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.


> +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
>
>