[Patch, RFC, c*, ObjC* ] make the translation unit decl avail. via a lang hook

[IainS <developer at sandoe-acoustics dot co dot uk>]

given that my current understanding is:
(a) we should make vars file-scope by setting DECL_CONTEXT =  
translation unit decl
(b) there should only be one translation unit decl per TU
(c) at present none of the FEs export the t_u_d where other parts of  
the machinery can see it.

would the following patch be appropriate?
(it can be extended to fortran and java, I believe, fairly easily).

---

(With this applied I can use
  DECL_CONTEXT (decl) = (*lang_hooks.decls.translation_unit_context)  
();

  in each place that it is currently set to NULL in objc-act.c
  and also replace the two instances of pushdecl_top_level () with  
the same.

 and I get no new test-suite fails for ObjC*
)

comments?
Iain


Index: gcc/c-family/c-common.h
===================================================================
--- gcc/c-family/c-common.h	(revision 166059)
+++ gcc/c-family/c-common.h	(working copy)
@@ -514,6 +514,7 @@ extern tree add_stmt (tree);
 extern void push_cleanup (tree, tree, bool);
 extern tree pushdecl_top_level (tree);
 extern tree pushdecl (tree);
+extern tree c_translation_unit_decl (void);
 extern tree build_modify_expr (location_t, tree, tree, enum tree_code,
 			       location_t, tree, tree);
 extern tree build_indirect_ref (location_t, tree, ref_operator);
Index: gcc/cp/decl.c
===================================================================
--- gcc/cp/decl.c	(revision 166059)
+++ gcc/cp/decl.c	(working copy)
@@ -3427,6 +3427,19 @@ initialize_predefined_identifiers (void)
     }
 }

+/* The current translation unit.  */
+static GTY(()) tree current_translation_unit = NULL_TREE;
+
+/* The function used to return the current t_u_d for the
+   translation_unit_context langhook.  */
+
+tree
+cp_translation_unit_decl (void)
+{
+  gcc_assert (current_translation_unit);
+  return current_translation_unit;
+}
+
 /* Create the predefined scalar types of C,
    and some nodes representing standard constants (0, 1, (void *)0).
    Initialize the global binding level.
@@ -3452,7 +3465,8 @@ cxx_init_decl_processing (void)
   gcc_assert (global_namespace == NULL_TREE);
   global_namespace = build_lang_decl (NAMESPACE_DECL,  
global_scope_name,
 				      void_type_node);
-  DECL_CONTEXT (global_namespace) = build_translation_unit_decl  
(NULL_TREE);
+  current_translation_unit = build_translation_unit_decl (NULL_TREE);
+  DECL_CONTEXT (global_namespace) = current_translation_unit;
   TREE_PUBLIC (global_namespace) = 1;
   begin_scope (sk_namespace, global_namespace);

Index: gcc/cp/cp-objcp-common.h
===================================================================
--- gcc/cp/cp-objcp-common.h	(revision 166059)
+++ gcc/cp/cp-objcp-common.h	(working copy)
@@ -132,6 +132,8 @@ extern bool cp_function_decl_explicit_p (tree decl
 #define LANG_HOOKS_GIMPLIFY_EXPR cp_gimplify_expr
 #undef LANG_HOOKS_FUNCTION_DECL_EXPLICIT_P
 #define LANG_HOOKS_FUNCTION_DECL_EXPLICIT_P  
cp_function_decl_explicit_p
+#undef  LANG_HOOKS_TUD
+#define LANG_HOOKS_TUD cp_translation_unit_decl
 #undef LANG_HOOKS_OMP_PREDETERMINED_SHARING
 #define LANG_HOOKS_OMP_PREDETERMINED_SHARING  
cxx_omp_predetermined_sharing
 #undef LANG_HOOKS_OMP_CLAUSE_DEFAULT_CTOR
Index: gcc/cp/cp-tree.h
===================================================================
--- gcc/cp/cp-tree.h	(revision 166059)
+++ gcc/cp/cp-tree.h	(working copy)
@@ -4764,6 +4764,7 @@ extern tree current_decl_namespace		(void);

 /* decl.c */
 extern tree poplevel				(int, int, int);
+extern tree cp_translation_unit_decl		(void);
 extern void cxx_init_decl_processing		(void);
 enum cp_tree_node_structure_enum cp_tree_node_structure
 						(union lang_tree_node *);
Index: gcc/c-objc-common.h
===================================================================
--- gcc/c-objc-common.h	(revision 166059)
+++ gcc/c-objc-common.h	(working copy)
@@ -85,6 +85,8 @@ along with GCC; see the file COPYING3.  If not see
 #define LANG_HOOKS_TO_TARGET_CHARSET c_common_to_target_charset
 #undef LANG_HOOKS_EXPR_TO_DECL
 #define LANG_HOOKS_EXPR_TO_DECL c_expr_to_decl
+#undef  LANG_HOOKS_TUD
+#define LANG_HOOKS_TUD c_translation_unit_decl

 /* The C front end's scoping structure is very different from
    that expected by the language-independent code; it is best
Index: gcc/c-decl.c
===================================================================
--- gcc/c-decl.c	(revision 166059)
+++ gcc/c-decl.c	(working copy)
@@ -454,6 +454,8 @@ static GTY((deletable)) struct c_binding *binding_
   t_->to##_last = f_->from##_last;				\
 } while (0)

+static GTY(()) tree current_translation_unit = NULL_TREE;
+
 /* A c_inline_static structure stores details of a static identifier
    referenced in a definition of a function that may be an inline
    definition if no subsequent declaration of that function uses
@@ -528,6 +530,14 @@ static tree grokdeclarator (const struct c_declara
 static tree grokparms (struct c_arg_info *, bool);
 static void layout_array_type (tree);
 
+/* Return the translation unit decl for the current TU.  */
+tree
+c_translation_unit_decl (void)
+{
+  gcc_assert (current_translation_unit);
+  return current_translation_unit;
+}
+
 /* T is a statement.  Add it to the statement-tree.  This is the
    C/ObjC version--C++ has a slightly different version of this
    function.  */
@@ -1066,8 +1076,7 @@ pop_scope (void)
     context = current_function_decl;
   else if (scope == file_scope)
     {
-      tree file_decl = build_translation_unit_decl (NULL_TREE);
-      context = file_decl;
+      context = (*lang_hooks.decls.translation_unit_context) ();
     }
   else
     context = block;
@@ -3461,6 +3470,9 @@ c_init_decl_processing (void)

   c_common_nodes_and_builtins ();

+  /* The current translation unit.  */
+  current_translation_unit = build_translation_unit_decl (NULL_TREE);
+
   /* In C, comparisons and TRUTH_* expressions have type int.  */
   truthvalue_type_node = integer_type_node;
   truthvalue_true_node = integer_one_node;
Index: gcc/langhooks.h
===================================================================
--- gcc/langhooks.h	(revision 166059)
+++ gcc/langhooks.h	(working copy)
@@ -152,6 +152,9 @@ struct lang_hooks_for_decls
      symbol is already declared, may return a different decl for that
      name.  */
   tree (*pushdecl) (tree);
+
+  /* To add a decl to 'file scope' set its DECL_CONTEXT to this.  */
+  tree (*translation_unit_context) (void);

   /* Returns the chain of decls so far in the current scope level.  */
   tree (*getdecls) (void);
Index: gcc/langhooks-def.h
===================================================================
--- gcc/langhooks-def.h	(revision 166059)
+++ gcc/langhooks-def.h	(working copy)
@@ -200,6 +200,7 @@ extern tree lhd_make_node (enum tree_code);
 /* Declaration hooks.  */
 #define LANG_HOOKS_GLOBAL_BINDINGS_P global_bindings_p
 #define LANG_HOOKS_PUSHDECL	pushdecl
+#define LANG_HOOKS_TUD	lhd_return_null_tree_v
 #define LANG_HOOKS_GETDECLS	getdecls
 #define LANG_HOOKS_FUNCTION_DECL_EXPLICIT_P hook_bool_tree_false
 #define LANG_HOOKS_WARN_UNUSED_GLOBAL_DECL lhd_warn_unused_global_decl
@@ -220,6 +221,7 @@ extern tree lhd_make_node (enum tree_code);
 #define LANG_HOOKS_DECLS { \
   LANG_HOOKS_GLOBAL_BINDINGS_P, \
   LANG_HOOKS_PUSHDECL, \
+  LANG_HOOKS_TUD, \
   LANG_HOOKS_GETDECLS, \
   LANG_HOOKS_FUNCTION_DECL_EXPLICIT_P, \
   LANG_HOOKS_GENERIC_GENERIC_PARAMETER_DECL_P, \