[libcxx-commits] [libcxx] [libc++] Use `__reference_constructs_from_temporary` if eligible (PR #141916)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

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

<details>
<summary>Changes</summary>

Currently, libc++'s `<tuple>` is using the deprecated `__reference_binds_to_temporary` intrinsic. This PR starts to use `__reference_constructs_from_temporary` if possible.

It seems that `__reference_constructs_from_temporary` should be used via an internal type traits provided in
`<__type_traits/reference_constructs_from_temporary.h>`. But given the old intrinsic was directly used, this PR doesn't switch to the current convention yet.

P2255R2 is related. Although the paper indicated that constructors of `tuple` should be deleted in such a case.

---
Full diff: https://github.com/llvm/llvm-project/pull/141916.diff


3 Files Affected:

- (modified) libcxx/include/tuple (+3-1) 
- (modified) libcxx/test/libcxx/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.verify.cpp (+1-1) 
- (modified) libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp (+6-5) 


``````````diff
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 8dd62ae624f5e..5aef90ac19cfe 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -310,7 +310,9 @@ class __tuple_leaf {
 
   template <class _Tp>
   static _LIBCPP_HIDE_FROM_ABI constexpr bool __can_bind_reference() {
-#    if __has_keyword(__reference_binds_to_temporary)
+#    if __has_builtin(__reference_constructs_from_temporary)
+    return !__reference_constructs_from_temporary(_Hp, _Tp);
+#    else if __has_keyword(__reference_binds_to_temporary)
     return !__reference_binds_to_temporary(_Hp, _Tp);
 #    else
     return true;
diff --git a/libcxx/test/libcxx/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.verify.cpp b/libcxx/test/libcxx/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.verify.cpp
index 4a6e3095c1019..df068bf35f2e5 100644
--- a/libcxx/test/libcxx/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.verify.cpp
+++ b/libcxx/test/libcxx/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.verify.cpp
@@ -40,7 +40,7 @@ void F(typename CannotDeduce<std::tuple<Args...>>::type const&) {}
 
 
 void f() {
-#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_binds_to_temporary)
+#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_constructs_from_temporary)
   // Test that we emit our diagnostic from the library.
   // expected-error at tuple:* 8 {{Attempted construction of reference element binds to a temporary whose lifetime has ended}}
 
diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
index 463816929353b..1da967d89718f 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp
@@ -18,12 +18,13 @@
 #include <cassert>
 #include "test_macros.h"
 
-#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_binds_to_temporary)
-# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(__reference_binds_to_temporary(__VA_ARGS__), "")
-# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(!__reference_binds_to_temporary(__VA_ARGS__), "")
+#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_constructs_from_temporary)
+#  define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(__reference_constructs_from_temporary(__VA_ARGS__), "")
+#  define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...)                                                                    \
+    static_assert(!__reference_constructs_from_temporary(__VA_ARGS__), "")
 #else
-# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
-# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+#  define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
+#  define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
 #endif
 
 template <class Tp>

``````````

</details>


https://github.com/llvm/llvm-project/pull/141916