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, 18 insertions, 0 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index d0f1b18..ff9913c 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -1437,6 +1437,22 @@ struct GTY (()) tree_trait_expr {
   enum cp_trait_kind kind;
 };
 
+/* An INTEGER_CST containing the kind of the trait type NODE.  */
+#define TRAIT_TYPE_KIND_RAW(NODE) \
+  TYPE_VALUES_RAW (TRAIT_TYPE_CHECK (NODE))
+
+/* The kind of the trait type NODE.  */
+#define TRAIT_TYPE_KIND(NODE) \
+  ((enum cp_trait_kind) TREE_INT_CST_LOW (TRAIT_TYPE_KIND_RAW (NODE)))
+
+/* The first argument of the trait type NODE.  */
+#define TRAIT_TYPE_TYPE1(NODE) \
+  TYPE_MIN_VALUE_RAW (TRAIT_TYPE_CHECK (NODE))
+
+/* The rest of the arguments of the trait type NODE.  */
+#define TRAIT_TYPE_TYPE2(NODE) \
+  TYPE_MAX_VALUE_RAW (TRAIT_TYPE_CHECK (NODE))
+
 /* Identifiers used for lambda types are almost anonymous.  Use this
    spare flag to distinguish them (they also have the anonymous flag).  */
 #define IDENTIFIER_LAMBDA_P(NODE) \
@@ -2226,6 +2242,7 @@ enum languages { lang_c, lang_cplusplus };
    || TREE_CODE (T) == TYPEOF_TYPE			\
    || TREE_CODE (T) == BOUND_TEMPLATE_TEMPLATE_PARM	\
    || TREE_CODE (T) == DECLTYPE_TYPE			\
+   || TREE_CODE (T) == TRAIT_TYPE			\
    || TREE_CODE (T) == DEPENDENT_OPERATOR_TYPE)
 
 /* Nonzero if T is a class (or struct or union) type.  Also nonzero
@@ -7736,6 +7753,7 @@ extern tree finish_decltype_type                (tree, bool, tsubst_flags_t);
 extern tree fold_builtin_is_corresponding_member (location_t, int, tree *);
 extern tree fold_builtin_is_pointer_inverconvertible_with_class (location_t, int, tree *);
 extern tree finish_trait_expr			(location_t, enum cp_trait_kind, tree, tree);
+extern tree finish_trait_type			(enum cp_trait_kind, tree, tree);
 extern tree build_lambda_expr                   (void);
 extern tree build_lambda_object			(tree);
 extern tree begin_lambda_type                   (tree);