedback_index(slot));
    switch_builder.Case(ToBooleanMode::kAlreadyBoolean, i);
  }

  if (default_index >= 0) {
    // Emit default jump if there is a default case.
    switch_builder.DefaultAt(default_index);
  } else {
    // Otherwise if we have reached here none of the cases matched, so jump to
    // the end.
    switch_builder.Break();
  }

  // Iterate over all cases and create the case bodies.
  for (int i = 0; i < clauses->length(); i++) {
    CaseClause* clause = clauses->at(i);
    switch_builder.SetCaseTarget(i, clause);
    VisitStatements(clause->statements());
  }
}

void BytecodeGenerator::VisitIterationBody(IterationStatement* stmt,
                                           LoopBuilder* loop_builder) {
  loop_builder->LoopBody();
  ControlScopeForIteration execution_control(this, stmt, loop_builder);
  builder()->StackCheck(stmt->position());
  Visit(stmt->body());
  loop_builder->BindContinueTarget();
}

void BytecodeGenerator::VisitDoWhileStatement(DoWhileStatement* stmt) {
  LoopBuilder loop_builder(builder(), block_coverage_builder_, stmt);
  if (stmt->cond()->ToBooleanIsFalse()) {
    VisitIterationBody(stmt, &loop_builder);
  } else if (stmt->cond()->ToBooleanIsTrue()) {
    VisitIterationHeader(stmt, &loop_builder);
    VisitIterationBody(stmt, &loop_builder);
    loop_builder.JumpToHeader(loop_depth_);
  } else {
    VisitIterationHeader(stmt, &loop_builder);
    VisitIterationBody(stmt, &loop_builder);
    builder()->SetExpressionAsStatementPosition(stmt->cond());
    BytecodeLabels loop_backbranch(zone());
    VisitForTest(stmt->cond(), &loop_backbranch, loop_builder.break_labels(),
                 TestFallthrough::kThen);
    loop_backbranch.Bind(builder());
    loop_builder.JumpToHeader(loop_depth_);
  }
}

void BytecodeGenerator::VisitWhileStatement(WhileStatement* stmt) {
  LoopBuilder loop_builder(builder(), block_coverage_builder_, stmt);

  if (stmt->cond()->ToBooleanIsFalse()) {
    // If the condition is false there is no need to generate the loop.
    return;
  }

  VisitIterationHeader(stmt, &loop_builder);
  if (!stmt->cond()->ToBooleanIsTrue()) {
    builder()->SetExpressionAsStatementPosition(stmt->cond());
    BytecodeLabels loop_body(zone());
    VisitForTest(stmt->cond(), &loop_body, loop_builder.break_labels(),
                 TestFallthrough::kThen);
    loop_body.Bind(builder());
  }
  VisitIterationBody(stmt, &loop_builder);
  loop_builder.JumpToHeader(loop_depth_);
}

void BytecodeGenerator::VisitForStatement(ForStatement* stmt) {
  LoopBuilder loop_builder(builder(), block_coverage_builder_, stmt);

  if (stmt->init() != nullptr) {
    Visit(stmt->init());
  }
  if (stmt->cond() && stmt->cond()->ToBooleanIsFalse()) {
    // If the condition is known to be false there is no need to generate
    // body, next or condition blocks. Init block should be generated.
    return;
  }

  VisitIterationHeader(stmt, &loop_builder);
  if (stmt->cond() && !stmt->cond()->ToBooleanIsTrue()) {
    builder()->SetExpressionAsStatementPosition(stmt->cond());
    BytecodeLabels loop_body(zone());
    VisitForTest(stmt->cond(), &loop_body, loop_builder.break_labels(),
                 TestFallthrough::kThen);
    loop_body.Bind(builder());
  }
  VisitIterationBody(stmt, &loop_builder);
  if (stmt->next() != nullptr) {
    builder()->SetStatementPosition(stmt->next());
    Visit(stmt->next());
  }
  loop_builder.JumpToHeader(loop_depth_);
}

void BytecodeGenerator::VisitForInAssignment(Expression* expr) {
  DCHECK(expr->IsValidReferenceExpression());

  // Evaluate assignment starting with the value to be stored in the
  // accumulator.
  Property* property = expr->AsProperty();
  LhsKind assign_type = Property::GetAssignType(property);
  switch (assign_type) {
    case VARIABLE: {
      VariableProxy* proxy = expr->AsVariableProxy();
      BuildVariableAssignment(proxy->var(), Token::ASSIGN,
                              proxy->hole_check_mode());
      break;
    }
    case NAMED_PROPERTY: {
      RegisterAllocationScope register_scope(this);
      Register value = register_allocator()->NewRegister();
      builder()->StoreAccumulatorInRegister(value);
      Register object = VisitForRegisterValue(property->obj());
      const AstRawString* name =
          property->key()->AsLiteral()->AsRawPropertyName();
      builder()->LoadAccumulatorWithRegister(value);
      FeedbackSlot slot = feedback_spec()->AddStoreICSlot(language_mode());
      builder()->StoreNamedProperty(object, name, feedback_index(slot),
                                    language_mode());
      builder()->LoadAccumulatorWithRegister(value);
      break;
    }
    case KEYED_PROPERTY: {
      RegisterAllocationScope register_scope(this);
      Register value = register_allocator()->NewRegister();
      builder()->StoreAccumulatorInRegister(value);
      Register object = VisitForRegisterValue(property->obj());
      Register key = VisitForRegisterValue(property->key());
      builder()->LoadAccumulatorWithRegister(value);
      FeedbackSlot slot = feedback_spec()->AddKeyedStoreICSlot(language_mode());
      builder()->StoreKeyedProperty(object, key, feedback_index(slot),
                                    language_mode());
      builder()->LoadAccumulatorWithRegister(value);
      break;
    }
    case NAMED_SUPER_PROPERTY: {
      RegisterAllocationScope register_scope(this);
      RegisterList args = register_allocator()->NewRegisterList(4);
      builder()->StoreAccumulatorInRegister(args[3]);
      SuperPropertyReference* super_property =
          property->obj()->AsSuperPropertyReference();
      VisitForRegisterValue(super_property->this_var(), args[0]);
      VisitForRegisterValue(super_property->home_object(), args[1]);
      builder()
          ->LoadLiteral(property->key()->AsLiteral()->AsRawPropertyName())
          .StoreAccumulatorInRegister(args[2])
          .CallRuntime(StoreToSuperRuntimeId(), args);
      break;
    }
    case KEYED_SUPER_PROPERTY: {
      RegisterAllocationScope register_scope(this);
      RegisterList args = register_allocator()->NewRegisterList(4);
      builder()->StoreAccumulatorInRegister(args[3]);
      SuperPropertyReference* super_property =
          property->obj()->AsSuperPropertyReference();
      VisitForRegisterValue(super_property->this_var(), args[0]);
      VisitForRegisterValue(super_property->home_object(), args[1]);
      VisitForRegisterValue(property->key(), args[2]);
      builder()->CallRuntime(StoreKeyedToSuperRuntimeId(), args);
      break;
    }
  }
}

void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
  if (stmt->subject()->IsNullLiteral() ||
      stmt->subject()->IsUndefinedLiteral()) {
    // ForIn generates lots of code, skip if it wouldn't produce any effects.
    return;
  }

  BytecodeLabel subject_null_label, subject_undefined_label;
  FeedbackSlot slot = feedback_spec()->AddForInSlot();

  // Prepare the state for executing ForIn.
  builder()->SetExpressionAsStatementPosition(stmt->subject());
  VisitForAccumulatorValue(stmt->subject());
  builder()->JumpIfUndefined(&subject_undefined_label);
  builder()->JumpIfNull(&subject_null_label);
  Register receiver = register_allocator()->NewRegister();
  builder()->ToObject(receiver);

  // Used as kRegTriple and kRegPair in ForInPrepare and ForInNext.
  RegisterList triple = register_allocator()->NewRegisterList(3);
  Register cache_length = triple[2];
  builder()->ForInEnumerate(receiver);
  builder()->ForInPrepare(triple, feedback_index(slot));

  // Set up loop counter
  Register index = register_allocator()->NewRegister();
  builder()->LoadLiteral(Smi::kZero);
  builder()->StoreAccumulatorInRegister(index);

  // The loop
  {
    LoopBuilder loop_builder(builder(), block_coverage_builder_, stmt);
    VisitIterationHeader(stmt, &loop_builder);
    builder()->SetExpressionAsStatementPosition(stmt->each());
    builder()->ForInContinue(index, cache_length);
    loop_builder.BreakIfFalse(ToBooleanMode::kAlreadyBoolean);
    builder()->ForInNext(receiver, index, triple.Truncate(2),
                         feedback_index(slot));
    loop_builder.ContinueIfUndefined();
    VisitForInAssignment(stmt->each());
    VisitIterationBody(stmt, &loop_builder);
    builder()->ForInStep(index);
    builder()->StoreAccumulatorInRegister(index);
    loop_builder.JumpToHeader(loop_depth_);
  }
  builder()->Bind(&subject_null_label);
  builder()->Bind(&subject_undefined_label);
}

void BytecodeGenerator::VisitForOfStatement(ForOfStatement* stmt) {
  LoopBuilder loop_builder(builder(), block_coverage_builder_, stmt);

  builder()->SetExpressionAsStatementPosition(stmt->assign_iterator());
  VisitForEffect(stmt->assign_iterator());
  VisitForEffect(stmt->assign_next());

  VisitIterationHeader(stmt, &loop_builder);
  builder()->SetExpressionAsStatementPosition(stmt->next_result());
  VisitForEffect(stmt->next_result());
  TypeHint type_hint = VisitForAccumulatorValue(stmt->result_done());
  loop_builder.BreakIfTrue(ToBooleanModeFromTypeHint(type_hint));

  VisitForEffect(stmt->assign_each());
  VisitIterationBody(stmt, &loop_builder);
  loop_builder.JumpToHeader(loop_depth_);
}

void BytecodeGenerator::VisitTryCatchStatement(TryCatchStatement* stmt) {
  // Update catch prediction tracking. The updated catch_prediction value lasts
  // until the end of the try_block in the AST node, and does not apply to the
  // catch_block.
  HandlerTable::CatchPrediction outer_catch_prediction = catch_prediction();
  set_catch_prediction(stmt->GetCatchPrediction(outer_catch_prediction));

  TryCatchBuilder try_control_builder(builder(), block_coverage_builder_, stmt,
                                      catch_prediction());

  // Preserve the context in a dedicated register, so that it can be restored
  // when the handler is entered by the stack-unwinding machinery.
  // TODO(mstarzinger): Be smarter about register allocation.
  Register context = register_allocator()->NewRegister();
  builder()->MoveRegister(Register::current_context(), context);

  // Evaluate the try-block inside a control scope. This simulates a handler
  // that is intercepting 'throw' control commands.
  try_control_builder.BeginTry(context);
  {
    ControlScopeForTryCatch scope(this, &try_control_builder);
    Visit(stmt->try_block());
    set_catch_prediction(outer_catch_prediction);
  }
  try_control_builder.EndTry();

  if (stmt->scope()) {
    // Create a catch scope that binds the exception.
    BuildNewLocalCatchContext(stmt->scope());
    builder()->StoreAccumulatorInRegister(context);
  }

  // If requested, clear message object as we enter the catch block.
  if (stmt->ShouldClearPendingException(outer_catch_prediction)) {
    builder()->LoadTheHole().SetPendingMessage();
  }

  // Load the catch context into the accumulator.
  builder()->LoadAccumulatorWithRegister(context);

  // Evaluate the catch-block.
  if (stmt->scope()) {
    VisitInScope(stmt->catch_block(), stmt->scope());
  } else {
    VisitBlock(stmt->catch_block());
  }
  try_control_builder.EndCatch();
}

void BytecodeGenerator::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
  // We can't know whether the finally block will override ("catch") an
  // exception thrown in the try block, so we just adopt the outer prediction.
  TryFinallyBuilder try_control_builder(builder(), block_coverage_builder_,
                                        stmt, catch_prediction());

  // We keep a record of all paths that enter the finally-block to be able to
  // dispatch to the correct continuation point after the statements in the
  // finally-block have been evaluated.
  //
  // The try-finally construct can enter the finally-block in three ways:
  // 1. By exiting the try-block normally, falling through at the end.
  // 2. By exiting the try-block with a function-local control flow transfer
  //    (i.e. through break/continue/return statements).
  // 3. By exiting the try-block with a thrown exception.
  //
  // The result register semantics depend on how the block was entered:
  //  - ReturnStatement: It represents the return value being returned.
  //  - ThrowStatement: It represents the exception being thrown.
  //  - BreakStatement/ContinueStatement: Undefined and not used.
  //  - Falling through into finally-block: Undefined and not used.
  Register token = register_allocator()->NewRegister();
  Register result = register_allocator()->NewRegister();
  ControlScope::DeferredCommands commands(this, token, result);

  // Preserve the context in a dedicated register, so that it can be restored
  // when the handler is entered by the stack-unwinding machinery.
  // TODO(mstarzinger): Be smarter about register allocation.
  Register context = register_allocator()->NewRegister();
  builder()->MoveRegister(Register::current_context(), context);

  // Evaluate the try-block inside a control scope. This simulates a handler
  // that is intercepting all control commands.
  try_control_builder.BeginTry(context);
  {
    ControlScopeForTryFinally scope(this, &try_control_builder, &commands);
    Visit(stmt->try_block());
  }
  try_control_builder.EndTry();

  // Record fall-through and exception cases.
  commands.RecordFallThroughPath();
  try_control_builder.LeaveTry();
  try_control_builder.BeginHandler();
  commands.RecordHandlerReThrowPath();

  // Pending message object is saved on entry.
  try_control_builder.BeginFinally();
  Register message = context;  // Reuse register.

  // Clear message object as we enter the finally block.
  builder()->LoadTheHole().SetPendingMessage().StoreAccumulatorInRegister(
      message);

  // Evaluate the finally-block.
  Visit(stmt->finally_block());
  try_control_builder.EndFinally();

  // Pending message object is restored on exit.
  builder()->LoadAccumulatorWithRegister(message).SetPendingMessage();

  // Dynamic dispatch after the finally-block.
  commands.ApplyDeferredCommands();
}

void BytecodeGenerator::VisitDebuggerStatement(DebuggerStatement* stmt) {
  builder()->SetStatementPosition(stmt);
  builder()->Debugger();
}

void BytecodeGenerator::VisitFunctionLiteral(FunctionLiteral* expr) {
  DCHECK(expr->scope()->outer_scope() == current_scope());
  uint8_t flags = CreateClosureFlags::Encode(
      expr->pretenure(), closure_scope()->is_function_scope());
  size_t entry = builder()->AllocateDeferredConstantPoolEntry();
  FeedbackSlot slot = GetCachedCreateClosureSlot(expr);
  builder()->CreateClosure(entry, feedback_index(slot), flags);
  function_literals_.push_back(std::make_pair(expr, entry));
}

void BytecodeGenerator::BuildClassLiteral(ClassLiteral* expr) {
  size_t class_boilerplate_entry =
      builder()->AllocateDeferredConstantPoolEntry();
  class_literals_.push_back(std::make_pair(expr, class_boilerplate_entry));

  VisitDeclarations(expr->scope()->declarations());
  Register class_constructor = register_allocator()->NewRegister();

  {
    RegisterAllocationScope register_scope(this);
    RegisterList args = register_allocator()->NewGrowableRegisterList();

    Register class_boilerplate = register_allocator()->GrowRegisterList(&args);
    Register class_constructor_in_args =
        register_allocator()->GrowRegisterList(&args);
    Register super_class = register_allocator()->GrowRegisterList(&args);
    DCHECK_EQ(ClassBoilerplate::kFirstDynamicArgumentIndex,
              args.register_count());

    VisitForAccumulatorValueOrTheHole(expr->extends());
    builder()->StoreAccumulatorInRegister(super_class);

    VisitFunctionLiteral(expr->constructor());
    builder()
        ->StoreAccumulatorInRegister(class_constructor)
        .MoveRegister(class_constructor, class_constructor_in_args)
        .LoadConstantPoolEntry(class_boilerplate_entry)
        .StoreAccumulatorInRegister(class_boilerplate);

    // Create computed names and method values nodes to store into the literal.
    for (int i = 0; i < expr->properties()->length(); i++) {
      ClassLiteral::Property* property = expr->properties()->at(i);
      if (property->is_computed_name()) {
        Register key = register_allocator()->GrowRegisterList(&args);

        BuildLoadPropertyKey(property, key);
        if (property->is_static()) {
          // The static prototype property is read only. We handle the non
          // computed property name case in the parser. Since this is the only
          // case where we need to check for an own read only property we
          // special case this so we do not need to do this for every property.
          BytecodeLabel done;
          builder()
              ->LoadLiteral(ast_string_constants()->prototype_string())
              .CompareOperation(Token::Value::EQ_STRICT, key)
              .JumpIfFalse(ToBooleanMode::kAlreadyBoolean, &done)
              .CallRuntime(Runtime::kThrowStaticPrototypeError)
              .Bind(&done);
        }

        if (property->kind() == ClassLiteral::Property::FIELD) {
          // Initialize field's name variable with the computed name.
          DCHECK_NOT_NULL(property->computed_name_var());
          builder()->LoadAccumulatorWithRegister(key);
          BuildVariableAssignment(property->computed_name_var(), Token::INIT,
                                  HoleCheckMode::kElided);
        }
      }
      if (property->kind() == ClassLiteral::Property::FIELD) {
        // We don't compute field's value here, but instead do it in the
        // initializer function.
        continue;
      }
      Register value = register_allocator()->GrowRegisterList(&args);
      VisitForRegisterValue(property->value(), value);
    }

    builder()->CallRuntime(Runtime::kDefineClass, args);
  }
  Register prototype = register_allocator()->NewRegister();
  builder()->StoreAccumulatorInRegister(prototype);

  // Assign to class variable.
  if (expr->class_variable() != nullptr) {
    DCHECK(expr->class_variable()->IsStackLocal() ||
           expr->class_variable()->IsContextSlot());
    builder()->LoadAccumulatorWithRegister(class_constructor);
    BuildVariableAssignment(expr->class_variable(), Token::INIT,
                            HoleCheckMode::kElided);
  }

  if (expr->instance_fields_initializer_function() != nullptr) {
    Register initializer =
        VisitForRegisterValue(expr->instance_fields_initializer_function());

    if (FunctionLiteral::NeedsHomeObject(
            expr->instance_fields_initializer_function())) {
      FeedbackSlot slot = feedback_spec()->AddStoreICSlot(language_mode());
      builder()->LoadAccumulatorWithRegister(prototype).StoreHomeObjectProperty(
          initializer, feedback_index(slot), language_mode());
    }

    FeedbackSlot slot = feedback_spec()->AddStoreICSlot(language_mode());
    builder()
        ->LoadAccumulatorWithRegister(initializer)
        .StoreClassFieldsInitializer(class_constructor, feedback_index(slot))
        .LoadAccumulatorWithRegister(class_constructor);
  }

  if (expr->static_fields_initializer() != nullptr) {
    RegisterList args = register_allocator()->NewRegisterList(1);
    Register initializer =
        VisitForRegisterValue(expr->static_fields_initializer());

    if (FunctionLiteral::NeedsHomeObject(expr->static_fields_initializer())) {
      FeedbackSlot slot = feedback_spec()->AddStoreICSlot(language_mode());
      builder()
          ->LoadAccumulatorWithRegister(class_constructor)
          .StoreHomeObjectProperty(initializer, feedback_index(slot),
                                   language_mode());
    }

    builder()
        ->MoveRegister(class_constructor, args[0])
        .CallProperty(initializer, args,
                      feedback_index(feedback_spec()->AddCallICSlot()));
  }
  builder()->LoadAccumulatorWithRegister(class_constructor);
}

void BytecodeGenerator::VisitClassLiteral(ClassLiteral* expr) {
  CurrentScope current_scope(this, expr->scope());
  DCHECK_NOT_NULL(expr->scope());
  if (expr->scope()->NeedsContext()) {
    BuildNewLocalBlockContext(expr->scope());
    ContextScope scope(this, expr->scope());
    BuildClassLiteral(expr);
  } else {
    BuildClassLiteral(expr);
  }
}

void BytecodeGenerator::VisitInitializeClassFieldsStatement(
    InitializeClassFieldsStatement* expr) {
  RegisterList args = register_allocator()->NewRegisterList(3);
  Register constructor = args[0], key = args[1], value = args[2];
  builder()->MoveRegister(builder()->Receiver(), constructor);

  for (int i = 0; i < expr->fields()->length(); i++) {
    ClassLiteral::Property* property = expr->fields()->at(i);

    if (property->is_computed_name()) {
      Variable* var = property->computed_name_var();
      DCHECK_NOT_NULL(var);
      // The computed name is already evaluated and stored in a
      // variable at class definition time.
      BuildVariableLoad(var, HoleCheckMode::kElided);
      builder()->StoreAccumulatorInRegister(key);
    } else {
      BuildLoadPropertyKey(property, key);
    }

    VisitForRegisterValue(property->value(), value);
    VisitSetHomeObject(value, constructor, property);

    builder()->CallRuntime(Runtime::kCreateDataProperty, args);
  }
}

void BytecodeGenerator::BuildInstanceFieldInitialization(Register constructor,
                                                         Register instance) {
  RegisterList args = register_allocator()->NewRegisterList(1);
  Register initializer = register_allocator()->NewRegister();

  FeedbackSlot slot = feedback_spec()->AddLoadICSlot();
  BytecodeLabel done;

  builder()
      ->LoadClassFieldsInitializer(constructor, feedback_index(slot))
      // TODO(gsathya): This jump can be elided for the base
      // constructor and derived constructor. This is only required
      // when called from an arrow function.
      .JumpIfUndefined(&done)
      .StoreAccumulatorInRegister(initializer)
      .MoveRegister(instance, args[0])
      .CallProperty(initializer, args,
                    feedback_index(feedback_spec()->AddCallICSlot()))
      .Bind(&done);
}

void BytecodeGenerator::VisitNativeFunctionLiteral(
    NativeFunctionLiteral* expr) {
  size_t entry = builder()->AllocateDeferredConstantPoolEntry();
  FeedbackSlot slot = feedback_spec()->AddCreateClosureSlot();
  builder()->CreateClosure(entry, feedback_index(slot), NOT_TENURED);
  native_function_literals_.push_back(std::make_pair(expr, entry));
}

void BytecodeGenerator::VisitDoExpression(DoExpression* expr) {
  VisitBlock(expr->block());
  VisitVariableProxy(expr->result());
}

void BytecodeGenerator::VisitConditional(Conditional* expr) {
  ConditionalControlFlowBuilder conditional_builder(
      builder(), block_coverage_builder_, expr);

  if (expr->condition()->ToBooleanIsTrue()) {
    // Generate then block unconditionally as always true.
    conditional_builder.Then();
    VisitForAccumulatorValue(expr->then_expression());
  } else if (expr->condition()->ToBooleanIsFalse()) {
    // Generate else block unconditionally if it exists.
    conditional_builder.Else();
    VisitForAccumulatorValue(expr->else_expression());
  } else {
    VisitForTest(expr->condition(), conditional_builder.then_labels(),
                 conditional_builder.else_labels(), TestFallthrough::kThen);

    conditional_builder.Then();
    VisitForAccumulatorValue(expr->then_expression());
    conditional_builder.JumpToEnd();

    conditional_builder.Else();
    VisitForAccumulatorValue(expr->else_expression());
  }
}

void BytecodeGenerator::VisitLiteral(Literal* expr) {
  if (execution_result()->IsEffect()) return;
  switch (expr->type()) {
    case Literal::kSmi:
      builder()->LoadLiteral(expr->AsSmiLiteral());
      break;
    case Literal::kHeapNumber:
      builder()->LoadLiteral(expr->AsNumber());
      break;
    case Literal::kUndefined:
      builder()->LoadUndefined();
      break;
    case Literal::kBoolean:
      builder()->LoadBoolean(expr->ToBooleanIsTrue());
      execution_result()->SetResultIsBoolean();
      break;
    case Literal::kNull:
      builder()->LoadNull();
      break;
    case Literal::kTheHole:
      builder()->LoadTheHole();
      break;
    case Literal::kString:
      builder()->LoadLiteral(expr->AsRawString());
      break;
    case Literal::kSymbol:
      builder()->LoadLiteral(expr->AsSymbol());
      break;
    case Literal::kBigInt:
      builder()->LoadLiteral(expr->AsBigInt());
      break;
  }
}

void BytecodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
  // Materialize a regular expression literal.
  builder()->CreateRegExpLiteral(
      expr->raw_pattern(), feedback_index(feedback_spec()->AddLiteralSlot()),
      expr->flags());
}

void BytecodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
  expr->InitDepthAndFlags();

  // Fast path for the empty object literal which doesn't need an
  // AllocationSite.
  if (expr->IsEmptyObjectLiteral()) {
    DCHECK(expr->IsFastCloningSupported());
    builder()->CreateEmptyObjectLiteral();
    return;
  }

  int literal_index = feedback_index(feedback_spec()->AddLiteralSlot());
  // Deep-copy the literal boilerplate.
  uint8_t flags = CreateObjectLiteralFlags::Encode(
      expr->ComputeFlags(), expr->IsFastCloningSupported());

  Register literal = register_allocator()->NewRegister();
  size_t entry;
  // If constant properties is an empty fixed array, use a cached empty fixed
  // array to ensure it's only added to the constant pool once.
  if (expr->properties_count() == 0) {
    entry = builder()->EmptyFixedArrayConstantPoolEntry();
  } else {
    entry = builder()->AllocateDeferredConstantPoolEntry();
    object_literals_.push_back(std::make_pair(expr, entry));
  }
  // TODO(cbruni): Directly generate runtime call for literals we cannot
  // optimize once the CreateShallowObjectLiteral stub is in sync with the TF
  // optimizations.
  builder()->CreateObjectLiteral(entry, literal_index, flags, literal);

  // Store computed values into the literal.
  int property_index = 0;
  AccessorTable accessor_table(zone());
  for (; property_index < expr->properties()->length(); property_index++) {
    ObjectLiteral::Property* property = expr->properties()->at(property_index);
    if (property->is_computed_name()) break;
    if (property->IsCompileTimeValue()) continue;

    RegisterAllocationScope inner_register_scope(this);
    Literal* key = property->key()->AsLiteral();
    switch (property->kind()) {
      case ObjectLiteral::Property::SPREAD:
      case ObjectLiteral::Property::CONSTANT:
        UNREACHABLE();
      case ObjectLiteral::Property::MATERIALIZED_LITERAL:
        DCHECK(!CompileTimeValue::IsCompileTimeValue(property->value()));
      // Fall through.
      case ObjectLiteral::Property::COMPUTED: {
        // It is safe to use [[Put]] here because the boilerplate already
        // contains computed properties with an uninitialized value.
        if (key->IsStringLiteral()) {
          DCHECK(key->IsPropertyName());
          if (property->emit_store()) {
            VisitForAccumulatorValue(property->value());
            FeedbackSlot slot = feedback_spec()->AddStoreOwnICSlot();
            if (FunctionLiteral::NeedsHomeObject(property->value())) {
              RegisterAllocationScope register_scope(this);
              Register value = register_allocator()->NewRegister();
              builder()->StoreAccumulatorInRegister(value);
              builder()->StoreNamedOwnProperty(
                  literal, key->AsRawPropertyName(), feedback_index(slot));
              VisitSetHomeObject(value, literal, property);
            } else {
              builder()->StoreNamedOwnProperty(
                  literal, key->AsRawPropertyName(), feedback_index(slot));
            }
          } else {
            VisitForEffect(property->value());
          }
        } else {
          RegisterList args = register_allocator()->NewRegisterList(4);

          builder()->MoveRegister(literal, args[0]);
          VisitForRegisterValue(property->key(), args[1]);
          VisitForRegisterValue(property->value(), args[2]);
          if (property->emit_store()) {
            builder()
                ->LoadLiteral(Smi::FromEnum(LanguageMode::kSloppy))
                .StoreAccumulatorInRegister(args[3])
                .CallRuntime(Runtime::kSetProperty, args);
            Register value = args[2];
            VisitSetHomeObject(value, literal, property);
          }
        }
        break;
      }
      case ObjectLiteral::Property::PROTOTYPE: {
        // __proto__:null is handled by CreateObjectLiteral.
        if (property->IsNullPrototype()) break;
        DCHECK(property->emit_store());
        DCHECK(!property->NeedsSetFunctionName());
        RegisterList args = register_allocator()->NewRegisterList(2);
        builder()->MoveRegister(literal, args[0]);
        VisitForRegisterValue(property->value(), args[1]);
        builder()->CallRuntime(Runtime::kInternalSetPrototype, args);
        break;
      }
      case ObjectLiteral::Property::GETTER:
        if (property->emit_store()) {
          accessor_table.lookup(key)->second->getter = property;
        }
        break;
      case ObjectLiteral::Property::SETTER:
        if (property->emit_store()) {
          accessor_table.lookup(key)->second->setter = property;
        }
        break;
    }
  }

  // Define accessors, using only a single call to the runtime for each pair of
  // corresponding getters and setters.
  for (AccessorTable::Iterator it = accessor_table.begin();
       it != accessor_table.end(); ++it) {
    RegisterAllocationScope inner_register_scope(this);
    RegisterList args = register_allocator()->NewRegisterList(5);
    builder()->MoveRegister(literal, args[0]);
    VisitForRegisterValue(it->first, args[1]);
    VisitObjectLiteralAccessor(literal, it->second->getter, args[2]);
    VisitObjectLiteralAccessor(literal, it->second->setter, args[3]);
    builder()
        ->LoadLiteral(Smi::FromInt(NONE))
        .StoreAccumulatorInRegister(args[4])
        .CallRuntime(Runtime::kDefineAccessorPropertyUnchecked, args);
  }

  // Object literals have two parts. The "static" part on the left contains no
  // computed property names, and so we can compute its map ahead of time; see
  // Runtime_CreateObjectLiteralBoilerplate. The second "dynamic" part starts
  // with the first computed property name and continues with all properties to
  // its right. All the code from above initializes the static component of the
  // object literal, and arranges for the map of the result to reflect the
  // static order in which the keys appear. For the dynamic properties, we
  // compile them into a series of "SetOwnProperty" runtime calls. This will
  // preserve insertion order.
  for (; property_index < expr->properties()->length(); property_index++) {
    ObjectLiteral::Property* property = expr->properties()->at(property_index);
    RegisterAllocationScope inner_register_scope(this);

    if (property->IsPrototype()) {
      // __proto__:null is handled by CreateObjectLiteral.
      if (property->IsNullPrototype()) continue;
      DCHECK(property->emit_store());
      DCHECK(!property->NeedsSetFunctionName());
      RegisterList args = register_allocator()->NewRegisterList(2);
      builder()->MoveRegister(literal, args[0]);
      VisitForRegisterValue(property->value(), args[1]);
      builder()->CallRuntime(Runtime::kInternalSetPrototype, args);
      continue;
    }

    switch (property->kind()) {
      case ObjectLiteral::Property::CONSTANT:
      case ObjectLiteral::Property::COMPUTED:
      case ObjectLiteral::Property::MATERIALIZED_LITERAL: {
        Register key = register_allocator()->NewRegister();
        BuildLoadPropertyKey(property, key);
        Register value = VisitForRegisterValue(property->value());
        VisitSetHomeObject(value, literal, property);

        DataPropertyInLiteralFlags data_property_flags =
            DataPropertyInLiteralFlag::kNoFlags;
        if (property->NeedsSetFunctionName()) {
          data_property_flags |= DataPropertyInLiteralFlag::kSetFunctionName;
        }

        FeedbackSlot slot =
            feedback_spec()->AddStoreDataPropertyInLiteralICSlot();
        builder()
            ->LoadAccumulatorWithRegister(value)
            .StoreDataPropertyInLiteral(literal, key, data_property_flags,
                                        feedback_index(slot));
        break;
      }
      case ObjectLiteral::Property::GETTER:
      case ObjectLiteral::Property::SETTER: {
        RegisterList args = register_allocator()->NewRegisterList(4);
        builder()->MoveRegister(literal, args[0]);
        BuildLoadPropertyKey(property, args[1]);
        VisitForRegisterValue(property->value(), args[2]);
        VisitSetHomeObject(args[2], literal, property);
        builder()
            ->LoadLiteral(Smi::FromInt(NONE))
            .StoreAccumulatorInRegister(args[3]);
        Runtime::FunctionId function_id =
            property->kind() == ObjectLiteral::Property::GETTER
                ? Runtime::kDefineGetterPropertyUnchecked
                : Runtime::kDefineSetterPropertyUnchecked;
        builder()->CallRuntime(function_id, args);
        break;
      }
      case ObjectLiteral::Property::SPREAD: {
        RegisterList args = register_allocator()->NewRegisterList(2);
        builder()->MoveRegister(literal, args[0]);
        VisitForRegisterValue(property->value(), args[1]);
        builder()->CallRuntime(Runtime::kCopyDataProperties, args);
        break;
      }
      case ObjectLiteral::Property::PROTOTYPE:
        UNREACHABLE();  // Handled specially above.
        break;
    }
  }

  builder()->LoadAccumulatorWithRegister(literal);
}

void BytecodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
  expr->InitDepthAndFlags();

  // Deep-copy the literal boilerplate.
  int literal_index = feedback_index(feedback_spec()->AddLiteralSlot());
  if (expr->is_empty()) {
    // Empty array literal fast-path.
    DCHECK(expr->IsFastCloningSupported());
    builder()->CreateEmptyArrayLiteral(literal_index);
    return;
  }

  uint8_t flags = CreateArrayLiteralFlags::Encode(
      expr->IsFastCloningSupported(), expr->ComputeFlags());
  size_t entry = builder()->AllocateDeferredConstantPoolEntry();
  builder()->CreateArrayLiteral(entry, literal_index, flags);
  array_literals_.push_back(std::make_pair(expr, entry));

  Register index = register_allocator()->NewRegister();
  Register literal = register_allocator()->NewRegister();
  builder()->StoreAccumulatorInRegister(literal);

  // We'll reuse the same literal slot for all of the non-constant
  // subexpressions that use a keyed store IC.

  // Evaluate all the non-constant subexpressions and store them into the
  // newly cloned array.
  FeedbackSlot slot;
  int array_index = 0;
  ZoneList<Expression*>::iterator iter = expr->BeginValue();
  for (; iter != expr->FirstSpreadOrEndValue(); ++iter, array_index++) {
    Expression* subexpr = *iter;
    DCHECK(!subexpr->IsSpread());
    if (CompileTimeValue::IsCompileTimeValue(subexpr)) continue;
    if (slot.IsInvalid()) {
      slot = feedback_spec()->AddKeyedStoreICSlot(language_mode());
    }
    builder()
        ->LoadLiteral(Smi::FromInt(array_index))
        .StoreAccumulatorInRegister(index);
    VisitForAccumulatorValue(subexpr);
    builder()->StoreKeyedProperty(literal, index, feedback_index(slot),
                                  language_mode());
  }

  // Handle spread elements and elements following.
  for (; iter != expr->EndValue(); ++iter) {
    Expression* subexpr = *iter;
    if (subexpr->IsSpread()) {
      BuildArrayLiteralSpread(subexpr->AsSpread(), literal);
    } else if (!subexpr->IsTheHoleLiteral()) {
      // Perform %AppendElement(array, <subexpr>)
      RegisterAllocationScope register_scope(this);
      RegisterList args = register_allocator()->NewRegisterList(2);
      builder()->MoveRegister(literal, args[0]);
      VisitForRegisterValue(subexpr, args[1]);
      builder()->CallRuntime(Runtime::kAppendElement, args);
    } else {
      // Peform ++<array>.length;
      // TODO(caitp): Why can't we just %AppendElement(array, <The Hole>?)
      auto length = ast_string_constants()->length_string();
      builder()->LoadNamedProperty(
          literal, length, feedback_index(feedback_spec()->AddLoadICSlot()));
      builder()->UnaryOperation(
          Token::INC, feedback_index(feedback_spec()->AddBinaryOpICSlot()));
      builder()->StoreNamedProperty(
          literal, length,
          feedback_index(
              feedback_spec()->AddStoreICSlot(LanguageMode::kStrict)),
          LanguageMode::kStrict);
    }
  }

  // Restore literal array into accumulator.
  builder()->LoadAccumulatorWithRegister(literal);
}

void BytecodeGenerator::BuildArrayLiteralSpread(Spread* spread,
                                                Register array) {
  RegisterAllocationScope register_scope(this);
  RegisterList args = register_allocator()->NewRegisterList(2);
  builder()->MoveRegister(array, args[0]);
  Register next_result = args[1];

  builder()->SetExpressionAsStatementPosition(spread->expression());
  IteratorRecord iterator =
      BuildGetIteratorRecord(spread->expression(), IteratorType::kNormal);
  LoopBuilder loop_builder(builder(), nullptr, nullptr);
  loop_builder.LoopHeader();

  // Call the iterator's .next() method. Break from the loop if the `done`
  // property is truthy, otherwise load the value from the iterator result and
  // append the argument.
  BuildIteratorNext(iterator, next_result);
  builder()->LoadNamedProperty(
      next_result, ast_string_constants()->done_string(),
      feedback_index(feedback_spec()->AddLoadICSlot()));
  loop_builder.BreakIfTrue(ToBooleanMode::kConvertToBoolean);

  loop_builder.LoopBody();
  builder()
      ->LoadNamedProperty(next_result, ast_string_constants()->value_string(),
                          feedback_index(feedback_spec()->AddLoadICSlot()))
      .StoreAccumulatorInRegister(args[1])
      .CallRuntime(Runtime::kAppendElement, args);
  loop_builder.BindContinueTarget();
  loop_builder.JumpToHeader(loop_depth_);
}

void BytecodeGenerator::VisitVariableProxy(VariableProxy* proxy) {
  builder()->SetExpressionPosition(proxy);
  BuildVariableLoad(proxy->var(), proxy->hole_check_mode());
}

void BytecodeGenerator::BuildVariableLoad(Variable* variable,
                                          HoleCheckMode hole_check_mode,
                                          TypeofMode typeof_mode) {
  switch (variable->location()) {
    case VariableLocation::LOCAL: {
      Register source(builder()->Local(variable->index()));
      // We need to load the variable into the accumulator, even when in a
      // VisitForRegisterScope, in order to avoid register aliasing if
      // subsequent expressions assign to the same variable.
      builder()->LoadAccumulatorWithRegister(source);
      if (hole_check_mode == HoleCheckMode::kRequired) {
        BuildThrowIfHole(variable);
      }
      break;
    }
    case VariableLocation::PARAMETER: {
      Register source;
      if (variable->IsReceiver()) {
        source = builder()->Receiver();
      } else {
        source = builder()->Parameter(variable->index());
      }
      // We need to load the variable into the accumulator, even when in a
      // VisitForRegisterScope, in order to avoid register aliasing if
      // subsequent expressions assign to the same variable.
      builder()->LoadAccumulatorWithRegister(source);
      if (hole_check_mode == HoleCheckMode::kRequired) {
        BuildThrowIfHole(variable);
      }
      break;
    }
    case VariableLocation::UNALLOCATED: {
      // The global identifier "undefined" is immutable. Everything
      // else could be reassigned. For performance, we do a pointer comparison
      // rather than checking if the raw_name is really "undefined".
      if (variable->raw_name() == ast_string_constants()->undefined_string()) {
        builder()->LoadUndefined();
      } else {
        FeedbackSlot slot = GetCachedLoadGlobalICSlot(typeof_mode, variable);
        builder()->LoadGlobal(variable->raw_name(), feedback_index(slot),
                              typeof_mode);
      }
      break;
    }
    case VariableLocation::CONTEXT: {
      int depth = execution_context()->ContextChainDepth(variable->scope());
      ContextScope* context = execution_context()->Previous(depth);
      Register context_reg;
      if (context) {
        context_reg = context->reg();
        depth = 0;
      } else {
        context_reg = execution_context()->reg();
      }

      BytecodeArrayBuilder::ContextSlotMutability immutable =
          (variable->maybe_assigned() == kNotAssigned)
              ? BytecodeArrayBuilder::kImmutableSlot
              : BytecodeArrayBuilder::kMutableSlot;

      builder()->LoadContextSlot(context_reg, variable->index(), depth,
                                 immutable);
      if (hole_check_mode == HoleCheckMode::kRequired) {
        BuildThrowIfHole(variable);
      }
      break;
    }
    case VariableLocation::LOOKUP: {
      switch (variable->mode()) {
        case DYNAMIC_LOCAL: {
          Variable* local_variable = variable->local_if_not_shadowed();
          int depth =
              execution_context()->ContextChainDepth(local_variable->scope());
          builder()->LoadLookupContextSlot(variable->raw_name(), typeof_mode,
                                           local_variable->index(), depth);
          if (hole_check_mode == HoleCheckMode::kRequired) {
            BuildThrowIfHole(variable);
          }
          break;
        }
        case DYNAMIC_GLOBAL: {
          int depth =
              current_scope()->ContextChainLengthUntilOutermostSloppyEval();
          FeedbackSlot slot = GetCachedLoadGlobalICSlot(typeof_mode, variable);
          builder()->LoadLookupGlobalSlot(variable->raw_name(), typeof_mode,
                                          feedback_index(slot), depth);
          break;
        }
        default:
          builder()->LoadLookupSlot(variable->raw_name(), typeof_mode);
      }
      break;
    }
    case VariableLocation::MODULE: {
      int depth = execution_context()->ContextChainDepth(variable->scope());
      builder()->LoadModuleVariable(variable->index(), depth);
      if (hole_check_mode == HoleCheckMode::kRequired) {
        BuildThrowIfHole(variable);
      }
      break;
    }
  }
}

void BytecodeGenerator::BuildVariableLoadForAccumulatorValue(
    Variable* variable, HoleCheckMode hole_check_mode, TypeofMode typeof_mode) {
  ValueResultScope accumulator_result(this);
  BuildVariableLoad(variable, hole_check_mode, typeof_mode);
}

void BytecodeGenerator::BuildReturn(int source_position) {
  if (FLAG_trace) {
    RegisterAllocationScope register_scope(this);
    Register result = register_allocator()->NewRegister();
    // Runtime returns {result} value, preserving accumulator.
    builder()->StoreAccumulatorInRegister(result).CallRuntime(
        Runtime::kTraceExit, result);
  }
  if (info()->collect_type_profile()) {
    builder()->CollectTypeProfile(info()->literal()->return_position());
  }
  builder()->SetReturnPosition(source_position, info()->literal());
  builder()->Return();
}

void BytecodeGenerator::BuildAsyncReturn(int source_position) {
  RegisterAllocationScope register_scope(this);

  if (IsAsyncGeneratorFunction(info()->literal()->kind())) {
    RegisterList args = register_allocator()->NewRegisterList(3);
    builder()
        ->MoveRegister(generator_object(), args[0])  // generator
        .StoreAccumulatorInRegister(args[1])         // value
        .LoadTrue()
        .StoreAccumulatorInRegister(args[2])  // done
        .CallRuntime(Runtime::kInlineAsyncGeneratorResolve, args);
  } else {
    DCHECK(IsAsyncFunction(info()->literal()->kind()));
    RegisterList args = register_allocator()->NewRegisterList(2);
    Register promise = args[0];
    Register return_value = args[1];
    builder()->StoreAccumulatorInRegister(return_value);

    Variable* var_promise = closure_scope()->promise_var();
    DCHECK_NOT_NULL(var_promise);
    BuildVariableLoad(var_promise, HoleCheckMode::kElided);
    builder()
        ->StoreAccumulatorInRegister(promise)
        .CallJSRuntime(Context::PROMISE_RESOLVE_INDEX, args)
        .LoadAccumulatorWithRegister(promise);
  }

  BuildReturn(source_position);
}

void BytecodeGenerator::BuildReThrow() { builder()->ReThrow(); }

void BytecodeGenerator::BuildThrowIfHole(Variable* variable) {
  if (variable->is_this()) {
    DCHECK(variable->mode() == CONST);
    builder()->ThrowSuperNotCalledIfHole();
  } else {
    builder()->ThrowReferenceErrorIfHole(variable->raw_name());
  }
}

void BytecodeGenerator::BuildHoleCheckForVariableAssignment(Variable* variable,
                                                            Token::Value op) {
  if (variable->is_this() && variable->mode() == CONST && op == Token::INIT) {
    // Perform an initialization check for 'this'. 'this' variable is the
    // only variable able to trigger bind operations outside the TDZ
    // via 'super' calls.
    builder()->ThrowSuperAlreadyCalledIfNotHole();
  } else {
    // Perform an initialization check for let/const declared variables.
    // E.g. let x = (x = 20); is not allowed.
    DCHECK(IsLexicalVariableMode(variable->mode()));
    BuildThrowIfHole(variable);
  }
}

void BytecodeGenerator::BuildVariableAssignment(
    Variable* variable, Token::Value op, HoleCheckMode hole_check_mode,
    LookupHoistingMode lookup_hoisting_mode) {
  VariableMode mode = variable->mode();
  RegisterAllocationScope assignment_register_scope(this);
  BytecodeLabel end_label;
  switch (variable->location()) {
    case VariableLocation::PARAMETER:
    case VariableLocation::LOCAL: {
      Register destination;
      if (VariableLocation::PARAMETER == variable->location()) {
        if (variable->IsReceiver()) {
          destination = builder()->Receiver();
        } else {
          destination = builder()->Parameter(variable->index());
        }
      } else {
        destination = builder()->Local(variable->index());
      }

      if (hole_check_mode == HoleCheckMode::kRequired) {
        // Load destination to check for hole.
        Register value_temp = register_allocator()->NewRegister();
        builder()
            ->StoreAccumulatorInRegister(value_temp)
            .LoadAccumulatorWithRegister(destination);

        BuildHoleCheckForVariableAssignment(variable, op);
        builder()->LoadAccumulatorWithRegister(value_temp);
      }

      if (mode != CONST || op == Token::INIT) {
        builder()->StoreAccumulatorInRegister(destination);
      } else if (variable->throw_on_const_assignment(language_mode())) {
        builder()->CallRuntime(Runtime::kThrowConstAssignError);
      }
      break;
    }
    case VariableLocation::UNALLOCATED: {
      // TODO(ishell): consider using FeedbackSlotCache for variables here.
      FeedbackSlot slot =
          feedback_spec()->AddStoreGlobalICSlot(language_mode());
      builder()->StoreGlobal(variable->raw_name(), feedback_index(slot));
      break;
    }
    case VariableLocation::CONTEXT: {
      int depth = execution_context()->ContextChainDepth(variable->scope());
      ContextScope* context = execution_context()->Previous(depth);
      Register context_reg;

      if (context) {
        context_reg = context->reg();
        depth = 0;
      } else {
        context_reg = execution_context()->reg();
      }

      if (hole_check_mode == HoleCheckMode::kRequired) {
        // Load destination to check for hole.
        Register value_temp = register_allocator()->NewRegister();
        builder()
            ->StoreAccumulatorInRegister(value_temp)
            .LoadContextSlot(context_reg, variable->index(), depth,
                             BytecodeArrayBuilder::kMutableSlot);

        BuildHoleCheckForVariableAssignment(variable, op);
        builder()->LoadAccumulatorWithRegister(value_temp);
      }

      if (mode != CONST || op == Token::INIT) {
        builder()->StoreContextSlot(context_reg, variable->index(), depth);
      } else if (variable->throw_on_const_assignment(language_mode())) {
        builder()->CallRuntime(Runtime::kThrowConstAssignError);
      }
      break;
    }
    case VariableLocation::LOOKUP: {
      builder()->StoreLookupSlot(variable->raw_name(), language_mode(),
                                 lookup_hoisting_mode);
      break;
    }
    case VariableLocation::MODULE: {
      DCHECK(IsDeclaredVariableMode(mode));

      if (mode == CONST && op != Token::INIT) {
        builder()->CallRuntime(Runtime::kThrowConstAssignError);
        break;
      }

      // If we don't throw above, we know that we're dealing with an
      // export because imports are const and we do not generate initializing
      // assignments for them.
      DCHECK(variable->IsExport());

      int depth = execution_context()->ContextChainDepth(variable->scope());
      if (hole_check_mode == HoleCheckMode::kRequired) {
        Register value_temp = register_allocator()->NewRegister();
        builder()
            ->StoreAccumulatorInRegister(value_temp)
            .LoadModuleVariable(variable->index(), depth);
        BuildHoleCheckForVariableAssignment(variable, op);
        builder()->LoadAccumulatorWithRegister(value_temp);
      }
      builder()->StoreModuleVariable(variable->index(), depth);
      break;
    }
  }
}

void BytecodeGenerator::VisitAssignment(Assignment* expr) {
  DCHECK(expr->target()->IsValidReferenceExpression() ||
         (expr->op() == Token::INIT && expr->target()->IsVariableProxy() &&
          expr->target()->AsVariableProxy()->is_this()));
  Register object, key;
  RegisterList super_property_args;
  const AstRawString* name;

  // Left-hand side can only be a property, a global or a variable slot.
  Property* property = expr->target()->AsProperty();
  LhsKind assign_type = Property::GetAssignType(property);

  // Evaluate LHS expression.
  switch (assign_type) {
    case VARIABLE:
      // Nothing to do to evaluate variable assignment LHS.
      break;
    case NAMED_PROPERTY: {
      object = VisitForRegisterValue(property->obj());
      name = property->key()->AsLiteral()->AsRawPropertyName();
      break;
    }
    case KEYED_PROPERTY: {
      object = VisitForRegisterValue(property->obj());
      key = VisitForRegisterValue(property->key());
      break;
    }
    case NAMED_SUPER_PROPERTY: {
      super_property_args = register_allocator()->NewRegisterList(4);
      SuperPropertyReference* super_property =
          property->obj()->AsSuperPropertyReference();
      VisitForRegisterValue(super_property->this_var(), super_property_args[0]);
      VisitForRegisterValue(super_property->home_object(),
                            super_property_args[1]);
      builder()
          ->LoadLiteral(property->key()->AsLiteral()->AsRawPropertyName())
          .StoreAccumulatorInRegister(super_property_args[2]);
      break;
    }
    case KEYED_SUPER_PROPERTY: {
      super_property_args = register_allocator()->NewRegisterList(4);
      SuperPropertyReference* super_property =
          property->obj()->AsSuperPropertyReference();
      VisitForRegisterValue(super_property->this_var(), super_property_args[0]);
      VisitForRegisterValue(super_property->home_object(),
                            super_property_args[1]);
      VisitForRegisterValue(property->key(), super_property_args[2]);
      break;
    }
  }

  // Evaluate the value and potentially handle compound assignments by loading
  // the left-hand side value and performing a binary operation.
  if (expr->IsCompoundAssignment()) {
    switch (assign_type) {
      case VARIABLE: {
        VariableProxy* proxy = expr->target()->AsVariableProxy();
        BuildVariableLoad(proxy->var(), proxy->hole_check_mode());
        break;
      }
      case NAMED_PROPERTY: {
        FeedbackSlot slot = feedback_spec()->AddLoadICSlot();
        builder()->LoadNamedProperty(object, name, feedback_index(slot));
        break;
      }
      case KEYED_PROPERTY: {
        // Key is already in accumulator at this point due to evaluating the
        // LHS above.
        FeedbackSlot slot = feedback_spec()->AddKeyedLoadICSlot();
        builder()->LoadKeyedProperty(object, feedback_index(slot));
        break;
      }
      case NAMED_SUPER_PROPERTY: {
        builder()->CallRuntime(Runtime::kLoadFromSuper,
                               super_property_args.Truncate(3));
        break;
      }
      case KEYED_SUPER_PROPERTY: {
        builder()->CallRuntime(Runtime::kLoadKeyedFromSuper,
                               super_property_args.Truncate(3));
        break;
      }
    }
    BinaryOperation* binop = expr->AsCompoundAssignment()->binary_operation();
    FeedbackSlot slot = feedback_spec()->AddBinaryOpICSlot();
    if (expr->value()->IsSmiLiteral()) {
      builder()->BinaryOperationSmiLiteral(
          binop->op(), expr->value()->AsLiteral()->AsSmiLiteral(),
          feedback_index(slot));
    } else {
      Register old_value = register_allocator()->NewRegister();
      builder()->StoreAccumulatorInRegister(old_value);
      VisitForAccumulatorValue(expr->value());
      builder()->BinaryOperation(binop->op(), old_value, feedback_index(slot));
    }
  } else {
    VisitForAccumulatorValue(expr->value());
  }

  // Store the value.
  builder()->SetExpressionPosition(expr);
  switch (assign_type) {
    case VARIABLE: {
      // TODO(oth): The BuildVariableAssignment() call is hard to reason about.
      // Is the value in the accumulator safe? Yes, but scary.
      VariableProxy* proxy = expr->target()->AsVariableProxy();
      BuildVariableAssignment(proxy->var(), expr->op(),
                              proxy->hole_check_mode(),
                              expr->lookup_hoisting_mode());
      break;
    }
    case NAMED_PROPERTY: {
      FeedbackSlot slot = feedback_spec()->AddStoreICSlot(language_mode());
      Register value;
      if (!execution_result()->IsEffect()) {
        value = register_allocator()->NewRegister();
        builder()->StoreAccumulatorInRegister(value);
      }
      builder()->StoreNamedProperty(object, name, feedback_index(slot),
                                    language_mode());
      if (!execution_result()->IsEffect()) {
        builder()->LoadAccumulatorWithRegister(value);
      }
      break;
    }
    case KEYED_PROPERTY: {
      FeedbackSlot slot = feedback_spec()->AddKeyedStoreICSlot(language_mode());
      Register value;
      if (!execution_result()->IsEffect()) {
        value = register_allocator()->NewRegister();
        builder()->StoreAccumulatorInRegister(value);
      }
      builder()->StoreKeyedProperty(object, key, feedback_index(slot),
                                    language_mode());
      if (!execution_result()->IsEffect()) {
        builder()->LoadAccumulatorWithRegister(value);
      }
      break;
    }
    case NAMED_SUPER_PROPERTY: {
      builder()
          ->StoreAccumulatorInRegister(super_property_args[3])
          .CallRuntime(StoreToSuperRuntimeId(), super_property_args);
      break;
    }
    case KEYED_SUPER_PROPERTY: {
      builder()
          ->StoreAccumulatorInRegister(super_property_args[