[PATCH 1/2] c++: implement __add_const built-in trait

[Ken Matsui]

This patch implements built-in trait for std::add_const.

gcc/cp/ChangeLog:

	* cp-trait.def: Define __add_const.
	* semantics.cc (finish_trait_type): Handle CPTK_ADD_CONST.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/has-builtin-1.C: Test existence of __add_const.
	* g++.dg/ext/add_const.C: New test.
---
 gcc/cp/cp-trait.def                      |  1 +
 gcc/cp/semantics.cc                      |  6 ++++
 gcc/testsuite/g++.dg/ext/add_const.C     | 39 ++++++++++++++++++++++++
 gcc/testsuite/g++.dg/ext/has-builtin-1.C |  3 ++
 4 files changed, 49 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/ext/add_const.C

diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index bac593c0094..e362c448c84 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -91,6 +91,7 @@ DEFTRAIT_TYPE (REMOVE_CV, "__remove_cv", 1)
 DEFTRAIT_TYPE (REMOVE_REFERENCE, "__remove_reference", 1)
 DEFTRAIT_TYPE (REMOVE_CVREF, "__remove_cvref", 1)
 DEFTRAIT_TYPE (UNDERLYING_TYPE,  "__underlying_type", 1)
+DEFTRAIT_TYPE (ADD_CONST,  "__add_const", 1)
 
 /* These traits yield a type pack, not a type, and are represented by
    cp_parser_trait as a special BASES tree instead of a TRAIT_TYPE tree.  */
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 87c2e8a7111..14e27a71a55 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12273,6 +12273,12 @@ finish_trait_type (cp_trait_kind kind, tree type1, tree type2)
       if (TYPE_REF_P (type1))
 	type1 = TREE_TYPE (type1);
       return cv_unqualified (type1);
+    case CPTK_ADD_CONST:
+      if (TYPE_REF_P (type1) || TYPE_PTRFN_P (type1))
+        return type1;
+      return cp_build_qualified_type (type1,
+                      cp_type_quals (type1) |
+                      TYPE_QUAL_CONST);
 
 #define DEFTRAIT_EXPR(CODE, NAME, ARITY) \
     case CPTK_##CODE:
diff --git a/gcc/testsuite/g++.dg/ext/add_const.C b/gcc/testsuite/g++.dg/ext/add_const.C
new file mode 100644
index 00000000000..1c8618a8b00
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/add_const.C
@@ -0,0 +1,39 @@
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+SA(__is_same(__add_const(void), const void));
+SA(__is_same(__add_const(int), const int));
+
+SA(__is_same(__add_const(const int), const int));
+SA(__is_same(__add_const(volatile int), const volatile int));
+SA(__is_same(__add_const(const volatile int), const volatile int));
+
+SA(__is_same(__add_const(int*), int* const));
+SA(__is_same(__add_const(int* const), int* const));
+SA(__is_same(__add_const(int* volatile), int* const volatile));
+SA(__is_same(__add_const(int* const volatile), int* const volatile));
+
+SA(__is_same(__add_const(const int*), const int* const));
+SA(__is_same(__add_const(volatile int*), volatile int* const));
+SA(__is_same(__add_const(const volatile int*), const volatile int* const));
+
+SA(__is_same(__add_const(int&), int&));
+SA(__is_same(__add_const(const int&), const int&));
+SA(__is_same(__add_const(volatile int&), volatile int&));
+SA(__is_same(__add_const(const volatile int&), const volatile int&));
+
+SA(__is_same(__add_const(int&&), int&&));
+SA(__is_same(__add_const(const int&&), const int&&));
+SA(__is_same(__add_const(volatile int&&), volatile int&&));
+SA(__is_same(__add_const(const volatile int&&), const volatile int&&));
+
+SA(__is_same(__add_const(int[3]), const int[3]));
+SA(__is_same(__add_const(const int[3]), const int[3]));
+SA(__is_same(__add_const(volatile int[3]), const volatile int[3]));
+SA(__is_same(__add_const(const volatile int[3]), const volatile int[3]));
+
+SA(__is_same(__add_const(int(int)), int(int)));
+SA(__is_same(__add_const(int(*const)(int)), int(*const)(int)));
+SA(__is_same(__add_const(int(*volatile)(int)), int(*volatile)(int)));
+SA(__is_same(__add_const(int(*const volatile)(int)), int(*const volatile)(int)));
diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
index f343e153e56..dd331ebbc9a 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -146,3 +146,6 @@
 #if !__has_builtin (__remove_cvref)
 # error "__has_builtin (__remove_cvref) failed"
 #endif
+#if !__has_builtin (__add_const)
+# error "__has_builtin (__add_const) failed"
+#endif
-- 
2.40.0