c++: introduce TRAIT_TYPE alongside TRAIT_EXPR

We already have generic support for predicate-like traits that yield a
boolean value via TRAIT_EXPR, but we lack the same support for traits
that yield a type instead of a value.  Such support would streamline
implementing efficient builtins for the standard library type traits.

To that end this patch implements a generic TRAIT_TYPE type alongside
TRAIT_EXPR, and reimplements the existing UNDERLYING_TYPE builtin trait
using this new TRAIT_TYPE.

gcc/cp/ChangeLog:

	* cp-objcp-common.cc (cp_common_init_ts): Replace
	UNDERLYING_TYPE with TRAIT_TYPE.
	* cp-tree.def (TRAIT_TYPE): Define.
	(UNDERLYING_TYPE): Remove.
	* cp-tree.h (TRAIT_TYPE_KIND_RAW): Define.
	(TRAIT_TYPE_KIND): Define.
	(TRAIT_TYPE_TYPE1): Define.
	(TRAIT_TYPE_TYPE2): Define.
	(WILDCARD_TYPE_P): Return true for TRAIT_TYPE.
	(finish_trait_type): Declare.
	* cxx-pretty-print.cc (cxx_pretty_printer::primary_expression):
	Adjust after renaming pp_cxx_trait_expression.
	(cxx_pretty_printer::simple_type_specifier) <case TRAIT_TYPE>:
	New.
	(cxx_pretty_printer::type_id): Replace UNDERLYING_TYPE with
	TRAIT_TYPE.
	(pp_cxx_trait_expression): Rename to ...
	(pp_cxx_trait): ... this.  Handle TRAIT_TYPE as well.  Correct
	pretty printing of the trailing arguments.
	* cxx-pretty-print.h (pp_cxx_trait_expression): Rename to ...
	(pp_cxx_trait_type): ... this.
	* error.cc (dump_type) <case UNDERLYING_TYPE>: Remove.
	<case TRAIT_TYPE>: New.
	(dump_type_prefix): Replace UNDERLYING_WITH with TRAIT_TYPE.
	(dump_type_suffix): Likewise.
	* mangle.cc (write_type) <case UNDERLYING_TYPE>: Remove.
	<case TRAIT_TYPE>: New.
	* module.cc (trees_out::type_node) <case UNDERLYING_TYPE>:
	Remove.
	<case TRAIT_TYPE>: New.
	(trees_in::tree_node): Likewise.
	* parser.cc (cp_parser_primary_expression): Adjust after
	renaming cp_parser_trait_expr.
	(cp_parser_trait_expr): Rename to ...
	(cp_parser_trait): ... this.  Call finish_trait_type for traits
	that yield a type.
	(cp_parser_simple_type_specifier): Adjust after renaming
	cp_parser_trait_expr.
	* pt.cc (for_each_template_parm_r) <case UNDERLYING_TYPE>:
	Remove.
	<case TRAIT_TYPE>: New.
	(tsubst): Likewise.
	(unify): Replace UNDERLYING_TYPE with TRAIT_TYPE.
	(dependent_type_p_r): Likewise.
	* semantics.cc (finish_underlying_type): Don't return
	UNDERLYING_TYPE anymore when processing_template_decl.
	(finish_trait_type): Define.
	* tree.cc (strip_typedefs) <case UNDERLYING_TYPE>: Remove.
	<case TRAIT_TYPE>: New.
	(cp_walk_subtrees): Likewise.
	* typeck.cc (structural_comptypes): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/alias-decl-59.C: Adjust expected error message.
	* g++.dg/ext/underlying_type7.C: Likewise.
	* g++.dg/ext/underlying_type13.C: New test.
	* g++.dg/ext/underlying_type14.C: New test.

1 files changed, 17 insertions, 5 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index ea4dfc6..aa9c1b7 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1776,10 +1776,17 @@ strip_typedefs (tree t, bool *remove_attributes /* = NULL */,
 		   DECLTYPE_TYPE_ID_EXPR_OR_MEMBER_ACCESS_P (t),
 		   tf_none));
       break;
-    case UNDERLYING_TYPE:
-      type = strip_typedefs (UNDERLYING_TYPE_TYPE (t),
-			     remove_attributes, flags);
-      result = finish_underlying_type (type);
+    case TRAIT_TYPE:
+      {
+	tree type1 = strip_typedefs (TRAIT_TYPE_TYPE1 (t),
+				     remove_attributes, flags);
+	tree type2 = strip_typedefs (TRAIT_TYPE_TYPE2 (t),
+				     remove_attributes, flags);
+	if (type1 == TRAIT_TYPE_TYPE1 (t) && type2 == TRAIT_TYPE_TYPE2 (t))
+	  result = NULL_TREE;
+	else
+	  result = finish_trait_type (TRAIT_TYPE_KIND (t), type1, type2);
+      }
       break;
     case TYPE_PACK_EXPANSION:
       {
@@ -5383,7 +5390,6 @@ cp_walk_subtrees (tree *tp, int *walk_subtrees_p, walk_tree_fn func,
     case UNBOUND_CLASS_TEMPLATE:
     case TEMPLATE_PARM_INDEX:
     case TYPEOF_TYPE:
-    case UNDERLYING_TYPE:
       /* None of these have subtrees other than those already walked
 	 above.  */
       *walk_subtrees_p = 0;
@@ -5472,6 +5478,12 @@ cp_walk_subtrees (tree *tp, int *walk_subtrees_p, walk_tree_fn func,
       *walk_subtrees_p = 0;
       break;
 
+    case TRAIT_TYPE:
+      WALK_SUBTREE (TRAIT_TYPE_TYPE1 (*tp));
+      WALK_SUBTREE (TRAIT_TYPE_TYPE2 (*tp));
+      *walk_subtrees_p = 0;
+      break;
+
     case DECLTYPE_TYPE:
       ++cp_unevaluated_operand;
       /* We can't use WALK_SUBTREE here because of the goto.  */