Do not look for the slot in the ScopeInfo's global range when it's not necessary.

src/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/scopes.h"
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
 #include "src/messages.h"
 #include "src/parser.h"
@@ skipping 376 matching lines @@
   Handle<String> name_handle = name->string();
   // The Scope is backed up by ScopeInfo. This means it cannot operate in a
   // heap-independent mode, and all strings must be internalized immediately. So
   // it's ok to get the Handle<String> here.
   // If we have a serialized scope info, we might find the variable there.
   // There should be no local slot with the given name.
   DCHECK(scope_info_->StackSlotIndex(*name_handle) < 0 || is_block_scope());
 
   // Check context slot lookup.
   VariableMode mode;
-  VariableLocation location;
+  VariableLocation location = VariableLocation::CONTEXT;
   InitializationFlag init_flag;
   MaybeAssignedFlag maybe_assigned_flag;
-  int index =
-      ScopeInfo::ContextSlotIndex(scope_info_, name_handle, &mode, &location,
-                                  &init_flag, &maybe_assigned_flag);
+  int index = ScopeInfo::ContextSlotIndex(scope_info_, name_handle, &mode,
+                                          &init_flag, &maybe_assigned_flag);
+  if (index < 0) {
+    location = VariableLocation::GLOBAL;
+    index = ScopeInfo::ContextGlobalSlotIndex(scope_info_, name_handle, &mode,
+                                              &init_flag, &maybe_assigned_flag);
+  }
   if (index < 0) {
     // Check parameters.
     index = scope_info_->ParameterIndex(*name_handle);
     if (index < 0) return NULL;
 
     mode = DYNAMIC;
     location = VariableLocation::LOOKUP;
     init_flag = kCreatedInitialized;
     // Be conservative and flag parameters as maybe assigned. Better information
     // would require ScopeInfo to serialize the maybe_assigned bit also for
@@ skipping 1208 matching lines @@
       function_ != NULL && function_->proxy()->var()->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS - num_global_slots() -
          (is_function_var_in_context ? 1 : 0);
 }
 
 
 int Scope::ContextGlobalCount() const { return num_global_slots(); }
 
 }  // namespace internal
 }  // namespace v8