Re: [PATCH] c++: Enable __has_builtin for new reference binding built-ins

[Jason Merrill via Gcc-patches]

On 7/19/22 09:11, Jonathan Wakely wrote:

Tested x86_64-linux, OK for trunk?

OK.

-- >8 --

The new built-ins need to be detectable using __has_builtin, and the
library should use that to check for them.

This fixes an error with Clang when C++23 is enabled.

gcc/cp/ChangeLog:

        * cp-objcp-common.cc (names_builtin_p): Return true for
        RID_REF_CONSTRUCTS_FROM_TEMPORARY and
        RID_REF_CONVERTS_FROM_TEMPORARY.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (__cpp_lib_reference_from_temporary)
        (reference_constructs_from_temporary)
        (reference_converts_from_temporary): Only define when the
        built-ins are available.
---
  gcc/cp/cp-objcp-common.cc            | 2 ++
  libstdc++-v3/include/std/type_traits | 4 ++++
  2 files changed, 6 insertions(+)

diff --git a/gcc/cp/cp-objcp-common.cc b/gcc/cp/cp-objcp-common.cc
index 0b70d5567e4..4079a4b4aec 100644
--- a/gcc/cp/cp-objcp-common.cc
+++ b/gcc/cp/cp-objcp-common.cc
@@ -461,6 +461,8 @@ names_builtin_p (const char *name)
      case RID_IS_ASSIGNABLE:
      case RID_IS_CONSTRUCTIBLE:
      case RID_UNDERLYING_TYPE:
+    case RID_REF_CONSTRUCTS_FROM_TEMPORARY:
+    case RID_REF_CONVERTS_FROM_TEMPORARY:
        return true;
      default:
        break;
diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index b1a1deecf66..14b029cec64 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3505,6 +3505,9 @@ template<typename _Ret, typename _Fn, typename... _Args>
    template<typename _Tp>
      inline constexpr bool is_scoped_enum_v = is_scoped_enum<_Tp>::value;

+#if __has_builtin(__reference_constructs_from_temporary) \

+  && __has_builtin(__reference_converts_from_temporary)
+
  #define __cpp_lib_reference_from_temporary 202202L

/// True if _Tp is a reference type, a _Up value can be bound to _Tp in

@@ -3544,6 +3547,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
    template<typename _Tp, typename _Up>
      inline constexpr bool reference_converts_from_temporary_v
        = reference_converts_from_temporary<_Tp, _Up>::value;
+#endif // __has_builtin for reference_from_temporary
  #endif // C++23

#if _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED