Support for global var shortcuts in script contexts.

src/contexts.cc

Index: src/contexts.cc
diff --git a/src/contexts.cc b/src/contexts.cc
index 0c27681a7dca42554f6d835e626d84d058708c79..b29405b505b2316236fad7168366207d54bfbd92 100644
--- a/src/contexts.cc
+++ b/src/contexts.cc
@@ -40,10 +40,10 @@ bool ScriptContextTable::Lookup(Handle<ScriptContextTable> table,
     DCHECK(context->IsScriptContext());
     Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));
     int slot_index = ScopeInfo::ContextSlotIndex(
-        scope_info, name, &result->mode, &result->init_flag,
+        scope_info, name, &result->mode, &result->location, &result->init_flag,
         &result->maybe_assigned_flag);
 
-    if (slot_index >= 0) {
+    if (slot_index >= 0 && result->location == VariableLocation::CONTEXT) {
       result->context_index = i;
       result->slot_index = slot_index;
       return true;
@@ -287,14 +287,15 @@ Handle<Object> Context::Lookup(Handle<String> name,
             ScopeInfo::cast(context->extension()), isolate);
       }
       VariableMode mode;
+      VariableLocation location;
       InitializationFlag init_flag;
       // TODO(sigurds) Figure out whether maybe_assigned_flag should
       // be used to compute binding_flags.
       MaybeAssignedFlag maybe_assigned_flag;
       int slot_index = ScopeInfo::ContextSlotIndex(
-          scope_info, name, &mode, &init_flag, &maybe_assigned_flag);
+          scope_info, name, &mode, &location, &init_flag, &maybe_assigned_flag);
       DCHECK(slot_index < 0 || slot_index >= MIN_CONTEXT_SLOTS);
-      if (slot_index >= 0) {
+      if (slot_index >= 0 && location == VariableLocation::CONTEXT) {
         if (FLAG_trace_contexts) {
           PrintF("=> found local in context slot %d (mode = %d)\n",
                  slot_index, mode);
@@ -352,6 +353,27 @@ Handle<Object> Context::Lookup(Handle<String> name,
 }
 
 
+void Context::InitializeGlobalSlots() {
+  DCHECK(IsScriptContext());
+  DisallowHeapAllocation no_gc;
+
+  ScopeInfo* scope_info = ScopeInfo::cast(extension());
+
+  int context_globals = scope_info->ContextGlobalCount();
+  if (context_globals > 0) {
+    PropertyCell* empty_cell = GetHeap()->empty_property_cell();
+
+    int context_locals = scope_info->ContextLocalCount();
+    int index = Context::MIN_CONTEXT_SLOTS + context_locals;
+    for (int i = 0; i < context_globals; i++) {
+      // Clear both read and write slots.
+      set(index++, empty_cell);
+      set(index++, empty_cell);
+    }
+  }
+}
+
+
 void Context::AddOptimizedFunction(JSFunction* function) {
   DCHECK(IsNativeContext());
 #ifdef ENABLE_SLOW_DCHECKS