Re: [PATCH 1/2] c++, libstdc++: implement __is_pointer built-in trait

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 12 Jul 2023 at 05:41, François Dumont via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
>
> On 10/07/2023 07:23, Ken Matsui via Libstdc++ wrote:
> > This patch implements built-in trait for std::is_pointer.
> >
> > gcc/cp/ChangeLog:
> >
> >       * cp-trait.def: Define __is_pointer.
> >       * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_POINTER.
> >       * semantics.cc (trait_expr_value): Likewise.
> >       (finish_trait_expr): Likewise.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       * g++.dg/ext/has-builtin-1.C: Test existence of __is_pointer.
> >       * g++.dg/ext/is_pointer.C: New test.
> >       * g++.dg/tm/pr46567.C (__is_pointer): Rename to ...
> >       (____is_pointer): ... this.
> >       * g++.dg/torture/20070621-1.C: Likewise.
> >       * g++.dg/torture/pr57107.C: Likewise.
> >
> > libstdc++-v3/ChangeLog:
> >
> >       * include/bits/cpp_type_traits.h (__is_pointer): Rename to ...
> >       (____is_pointer): ... this.
> >       * include/bits/deque.tcc: Use ____is_pointer instead.
> >       * include/bits/stl_algobase.h: Likewise.
> >
> > Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> > ---
> >   gcc/cp/constraint.cc                        |  3 ++
> >   gcc/cp/cp-trait.def                         |  1 +
> >   gcc/cp/semantics.cc                         |  4 ++
> >   gcc/testsuite/g++.dg/ext/has-builtin-1.C    |  3 ++
> >   gcc/testsuite/g++.dg/ext/is_pointer.C       | 51 +++++++++++++++++++++
> >   gcc/testsuite/g++.dg/tm/pr46567.C           | 22 ++++-----
> >   gcc/testsuite/g++.dg/torture/20070621-1.C   |  4 +-
> >   gcc/testsuite/g++.dg/torture/pr57107.C      |  4 +-
> >   libstdc++-v3/include/bits/cpp_type_traits.h |  6 +--
> >   libstdc++-v3/include/bits/deque.tcc         |  6 +--
> >   libstdc++-v3/include/bits/stl_algobase.h    |  6 +--
> >   11 files changed, 86 insertions(+), 24 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/ext/is_pointer.C
> >
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index 8cf0f2d0974..30266204eb5 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3751,6 +3751,9 @@ diagnose_trait_expr (tree expr, tree args)
> >       case CPTK_IS_UNION:
> >         inform (loc, "  %qT is not a union", t1);
> >         break;
> > +    case CPTK_IS_POINTER:
> > +      inform (loc, "  %qT is not a pointer", t1);
> > +      break;
> >       case CPTK_IS_AGGREGATE:
> >         inform (loc, "  %qT is not an aggregate", t1);
> >         break;
> > diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
> > index 8b7fece0cc8..b7c263e9a77 100644
> > --- a/gcc/cp/cp-trait.def
> > +++ b/gcc/cp/cp-trait.def
> > @@ -82,6 +82,7 @@ DEFTRAIT_EXPR (IS_TRIVIALLY_ASSIGNABLE, "__is_trivially_assignable", 2)
> >   DEFTRAIT_EXPR (IS_TRIVIALLY_CONSTRUCTIBLE, "__is_trivially_constructible", -1)
> >   DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE, "__is_trivially_copyable", 1)
> >   DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
> > +DEFTRAIT_EXPR (IS_POINTER, "__is_pointer", 1)
> >   DEFTRAIT_EXPR (REF_CONSTRUCTS_FROM_TEMPORARY, "__reference_constructs_from_temporary", 2)
> >   DEFTRAIT_EXPR (REF_CONVERTS_FROM_TEMPORARY, "__reference_converts_from_temporary", 2)
> >   /* FIXME Added space to avoid direct usage in GCC 13.  */
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index 8fb47fd179e..68f8a4fe85b 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -12118,6 +12118,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
> >       case CPTK_IS_UNION:
> >         return type_code1 == UNION_TYPE;
> >
> > +    case CPTK_IS_POINTER:
> > +      return TYPE_PTR_P (type1);
> > +
> >       case CPTK_IS_ASSIGNABLE:
> >         return is_xible (MODIFY_EXPR, type1, type2);
> >
> > @@ -12296,6 +12299,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
> >       case CPTK_IS_ENUM:
> >       case CPTK_IS_UNION:
> >       case CPTK_IS_SAME:
> > +    case CPTK_IS_POINTER:
> >         break;
> >
> >       case CPTK_IS_LAYOUT_COMPATIBLE:
> > diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > index f343e153e56..9dace5cbd48 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 (__is_pointer)
> > +# error "__has_builtin (__is_pointer) failed"
> > +#endif
> > diff --git a/gcc/testsuite/g++.dg/ext/is_pointer.C b/gcc/testsuite/g++.dg/ext/is_pointer.C
> > new file mode 100644
> > index 00000000000..d6e39565950
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_pointer.C
> > @@ -0,0 +1,51 @@
> > +// { dg-do compile { target c++11 } }
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +SA(!__is_pointer(int));
> > +SA(__is_pointer(int*));
> > +SA(__is_pointer(int**));
> > +
> > +SA(__is_pointer(const int*));
> > +SA(__is_pointer(const int**));
> > +SA(__is_pointer(int* const));
> > +SA(__is_pointer(int** const));
> > +SA(__is_pointer(int* const* const));
> > +
> > +SA(__is_pointer(volatile int*));
> > +SA(__is_pointer(volatile int**));
> > +SA(__is_pointer(int* volatile));
> > +SA(__is_pointer(int** volatile));
> > +SA(__is_pointer(int* volatile* volatile));
> > +
> > +SA(__is_pointer(const volatile int*));
> > +SA(__is_pointer(const volatile int**));
> > +SA(__is_pointer(const int* volatile));
> > +SA(__is_pointer(volatile int* const));
> > +SA(__is_pointer(int* const volatile));
> > +SA(__is_pointer(const int** volatile));
> > +SA(__is_pointer(volatile int** const));
> > +SA(__is_pointer(int** const volatile));
> > +SA(__is_pointer(int* const* const volatile));
> > +SA(__is_pointer(int* volatile* const volatile));
> > +SA(__is_pointer(int* const volatile* const volatile));
> > +
> > +SA(!__is_pointer(int&));
> > +SA(!__is_pointer(const int&));
> > +SA(!__is_pointer(volatile int&));
> > +SA(!__is_pointer(const volatile int&));
> > +
> > +SA(!__is_pointer(int&&));
> > +SA(!__is_pointer(const int&&));
> > +SA(!__is_pointer(volatile int&&));
> > +SA(!__is_pointer(const volatile int&&));
> > +
> > +SA(!__is_pointer(int[3]));
> > +SA(!__is_pointer(const int[3]));
> > +SA(!__is_pointer(volatile int[3]));
> > +SA(!__is_pointer(const volatile int[3]));
> > +
> > +SA(!__is_pointer(int(int)));
> > +SA(__is_pointer(int(*const)(int)));
> > +SA(__is_pointer(int(*volatile)(int)));
> > +SA(__is_pointer(int(*const volatile)(int)));
> > diff --git a/gcc/testsuite/g++.dg/tm/pr46567.C b/gcc/testsuite/g++.dg/tm/pr46567.C
> > index 6d791484448..0896035390e 100644
> > --- a/gcc/testsuite/g++.dg/tm/pr46567.C
> > +++ b/gcc/testsuite/g++.dg/tm/pr46567.C
> > @@ -192,13 +192,13 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >         typedef __true_type __type;
> >       };
> >     template<typename _Tp>
> > -    struct __is_pointer
> > +    struct ____is_pointer
> >       {
> >         enum { __value = 0 };
> >         typedef __false_type __type;
> >       };
> >     template<typename _Tp>
> > -    struct __is_pointer<_Tp*>
> > +    struct ____is_pointer<_Tp*>
> >       {
> >         enum { __value = 1 };
> >         typedef __true_type __type;
> > @@ -226,7 +226,7 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >       { };
> >     template<typename _Tp>
> >       struct __is_scalar
> > -    : public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> >
> > +    : public __traitor<__is_arithmetic<_Tp>, ____is_pointer<_Tp> >
> >       { };
> >     template<typename _Tp>
> >       struct __is_char
> > @@ -1202,8 +1202,8 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >         typedef typename iterator_traits<_OI>::value_type _ValueTypeO;
> >         typedef typename iterator_traits<_II>::iterator_category _Category;
> >         const bool __simple = (__is_pod(_ValueTypeI)
> > -                   && __is_pointer<_II>::__value
> > -                   && __is_pointer<_OI>::__value
> > +                   && ____is_pointer<_II>::__value
> > +                   && ____is_pointer<_OI>::__value
> >       && __are_same<_ValueTypeI, _ValueTypeO>::__value);
> >         return std::__copy_move<_IsMove, __simple,
> >                      _Category>::__copy_m(__first, __last, __result);
> > @@ -1294,8 +1294,8 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >         typedef typename iterator_traits<_BI2>::value_type _ValueType2;
> >         typedef typename iterator_traits<_BI1>::iterator_category _Category;
> >         const bool __simple = (__is_pod(_ValueType1)
> > -                   && __is_pointer<_BI1>::__value
> > -                   && __is_pointer<_BI2>::__value
> > +                   && ____is_pointer<_BI1>::__value
> > +                   && ____is_pointer<_BI2>::__value
> >       && __are_same<_ValueType1, _ValueType2>::__value);
> >         return std::__copy_move_backward<_IsMove, __simple,
> >                               _Category>::__copy_move_b(__first,
> > @@ -1426,8 +1426,8 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >         typedef typename iterator_traits<_II1>::value_type _ValueType1;
> >         typedef typename iterator_traits<_II2>::value_type _ValueType2;
> >         const bool __simple = (__is_integer<_ValueType1>::__value
> > -                   && __is_pointer<_II1>::__value
> > -                   && __is_pointer<_II2>::__value
> > +                   && ____is_pointer<_II1>::__value
> > +                   && ____is_pointer<_II2>::__value
> >       && __are_same<_ValueType1, _ValueType2>::__value);
> >         return std::__equal<__simple>::equal(__first1, __last1, __first2);
> >       }
> > @@ -1515,8 +1515,8 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >    (__is_byte<_ValueType1>::__value && __is_byte<_ValueType2>::__value
> >     && !__gnu_cxx::__numeric_traits<_ValueType1>::__is_signed
> >     && !__gnu_cxx::__numeric_traits<_ValueType2>::__is_signed
> > -  && __is_pointer<_II1>::__value
> > -  && __is_pointer<_II2>::__value);
> > +  && ____is_pointer<_II1>::__value
> > +  && ____is_pointer<_II2>::__value);
> >         return std::__lexicographical_compare<__simple>::__lc(__first1, __last1,
> >          __first2, __last2);
> >       }
> > diff --git a/gcc/testsuite/g++.dg/torture/20070621-1.C b/gcc/testsuite/g++.dg/torture/20070621-1.C
> > index d8a6a76b6b0..9ae96717e4f 100644
> > --- a/gcc/testsuite/g++.dg/torture/20070621-1.C
> > +++ b/gcc/testsuite/g++.dg/torture/20070621-1.C
> > @@ -18,7 +18,7 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >           enum {
> >     __value = 0 };
> >         };
> > -    template<typename _Tp>     struct __is_pointer     {
> > +    template<typename _Tp>     struct ____is_pointer     {
> >           enum {
> >     __value = 0 };
> >         };
> > @@ -49,7 +49,7 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >       template<typename _II1, typename _II2>     inline bool     __equal_aux(_II1 __first1, _II1 __last1, _II2 __first2)     {
> >           typedef typename iterator_traits<_II1>::value_type _ValueType1;
> >           typedef typename iterator_traits<_II2>::value_type _ValueType2;
> > -        const bool __simple = (__is_integer<_ValueType1>::__value                       && __is_pointer<_II1>::__value                       && __is_pointer<_II2>::__value         && __are_same<_ValueType1, _ValueType2>::__value);
> > +        const bool __simple = (__is_integer<_ValueType1>::__value                       && ____is_pointer<_II1>::__value                       && ____is_pointer<_II2>::__value         && __are_same<_ValueType1, _ValueType2>::__value);
> >           return std::__equal<__simple>::equal(__first1, __last1, __first2);
> >         }
> >       template<typename _II1, typename _II2>     inline bool     equal(_II1 __first1, _II1 __last1, _II2 __first2)     {
> > diff --git a/gcc/testsuite/g++.dg/torture/pr57107.C b/gcc/testsuite/g++.dg/torture/pr57107.C
> > index 4dbd32bd298..1fcf337ee58 100644
> > --- a/gcc/testsuite/g++.dg/torture/pr57107.C
> > +++ b/gcc/testsuite/g++.dg/torture/pr57107.C
> > @@ -17,7 +17,7 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >       enum {
> >           __value = 0 };
> >       };
> > -    template<typename _Tp>     struct __is_pointer     {
> > +    template<typename _Tp>     struct ____is_pointer     {
> >       enum {
> >           __value = 0 };
> >       };
> > @@ -27,7 +27,7 @@ namespace std __attribute__ ((__visibility__ ("default"))) {
> >       };
> >       template<typename _Tp>     struct __is_arithmetic     : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >     {
> >       };
> > -    template<typename _Tp>     struct __is_scalar     : public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> >     {
> > +    template<typename _Tp>     struct __is_scalar     : public __traitor<__is_arithmetic<_Tp>, ____is_pointer<_Tp> >     {
> >       };
> >   }
> >   namespace __gnu_cxx __attribute__ ((__visibility__ ("default"))) {
> > diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h b/libstdc++-v3/include/bits/cpp_type_traits.h
> > index 4312f32a4e0..3999898ffa6 100644
> > --- a/libstdc++-v3/include/bits/cpp_type_traits.h
> > +++ b/libstdc++-v3/include/bits/cpp_type_traits.h
> > @@ -364,14 +364,14 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
> >     // Pointer types
> >     //
> >     template<typename _Tp>
> > -    struct __is_pointer
> > +    struct ____is_pointer
>
> It makes the creation of builtin __is_pointer pointless for libstdc++ if
> you do it this way, no ?

This is [PATCH 1/2], see the [PATCH 2/2] which uses the new built-in
for std::is_pointer. So it's not pointless.

But I agree that we could make use of the new built-in in this
non-standard trait as well.


>
> IMHO you should do something like:
>
>    //
>    // Pointer types
>    //
>    template<typename _Tp>
>      struct ____is_pointer
>      {
> #if __has_builtin(__is_pointer)
>        enum { __value = __is_pointer(_Tp) };
>        typedef typename __truth_type<__value>::__type __type;

This would mean we instantiate a class template here anyway, and have
to match a partial specialization. If we do that, there's no point
using the built-in to avoid matching a partial specialization of this
trait.

> #else
>        enum { __value = 0 };
>        typedef __false_type __type;
> #endif
>      };
>
> #if !__has_builtin(__is_pointer)
>    template<typename _Tp>
>      struct __is_pointer<_Tp*>
>      {
>        enum { __value = 1 };
>        typedef __true_type __type;
>      };
> #endif

I think this would be simpler to read as two completely separate
blocks, and with the __type in a base class that won't be instantiated
unless needed.

#if __has_builtin(__is_pointer)
template<typename _Tp>
  struct __is_pointer_type : __truth_type<__is_pointer(_Tp)>
  {
    enum { __value = __is_pointer(_Tp) };
  };
#else
  existing code ...
#endif