Speed up access to global variables from eval scopes. Traverse the...

src/contexts.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 180 matching lines @@
   } while (follow_context_chain);
 
   // slot not found
   if (FLAG_trace_contexts) {
     PrintF("=> no property/slot found\n");
   }
   return Handle<Object>::null();
 }
 
 
+bool Context::GlobalIfNotShadowedByEval(Handle<String> name) {
+  Context* context = this;
+
+  // Check that there is no local with the given name in contexts
+  // before the global context and check that there are no context
+  // extension objects (conservative check for with statements).
+  while (!context->IsGlobalContext()) {
+    // Check if the context is a potentially a with context.
+    if (context->has_extension()) return false;
+
+    // Not a with context so it must be a function context.
+    ASSERT(context->is_function_context());
+
+    // Check non-parameter locals.
+    Handle<Code> code(context->closure()->code());
+    Variable::Mode mode;
+    int index = ScopeInfo<>::ContextSlotIndex(*code, *name, &mode);
+    ASSERT(index < 0 || index >= MIN_CONTEXT_SLOTS);
+    if (index >= 0) return false;
+
+    // Check parameter locals.
+    int param_index = ScopeInfo<>::ParameterIndex(*code, *name);
+    if (param_index >= 0) return false;
+
+    // Check context only holding the function name variable.
+    index = ScopeInfo<>::FunctionContextSlotIndex(*code, *name);
+    if (index >= 0) return false;
+    context = Context::cast(context->closure()->context());
+  }
+
+  // No local or potential with statement found so the variable is
+  // global unless it is shadowed by an eval-introduced variable.
+  return true;
+}
+
+
 #ifdef DEBUG
 bool Context::IsBootstrappingOrContext(Object* object) {
   // During bootstrapping we allow all objects to pass as
   // contexts. This is necessary to fix circular dependencies.
   return Bootstrapper::IsActive() || object->IsContext();
 }
 
 
 bool Context::IsBootstrappingOrGlobalObject(Object* object) {
   // During bootstrapping we allow all objects to pass as global
   // objects. This is necessary to fix circular dependencies.
   return Bootstrapper::IsActive() || object->IsGlobalObject();
 }
 #endif
 
 } }  // namespace v8::internal