[libc++] Remove guards for builtins for reference binding traits

[frederick-vs-ja]

We're only supporting Clang 20+ and Apple Clang 17 now, where these builtins are universally implemented.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

We're only supporting Clang 20+ and Apple Clang 17 now, where these builtins are universally implemented.

---

Full diff: https://github.com/llvm/llvm-project/pull/166288.diff

7 Files Affected:

• (modified) libcxx/include/__type_traits/reference_constructs_from_temporary.h (+1-1)
• (modified) libcxx/include/__type_traits/reference_converts_from_temporary.h (+1-1)
• (modified) libcxx/include/tuple (+1-1)
• (modified) libcxx/test/libcxx/type_traits/no_specializations.verify.cpp (+3-7)
• (modified) libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp (-3)
• (modified) libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp (-3)
• (modified) libcxx/test/std/utilities/tuple/tuple.tuple/tuple.apply/make_from_tuple.verify.cpp (-4)

diff --git a/libcxx/include/__type_traits/reference_constructs_from_temporary.h b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
index 3d097ce90cb09..a8325620414ea 100644
--- a/libcxx/include/__type_traits/reference_constructs_from_temporary.h
+++ b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
@@ -18,7 +18,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 23 && __has_builtin(__reference_constructs_from_temporary)
+#if _LIBCPP_STD_VER >= 23
 
 template <class _Tp, class _Up>
 struct _LIBCPP_NO_SPECIALIZATIONS reference_constructs_from_temporary
diff --git a/libcxx/include/__type_traits/reference_converts_from_temporary.h b/libcxx/include/__type_traits/reference_converts_from_temporary.h
index c68f1765af9d5..9c51225e53b8e 100644
--- a/libcxx/include/__type_traits/reference_converts_from_temporary.h
+++ b/libcxx/include/__type_traits/reference_converts_from_temporary.h
@@ -18,7 +18,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 23 && __has_builtin(__reference_converts_from_temporary)
+#if _LIBCPP_STD_VER >= 23
 
 template <class _Tp, class _Up>
 struct _LIBCPP_NO_SPECIALIZATIONS reference_converts_from_temporary
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 466f501b5f4f8..3c5330dd6e14e 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -1443,7 +1443,7 @@ template <class _Tp, class _Tuple, class = enable_if_t<__can_make_from_tuple<_Tp
 inline _LIBCPP_HIDE_FROM_ABI constexpr _Tp make_from_tuple(_Tuple&& __t)
   noexcept(noexcept(std::__make_from_tuple_impl<_Tp>(std::forward<_Tuple>(__t),
                     make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>()))) {
-#if _LIBCPP_STD_VER >= 23 && __has_builtin(__reference_constructs_from_temporary)
+#if _LIBCPP_STD_VER >= 23
   if constexpr (tuple_size_v<remove_reference_t<_Tuple>> == 1) {
     static_assert(!std::reference_constructs_from_temporary_v<_Tp, decltype(std::get<0>(std::declval<_Tuple>()))>,
                   "Attempted construction of reference element binds to a temporary whose lifetime has ended");
diff --git a/libcxx/test/libcxx/type_traits/no_specializations.verify.cpp b/libcxx/test/libcxx/type_traits/no_specializations.verify.cpp
index 897ae89365014..3fac952b9eb98 100644
--- a/libcxx/test/libcxx/type_traits/no_specializations.verify.cpp
+++ b/libcxx/test/libcxx/type_traits/no_specializations.verify.cpp
@@ -154,14 +154,10 @@ SPECIALIZE_UTT(is_unbounded_array);     // expected-error 2 {{cannot be speciali
 #  endif
 
 #  if TEST_STD_VER >= 23
-SPECIALIZE_UTT(is_implicit_lifetime); // expected-error 2 {{cannot be specialized}}
-SPECIALIZE_UTT(is_scoped_enum);       // expected-error 2 {{cannot be specialized}}
-#    if __has_builtin(__reference_constructs_from_temporary)
+SPECIALIZE_UTT(is_implicit_lifetime);                // expected-error 2 {{cannot be specialized}}
+SPECIALIZE_UTT(is_scoped_enum);                      // expected-error 2 {{cannot be specialized}}
 SPECIALIZE_BTT(reference_constructs_from_temporary); // expected-error 2 {{cannot be specialized}}
-#    endif
-#    if __has_builtin(__reference_converts_from_temporary)
-SPECIALIZE_BTT(reference_converts_from_temporary); // expected-error 2 {{cannot be specialized}}
-#    endif
+SPECIALIZE_BTT(reference_converts_from_temporary);   // expected-error 2 {{cannot be specialized}}
 #  endif
 
 #  if TEST_STD_VER >= 26
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
index ad53c8176cc92..84fe7cfb02208 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++23
 
-// These compilers don't support std::reference_converts_from_temporary yet.
-// UNSUPPORTED: apple-clang-16, clang-19.1
-
 // <type_traits>
 
 // template<class T, class U> struct reference_constructs_from_temporary;
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
index 73cc4f3e29d5a..8319d9e1563fe 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++23
 
-// These compilers don't support std::reference_converts_from_temporary yet.
-// UNSUPPORTED: apple-clang-16, clang-19.1
-
 // <type_traits>
 
 // template<class T, class U> struct reference_converts_from_temporary;
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.apply/make_from_tuple.verify.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.apply/make_from_tuple.verify.cpp
index 2dfbae9138864..12d778408d5ec 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.apply/make_from_tuple.verify.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.apply/make_from_tuple.verify.cpp
@@ -19,11 +19,7 @@
 #include "test_macros.h"
 
 void test() {
-  // FreeBSD ci use clang 19.1.1, which hasn't implement __reference_constructs_from_temporary.
-  // The static_assert inner std::make_from_tuple will not triggered.
-#if __has_builtin(__reference_constructs_from_temporary)
   // expected-error@*:* {{static assertion failed}}
-#endif
 
   // Turns to an error since C++26 (Disallow Binding a Returned Glvalue to a Temporary https://wg21.link/P2748R5).
 #if TEST_STD_VER >= 26

[H-G-Hristov]

@frederick-vs-ja I believe it may be a bit early for this. OpenXL maybe doesn't support these yet. The AIX CI is disabled right now.

[philnik777]

@frederick-vs-ja I believe it may be a bit early for this. OpenXL maybe doesn't support these yet. The AIX CI is disabled right now.

They're usually pretty good about that stuff, so I wouldn't be too worried. That part of the CI not being available shouldn't prevent us from moving forward.