Replace C++ bitfields with our own BitFields

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index aa23b4e237afa7602613a5b6a151adf0c5536608..c68c58c1789c05572109262d843209d80a6ffaad 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -359,11 +359,16 @@ class Expression : public AstNode {
   void set_bounds(Bounds bounds) { bounds_ = bounds; }
 
   // Whether the expression is parenthesized
-  bool is_parenthesized() const { return is_parenthesized_; }
-  bool is_multi_parenthesized() const { return is_multi_parenthesized_; }
+  bool is_parenthesized() const {
+    return IsParenthesizedField::decode(bit_field_);
+  }
+  bool is_multi_parenthesized() const {
+    return IsMultiParenthesizedField::decode(bit_field_);
+  }
   void increase_parenthesization_level() {
-    is_multi_parenthesized_ = is_parenthesized_;
-    is_parenthesized_ = true;
+    bit_field_ =
+        IsMultiParenthesizedField::update(bit_field_, is_parenthesized());
+    bit_field_ = IsParenthesizedField::update(bit_field_, true);
   }
 
   // Type feedback information for assignments and properties.
@@ -375,18 +380,20 @@ class Expression : public AstNode {
     UNREACHABLE();
     return NULL;
   }
-  virtual KeyedAccessStoreMode GetStoreMode() {
+  virtual KeyedAccessStoreMode GetStoreMode() const {
     UNREACHABLE();
     return STANDARD_STORE;
   }
-  virtual IcCheckType GetKeyType() {
+  virtual IcCheckType GetKeyType() const {
     UNREACHABLE();
     return ELEMENT;
   }
 
   // TODO(rossberg): this should move to its own AST node eventually.
   virtual void RecordToBooleanTypeFeedback(TypeFeedbackOracle* oracle);
-  byte to_boolean_types() const { return to_boolean_types_; }
+  byte to_boolean_types() const {
+    return ToBooleanTypesField::decode(bit_field_);
+  }
 
   void set_base_id(int id) { base_id_ = id; }
   static int num_ids() { return parent_num_ids() + 2; }
@@ -398,10 +405,11 @@ class Expression : public AstNode {
       : AstNode(pos),
         base_id_(BailoutId::None().ToInt()),
         bounds_(Bounds::Unbounded(zone)),
-        is_parenthesized_(false),
-        is_multi_parenthesized_(false) {}
+        bit_field_(0) {}
   static int parent_num_ids() { return 0; }
-  void set_to_boolean_types(byte types) { to_boolean_types_ = types; }
+  void set_to_boolean_types(byte types) {
+    bit_field_ = ToBooleanTypesField::update(bit_field_, types);
+  }
 
   int base_id() const {
     DCHECK(!BailoutId(base_id_).IsNone());
@@ -413,9 +421,10 @@ class Expression : public AstNode {
 
   int base_id_;
   Bounds bounds_;
-  byte to_boolean_types_;
-  bool is_parenthesized_ : 1;
-  bool is_multi_parenthesized_ : 1;
+  class ToBooleanTypesField : public BitField<byte, 0, 8> {};
+  class IsParenthesizedField : public BitField<bool, 8, 1> {};
+  class IsMultiParenthesizedField : public BitField<bool, 9, 1> {};
+  uint32_t bit_field_;

[brucedawson, 2014/11/05 01:33:17]

Why use a bit field at all? byte/bool/bool take up three bytes, pads to four
bytes, which should be perfectly space efficient, more run-time efficient.

[Sven Panne, 2014/11/05 09:11:49]

All the code in ast.h *must* stay as it is, for the reason see:
https://code.google.com/p/chromium/issues/detail?id=417697. This part of the CL
would basically revert all the goodness already done.

Quick explanation: The layout of the AST nodes is carefully tuned for space
efficiency because asm.js code results in *huge* ASTs. As it is,
to_boolean_types consumes one byte, is_parenthesized and is_multiparenthesized
go into the next byte. The important thing: The most common node VariableProxy
starts with 3 1bit fields, which go into the next byte. (With clang at least,
use "clang++ -c -Xclang -fdump-record-layouts" to see what really happens)

If we blindingly change the layout here, we will blow away hundreds of megabytes
for asm.js stuff. Yes, this is all very fragile, but it's important
nevertheless.

Perhaps we should have a look at the layout of the nodes under VC, but I don't
know how to do that. Hints? :-)

[Jakob Kummerow, 2014/11/05 12:13:46]

Used a smaller field per offline discussion.

 };
 
 
@@ -1697,13 +1706,17 @@ class VariableProxy FINAL : public Expression {
     var_ = v;
   }
 
-  bool is_this() const { return is_this_; }
+  bool is_this() const { return IsThisField::decode(bit_field_); }
 
-  bool is_assigned() const { return is_assigned_; }
-  void set_is_assigned() { is_assigned_ = true; }
+  bool is_assigned() const { return IsAssignedField::decode(bit_field_); }
+  void set_is_assigned() {
+    bit_field_ = IsAssignedField::update(bit_field_, true);
+  }
 
-  bool is_resolved() const { return is_resolved_; }
-  void set_is_resolved() { is_resolved_ = true; }
+  bool is_resolved() const { return IsResolvedField::decode(bit_field_); }
+  void set_is_resolved() {
+    bit_field_ = IsResolvedField::update(bit_field_, true);
+  }
 
   Interface* interface() const { return interface_; }
 
@@ -1727,9 +1740,10 @@ class VariableProxy FINAL : public Expression {
   VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
                 Interface* interface, int position);
 
-  bool is_this_ : 1;
-  bool is_assigned_ : 1;
-  bool is_resolved_ : 1;
+  class IsThisField : public BitField<bool, 0, 1> {};
+  class IsAssignedField : public BitField<bool, 1, 1> {};
+  class IsResolvedField : public BitField<bool, 2, 1> {};
+  uint32_t bit_field_;
   FeedbackVectorICSlot variable_feedback_slot_;
   union {
     const AstRawString* raw_name_;  // if !is_resolved_
@@ -1752,7 +1766,9 @@ class Property FINAL : public Expression {
   BailoutId LoadId() const { return BailoutId(local_id(0)); }
   TypeFeedbackId PropertyFeedbackId() { return TypeFeedbackId(local_id(1)); }
 
-  bool IsStringAccess() const { return is_string_access_; }
+  bool IsStringAccess() const {
+    return IsStringAccessField::decode(bit_field_);
+  }
 
   // Type feedback information.
   virtual bool IsMonomorphic() OVERRIDE {
@@ -1761,21 +1777,29 @@ class Property FINAL : public Expression {
   virtual SmallMapList* GetReceiverTypes() OVERRIDE {
     return &receiver_types_;
   }
-  virtual KeyedAccessStoreMode GetStoreMode() OVERRIDE {
+  virtual KeyedAccessStoreMode GetStoreMode() const OVERRIDE {
     return STANDARD_STORE;
   }
-  virtual IcCheckType GetKeyType() OVERRIDE {
+  virtual IcCheckType GetKeyType() const OVERRIDE {
     // PROPERTY key types currently aren't implemented for KeyedLoadICs.
     return ELEMENT;
   }
-  bool IsUninitialized() { return !is_for_call_ && is_uninitialized_; }
-  bool HasNoTypeInformation() {
-    return is_uninitialized_;
+  bool IsUninitialized() const {
+    return !is_for_call() && HasNoTypeInformation();
+  }
+  bool HasNoTypeInformation() const {
+    return IsUninitializedField::decode(bit_field_);
+  }
+  void set_is_uninitialized(bool b) {
+    bit_field_ = IsUninitializedField::update(bit_field_, b);
+  }
+  void set_is_string_access(bool b) {
+    bit_field_ = IsStringAccessField::update(bit_field_, b);
   }
-  void set_is_uninitialized(bool b) { is_uninitialized_ = b; }
-  void set_is_string_access(bool b) { is_string_access_ = b; }
-  void mark_for_call() { is_for_call_ = true; }
-  bool IsForCall() { return is_for_call_; }
+  void mark_for_call() {
+    bit_field_ = IsForCallField::update(bit_field_, true);
+  }
+  bool is_for_call() const { return IsForCallField::decode(bit_field_); }
 
   bool IsSuperAccess() {
     return obj()->IsSuperReference();
@@ -1795,9 +1819,9 @@ class Property FINAL : public Expression {
  protected:
   Property(Zone* zone, Expression* obj, Expression* key, int pos)
       : Expression(zone, pos),
-        is_for_call_(false),
-        is_uninitialized_(false),
-        is_string_access_(false),
+        bit_field_(IsForCallField::encode(false) |
+                   IsUninitializedField::encode(false) |
+                   IsStringAccessField::encode(false)),
         property_feedback_slot_(FeedbackVectorICSlot::Invalid()),
         obj_(obj),
         key_(key) {}
@@ -1806,9 +1830,10 @@ class Property FINAL : public Expression {
  private:
   int local_id(int n) const { return base_id() + parent_num_ids() + n; }
 
-  bool is_for_call_ : 1;
-  bool is_uninitialized_ : 1;
-  bool is_string_access_ : 1;
+  class IsForCallField : public BitField<bool, 0, 1> {};
+  class IsUninitializedField : public BitField<bool, 1, 1> {};
+  class IsStringAccessField : public BitField<bool, 2, 1> {};
+  uint32_t bit_field_;
   FeedbackVectorICSlot property_feedback_slot_;
   Expression* obj_;
   Expression* key_;
@@ -2120,8 +2145,8 @@ class CountOperation FINAL : public Expression {
  public:
   DECLARE_NODE_TYPE(CountOperation)
 
-  bool is_prefix() const { return is_prefix_; }
-  bool is_postfix() const { return !is_prefix_; }
+  bool is_prefix() const { return IsPrefixField::decode(bit_field_); }
+  bool is_postfix() const { return !is_prefix(); }
 
   Token::Value op() const { return op_; }
   Token::Value binary_op() {
@@ -2136,13 +2161,19 @@ class CountOperation FINAL : public Expression {
   virtual SmallMapList* GetReceiverTypes() OVERRIDE {
     return &receiver_types_;
   }
-  virtual IcCheckType GetKeyType() OVERRIDE { return key_type_; }
-  virtual KeyedAccessStoreMode GetStoreMode() OVERRIDE {
-    return store_mode_;
+  virtual IcCheckType GetKeyType() const OVERRIDE {
+    return KeyTypeField::decode(bit_field_);
+  }
+  virtual KeyedAccessStoreMode GetStoreMode() const OVERRIDE {
+    return StoreModeField::decode(bit_field_);
   }
   Type* type() const { return type_; }
-  void set_key_type(IcCheckType type) { key_type_ = type; }
-  void set_store_mode(KeyedAccessStoreMode mode) { store_mode_ = mode; }
+  void set_key_type(IcCheckType type) {
+    bit_field_ = KeyTypeField::update(bit_field_, type);
+  }
+  void set_store_mode(KeyedAccessStoreMode mode) {
+    bit_field_ = StoreModeField::update(bit_field_, mode);
+  }
   void set_type(Type* type) { type_ = type; }
 
   static int num_ids() { return parent_num_ids() + 3; }
@@ -2159,20 +2190,22 @@ class CountOperation FINAL : public Expression {
                  int pos)
       : Expression(zone, pos),
         op_(op),
-        is_prefix_(is_prefix),
-        key_type_(ELEMENT),
-        store_mode_(STANDARD_STORE),
+        bit_field_(IsPrefixField::encode(is_prefix) |
+                   KeyTypeField::encode(ELEMENT) |
+                   StoreModeField::encode(STANDARD_STORE)),
+        type_(NULL),
         expression_(expr) {}
   static int parent_num_ids() { return Expression::num_ids(); }
 
  private:
   int local_id(int n) const { return base_id() + parent_num_ids() + n; }
 
+  class IsPrefixField : public BitField<bool, 0, 1> {};
+  class KeyTypeField : public BitField<IcCheckType, 1, 1> {};
+  class StoreModeField : public BitField<KeyedAccessStoreMode, 2, 4> {};
+
   Token::Value op_;
-  bool is_prefix_ : 1;
-  IcCheckType key_type_ : 1;
-  KeyedAccessStoreMode store_mode_ : 5;  // Windows treats as signed,
-                                         // must have extra bit.
+  uint32_t bit_field_;
   Type* type_;
   Expression* expression_;
   SmallMapList receiver_types_;
@@ -2277,20 +2310,30 @@ class Assignment FINAL : public Expression {
   virtual bool IsMonomorphic() OVERRIDE {
     return receiver_types_.length() == 1;
   }
-  bool IsUninitialized() { return is_uninitialized_; }
+  bool IsUninitialized() const {
+    return IsUninitializedField::decode(bit_field_);
+  }
   bool HasNoTypeInformation() {
-    return is_uninitialized_;
+    return IsUninitializedField::decode(bit_field_);
   }
   virtual SmallMapList* GetReceiverTypes() OVERRIDE {
     return &receiver_types_;
   }
-  virtual IcCheckType GetKeyType() OVERRIDE { return key_type_; }
-  virtual KeyedAccessStoreMode GetStoreMode() OVERRIDE {
-    return store_mode_;
+  virtual IcCheckType GetKeyType() const OVERRIDE {
+    return KeyTypeField::decode(bit_field_);
+  }
+  virtual KeyedAccessStoreMode GetStoreMode() const OVERRIDE {
+    return StoreModeField::decode(bit_field_);
+  }
+  void set_is_uninitialized(bool b) {
+    bit_field_ = IsUninitializedField::update(bit_field_, b);
+  }
+  void set_key_type(IcCheckType key_type) {
+    bit_field_ = KeyTypeField::update(bit_field_, key_type);
+  }
+  void set_store_mode(KeyedAccessStoreMode mode) {
+    bit_field_ = StoreModeField::update(bit_field_, mode);
   }
-  void set_is_uninitialized(bool b) { is_uninitialized_ = b; }
-  void set_key_type(IcCheckType key_type) { key_type_ = key_type; }
-  void set_store_mode(KeyedAccessStoreMode mode) { store_mode_ = mode; }
 
  protected:
   Assignment(Zone* zone, Token::Value op, Expression* target, Expression* value,
@@ -2309,10 +2352,10 @@ class Assignment FINAL : public Expression {
  private:
   int local_id(int n) const { return base_id() + parent_num_ids() + n; }
 
-  bool is_uninitialized_ : 1;
-  IcCheckType key_type_ : 1;
-  KeyedAccessStoreMode store_mode_ : 5;  // Windows treats as signed,
-                                         // must have extra bit.
+  class IsUninitializedField : public BitField<bool, 0, 1> {};
+  class KeyTypeField : public BitField<IcCheckType, 1, 1> {};
+  class StoreModeField : public BitField<KeyedAccessStoreMode, 2, 4> {};
+  uint32_t bit_field_;
   Token::Value op_;
   Expression* target_;
   Expression* value_;