On Tue, 21 Mar 2023 at 11:26, Jonathan Wakely wrote:

>
>
> On Tue, 21 Mar 2023 at 11:12, Ken Matsui via Libstdc++ <
> libstdc++@gcc.gnu.org> wrote:
>
>> 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)));
>>
>
> This looks wrong.
>

It might be useful to test pointer-to-member types too. And for
completeness, a class type.



>
>> +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
>>
>>