Optimize the scope creation code by lazily allocating the hash maps...

src/scopes.h

 // 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 17 matching lines @@
 #ifndef V8_SCOPES_H_
 #define V8_SCOPES_H_
 
 #include "ast.h"
 #include "hashmap.h"
 
 namespace v8 { namespace internal {
 
 
 // A hash map to support fast local variable declaration and lookup.
-
 class LocalsMap: public HashMap {
  public:
   LocalsMap();
 
   // Dummy constructor.  This constructor doesn't set up the map
   // properly so don't use it unless you have a good reason.
   explicit LocalsMap(bool gotta_love_static_overloading);
 
   virtual ~LocalsMap();
 
   Variable* Declare(Scope* scope, Handle<String> name, Variable::Mode mode,
                     bool is_valid_LHS, bool is_this);
 
   Variable* Lookup(Handle<String> name);
 };
 
 
+// The dynamic scope part holds hash maps for the variables that will
+// be looked up dynamically from within eval and with scopes. The objects
+// are allocated on-demand from Scope::NonLocal to avoid wasting memory
+// and setup time for scopes that don't need them.
+class DynamicScopePart : public ZoneObject {
+ public:
+  LocalsMap* GetMap(Variable::Mode mode) {
+    int index = mode - Variable::DYNAMIC;
+    ASSERT(index >= 0 && index < 3);
+    return &maps_[index];
+  }
+
+ private:
+  LocalsMap maps_[3];
+};
+
+
 // Global invariants after AST construction: Each reference (i.e. identifier)
 // to a JavaScript variable (including global properties) is represented by a
 // VariableProxy node. Immediately after AST construction and before variable
 // allocation, most VariableProxy nodes are "unresolved", i.e. not bound to a
 // corresponding variable (though some are bound during parse time). Variable
 // allocation binds each unresolved VariableProxy to one Variable and assigns
 // a location. Note that many VariableProxy nodes may refer to the same Java-
 // Script variable.
 
 class Scope: public ZoneObject {
@@ skipping 205 matching lines @@
   Handle<String> scope_name_;
 
   // The variables declared in this scope:
   // all user-declared variables (incl. parameters)
   LocalsMap locals_;
   // compiler-allocated (user-invisible) temporaries
   ZoneList<Variable*> temps_;
   // parameter list in source order
   ZoneList<Variable*> params_;
   // variables that must be looked up dynamically
-  LocalsMap dynamics_;
-  LocalsMap dynamics_local_;
-  LocalsMap dynamics_global_;
+  DynamicScopePart* dynamics_;
   // unresolved variables referred to from this scope
   ZoneList<VariableProxy*> unresolved_;
   // declarations
   ZoneList<Declaration*> decls_;
   // convenience variable
   VariableProxy* receiver_;
   // function variable, if any; function scopes only
   Variable* function_;
   // convenience variable; function scopes only
   VariableProxy* arguments_;
@@ skipping 65 matching lines @@
   virtual VariableProxy* NewUnresolved(Handle<String> name, bool inside_with) {
     return NULL;
   }
   virtual VariableProxy* NewTemporary(Handle<String> name)  { return NULL; }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCOPES_H_