Make the AstValueFactory more efficient and less memory hungry

src/ast/ast-value-factory.h

Index: src/ast/ast-value-factory.h
diff --git a/src/ast/ast-value-factory.h b/src/ast/ast-value-factory.h
index 91e7d78c38b97720c10ecc5167091a045f38f243..98779cfab24b967f0925e4138ba416bc122608dc 100644
--- a/src/ast/ast-value-factory.h
+++ b/src/ast/ast-value-factory.h
@@ -43,9 +43,7 @@ namespace internal {
 class AstString : public ZoneObject {
  public:
   explicit AstString(bool is_raw)
-      : bit_field_(IsRawStringBits::encode(is_raw)) {}
-
-  ~AstString() {}
+      : next_(nullptr), bit_field_(IsRawStringBits::encode(is_raw)) {}
 
   int length() const;
   bool IsEmpty() const { return length() == 0; }
@@ -59,9 +57,15 @@ class AstString : public ZoneObject {
     return string_;
   }
 
+  AstString** next_location() { return &next_; }
+  AstString* next() const { return next_; }
+
  protected:
-  // This is null until the string is internalized.
-  Handle<String> string_;
+  // This is a pointer to the next uninternalized string until internalized.
+  union {
+    Handle<String> string_;
+    AstString* next_;
+  };
   // Poor-man's virtual dispatch to AstRawString / AstConsString. Takes less
   // memory.
   class IsRawStringBits : public BitField<bool, 0, 1> {};
@@ -201,6 +205,8 @@ class AstValue : public ZoneObject {
     DCHECK(!value_.is_null());
     return value_;
   }
+  AstValue* next() const { return next_; }
+  void set_next(AstValue* next) { next_ = next; }
 
  private:
   friend class AstValueFactory;
@@ -217,11 +223,15 @@ class AstValue : public ZoneObject {
     THE_HOLE
   };
 
-  explicit AstValue(const AstRawString* s) : type_(STRING) { string_ = s; }
+  explicit AstValue(const AstRawString* s) : type_(STRING), next_(nullptr) {
+    string_ = s;
+  }
 
-  explicit AstValue(const char* name) : type_(SYMBOL) { symbol_name_ = name; }
+  explicit AstValue(const char* name) : type_(SYMBOL), next_(nullptr) {
+    symbol_name_ = name;
+  }
 
-  explicit AstValue(double n, bool with_dot) {
+  explicit AstValue(double n, bool with_dot) : next_(nullptr) {
     if (with_dot) {
       type_ = NUMBER_WITH_DOT;
       number_ = n;
@@ -237,14 +247,14 @@ class AstValue : public ZoneObject {
     }
   }
 
-  AstValue(Type t, int i) : type_(t) {
+  AstValue(Type t, int i) : type_(t), next_(nullptr) {
     DCHECK(type_ == SMI);
     smi_ = i;
   }
 
-  explicit AstValue(bool b) : type_(BOOLEAN) { bool_ = b; }
+  explicit AstValue(bool b) : type_(BOOLEAN), next_(nullptr) { bool_ = b; }
 
-  explicit AstValue(Type t) : type_(t) {
+  explicit AstValue(Type t) : type_(t), next_(nullptr) {
     DCHECK(t == NULL_TYPE || t == UNDEFINED || t == THE_HOLE);
   }
 
@@ -256,12 +266,16 @@ class AstValue : public ZoneObject {
     double number_;
     int smi_;
     bool bool_;
-    ZoneList<const AstRawString*>* strings_;
+    const AstRawString* strings_;
     const char* symbol_name_;
   };
 
-  // Internalized value (empty before internalized).
-  Handle<Object> value_;
+  // Internalized value (pointer to the next uninternalized value until
+  // internalized).
+  union {
+    Handle<Object> value_;
+    AstValue* next_;
+  };
 };
 
 
@@ -314,9 +328,12 @@ class AstValueFactory {
  public:
   AstValueFactory(Zone* zone, uint32_t hash_seed)
       : string_table_(AstRawStringCompare),
+        values_(nullptr),
+        strings_end_(&strings_),
         zone_(zone),
         isolate_(NULL),
         hash_seed_(hash_seed) {
+    ResetStrings();
 #define F(name, str) name##_string_ = NULL;
     STRING_CONSTANTS(F)
 #undef F
@@ -371,6 +388,28 @@ class AstValueFactory {
   const AstValue* NewTheHole();
 
  private:
+  AstValue* AddValue(AstValue* value) {
+    if (isolate_) {
+      value->Internalize(isolate_);
+    } else {
+      value->set_next(values_);
+      values_ = value;
+    }
+    return value;
+  }
+  AstString* AddString(AstString* string) {
+    if (isolate_) {
+      string->Internalize(isolate_);
+    } else {
+      *strings_end_ = string;
+      strings_end_ = string->next_location();
+    }
+    return string;
+  }
+  void ResetStrings() {
+    strings_ = nullptr;
+    strings_end_ = &strings_;
+  }
   AstRawString* GetOneByteStringInternal(Vector<const uint8_t> literal);
   AstRawString* GetTwoByteStringInternal(Vector<const uint16_t> literal);
   AstRawString* GetString(uint32_t hash, bool is_one_byte,
@@ -382,8 +421,11 @@ class AstValueFactory {
   base::HashMap string_table_;
   // For keeping track of all AstValues and AstRawStrings we've created (so that
   // they can be internalized later).
-  List<AstValue*> values_;
-  List<AstString*> strings_;
+  AstValue* values_;
+  // We need to keep track of strings_ in order, since cons strings require
+  // their members to be internalized first.
+  AstString* strings_;
+  AstString** strings_end_;
   Zone* zone_;
   Isolate* isolate_;