runtime/vm/kernel_binary.cc

// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#if !defined(DART_PRECOMPILED_RUNTIME)

#include "platform/globals.h"
#include "vm/flags.h"
#include "vm/growable_array.h"
#include "vm/kernel.h"
#include "vm/kernel_to_il.h"
#include "vm/os.h"

#if defined(DEBUG)
#define TRACE_READ_OFFSET()                                                    \
  do {                                                                         \
    if (FLAG_trace_kernel_binary) reader->DumpOffset(DART_PRETTY_FUNCTION);    \
  } while (0)
#else
#define TRACE_READ_OFFSET()
#endif

namespace dart {


namespace kernel {


static const uint32_t kMagicProgramFile = 0x90ABCDEFu;


// Keep in sync with package:dynamo/lib/binary/tag.dart
enum Tag {
  kNothing = 0,
  kSomething = 1,

  kClass = 2,

  kField = 4,
  kConstructor = 5,
  kProcedure = 6,

  kInvalidInitializer = 7,
  kFieldInitializer = 8,
  kSuperInitializer = 9,
  kRedirectingInitializer = 10,
  kLocalInitializer = 11,

  kDirectPropertyGet = 15,
  kDirectPropertySet = 16,
  kDirectMethodInvocation = 17,
  kConstStaticInvocation = 18,
  kInvalidExpression = 19,
  kVariableGet = 20,
  kVariableSet = 21,
  kPropertyGet = 22,
  kPropertySet = 23,
  kSuperPropertyGet = 24,
  kSuperPropertySet = 25,
  kStaticGet = 26,
  kStaticSet = 27,
  kMethodInvocation = 28,
  kSuperMethodInvocation = 29,
  kStaticInvocation = 30,
  kConstructorInvocation = 31,
  kConstConstructorInvocation = 32,
  kNot = 33,
  kLogicalExpression = 34,
  kConditionalExpression = 35,
  kStringConcatenation = 36,
  kIsExpression = 37,
  kAsExpression = 38,
  kStringLiteral = 39,
  kDoubleLiteral = 40,
  kTrueLiteral = 41,
  kFalseLiteral = 42,
  kNullLiteral = 43,
  kSymbolLiteral = 44,
  kTypeLiteral = 45,
  kThisExpression = 46,
  kRethrow = 47,
  kThrow = 48,
  kListLiteral = 49,
  kMapLiteral = 50,
  kAwaitExpression = 51,
  kFunctionExpression = 52,
  kLet = 53,

  kPositiveIntLiteral = 55,
  kNegativeIntLiteral = 56,
  kBigIntLiteral = 57,
  kConstListLiteral = 58,
  kConstMapLiteral = 59,

  kInvalidStatement = 60,
  kExpressionStatement = 61,
  kBlock = 62,
  kEmptyStatement = 63,
  kAssertStatement = 64,
  kLabeledStatement = 65,
  kBreakStatement = 66,
  kWhileStatement = 67,
  kDoStatement = 68,
  kForStatement = 69,
  kForInStatement = 70,
  kSwitchStatement = 71,
  kContinueSwitchStatement = 72,
  kIfStatement = 73,
  kReturnStatement = 74,
  kTryCatch = 75,
  kTryFinally = 76,
  kYieldStatement = 77,
  kVariableDeclaration = 78,
  kFunctionDeclaration = 79,
  kAsyncForInStatement = 80,

  kInvalidType = 90,
  kDynamicType = 91,
  kVoidType = 92,
  kInterfaceType = 93,
  kFunctionType = 94,
  kTypeParameterType = 95,
  kSimpleInterfaceType = 96,
  kSimpleFunctionType = 97,

  kSpecializedTagHighBit = 0x80,  // 10000000
  kSpecializedTagMask = 0xF8,     // 11111000
  kSpecializedPayloadMask = 0x7,  // 00000111

  kSpecializedVariableGet = 128,
  kSpecializedVariableSet = 136,
  kSpecialIntLiteral = 144,
};


static const int SpecializedIntLiteralBias = 3;


template <typename T>
class BlockStack {
 public:
  BlockStack() : current_count_(0) {}

  void EnterScope() {
    variable_count_.Add(current_count_);
    current_count_ = 0;
  }

  void LeaveScope() {
    variables_.TruncateTo(variables_.length() - current_count_);
    current_count_ = variable_count_[variable_count_.length() - 1];
    variable_count_.RemoveLast();
  }

  T* Lookup(int index) {
    ASSERT(index < variables_.length());
    return variables_[index];
  }

  void Push(T* v) {
    variables_.Add(v);
    current_count_++;
  }

  void Push(List<T>* decl) {
    for (intptr_t i = 0; i < decl->length(); i++) {
      variables_.Add(decl[i]);
      current_count_++;
    }
  }

  void Pop(T* decl) {
    variables_.RemoveLast();
    current_count_--;
  }

  void Pop(List<T>* decl) {
    variables_.TruncateTo(variables_.length() - decl->length());
    current_count_ -= decl->length();
  }

 private:
  int current_count_;
  MallocGrowableArray<T*> variables_;
  MallocGrowableArray<int> variable_count_;
};


template <typename T>
class BlockMap {
 public:
  BlockMap() : current_count_(0), stack_height_(0) {}

  void EnterScope() {
    variable_count_.Add(current_count_);
    current_count_ = 0;
  }

  void LeaveScope() {
    stack_height_ -= current_count_;
    current_count_ = variable_count_[variable_count_.length() - 1];
    variable_count_.RemoveLast();
  }

  int Lookup(T* object) {
    typename MallocMap<T, int>::Pair* result = variables_.LookupPair(object);
    ASSERT(result != NULL);
    if (result == NULL) FATAL("lookup failure");
    return RawPointerKeyValueTrait<T, int>::ValueOf(*result);
  }

  void Push(T* v) {
    ASSERT(variables_.LookupPair(v) == NULL);
    int index = stack_height_++;
    variables_.Insert(v, index);
    current_count_++;
  }

  void Set(T* v, int index) {
    typename MallocMap<T, int>::Pair* entry = variables_.LookupPair(v);
    ASSERT(entry != NULL);
    entry->value = index;
  }

  void Push(List<T>* decl) {
    for (intptr_t i = 0; i < decl->length(); i++) {
      Push(decl[i]);
    }
  }

  void Pop(T* v) {
    current_count_--;
    stack_height_--;
  }

 private:
  int current_count_;
  int stack_height_;
  MallocMap<T, int> variables_;
  MallocGrowableArray<int> variable_count_;
};


template <typename T>
class VariableScope {
 public:
  explicit VariableScope(T* builder) : builder_(builder) {
    builder_->variables().EnterScope();
  }
  ~VariableScope() { builder_->variables().LeaveScope(); }

 private:
  T* builder_;
};


template <typename T>
class TypeParameterScope {
 public:
  explicit TypeParameterScope(T* builder) : builder_(builder) {
    builder_->type_parameters().EnterScope();
  }
  ~TypeParameterScope() { builder_->type_parameters().LeaveScope(); }

 private:
  T* builder_;
};


template <typename T>
class SwitchCaseScope {
 public:
  explicit SwitchCaseScope(T* builder) : builder_(builder) {
    builder_->switch_cases().EnterScope();
  }
  ~SwitchCaseScope() { builder_->switch_cases().LeaveScope(); }

 private:
  T* builder_;
};


// Unlike other scopes, labels from enclosing functions are not visible in
// nested functions.  The LabelScope class is used to hide outer labels.
template <typename Builder, typename Block>
class LabelScope {
 public:
  explicit LabelScope(Builder* builder) : builder_(builder) {
    outer_block_ = builder_->labels();
    builder_->set_labels(&block_);
  }
  ~LabelScope() { builder_->set_labels(outer_block_); }

 private:
  Builder* builder_;
  Block block_;
  Block* outer_block_;
};

class ReaderHelper {
 public:
  ReaderHelper() : program_(NULL), labels_(NULL) {}

  Program* program() { return program_; }
  void set_program(Program* program) { program_ = program; }

  BlockStack<VariableDeclaration>& variables() { return scope_; }
  BlockStack<TypeParameter>& type_parameters() { return type_parameters_; }
  BlockStack<SwitchCase>& switch_cases() { return switch_cases_; }

  BlockStack<LabeledStatement>* labels() { return labels_; }
  void set_labels(BlockStack<LabeledStatement>* labels) { labels_ = labels; }

  CanonicalName* GetCanonicalName(int index) { return canonical_names_[index]; }
  void SetCanonicalName(int index, CanonicalName* name) {
    canonical_names_[index] = name;
  }
  void SetCanonicalNameCount(int count) { canonical_names_.SetLength(count); }

 private:
  Program* program_;
  MallocGrowableArray<CanonicalName*> canonical_names_;
  BlockStack<VariableDeclaration> scope_;
  BlockStack<TypeParameter> type_parameters_;
  BlockStack<SwitchCase> switch_cases_;
  BlockStack<LabeledStatement>* labels_;
};


class Reader {
 public:
  Reader(const uint8_t* buffer, intptr_t size)
      : buffer_(buffer), size_(size), offset_(0) {}

  uint32_t ReadUInt32() {
    ASSERT(offset_ + 4 <= size_);

    uint32_t value = (buffer_[offset_ + 0] << 24) |
                     (buffer_[offset_ + 1] << 16) |
                     (buffer_[offset_ + 2] << 8) | (buffer_[offset_ + 3] << 0);
    offset_ += 4;
    return value;
  }

  uint32_t ReadUInt() {
    ASSERT(offset_ + 1 <= size_);
    uint8_t byte0 = buffer_[offset_];
    if ((byte0 & 0x80) == 0) {
      // 0...
      offset_++;
      return byte0;
    } else if ((byte0 & 0xc0) == 0x80) {
      // 10...
      ASSERT(offset_ + 2 <= size_);
      uint32_t value = ((byte0 & ~0x80) << 8) | (buffer_[offset_ + 1]);
      offset_ += 2;
      return value;
    } else {
      // 11...
      ASSERT(offset_ + 4 <= size_);
      uint32_t value = ((byte0 & ~0xc0) << 24) | (buffer_[offset_ + 1] << 16) |
                       (buffer_[offset_ + 2] << 8) |
                       (buffer_[offset_ + 3] << 0);
      offset_ += 4;
      return value;
    }
  }

  void add_token_position(
      MallocGrowableArray<MallocGrowableArray<intptr_t>*>* list,
      TokenPosition position) {
    intptr_t size = list->length();
    while (size <= current_script_id_) {
      MallocGrowableArray<intptr_t>* tmp = new MallocGrowableArray<intptr_t>();
      list->Add(tmp);
      size = list->length();
    }
    list->At(current_script_id_)->Add(position.value());
  }

  void record_token_position(TokenPosition position) {
    if (position.IsReal()) {
      add_token_position(&helper()->program()->valid_token_positions, position);
    }
  }

  void record_yield_token_position(TokenPosition position) {
    add_token_position(&helper()->program()->yield_token_positions, position);
  }

  /**
   * Read and return a TokenPosition from this reader.
   * @param record specifies whether or not the read position is saved as a
   * valid token position in the current script.
   * If not be sure to record it later by calling record_token_position (after
   * setting the correct current_script_id).
   */
  TokenPosition ReadPosition(bool record = true) {
    // Position is saved as unsigned,
    // but actually ranges from -1 and up (thus the -1)
    intptr_t value = ReadUInt() - 1;
    TokenPosition result = TokenPosition(value);
    max_position_ = Utils::Maximum(max_position_, result);
    if (min_position_.IsNoSource()) {
      min_position_ = result;
    } else if (result.IsReal()) {
      min_position_ = Utils::Minimum(min_position_, result);
    }

    if (record) {
      record_token_position(result);
    }
    return result;
  }

  intptr_t ReadListLength() { return ReadUInt(); }

  uint8_t ReadByte() { return buffer_[offset_++]; }

  bool ReadBool() { return (ReadByte() & 1) == 1; }

  word ReadFlags() { return ReadByte(); }

  Tag ReadTag(uint8_t* payload = NULL) {
    uint8_t byte = ReadByte();
    bool has_payload = (byte & kSpecializedTagHighBit) != 0;
    if (has_payload) {
      if (payload != NULL) {
        *payload = byte & kSpecializedPayloadMask;
      }
      return static_cast<Tag>(byte & kSpecializedTagMask);
    } else {
      return static_cast<Tag>(byte);
    }
  }

  const uint8_t* Consume(int count) {
    ASSERT(offset_ + count <= size_);
    const uint8_t* old = buffer_ + offset_;
    offset_ += count;
    return old;
  }

  void EnsureEnd() {
    if (offset_ != size_) {
      FATAL2(
          "Reading Kernel file: Expected to be at EOF "
          "(offset: %" Pd ", size: %" Pd ")",
          offset_, size_);
    }
  }

  void DumpOffset(const char* str) {
    OS::PrintErr("@%" Pd " %s\n", offset_, str);
  }

  // The largest position read yet (since last reset).
  // This is automatically updated when calling ReadPosition,
  // but can be overwritten (e.g. via the PositionScope class).
  TokenPosition max_position() { return max_position_; }
  // The smallest position read yet (since last reset).
  // This is automatically updated when calling ReadPosition,
  // but can be overwritten (e.g. via the PositionScope class).
  TokenPosition min_position() { return min_position_; }
  // The current script id for what we are currently processing.
  // Note though that this is only a convenience helper and has to be set
  // manually.
  intptr_t current_script_id() { return current_script_id_; }
  void set_current_script_id(intptr_t script_id) {
    current_script_id_ = script_id;
  }

  template <typename T, typename RT>
  T* ReadOptional() {
    Tag tag = ReadTag();
    if (tag == kNothing) {
      return NULL;
    }
    ASSERT(tag == kSomething);
    return RT::ReadFrom(this);
  }

  template <typename T>
  T* ReadOptional() {
    return ReadOptional<T, T>();
  }

  ReaderHelper* helper() { return &builder_; }

  CanonicalName* ReadCanonicalNameReference() {
    int index = ReadUInt();
    if (index == 0) return NULL;
    CanonicalName* name = builder_.GetCanonicalName(index - 1);
    ASSERT(name != NULL);
    return name;
  }

  intptr_t offset() { return offset_; }

 private:
  const uint8_t* buffer_;
  intptr_t size_;
  intptr_t offset_;
  ReaderHelper builder_;
  TokenPosition max_position_;
  TokenPosition min_position_;
  intptr_t current_script_id_;

  friend class PositionScope;
};


// A helper class that resets the readers min and max positions both upon
// initialization and upon destruction, i.e. when created the min an max
// positions will be reset to "noSource", when destructing the min and max will
// be reset to have they value they would have had, if they hadn't been reset in
// the first place.
class PositionScope {
 public:
  explicit PositionScope(Reader* reader)
      : reader_(reader),
        min_(reader->min_position_),
        max_(reader->max_position_) {
    reader->min_position_ = reader->max_position_ = TokenPosition::kNoSource;
  }

  ~PositionScope() {
    if (reader_->min_position_.IsNoSource()) {
      reader_->min_position_ = min_;
    } else if (min_.IsReal()) {
      reader_->min_position_ = Utils::Minimum(reader_->min_position_, min_);
    }
    reader_->max_position_ = Utils::Maximum(reader_->max_position_, max_);
  }

 private:
  Reader* reader_;
  TokenPosition min_;
  TokenPosition max_;
};

template <typename T>
template <typename IT>
void List<T>::ReadFrom(Reader* reader, TreeNode* parent) {
  TRACE_READ_OFFSET();
  ASSERT(parent != NULL);
  int length = reader->ReadListLength();
  EnsureInitialized(length);

  for (intptr_t i = 0; i < length_; i++) {
    IT* object = GetOrCreate<IT>(i, parent);
    object->ReadFrom(reader);
  }
}


template <typename T>
template <typename IT>
void List<T>::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  int length = reader->ReadListLength();
  EnsureInitialized(length);

  for (intptr_t i = 0; i < length_; i++) {
    GetOrCreate<IT>(i)->ReadFrom(reader);
  }
}


template <typename T>
template <typename IT>
void List<T>::ReadFromStatic(Reader* reader) {
  TRACE_READ_OFFSET();
  int length = reader->ReadListLength();
  EnsureInitialized(length);

  for (intptr_t i = 0; i < length_; i++) {
    ASSERT(array_[i] == NULL);
    array_[i] = IT::ReadFrom(reader);
  }
}

void TypeParameterList::ReadFrom(Reader* reader) {
  // It is possible for the bound of the first type parameter to refer to
  // the second type parameter. This means we need to create [TypeParameter]
  // objects before reading the bounds.
  int length = reader->ReadListLength();
  EnsureInitialized(length);

  // Make all [TypeParameter]s available in scope.
  for (intptr_t i = 0; i < length; i++) {
    TypeParameter* parameter = (*this)[i] = new TypeParameter();
    reader->helper()->type_parameters().Push(parameter);
  }

  // Read all [TypeParameter]s and their bounds.
  for (intptr_t i = 0; i < length; i++) {
    (*this)[i]->ReadFrom(reader);
  }
}


template <typename A, typename B>
Tuple<A, B>* Tuple<A, B>::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  A* first = A::ReadFrom(reader);
  B* second = B::ReadFrom(reader);
  return new Tuple<A, B>(first, second);
}


template <typename B, typename S>
class DowncastReader {
 public:
  static S* ReadFrom(Reader* reader) {
    TRACE_READ_OFFSET();
    return S::Cast(B::ReadFrom(reader));
  }
};


class StringImpl {
 public:
  static String* ReadFrom(Reader* reader) {
    TRACE_READ_OFFSET();
    return String::ReadFromImpl(reader);
  }
};


class VariableDeclarationImpl {
 public:
  static VariableDeclaration* ReadFrom(Reader* reader) {
    TRACE_READ_OFFSET();
    return VariableDeclaration::ReadFromImpl(reader, false);
  }
};


String* String::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return Reference::ReadStringFrom(reader);
}


String* String::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  uint32_t bytes = reader->ReadUInt();
  String* string = new String(reader->Consume(bytes), bytes);
  return string;
}

void StringTable::ReadFrom(Reader* reader) {
  strings_.ReadFromStatic<StringImpl>(reader);
}


void SourceTable::ReadFrom(Reader* reader) {
  size_ = reader->helper()->program()->source_uri_table().strings().length();
  source_code_ = new String*[size_];
  line_starts_ = new intptr_t*[size_];
  line_count_ = new intptr_t[size_];
  for (intptr_t i = 0; i < size_; ++i) {
    source_code_[i] = StringImpl::ReadFrom(reader);
    intptr_t line_count = reader->ReadUInt();
    intptr_t* line_starts = new intptr_t[line_count];
    line_count_[i] = line_count;
    intptr_t previous_line_start = 0;
    for (intptr_t j = 0; j < line_count; ++j) {
      intptr_t line_start = reader->ReadUInt() + previous_line_start;
      line_starts[j] = line_start;
      previous_line_start = line_start;
    }
    line_starts_[i] = line_starts;
  }
}


Library* Library::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  int flags = reader->ReadFlags();
  ASSERT(flags == 0);  // external libraries not supported

  canonical_name_ = reader->ReadCanonicalNameReference();
  name_ = Reference::ReadStringFrom(reader);
  import_uri_ = canonical_name_->name();
  source_uri_index_ = reader->ReadUInt();
  reader->set_current_script_id(source_uri_index_);

  int num_imports = reader->ReadUInt();
  if (num_imports != 0) {
    FATAL("Deferred imports not implemented in VM");
  }
  int num_classes = reader->ReadUInt();
  classes().EnsureInitialized(num_classes);
  for (intptr_t i = 0; i < num_classes; i++) {
    Tag tag = reader->ReadTag();
    ASSERT(tag == kClass);
    NormalClass* klass = classes().GetOrCreate<NormalClass>(i, this);
    klass->ReadFrom(reader);
  }

  fields().ReadFrom<Field>(reader, this);
  procedures().ReadFrom<Procedure>(reader, this);
  return this;
}


Class* Class::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();

  canonical_name_ = reader->ReadCanonicalNameReference();
  position_ = reader->ReadPosition(false);
  is_abstract_ = reader->ReadBool();
  name_ = Reference::ReadStringFrom(reader);
  source_uri_index_ = reader->ReadUInt();
  reader->set_current_script_id(source_uri_index_);
  reader->record_token_position(position_);
  annotations_.ReadFromStatic<Expression>(reader);

  return this;
}


NormalClass* NormalClass::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Class::ReadFrom(reader);
  TypeParameterScope<ReaderHelper> scope(reader->helper());

  type_parameters_.ReadFrom(reader);
  DartType* type = reader->ReadOptional<DartType>();

  super_class_ = InterfaceType::Cast(type);
  reader->ReadOptional<DartType>();  // Mixed-in type is unused.
  implemented_classes_.ReadFromStatic<DowncastReader<DartType, InterfaceType> >(
      reader);
  fields_.ReadFrom<Field>(reader, this);
  constructors_.ReadFrom<Constructor>(reader, this);
  procedures_.ReadFrom<Procedure>(reader, this);

  return this;
}


MixinClass* MixinClass::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  TypeParameterScope<ReaderHelper> scope(reader->helper());

  Class::ReadFrom(reader);
  type_parameters_.ReadFrom(reader);
  first_ = InterfaceType::Cast(DartType::ReadFrom(reader));
  second_ = InterfaceType::Cast(DartType::ReadFrom(reader));
  implemented_classes_.ReadFromStatic<DowncastReader<DartType, InterfaceType> >(
      reader);
  constructors_.ReadFrom<Constructor>(reader, this);
  return this;
}


CanonicalName* Reference::ReadMemberFrom(Reader* reader, bool allow_null) {
  TRACE_READ_OFFSET();

  CanonicalName* canonical_name = reader->ReadCanonicalNameReference();
  if (canonical_name == NULL && !allow_null) {
    FATAL("Expected a valid member reference, but got `null`");
  }

  if (canonical_name != NULL) {
    canonical_name->set_referenced(true);
  }

  return canonical_name;
}


CanonicalName* Reference::ReadClassFrom(Reader* reader, bool allow_null) {
  TRACE_READ_OFFSET();

  CanonicalName* canonical_name = reader->ReadCanonicalNameReference();
  if (canonical_name == NULL && !allow_null) {
    FATAL("Expected a valid class reference, but got `null`");
  }

  if (canonical_name != NULL) {
    canonical_name->set_referenced(true);
  }

  return canonical_name;
}


String* Reference::ReadStringFrom(Reader* reader) {
  int index = reader->ReadUInt();
  return reader->helper()->program()->string_table().strings()[index];
}


Field* Field::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  kernel_offset_ = reader->offset();  // Notice the ReadTag() below.
  Tag tag = reader->ReadTag();
  ASSERT(tag == kField);

  canonical_name_ = reader->ReadCanonicalNameReference();
  position_ = reader->ReadPosition(false);
  end_position_ = reader->ReadPosition(false);
  flags_ = reader->ReadFlags();
  name_ = Name::ReadFrom(reader);
  source_uri_index_ = reader->ReadUInt();
  reader->set_current_script_id(source_uri_index_);
  reader->record_token_position(position_);
  reader->record_token_position(end_position_);
  annotations_.ReadFromStatic<Expression>(reader);
  type_ = DartType::ReadFrom(reader);
  initializer_ = reader->ReadOptional<Expression>();
  return this;
}


Constructor* Constructor::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  ASSERT(tag == kConstructor);

  canonical_name_ = reader->ReadCanonicalNameReference();
  VariableScope<ReaderHelper> parameters(reader->helper());
  position_ = reader->ReadPosition();
  end_position_ = reader->ReadPosition();
  flags_ = reader->ReadFlags();
  name_ = Name::ReadFrom(reader);
  annotations_.ReadFromStatic<Expression>(reader);
  function_ = FunctionNode::ReadFrom(reader);
  initializers_.ReadFromStatic<Initializer>(reader);
  return this;
}


Procedure* Procedure::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  ASSERT(tag == kProcedure);

  canonical_name_ = reader->ReadCanonicalNameReference();
  VariableScope<ReaderHelper> parameters(reader->helper());
  position_ = reader->ReadPosition(false);
  end_position_ = reader->ReadPosition(false);
  kind_ = static_cast<ProcedureKind>(reader->ReadByte());
  flags_ = reader->ReadFlags();
  name_ = Name::ReadFrom(reader);
  source_uri_index_ = reader->ReadUInt();
  reader->set_current_script_id(source_uri_index_);
  reader->record_token_position(position_);
  reader->record_token_position(end_position_);
  annotations_.ReadFromStatic<Expression>(reader);
  function_ = reader->ReadOptional<FunctionNode>();
  return this;
}


Initializer* Initializer::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  switch (tag) {
    case kInvalidInitializer:
      return InvalidInitializer::ReadFromImpl(reader);
    case kFieldInitializer:
      return FieldInitializer::ReadFromImpl(reader);
    case kSuperInitializer:
      return SuperInitializer::ReadFromImpl(reader);
    case kRedirectingInitializer:
      return RedirectingInitializer::ReadFromImpl(reader);
    case kLocalInitializer:
      return LocalInitializer::ReadFromImpl(reader);
    default:
      UNREACHABLE();
  }
  return NULL;
}


InvalidInitializer* InvalidInitializer::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  return new InvalidInitializer();
}


FieldInitializer* FieldInitializer::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  FieldInitializer* initializer = new FieldInitializer();
  initializer->field_reference_ = Reference::ReadMemberFrom(reader);
  initializer->value_ = Expression::ReadFrom(reader);
  return initializer;
}


SuperInitializer* SuperInitializer::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  SuperInitializer* init = new SuperInitializer();
  init->target_reference_ = Reference::ReadMemberFrom(reader);
  init->arguments_ = Arguments::ReadFrom(reader);
  return init;
}


RedirectingInitializer* RedirectingInitializer::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  RedirectingInitializer* init = new RedirectingInitializer();
  init->target_reference_ = Reference::ReadMemberFrom(reader);
  init->arguments_ = Arguments::ReadFrom(reader);
  return init;
}


LocalInitializer* LocalInitializer::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  LocalInitializer* init = new LocalInitializer();
  init->variable_ = VariableDeclaration::ReadFromImpl(reader, false);
  return init;
}


Expression* Expression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  uint8_t payload = 0;
  Tag tag = reader->ReadTag(&payload);
  switch (tag) {
    case kInvalidExpression:
      return InvalidExpression::ReadFrom(reader);
    case kVariableGet:
      return VariableGet::ReadFrom(reader);
    case kSpecializedVariableGet:
      return VariableGet::ReadFrom(reader, payload);
    case kVariableSet:
      return VariableSet::ReadFrom(reader);
    case kSpecializedVariableSet:
      return VariableSet::ReadFrom(reader, payload);
    case kPropertyGet:
      return PropertyGet::ReadFrom(reader);
    case kPropertySet:
      return PropertySet::ReadFrom(reader);
    case kDirectPropertyGet:
      return DirectPropertyGet::ReadFrom(reader);
    case kDirectPropertySet:
      return DirectPropertySet::ReadFrom(reader);
    case kStaticGet:
      return StaticGet::ReadFrom(reader);
    case kStaticSet:
      return StaticSet::ReadFrom(reader);
    case kMethodInvocation:
      return MethodInvocation::ReadFrom(reader);
    case kDirectMethodInvocation:
      return DirectMethodInvocation::ReadFrom(reader);
    case kStaticInvocation:
      return StaticInvocation::ReadFrom(reader, false);
    case kConstStaticInvocation:
      return StaticInvocation::ReadFrom(reader, true);
    case kConstructorInvocation:
      return ConstructorInvocation::ReadFrom(reader, false);
    case kConstConstructorInvocation:
      return ConstructorInvocation::ReadFrom(reader, true);
    case kNot:
      return Not::ReadFrom(reader);
    case kLogicalExpression:
      return LogicalExpression::ReadFrom(reader);
    case kConditionalExpression:
      return ConditionalExpression::ReadFrom(reader);
    case kStringConcatenation:
      return StringConcatenation::ReadFrom(reader);
    case kIsExpression:
      return IsExpression::ReadFrom(reader);
    case kAsExpression:
      return AsExpression::ReadFrom(reader);
    case kSymbolLiteral:
      return SymbolLiteral::ReadFrom(reader);
    case kTypeLiteral:
      return TypeLiteral::ReadFrom(reader);
    case kThisExpression:
      return ThisExpression::ReadFrom(reader);
    case kRethrow:
      return Rethrow::ReadFrom(reader);
    case kThrow:
      return Throw::ReadFrom(reader);
    case kListLiteral:
      return ListLiteral::ReadFrom(reader, false);
    case kConstListLiteral:
      return ListLiteral::ReadFrom(reader, true);
    case kMapLiteral:
      return MapLiteral::ReadFrom(reader, false);
    case kConstMapLiteral:
      return MapLiteral::ReadFrom(reader, true);
    case kAwaitExpression:
      return AwaitExpression::ReadFrom(reader);
    case kFunctionExpression:
      return FunctionExpression::ReadFrom(reader);
    case kLet:
      return Let::ReadFrom(reader);
    case kBigIntLiteral:
      return BigintLiteral::ReadFrom(reader);
    case kStringLiteral:
      return StringLiteral::ReadFrom(reader);
    case kSpecialIntLiteral:
      return IntLiteral::ReadFrom(reader, payload);
    case kNegativeIntLiteral:
      return IntLiteral::ReadFrom(reader, true);
    case kPositiveIntLiteral:
      return IntLiteral::ReadFrom(reader, false);
    case kDoubleLiteral:
      return DoubleLiteral::ReadFrom(reader);
    case kTrueLiteral:
      return BoolLiteral::ReadFrom(reader, true);
    case kFalseLiteral:
      return BoolLiteral::ReadFrom(reader, false);
    case kNullLiteral:
      return NullLiteral::ReadFrom(reader);
    default:
      UNREACHABLE();
  }
  return NULL;
}


InvalidExpression* InvalidExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new InvalidExpression();
}


VariableGet* VariableGet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableGet* get = new VariableGet();
  get->position_ = reader->ReadPosition();
  get->variable_ = reader->helper()->variables().Lookup(reader->ReadUInt());
  reader->ReadOptional<DartType>();  // Unused promoted type.
  return get;
}


VariableGet* VariableGet::ReadFrom(Reader* reader, uint8_t payload) {
  TRACE_READ_OFFSET();
  VariableGet* get = new VariableGet();
  get->position_ = reader->ReadPosition();
  get->variable_ = reader->helper()->variables().Lookup(payload);
  return get;
}


VariableSet* VariableSet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableSet* set = new VariableSet();
  set->position_ = reader->ReadPosition();
  set->variable_ = reader->helper()->variables().Lookup(reader->ReadUInt());
  set->expression_ = Expression::ReadFrom(reader);
  return set;
}


VariableSet* VariableSet::ReadFrom(Reader* reader, uint8_t payload) {
  TRACE_READ_OFFSET();
  VariableSet* set = new VariableSet();
  set->variable_ = reader->helper()->variables().Lookup(payload);
  set->position_ = reader->ReadPosition();
  set->expression_ = Expression::ReadFrom(reader);
  return set;
}


PropertyGet* PropertyGet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  PropertyGet* get = new PropertyGet();
  get->position_ = reader->ReadPosition();
  get->receiver_ = Expression::ReadFrom(reader);
  get->name_ = Name::ReadFrom(reader);
  get->interface_target_reference_ = Reference::ReadMemberFrom(reader, true);
  return get;
}


PropertySet* PropertySet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  PropertySet* set = new PropertySet();
  set->position_ = reader->ReadPosition();
  set->receiver_ = Expression::ReadFrom(reader);
  set->name_ = Name::ReadFrom(reader);
  set->value_ = Expression::ReadFrom(reader);
  set->interface_target_reference_ = Reference::ReadMemberFrom(reader, true);
  return set;
}


DirectPropertyGet* DirectPropertyGet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  DirectPropertyGet* get = new DirectPropertyGet();
  get->position_ = reader->ReadPosition();
  get->receiver_ = Expression::ReadFrom(reader);
  get->target_reference_ = Reference::ReadMemberFrom(reader);
  return get;
}


DirectPropertySet* DirectPropertySet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  DirectPropertySet* set = new DirectPropertySet();
  set->position_ = reader->ReadPosition();
  set->receiver_ = Expression::ReadFrom(reader);
  set->target_reference_ = Reference::ReadMemberFrom(reader);
  set->value_ = Expression::ReadFrom(reader);
  return set;
}


StaticGet* StaticGet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  StaticGet* get = new StaticGet();
  get->position_ = reader->ReadPosition();
  get->target_reference_ = Reference::ReadMemberFrom(reader);
  return get;
}


StaticSet* StaticSet::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  StaticSet* set = new StaticSet();
  set->position_ = reader->ReadPosition();
  set->target_reference_ = Reference::ReadMemberFrom(reader);
  set->expression_ = Expression::ReadFrom(reader);
  return set;
}


Arguments* Arguments::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Arguments* arguments = new Arguments();
  arguments->types().ReadFromStatic<DartType>(reader);
  arguments->positional().ReadFromStatic<Expression>(reader);
  arguments->named().ReadFromStatic<NamedExpression>(reader);
  return arguments;
}


NamedExpression* NamedExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  String* name = Reference::ReadStringFrom(reader);
  Expression* expression = Expression::ReadFrom(reader);
  return new NamedExpression(name, expression);
}


MethodInvocation* MethodInvocation::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  MethodInvocation* invocation = new MethodInvocation();
  invocation->position_ = reader->ReadPosition();
  invocation->receiver_ = Expression::ReadFrom(reader);
  invocation->name_ = Name::ReadFrom(reader);
  invocation->arguments_ = Arguments::ReadFrom(reader);
  invocation->interface_target_reference_ =
      Reference::ReadMemberFrom(reader, true);
  return invocation;
}


DirectMethodInvocation* DirectMethodInvocation::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  DirectMethodInvocation* invocation = new DirectMethodInvocation();
  invocation->receiver_ = Expression::ReadFrom(reader);
  invocation->target_reference_ = Reference::ReadMemberFrom(reader);
  invocation->arguments_ = Arguments::ReadFrom(reader);
  return invocation;
}


StaticInvocation* StaticInvocation::ReadFrom(Reader* reader, bool is_const) {
  TRACE_READ_OFFSET();
  StaticInvocation* invocation = new StaticInvocation();
  invocation->is_const_ = is_const;
  invocation->position_ = reader->ReadPosition();
  invocation->procedure_reference_ = Reference::ReadMemberFrom(reader);
  invocation->arguments_ = Arguments::ReadFrom(reader);
  return invocation;
}


ConstructorInvocation* ConstructorInvocation::ReadFrom(Reader* reader,
                                                       bool is_const) {
  TRACE_READ_OFFSET();
  ConstructorInvocation* invocation = new ConstructorInvocation();
  invocation->is_const_ = is_const;
  invocation->position_ = reader->ReadPosition();
  invocation->target_reference_ = Reference::ReadMemberFrom(reader);
  invocation->arguments_ = Arguments::ReadFrom(reader);
  return invocation;
}


Not* Not::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Not* n = new Not();
  n->expression_ = Expression::ReadFrom(reader);
  return n;
}


LogicalExpression* LogicalExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  LogicalExpression* expr = new LogicalExpression();
  expr->left_ = Expression::ReadFrom(reader);
  expr->operator_ = static_cast<Operator>(reader->ReadByte());
  expr->right_ = Expression::ReadFrom(reader);
  return expr;
}


ConditionalExpression* ConditionalExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  ConditionalExpression* expr = new ConditionalExpression();
  expr->condition_ = Expression::ReadFrom(reader);
  expr->then_ = Expression::ReadFrom(reader);
  expr->otherwise_ = Expression::ReadFrom(reader);
  reader->ReadOptional<DartType>();  // Unused static type.
  return expr;
}


StringConcatenation* StringConcatenation::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  StringConcatenation* concat = new StringConcatenation();
  concat->position_ = reader->ReadPosition();
  concat->expressions_.ReadFromStatic<Expression>(reader);
  return concat;
}


IsExpression* IsExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  IsExpression* expr = new IsExpression();
  expr->position_ = reader->ReadPosition();
  expr->operand_ = Expression::ReadFrom(reader);
  expr->type_ = DartType::ReadFrom(reader);
  return expr;
}


AsExpression* AsExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  AsExpression* expr = new AsExpression();
  expr->position_ = reader->ReadPosition();
  expr->operand_ = Expression::ReadFrom(reader);
  expr->type_ = DartType::ReadFrom(reader);
  return expr;
}


StringLiteral* StringLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new StringLiteral(Reference::ReadStringFrom(reader));
}


BigintLiteral* BigintLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new BigintLiteral(Reference::ReadStringFrom(reader));
}


IntLiteral* IntLiteral::ReadFrom(Reader* reader, bool is_negative) {
  TRACE_READ_OFFSET();
  IntLiteral* literal = new IntLiteral();
  literal->value_ = is_negative ? -static_cast<int64_t>(reader->ReadUInt())
                                : reader->ReadUInt();
  return literal;
}


IntLiteral* IntLiteral::ReadFrom(Reader* reader, uint8_t payload) {
  TRACE_READ_OFFSET();
  IntLiteral* literal = new IntLiteral();
  literal->value_ = static_cast<int32_t>(payload) - SpecializedIntLiteralBias;
  return literal;
}


DoubleLiteral* DoubleLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  DoubleLiteral* literal = new DoubleLiteral();
  literal->value_ = Reference::ReadStringFrom(reader);
  return literal;
}


BoolLiteral* BoolLiteral::ReadFrom(Reader* reader, bool value) {
  TRACE_READ_OFFSET();
  BoolLiteral* lit = new BoolLiteral();
  lit->value_ = value;
  return lit;
}


NullLiteral* NullLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new NullLiteral();
}


SymbolLiteral* SymbolLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  SymbolLiteral* lit = new SymbolLiteral();
  lit->value_ = Reference::ReadStringFrom(reader);
  return lit;
}


TypeLiteral* TypeLiteral::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  TypeLiteral* literal = new TypeLiteral();
  literal->type_ = DartType::ReadFrom(reader);
  return literal;
}


ThisExpression* ThisExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new ThisExpression();
}


Rethrow* Rethrow::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Rethrow* rethrow = new Rethrow();
  rethrow->position_ = reader->ReadPosition();
  return rethrow;
}


Throw* Throw::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Throw* t = new Throw();
  t->position_ = reader->ReadPosition();
  t->expression_ = Expression::ReadFrom(reader);
  return t;
}


ListLiteral* ListLiteral::ReadFrom(Reader* reader, bool is_const) {
  TRACE_READ_OFFSET();
  ListLiteral* literal = new ListLiteral();
  literal->is_const_ = is_const;
  literal->position_ = reader->ReadPosition();
  literal->type_ = DartType::ReadFrom(reader);
  literal->expressions_.ReadFromStatic<Expression>(reader);
  return literal;
}


MapLiteral* MapLiteral::ReadFrom(Reader* reader, bool is_const) {
  TRACE_READ_OFFSET();
  MapLiteral* literal = new MapLiteral();
  literal->is_const_ = is_const;
  literal->position_ = reader->ReadPosition();
  literal->key_type_ = DartType::ReadFrom(reader);
  literal->value_type_ = DartType::ReadFrom(reader);
  literal->entries_.ReadFromStatic<MapEntry>(reader);
  return literal;
}


MapEntry* MapEntry::ReadFrom(Reader* reader) {
  MapEntry* entry = new MapEntry();
  entry->key_ = Expression::ReadFrom(reader);
  entry->value_ = Expression::ReadFrom(reader);
  return entry;
}


AwaitExpression* AwaitExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  AwaitExpression* await = new AwaitExpression();
  await->operand_ = Expression::ReadFrom(reader);
  return await;
}


FunctionExpression* FunctionExpression::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableScope<ReaderHelper> parameters(reader->helper());
  FunctionExpression* expr = new FunctionExpression();
  expr->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  expr->function_ = FunctionNode::ReadFrom(reader);
  return expr;
}


Let* Let::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableScope<ReaderHelper> vars(reader->helper());
  PositionScope scope(reader);

  Let* let = new Let();
  let->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  let->variable_ = VariableDeclaration::ReadFromImpl(reader, false);
  let->body_ = Expression::ReadFrom(reader);
  let->position_ = reader->min_position();
  let->end_position_ = reader->max_position();

  return let;
}


Statement* Statement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  switch (tag) {
    case kInvalidStatement:
      return InvalidStatement::ReadFrom(reader);
    case kExpressionStatement:
      return ExpressionStatement::ReadFrom(reader);
    case kBlock:
      return Block::ReadFromImpl(reader);
    case kEmptyStatement:
      return EmptyStatement::ReadFrom(reader);
    case kAssertStatement:
      return AssertStatement::ReadFrom(reader);
    case kLabeledStatement:
      return LabeledStatement::ReadFrom(reader);
    case kBreakStatement:
      return BreakStatement::ReadFrom(reader);
    case kWhileStatement:
      return WhileStatement::ReadFrom(reader);
    case kDoStatement:
      return DoStatement::ReadFrom(reader);
    case kForStatement:
      return ForStatement::ReadFrom(reader);
    case kForInStatement:
      return ForInStatement::ReadFrom(reader, false);
    case kAsyncForInStatement:
      return ForInStatement::ReadFrom(reader, true);
    case kSwitchStatement:
      return SwitchStatement::ReadFrom(reader);
    case kContinueSwitchStatement:
      return ContinueSwitchStatement::ReadFrom(reader);
    case kIfStatement:
      return IfStatement::ReadFrom(reader);
    case kReturnStatement:
      return ReturnStatement::ReadFrom(reader);
    case kTryCatch:
      return TryCatch::ReadFrom(reader);
    case kTryFinally:
      return TryFinally::ReadFrom(reader);
    case kYieldStatement:
      return YieldStatement::ReadFrom(reader);
    case kVariableDeclaration:
      return VariableDeclaration::ReadFromImpl(reader, true);
    case kFunctionDeclaration:
      return FunctionDeclaration::ReadFrom(reader);
    default:
      UNREACHABLE();
  }
  return NULL;
}


InvalidStatement* InvalidStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new InvalidStatement();
}


ExpressionStatement* ExpressionStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new ExpressionStatement(Expression::ReadFrom(reader));
}


Block* Block::ReadFromImpl(Reader* reader) {
  TRACE_READ_OFFSET();
  PositionScope scope(reader);

  VariableScope<ReaderHelper> vars(reader->helper());
  Block* block = new Block();
  block->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  block->statements().ReadFromStatic<Statement>(reader);
  block->position_ = reader->min_position();
  block->end_position_ = reader->max_position();

  return block;
}


EmptyStatement* EmptyStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new EmptyStatement();
}


AssertStatement* AssertStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  AssertStatement* stmt = new AssertStatement();
  stmt->condition_ = Expression::ReadFrom(reader);
  stmt->message_ = reader->ReadOptional<Expression>();
  return stmt;
}


LabeledStatement* LabeledStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  LabeledStatement* stmt = new LabeledStatement();
  reader->helper()->labels()->Push(stmt);
  stmt->body_ = Statement::ReadFrom(reader);
  reader->helper()->labels()->Pop(stmt);
  return stmt;
}


BreakStatement* BreakStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  BreakStatement* stmt = new BreakStatement();
  stmt->position_ = reader->ReadPosition();
  stmt->target_ = reader->helper()->labels()->Lookup(reader->ReadUInt());
  return stmt;
}


WhileStatement* WhileStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  WhileStatement* stmt = new WhileStatement();
  stmt->condition_ = Expression::ReadFrom(reader);
  stmt->body_ = Statement::ReadFrom(reader);
  return stmt;
}


DoStatement* DoStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  DoStatement* dostmt = new DoStatement();
  dostmt->body_ = Statement::ReadFrom(reader);
  dostmt->condition_ = Expression::ReadFrom(reader);
  return dostmt;
}


ForStatement* ForStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableScope<ReaderHelper> vars(reader->helper());
  PositionScope scope(reader);

  ForStatement* forstmt = new ForStatement();
  forstmt->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  forstmt->variables_.ReadFromStatic<VariableDeclarationImpl>(reader);
  forstmt->condition_ = reader->ReadOptional<Expression>();
  forstmt->updates_.ReadFromStatic<Expression>(reader);
  forstmt->body_ = Statement::ReadFrom(reader);
  forstmt->end_position_ = reader->max_position();
  forstmt->position_ = reader->min_position();

  return forstmt;
}


ForInStatement* ForInStatement::ReadFrom(Reader* reader, bool is_async) {
  TRACE_READ_OFFSET();
  VariableScope<ReaderHelper> vars(reader->helper());
  PositionScope scope(reader);

  ForInStatement* forinstmt = new ForInStatement();
  forinstmt->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  forinstmt->is_async_ = is_async;
  forinstmt->position_ = reader->ReadPosition();
  forinstmt->variable_ = VariableDeclaration::ReadFromImpl(reader, false);
  forinstmt->iterable_ = Expression::ReadFrom(reader);
  forinstmt->body_ = Statement::ReadFrom(reader);
  forinstmt->end_position_ = reader->max_position();
  if (!forinstmt->position_.IsReal()) {
    forinstmt->position_ = reader->min_position();
  }
  forinstmt->variable_->set_end_position(forinstmt->position_);

  return forinstmt;
}


SwitchStatement* SwitchStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  SwitchCaseScope<ReaderHelper> scope(reader->helper());
  SwitchStatement* stmt = new SwitchStatement();
  stmt->condition_ = Expression::ReadFrom(reader);
  // We need to explicitly create empty [SwitchCase]s first in order to add them
  // to the [SwitchCaseScope]. This is necessary since a [Statement] in a switch
  // case can refer to one defined later on.
  int count = reader->ReadUInt();
  for (intptr_t i = 0; i < count; i++) {
    SwitchCase* sc = stmt->cases_.GetOrCreate<SwitchCase>(i);
    reader->helper()->switch_cases().Push(sc);
  }
  for (intptr_t i = 0; i < count; i++) {
    SwitchCase* sc = stmt->cases_[i];
    sc->ReadFrom(reader);
  }
  return stmt;
}


SwitchCase* SwitchCase::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  expressions_.ReadFromStatic<Expression>(reader);
  for (intptr_t i = 0; i < expressions_.length(); ++i) {
    expressions_[i]->set_position(reader->ReadPosition());
  }
  is_default_ = reader->ReadBool();
  body_ = Statement::ReadFrom(reader);
  return this;
}


ContinueSwitchStatement* ContinueSwitchStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  ContinueSwitchStatement* stmt = new ContinueSwitchStatement();
  stmt->target_ = reader->helper()->switch_cases().Lookup(reader->ReadUInt());
  return stmt;
}


IfStatement* IfStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  IfStatement* ifstmt = new IfStatement();
  ifstmt->condition_ = Expression::ReadFrom(reader);
  ifstmt->then_ = Statement::ReadFrom(reader);
  ifstmt->otherwise_ = Statement::ReadFrom(reader);
  return ifstmt;
}


ReturnStatement* ReturnStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  ReturnStatement* ret = new ReturnStatement();
  ret->position_ = reader->ReadPosition();
  ret->expression_ = reader->ReadOptional<Expression>();
  return ret;
}


TryCatch* TryCatch::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  PositionScope scope(reader);

  TryCatch* tc = new TryCatch();
  tc->body_ = Statement::ReadFrom(reader);
  tc->catches_.ReadFromStatic<Catch>(reader);
  tc->position_ = reader->min_position();

  return tc;
}


Catch* Catch::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  VariableScope<ReaderHelper> vars(reader->helper());
  PositionScope scope(reader);

  Catch* c = new Catch();
  c->kernel_offset_ = reader->offset();  // Catch has no tag.
  c->guard_ = DartType::ReadFrom(reader);
  c->exception_ =
      reader->ReadOptional<VariableDeclaration, VariableDeclarationImpl>();
  c->stack_trace_ =
      reader->ReadOptional<VariableDeclaration, VariableDeclarationImpl>();
  c->body_ = Statement::ReadFrom(reader);
  c->end_position_ = reader->max_position();
  c->position_ = reader->min_position();

  return c;
}


TryFinally* TryFinally::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  TryFinally* tf = new TryFinally();
  tf->body_ = Statement::ReadFrom(reader);
  tf->finalizer_ = Statement::ReadFrom(reader);
  return tf;
}


YieldStatement* YieldStatement::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  YieldStatement* stmt = new YieldStatement();
  stmt->position_ = reader->ReadPosition();
  reader->record_yield_token_position(stmt->position_);
  stmt->flags_ = reader->ReadByte();
  stmt->expression_ = Expression::ReadFrom(reader);
  return stmt;
}


VariableDeclaration* VariableDeclaration::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  ASSERT(tag == kVariableDeclaration);
  return VariableDeclaration::ReadFromImpl(reader, true);
}


VariableDeclaration* VariableDeclaration::ReadFromImpl(Reader* reader,
                                                       bool read_tag) {
  TRACE_READ_OFFSET();
  PositionScope scope(reader);

  VariableDeclaration* decl = new VariableDeclaration();
  // -1 or -0 depending on whether there's a tag or not.
  decl->kernel_offset_ = reader->offset() - (read_tag ? 1 : 0);
  decl->position_ = reader->ReadPosition();
  decl->equals_position_ = reader->ReadPosition();
  decl->flags_ = reader->ReadFlags();
  decl->name_ = Reference::ReadStringFrom(reader);
  decl->type_ = DartType::ReadFrom(reader);
  decl->initializer_ = reader->ReadOptional<Expression>();

  // Go to next token position so it ends *after* the last potentially
  // debuggable position in the initializer.
  TokenPosition position = reader->max_position();
  if (position.IsReal()) position.Next();
  decl->end_position_ = position;
  reader->helper()->variables().Push(decl);

  return decl;
}


FunctionDeclaration* FunctionDeclaration::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  FunctionDeclaration* decl = new FunctionDeclaration();
  decl->kernel_offset_ = reader->offset() - 1;  // -1 to include tag byte.
  decl->position_ = reader->ReadPosition();
  decl->variable_ = VariableDeclaration::ReadFromImpl(reader, false);
  VariableScope<ReaderHelper> parameters(reader->helper());
  decl->function_ = FunctionNode::ReadFrom(reader);
  return decl;
}


Name* Name::ReadFrom(Reader* reader) {
  String* string = Reference::ReadStringFrom(reader);
  if (string->size() >= 1 && string->buffer()[0] == '_') {
    CanonicalName* library_reference = reader->ReadCanonicalNameReference();
    return new Name(string, library_reference);
  } else {
    return new Name(string, NULL);
  }
}


DartType* DartType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  Tag tag = reader->ReadTag();
  switch (tag) {
    case kInvalidType:
      return InvalidType::ReadFrom(reader);
    case kDynamicType:
      return DynamicType::ReadFrom(reader);
    case kVoidType:
      return VoidType::ReadFrom(reader);
    case kInterfaceType:
      return InterfaceType::ReadFrom(reader);
    case kSimpleInterfaceType:
      return InterfaceType::ReadFrom(reader, true);
    case kFunctionType:
      return FunctionType::ReadFrom(reader);
    case kSimpleFunctionType:
      return FunctionType::ReadFrom(reader, true);
    case kTypeParameterType:
      return TypeParameterType::ReadFrom(reader);
    default:
      UNREACHABLE();
  }
  UNREACHABLE();
  return NULL;
}


InvalidType* InvalidType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new InvalidType();
}


DynamicType* DynamicType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new DynamicType();
}


VoidType* VoidType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  return new VoidType();
}


InterfaceType* InterfaceType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  CanonicalName* klass_name = Reference::ReadClassFrom(reader);
  InterfaceType* type = new InterfaceType(klass_name);
  type->type_arguments().ReadFromStatic<DartType>(reader);
  return type;
}


InterfaceType* InterfaceType::ReadFrom(Reader* reader,
                                       bool _without_type_arguments_) {
  TRACE_READ_OFFSET();
  CanonicalName* klass_name = Reference::ReadClassFrom(reader);
  InterfaceType* type = new InterfaceType(klass_name);
  ASSERT(_without_type_arguments_);
  return type;
}


FunctionType* FunctionType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  FunctionType* type = new FunctionType();
  TypeParameterScope<ReaderHelper> scope(reader->helper());
  type->type_parameters().ReadFrom(reader);
  type->required_parameter_count_ = reader->ReadUInt();
  type->positional_parameters().ReadFromStatic<DartType>(reader);
  type->named_parameters().ReadFromStatic<Tuple<String, DartType> >(reader);
  type->return_type_ = DartType::ReadFrom(reader);
  return type;
}


FunctionType* FunctionType::ReadFrom(Reader* reader, bool _is_simple_) {
  TRACE_READ_OFFSET();
  FunctionType* type = new FunctionType();
  ASSERT(_is_simple_);
  type->positional_parameters().ReadFromStatic<DartType>(reader);
  type->required_parameter_count_ = type->positional_parameters().length();
  type->return_type_ = DartType::ReadFrom(reader);
  return type;
}


TypeParameterType* TypeParameterType::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  TypeParameterType* type = new TypeParameterType();
  type->parameter_ =
      reader->helper()->type_parameters().Lookup(reader->ReadUInt());
  return type;
}


Program* Program::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  uint32_t magic = reader->ReadUInt32();
  if (magic != kMagicProgramFile) FATAL("Invalid magic identifier");

  Program* program = new Program();
  program->canonical_name_root_ = CanonicalName::NewRoot();
  reader->helper()->set_program(program);

  program->string_table_.ReadFrom(reader);
  program->source_uri_table_.ReadFrom(reader);
  program->source_table_.ReadFrom(reader);

  int canonical_names = reader->ReadUInt();
  reader->helper()->SetCanonicalNameCount(canonical_names);
  for (int i = 0; i < canonical_names; ++i) {
    int biased_parent_index = reader->ReadUInt();
    CanonicalName* parent;
    if (biased_parent_index != 0) {
      parent = reader->helper()->GetCanonicalName(biased_parent_index - 1);
    } else {
      parent = program->canonical_name_root();
    }
    ASSERT(parent != NULL);
    int name_index = reader->ReadUInt();
    String* name = program->string_table().strings()[name_index];
    CanonicalName* canonical_name = parent->AddChild(name);
    reader->helper()->SetCanonicalName(i, canonical_name);
  }

  int libraries = reader->ReadUInt();
  program->libraries().EnsureInitialized(libraries);
  for (intptr_t i = 0; i < libraries; i++) {
    program->libraries().GetOrCreate<Library>(i)->ReadFrom(reader);
  }

  program->main_method_reference_ = Reference::ReadMemberFrom(reader);

  return program;
}


FunctionNode* FunctionNode::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  TypeParameterScope<ReaderHelper> scope(reader->helper());

  FunctionNode* function = new FunctionNode();
  function->kernel_offset_ = reader->offset();  // FunctionNode has no tag.
  function->position_ = reader->ReadPosition();
  function->end_position_ = reader->ReadPosition();
  function->async_marker_ =
      static_cast<FunctionNode::AsyncMarker>(reader->ReadByte());
  function->dart_async_marker_ =
      static_cast<FunctionNode::AsyncMarker>(reader->ReadByte());
  function->type_parameters().ReadFrom(reader);
  function->required_parameter_count_ = reader->ReadUInt();
  function->positional_parameters().ReadFromStatic<VariableDeclarationImpl>(
      reader);
  function->named_parameters().ReadFromStatic<VariableDeclarationImpl>(reader);
  function->return_type_ = DartType::ReadFrom(reader);

  LabelScope<ReaderHelper, BlockStack<LabeledStatement> > labels(
      reader->helper());
  VariableScope<ReaderHelper> vars(reader->helper());
  function->body_ = reader->ReadOptional<Statement>();
  return function;
}


TypeParameter* TypeParameter::ReadFrom(Reader* reader) {
  TRACE_READ_OFFSET();
  name_ = Reference::ReadStringFrom(reader);
  bound_ = DartType::ReadFrom(reader);
  return this;
}


}  // namespace kernel


kernel::Program* ReadPrecompiledKernelFromBuffer(const uint8_t* buffer,
                                                 intptr_t buffer_length) {
  kernel::Reader reader(buffer, buffer_length);
  return kernel::Program::ReadFrom(&reader);
}


}  // namespace dart
#endif  // !defined(DART_PRECOMPILED_RUNTIME)