diff mbox series

[v19,04/40] c++: Implement __is_const built-in trait

Message ID 20231013223957.1634024-5-kmatsui@gcc.gnu.org
State Unresolved
Headers
Series Optimize type traits performance |

Checks

Context Check Description
snail/gcc-patch-check warning Git am fail log

Commit Message

Ken Matsui Oct. 13, 2023, 10:37 p.m. UTC 
  This patch implements built-in trait for std::is_const.

gcc/cp/ChangeLog:

	* Make-lang.in: Update key positions for gperf, based on
	automatically computed values.
	* cp-trait.def: Define __is_const.
	* cp-trait.gperf: Reflect cp-trait.def change.
	* cp-trait.h: Likewise.
	* constraint.cc (diagnose_trait_expr): Handle CPTK_IS_CONST.
	* semantics.cc (trait_expr_value): Likewise.
	(finish_trait_expr): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/has-builtin-1.C: Test existence of __is_const.
	* g++.dg/ext/is_const.C: New test.

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
---
 gcc/cp/Make-lang.in                      |   2 +-
 gcc/cp/constraint.cc                     |   3 +
 gcc/cp/cp-trait.def                      |   1 +
 gcc/cp/cp-trait.gperf                    |   1 +
 gcc/cp/cp-trait.h                        | 202 ++++++++++++-----------
 gcc/cp/semantics.cc                      |   4 +
 gcc/testsuite/g++.dg/ext/has-builtin-1.C |   3 +
 gcc/testsuite/g++.dg/ext/is_const.C      |  19 +++
 8 files changed, 135 insertions(+), 100 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/ext/is_const.C
diff mbox series

Patch

diff --git a/gcc/cp/Make-lang.in b/gcc/cp/Make-lang.in
index a67d1c3e9f3..7479e7dc00b 100644
--- a/gcc/cp/Make-lang.in
+++ b/gcc/cp/Make-lang.in
@@ -195,7 +195,7 @@  $(srcdir)/cp/cp-trait.h: $(srcdir)/cp/cp-trait.gperf
 else
 $(srcdir)/cp/cp-trait.h: | $(srcdir)/cp/cp-trait.gperf
 endif
-	gperf -o -C -E -k '8' -D -N 'find' -L C++ \
+	gperf -o -C -E -k '6,8' -D -N 'find' -L C++ \
 		$(srcdir)/cp/cp-trait.gperf --output-file $(srcdir)/cp/cp-trait.h
 
 # The cp-trait.gperf file itself is generated from
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 722fc334e6f..567dd35fe0a 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3723,6 +3723,9 @@  diagnose_trait_expr (tree expr, tree args)
     case CPTK_IS_CLASS:
       inform (loc, "  %qT is not a class", t1);
       break;
+    case CPTK_IS_CONST:
+      inform (loc, "  %qT is not a const type", t1);
+      break;
     case CPTK_IS_CONSTRUCTIBLE:
       if (!t2)
     inform (loc, "  %qT is not default constructible", t1);
diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index 0e48e64b8dd..9e4e6d798a0 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -62,6 +62,7 @@  DEFTRAIT_EXPR (IS_AGGREGATE, "__is_aggregate", 1)
 DEFTRAIT_EXPR (IS_ASSIGNABLE, "__is_assignable", 2)
 DEFTRAIT_EXPR (IS_BASE_OF, "__is_base_of", 2)
 DEFTRAIT_EXPR (IS_CLASS, "__is_class", 1)
+DEFTRAIT_EXPR (IS_CONST, "__is_const", 1)
 DEFTRAIT_EXPR (IS_CONSTRUCTIBLE, "__is_constructible", -1)
 DEFTRAIT_EXPR (IS_CONVERTIBLE, "__is_convertible", 2)
 DEFTRAIT_EXPR (IS_EMPTY, "__is_empty", 1)
diff --git a/gcc/cp/cp-trait.gperf b/gcc/cp/cp-trait.gperf
index 47e3c1af499..47a5ec9ee6f 100644
--- a/gcc/cp/cp-trait.gperf
+++ b/gcc/cp/cp-trait.gperf
@@ -42,6 +42,7 @@  struct cp_trait {
 "__is_assignable", CPTK_IS_ASSIGNABLE, 2, false
 "__is_base_of", CPTK_IS_BASE_OF, 2, false
 "__is_class", CPTK_IS_CLASS, 1, false
+"__is_const", CPTK_IS_CONST, 1, false
 "__is_constructible", CPTK_IS_CONSTRUCTIBLE, -1, false
 "__is_convertible", CPTK_IS_CONVERTIBLE, 2, false
 "__is_empty", CPTK_IS_EMPTY, 1, false
diff --git a/gcc/cp/cp-trait.h b/gcc/cp/cp-trait.h
index 97ba8492d15..c9005eee1ff 100644
--- a/gcc/cp/cp-trait.h
+++ b/gcc/cp/cp-trait.h
@@ -1,5 +1,5 @@ 
 /* C++ code produced by gperf version 3.1 */
-/* Command-line: gperf -o -C -E -k 8 -D -N find -L C++ --output-file ../../gcc/cp/cp-trait.h ../../gcc/cp/cp-trait.gperf  */
+/* Command-line: gperf -o -C -E -k 6,8 -D -N find -L C++ --output-file ../../gcc/cp/cp-trait.h ../../gcc/cp/cp-trait.gperf  */
 
 #if !((' ' == 32) && ('!' == 33) && ('"' == 34) && ('#' == 35) \
       && ('%' == 37) && ('&' == 38) && ('\'' == 39) && ('(' == 40) \
@@ -54,7 +54,7 @@  struct cp_trait {
   short arity;
   bool type;
 };
-/* maximum key range = 79, duplicates = 0 */
+/* maximum key range = 89, duplicates = 0 */
 
 class cp_trait_lookup
 {
@@ -69,32 +69,32 @@  cp_trait_lookup::hash (const char *str, size_t len)
 {
   static const unsigned char asso_values[] =
     {
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86,  1, 86, 86,
-       0, 35, 86,  0, 86,  0, 86, 86, 10, 10,
-      50, 15, 55, 86, 30,  5, 15,  0, 86, 86,
-      86, 20, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86, 86, 86, 86, 86,
-      86, 86, 86, 86, 86, 86
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 20, 96, 35, 10, 20,
+      40,  0, 30, 15, 96,  0, 96, 96,  5, 15,
+      30,  0,  5, 96, 10, 25,  5,  0, 96, 96,
+      96,  5, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96, 96, 96, 96, 96,
+      96, 96, 96, 96, 96, 96
     };
   unsigned int hval = len;
 
@@ -104,6 +104,8 @@  cp_trait_lookup::hash (const char *str, size_t len)
         hval += asso_values[static_cast<unsigned char>(str[7])];
       /*FALLTHROUGH*/
       case 7:
+      case 6:
+        hval += asso_values[static_cast<unsigned char>(str[5])];
         break;
     }
   return hval;
@@ -114,116 +116,118 @@  cp_trait_lookup::find (const char *str, size_t len)
 {
   enum
     {
-      TOTAL_KEYWORDS = 45,
+      TOTAL_KEYWORDS = 46,
       MIN_WORD_LENGTH = 7,
       MAX_WORD_LENGTH = 37,
       MIN_HASH_VALUE = 7,
-      MAX_HASH_VALUE = 85
+      MAX_HASH_VALUE = 95
     };
 
   static const struct cp_trait wordlist[] =
     {
-#line 73 "../../gcc/cp/cp-trait.gperf"
+#line 74 "../../gcc/cp/cp-trait.gperf"
       {"__bases", CPTK_BASES, 1, true},
-#line 56 "../../gcc/cp/cp-trait.gperf"
-      {"__is_pod", CPTK_IS_POD, 1, false},
-#line 48 "../../gcc/cp/cp-trait.gperf"
+#line 49 "../../gcc/cp/cp-trait.gperf"
       {"__is_enum", CPTK_IS_ENUM, 1, false},
-#line 64 "../../gcc/cp/cp-trait.gperf"
+#line 65 "../../gcc/cp/cp-trait.gperf"
       {"__is_union", CPTK_IS_UNION, 1, false},
-#line 44 "../../gcc/cp/cp-trait.gperf"
-      {"__is_class", CPTK_IS_CLASS, 1, false},
-#line 60 "../../gcc/cp/cp-trait.gperf"
+#line 68 "../../gcc/cp/cp-trait.gperf"
+      {"__remove_cv", CPTK_REMOVE_CV, 1, true},
+#line 69 "../../gcc/cp/cp-trait.gperf"
+      {"__remove_cvref", CPTK_REMOVE_CVREF, 1, true},
+#line 48 "../../gcc/cp/cp-trait.gperf"
+      {"__is_empty", CPTK_IS_EMPTY, 1, false},
+#line 61 "../../gcc/cp/cp-trait.gperf"
       {"__is_trivial", CPTK_IS_TRIVIAL, 1, false},
-#line 41 "../../gcc/cp/cp-trait.gperf"
-      {"__is_aggregate", CPTK_IS_AGGREGATE, 1, false},
+#line 70 "../../gcc/cp/cp-trait.gperf"
+      {"__remove_reference", CPTK_REMOVE_REFERENCE, 1, true},
+#line 75 "../../gcc/cp/cp-trait.gperf"
+      {"__direct_bases", CPTK_DIRECT_BASES, 1, true},
 #line 72 "../../gcc/cp/cp-trait.gperf"
-      {"__is_deducible ", CPTK_IS_DEDUCIBLE, 2, false},
-#line 43 "../../gcc/cp/cp-trait.gperf"
-      {"__is_base_of", CPTK_IS_BASE_OF, 2, false},
-#line 40 "../../gcc/cp/cp-trait.gperf"
-      {"__is_abstract", CPTK_IS_ABSTRACT, 1, false},
+      {"__underlying_type", CPTK_UNDERLYING_TYPE, 1, true},
+#line 71 "../../gcc/cp/cp-trait.gperf"
+      {"__type_pack_element", CPTK_TYPE_PACK_ELEMENT, -1, true},
 #line 58 "../../gcc/cp/cp-trait.gperf"
-      {"__is_same", CPTK_IS_SAME, 2, false},
-#line 42 "../../gcc/cp/cp-trait.gperf"
-      {"__is_assignable", CPTK_IS_ASSIGNABLE, 2, false},
-#line 59 "../../gcc/cp/cp-trait.gperf"
-      {"__is_standard_layout", CPTK_IS_STD_LAYOUT, 1, false},
-#line 30 "../../gcc/cp/cp-trait.gperf"
-      {"__is_same_as", CPTK_IS_SAME, 2, false},
-#line 63 "../../gcc/cp/cp-trait.gperf"
-      {"__is_trivially_copyable", CPTK_IS_TRIVIALLY_COPYABLE, 1, false},
-#line 39 "../../gcc/cp/cp-trait.gperf"
-      {"__has_virtual_destructor", CPTK_HAS_VIRTUAL_DESTRUCTOR, 1, false},
-#line 61 "../../gcc/cp/cp-trait.gperf"
-      {"__is_trivially_assignable", CPTK_IS_TRIVIALLY_ASSIGNABLE, 2, false},
-#line 57 "../../gcc/cp/cp-trait.gperf"
       {"__is_polymorphic", CPTK_IS_POLYMORPHIC, 1, false},
-#line 71 "../../gcc/cp/cp-trait.gperf"
-      {"__underlying_type", CPTK_UNDERLYING_TYPE, 1, true},
+#line 52 "../../gcc/cp/cp-trait.gperf"
+      {"__is_literal_type", CPTK_IS_LITERAL_TYPE, 1, false},
+#line 64 "../../gcc/cp/cp-trait.gperf"
+      {"__is_trivially_copyable", CPTK_IS_TRIVIALLY_COPYABLE, 1, false},
 #line 62 "../../gcc/cp/cp-trait.gperf"
-      {"__is_trivially_constructible", CPTK_IS_TRIVIALLY_CONSTRUCTIBLE, -1, false},
-#line 74 "../../gcc/cp/cp-trait.gperf"
-      {"__direct_bases", CPTK_DIRECT_BASES, 1, true},
+      {"__is_trivially_assignable", CPTK_IS_TRIVIALLY_ASSIGNABLE, 2, false},
 #line 51 "../../gcc/cp/cp-trait.gperf"
-      {"__is_literal_type", CPTK_IS_LITERAL_TYPE, 1, false},
+      {"__is_layout_compatible", CPTK_IS_LAYOUT_COMPATIBLE, 2, false},
+#line 63 "../../gcc/cp/cp-trait.gperf"
+      {"__is_trivially_constructible", CPTK_IS_TRIVIALLY_CONSTRUCTIBLE, -1, false},
+#line 67 "../../gcc/cp/cp-trait.gperf"
+      {"__reference_converts_from_temporary", CPTK_REF_CONVERTS_FROM_TEMPORARY, 2, false},
+#line 66 "../../gcc/cp/cp-trait.gperf"
+      {"__reference_constructs_from_temporary", CPTK_REF_CONSTRUCTS_FROM_TEMPORARY, 2, false},
 #line 33 "../../gcc/cp/cp-trait.gperf"
       {"__has_nothrow_copy", CPTK_HAS_NOTHROW_COPY, 1, false},
 #line 31 "../../gcc/cp/cp-trait.gperf"
       {"__has_nothrow_assign", CPTK_HAS_NOTHROW_ASSIGN, 1, false},
-#line 55 "../../gcc/cp/cp-trait.gperf"
+#line 56 "../../gcc/cp/cp-trait.gperf"
       {"__is_pointer_interconvertible_base_of", CPTK_IS_POINTER_INTERCONVERTIBLE_BASE_OF, 2, false},
-#line 52 "../../gcc/cp/cp-trait.gperf"
-      {"__is_nothrow_assignable", CPTK_IS_NOTHROW_ASSIGNABLE, 2, false},
-#line 54 "../../gcc/cp/cp-trait.gperf"
-      {"__is_nothrow_convertible", CPTK_IS_NOTHROW_CONVERTIBLE, 2, false},
+#line 39 "../../gcc/cp/cp-trait.gperf"
+      {"__has_virtual_destructor", CPTK_HAS_VIRTUAL_DESTRUCTOR, 1, false},
 #line 32 "../../gcc/cp/cp-trait.gperf"
       {"__has_nothrow_constructor", CPTK_HAS_NOTHROW_CONSTRUCTOR, 1, false},
-#line 53 "../../gcc/cp/cp-trait.gperf"
-      {"__is_nothrow_constructible", CPTK_IS_NOTHROW_CONSTRUCTIBLE, -1, false},
-#line 50 "../../gcc/cp/cp-trait.gperf"
-      {"__is_layout_compatible", CPTK_IS_LAYOUT_COMPATIBLE, 2, false},
-#line 67 "../../gcc/cp/cp-trait.gperf"
-      {"__remove_cv", CPTK_REMOVE_CV, 1, true},
+#line 43 "../../gcc/cp/cp-trait.gperf"
+      {"__is_base_of", CPTK_IS_BASE_OF, 2, false},
 #line 36 "../../gcc/cp/cp-trait.gperf"
       {"__has_trivial_copy", CPTK_HAS_TRIVIAL_COPY, 1, false},
-#line 68 "../../gcc/cp/cp-trait.gperf"
-      {"__remove_cvref", CPTK_REMOVE_CVREF, 1, true},
+#line 59 "../../gcc/cp/cp-trait.gperf"
+      {"__is_same", CPTK_IS_SAME, 2, false},
 #line 34 "../../gcc/cp/cp-trait.gperf"
       {"__has_trivial_assign", CPTK_HAS_TRIVIAL_ASSIGN, 1, false},
-#line 69 "../../gcc/cp/cp-trait.gperf"
-      {"__remove_reference", CPTK_REMOVE_REFERENCE, 1, true},
+#line 30 "../../gcc/cp/cp-trait.gperf"
+      {"__is_same_as", CPTK_IS_SAME, 2, false},
+#line 57 "../../gcc/cp/cp-trait.gperf"
+      {"__is_pod", CPTK_IS_POD, 1, false},
 #line 37 "../../gcc/cp/cp-trait.gperf"
       {"__has_trivial_destructor", CPTK_HAS_TRIVIAL_DESTRUCTOR, 1, false},
 #line 35 "../../gcc/cp/cp-trait.gperf"
       {"__has_trivial_constructor", CPTK_HAS_TRIVIAL_CONSTRUCTOR, 1, false},
-#line 49 "../../gcc/cp/cp-trait.gperf"
-      {"__is_final", CPTK_IS_FINAL, 1, false},
+#line 53 "../../gcc/cp/cp-trait.gperf"
+      {"__is_nothrow_assignable", CPTK_IS_NOTHROW_ASSIGNABLE, 2, false},
+#line 55 "../../gcc/cp/cp-trait.gperf"
+      {"__is_nothrow_convertible", CPTK_IS_NOTHROW_CONVERTIBLE, 2, false},
+#line 45 "../../gcc/cp/cp-trait.gperf"
+      {"__is_const", CPTK_IS_CONST, 1, false},
+#line 54 "../../gcc/cp/cp-trait.gperf"
+      {"__is_nothrow_constructible", CPTK_IS_NOTHROW_CONSTRUCTIBLE, -1, false},
+#line 41 "../../gcc/cp/cp-trait.gperf"
+      {"__is_aggregate", CPTK_IS_AGGREGATE, 1, false},
+#line 44 "../../gcc/cp/cp-trait.gperf"
+      {"__is_class", CPTK_IS_CLASS, 1, false},
 #line 47 "../../gcc/cp/cp-trait.gperf"
-      {"__is_empty", CPTK_IS_EMPTY, 1, false},
-#line 46 "../../gcc/cp/cp-trait.gperf"
       {"__is_convertible", CPTK_IS_CONVERTIBLE, 2, false},
-#line 45 "../../gcc/cp/cp-trait.gperf"
+#line 46 "../../gcc/cp/cp-trait.gperf"
       {"__is_constructible", CPTK_IS_CONSTRUCTIBLE, -1, false},
-#line 66 "../../gcc/cp/cp-trait.gperf"
-      {"__reference_converts_from_temporary", CPTK_REF_CONVERTS_FROM_TEMPORARY, 2, false},
-#line 65 "../../gcc/cp/cp-trait.gperf"
-      {"__reference_constructs_from_temporary", CPTK_REF_CONSTRUCTS_FROM_TEMPORARY, 2, false},
-#line 70 "../../gcc/cp/cp-trait.gperf"
-      {"__type_pack_element", CPTK_TYPE_PACK_ELEMENT, -1, true},
+#line 50 "../../gcc/cp/cp-trait.gperf"
+      {"__is_final", CPTK_IS_FINAL, 1, false},
+#line 40 "../../gcc/cp/cp-trait.gperf"
+      {"__is_abstract", CPTK_IS_ABSTRACT, 1, false},
+#line 42 "../../gcc/cp/cp-trait.gperf"
+      {"__is_assignable", CPTK_IS_ASSIGNABLE, 2, false},
+#line 60 "../../gcc/cp/cp-trait.gperf"
+      {"__is_standard_layout", CPTK_IS_STD_LAYOUT, 1, false},
 #line 38 "../../gcc/cp/cp-trait.gperf"
-      {"__has_unique_object_representations", CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS, 1, false}
+      {"__has_unique_object_representations", CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS, 1, false},
+#line 73 "../../gcc/cp/cp-trait.gperf"
+      {"__is_deducible ", CPTK_IS_DEDUCIBLE, 2, false}
     };
 
   static const signed char lookup[] =
     {
-      -1, -1, -1, -1, -1, -1, -1,  0,  1,  2,  3,  4,  5, -1,
-       6,  7, -1,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
-      19, 20, -1, -1, 21, 22, -1, 23, -1, 24, 25, 26, 27, 28,
-      29, -1, -1, -1, 30, -1, 31, 32, 33, -1, -1, 34, 35, 36,
-      -1, -1, -1, -1, 37, -1, -1, -1, -1, 38, 39, -1, 40, -1,
-      41, -1, 42, -1, 43, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-      -1, 44
+      -1, -1, -1, -1, -1, -1, -1,  0, -1,  1,  2,  3, -1, -1,
+       4,  5, -1,  6,  7,  8, -1, -1,  9, -1, 10, -1, 11, 12,
+      13, -1, 14, -1, 15, 16, -1, 17, -1, 18, 19, -1, 20, -1,
+      21, -1, 22, 23, -1, 24, 25, 26, 27, -1, 28, 29, 30, 31,
+      -1, -1, 32, 33, 34, 35, -1, -1, 36, 37, 38, -1, 39, -1,
+      40, -1, -1, 41, -1, 42, -1, -1, -1, -1, 43, -1, -1, -1,
+      -1, 44, -1, -1, -1, -1, -1, -1, -1, -1, -1, 45
     };
 
   if (len <= MAX_WORD_LENGTH && len >= MIN_WORD_LENGTH)
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 782aa515da0..23f1d1c249a 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12154,6 +12154,9 @@  trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_CLASS:
       return NON_UNION_CLASS_TYPE_P (type1);
 
+    case CPTK_IS_CONST:
+      return CP_TYPE_CONST_P (type1);
+
     case CPTK_IS_CONSTRUCTIBLE:
       return is_xible (INIT_EXPR, type1, type2);
 
@@ -12371,6 +12374,7 @@  finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
       break;
 
     case CPTK_IS_CLASS:
+    case CPTK_IS_CONST:
     case CPTK_IS_ENUM:
     case CPTK_IS_SAME:
     case CPTK_IS_UNION:
diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
index 2223f08a628..e6e481b13c5 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -65,6 +65,9 @@ 
 #if !__has_builtin (__is_class)
 # error "__has_builtin (__is_class) failed"
 #endif
+#if !__has_builtin (__is_const)
+# error "__has_builtin (__is_const) failed"
+#endif
 #if !__has_builtin (__is_constructible)
 # error "__has_builtin (__is_constructible) failed"
 #endif
diff --git a/gcc/testsuite/g++.dg/ext/is_const.C b/gcc/testsuite/g++.dg/ext/is_const.C
new file mode 100644
index 00000000000..8f2d7c2fce9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_const.C
@@ -0,0 +1,19 @@ 
+// { dg-do compile { target c++11 } }
+
+#include <testsuite_tr1.h>
+
+using namespace __gnu_test;
+
+#define SA(X) static_assert((X),#X)
+
+// Positive tests.
+SA(__is_const(const int));
+SA(__is_const(const volatile int));
+SA(__is_const(cClassType));
+SA(__is_const(cvClassType));
+
+// Negative tests.
+SA(!__is_const(int));
+SA(!__is_const(volatile int));
+SA(!__is_const(ClassType));
+SA(!__is_const(vClassType));