Remove the fcontext field from all contexts.

src/contexts.h

 // Copyright 2011 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 112 matching lines @@
 //
 // [ closure   ]  This is the current function. It is the same for all
 //                contexts inside a function. It provides access to the
 //                incoming context (i.e., the outer context, which may
 //                or may not become the current function's context), and
 //                it provides access to the functions code and thus it's
 //                scope information, which in turn contains the names of
 //                statically allocated context slots. The names are needed
 //                for dynamic lookups in the presence of 'with' or 'eval'.
 //
-// [ fcontext  ]  A pointer to the innermost enclosing function context.
-//                It is the same for all contexts *allocated* inside a
-//                function, and the function context's fcontext points
-//                to itself. It is only needed for fast access of the
-//                function context (used for declarations, and static
-//                context slot access).
-//
 // [ previous  ]  A pointer to the previous context. It is NULL for
 //                function contexts, and non-NULL for 'with' contexts.
 //                Used to implement the 'with' statement.
 //
 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
 //                implement 'with' statements and dynamic declarations
 //                (through 'eval'). The object in a 'with' statement is
 //                stored in the extension slot of a 'with' context.
 //                Dynamically declared variables/functions are also added
 //                to lazily allocated extension object. Context::Lookup
 //                searches the extension object for properties.
 //
 // [ global    ]  A pointer to the global object. Provided for quick
 //                access to the global object from inside the code (since
 //                we always have a context pointer).
 //
 // In addition, function contexts may have statically allocated context slots
 // to store local variables/functions that are accessed from inner functions
 // (via static context addresses) or through 'eval' (dynamic context lookups).
 // Finally, the global context contains additional slots for fast access to
 // global properties.
-//
-// We may be able to simplify the implementation:
-//
-// - We may be able to get rid of 'fcontext': We can always use the fact that
-//   previous == NULL for function contexts and so we can search for them. They
-//   are only needed when doing dynamic declarations, and the context chains
-//   tend to be very very short (depth of nesting of 'with' statements). At
-//   the moment we also use it in generated code for context slot accesses -
-//   and there we don't want a loop because of code bloat - but we may not
-//   need it there after all (see comment in codegen_*.cc).
 
 class Context: public FixedArray {
  public:
   // Conversions.
   static Context* cast(Object* context) {
     ASSERT(context->IsContext());
     return reinterpret_cast<Context*>(context);
   }
 
   // The default context slot layout; indices are FixedArray slot indices.
   enum {
     // These slots are in all contexts.
     CLOSURE_INDEX,
-    FCONTEXT_INDEX,
     PREVIOUS_INDEX,
     // The extension slot is used for either the global object (in global
     // contexts), eval extension object (function contexts), subject of with
     // (with contexts), or the variable name (catch contexts).
     EXTENSION_INDEX,
     GLOBAL_INDEX,
     MIN_CONTEXT_SLOTS,
 
     // This slot holds the thrown value in catch contexts.
     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
@@ skipping 62 matching lines @@
     // Total number of slots.
     GLOBAL_CONTEXT_SLOTS,
 
     FIRST_WEAK_SLOT = OPTIMIZED_FUNCTIONS_LIST
   };
 
   // Direct slot access.
   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
   void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
 
-  Context* fcontext() { return Context::cast(get(FCONTEXT_INDEX)); }
-  void set_fcontext(Context* context) { set(FCONTEXT_INDEX, context); }
-
   Context* previous() {
     Object* result = unchecked_previous();
     ASSERT(IsBootstrappingOrContext(result));
     return reinterpret_cast<Context*>(result);
   }
   void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
 
   bool has_extension() { return extension() != NULL; }
   Object* extension() { return get(EXTENSION_INDEX); }
   void set_extension(Object* object) { set(EXTENSION_INDEX, object); }
 
+  // Get the context where var declarations will be hoisted to, which
+  // may be the context itself.
+  Context* declaration_context();
+
   GlobalObject* global() {
     Object* result = get(GLOBAL_INDEX);
     ASSERT(IsBootstrappingOrGlobalObject(result));
     return reinterpret_cast<GlobalObject*>(result);
   }
   void set_global(GlobalObject* global) { set(GLOBAL_INDEX, global); }
 
   // Returns a JSGlobalProxy object or null.
   JSObject* global_proxy();
   void set_global_proxy(JSObject* global);
@@ skipping 111 matching lines @@
 #ifdef DEBUG
   // Bootstrapping-aware type checks.
   static bool IsBootstrappingOrContext(Object* object);
   static bool IsBootstrappingOrGlobalObject(Object* object);
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_