Do not waste space for the fast-case elements backing storage for ...

src/parser.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 193 matching lines @@
   Expression* ParseArrayLiteral(bool* ok);
   Expression* ParseObjectLiteral(bool* ok);
   Expression* ParseRegExpLiteral(bool seen_equal, bool* ok);
 
   // Populate the constant properties fixed array for a materialized object
   // literal.
   void BuildObjectLiteralConstantProperties(
       ZoneList<ObjectLiteral::Property*>* properties,
       Handle<FixedArray> constants,
       bool* is_simple,
+      bool* fast_elements,
       int* depth);
 
   // Populate the literals fixed array for a materialized array literal.
   void BuildArrayLiteralBoilerplateLiterals(ZoneList<Expression*>* properties,
                                             Handle<FixedArray> constants,
                                             bool* is_simple,
                                             int* depth);
 
   // Decide if a property should be in the object boilerplate.
   bool IsBoilerplateProperty(ObjectLiteral::Property* property);
@@ skipping 3214 matching lines @@
   MaterializedLiteral* lit = expression->AsMaterializedLiteral();
   return lit != NULL && lit->is_simple();
 }
 
 Handle<FixedArray> CompileTimeValue::GetValue(Expression* expression) {
   ASSERT(IsCompileTimeValue(expression));
   Handle<FixedArray> result = Factory::NewFixedArray(2, TENURED);
   ObjectLiteral* object_literal = expression->AsObjectLiteral();
   if (object_literal != NULL) {
     ASSERT(object_literal->is_simple());
-    result->set(kTypeSlot, Smi::FromInt(OBJECT_LITERAL));
+    if (object_literal->fast_elements()) {
+      result->set(kTypeSlot, Smi::FromInt(OBJECT_LITERAL_FAST_ELEMENTS));
+    } else {
+      result->set(kTypeSlot, Smi::FromInt(OBJECT_LITERAL_SLOW_ELEMENTS));
+    }
     result->set(kElementsSlot, *object_literal->constant_properties());
   } else {
     ArrayLiteral* array_literal = expression->AsArrayLiteral();
     ASSERT(array_literal != NULL && array_literal->is_simple());
     result->set(kTypeSlot, Smi::FromInt(ARRAY_LITERAL));
     result->set(kElementsSlot, *array_literal->constant_elements());
   }
   return result;
 }
 
@@ skipping 17 matching lines @@
     return CompileTimeValue::GetValue(expression);
   }
   return Factory::undefined_value();
 }
 
 
 void Parser::BuildObjectLiteralConstantProperties(
     ZoneList<ObjectLiteral::Property*>* properties,
     Handle<FixedArray> constant_properties,
     bool* is_simple,
+    bool* fast_elements,
     int* depth) {
   int position = 0;
   // Accumulate the value in local variables and store it at the end.
   bool is_simple_acc = true;
   int depth_acc = 1;
+  uint32_t max_element_index = 0;
+  uint32_t elements = 0;
   for (int i = 0; i < properties->length(); i++) {
     ObjectLiteral::Property* property = properties->at(i);
     if (!IsBoilerplateProperty(property)) {
       is_simple_acc = false;
       continue;
     }
     MaterializedLiteral* m_literal = property->value()->AsMaterializedLiteral();
     if (m_literal != NULL && m_literal->depth() >= depth_acc) {
       depth_acc = m_literal->depth() + 1;
     }
 
     // Add CONSTANT and COMPUTED properties to boilerplate. Use undefined
     // value for COMPUTED properties, the real value is filled in at
     // runtime. The enumeration order is maintained.
     Handle<Object> key = property->key()->handle();
     Handle<Object> value = GetBoilerplateValue(property->value());
     is_simple_acc = is_simple_acc && !value->IsUndefined();
 
+    // Keep track of the number of elements in the object literal and
+    // the largest element index.  If the largest element index is
+    // much larger than the number of elements, creating an object
+    // literal with fast elements will be a waste of space.
+    uint32_t element_index = 0;
+    if (key->IsString()
+        && Handle<String>::cast(key)->AsArrayIndex(&element_index)
+        && element_index > max_element_index) {
+      max_element_index = element_index;
+      elements++;
+    } else if (key->IsSmi()) {
+      int key_value = Smi::cast(*key)->value();
+      if (key_value > 0
+          && static_cast<uint32_t>(key_value) > max_element_index) {
+        max_element_index = key_value;
+      }
+      elements++;
+    }
+
     // Add name, value pair to the fixed array.
     constant_properties->set(position++, *key);
     constant_properties->set(position++, *value);
   }
-
+  *fast_elements =
+      (max_element_index <= 32) || ((2 * elements) >= max_element_index);
   *is_simple = is_simple_acc;
   *depth = depth_acc;
 }
 
 
 Expression* Parser::ParseObjectLiteral(bool* ok) {
   // ObjectLiteral ::
   //   '{' (
   //       ((Identifier | String | Number) ':' AssignmentExpression)
   //     | (('get' | 'set') FunctionLiteral)
@@ skipping 77 matching lines @@
   }
   Expect(Token::RBRACE, CHECK_OK);
   // Computation of literal_index must happen before pre parse bailout.
   int literal_index = temp_scope_->NextMaterializedLiteralIndex();
   if (is_pre_parsing_) return NULL;
 
   Handle<FixedArray> constant_properties =
       Factory::NewFixedArray(number_of_boilerplate_properties * 2, TENURED);
 
   bool is_simple = true;
+  bool fast_elements = true;
   int depth = 1;
   BuildObjectLiteralConstantProperties(properties.elements(),
                                        constant_properties,
                                        &is_simple,
+                                       &fast_elements,
                                        &depth);
   return new ObjectLiteral(constant_properties,
                            properties.elements(),
                            literal_index,
                            is_simple,
+                           fast_elements,
                            depth);
 }
 
 
 Expression* Parser::ParseRegExpLiteral(bool seen_equal, bool* ok) {
   if (!scanner_.ScanRegExpPattern(seen_equal)) {
     Next();
     ReportMessage("unterminated_regexp", Vector<const char*>::empty());
     *ok = false;
     return NULL;
@@ skipping 486 matching lines @@
     } while (Check(Token::COMMA));
   }
   Expect(Token::RBRACE, CHECK_OK);
 
   int literal_index = temp_scope_->NextMaterializedLiteralIndex();
   if (is_pre_parsing_) return NULL;
 
   Handle<FixedArray> constant_properties =
         Factory::NewFixedArray(boilerplate_properties * 2, TENURED);
   bool is_simple = true;
+  bool fast_elements = true;
   int depth = 1;
   BuildObjectLiteralConstantProperties(properties.elements(),
                                        constant_properties,
                                        &is_simple,
+                                       &fast_elements,
                                        &depth);
   return new ObjectLiteral(constant_properties,
                            properties.elements(),
                            literal_index,
                            is_simple,
+                           fast_elements,
                            depth);
 }
 
 
 // Parse a JSON array. Scanner must be right after '[' token.
 Expression* Parser::ParseJsonArray(bool* ok) {
   Consume(Token::LBRACK);
 
   ZoneListWrapper<Expression> values = factory()->NewList<Expression>(4);
   if (peek() != Token::RBRACK) {
@@ skipping 944 matching lines @@
       parser.ParseLazy(script_source, name,
                        start_position, end_position, is_expression);
   return result;
 }
 
 
 #undef NEW
 
 
 } }  // namespace v8::internal