[libcxx-commits] [libcxx] [libc++] Use `__reference_constructs_from_temporary` if eligible (PR #141916)
A. Jiang via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Jun 2 16:33:15 PDT 2025
https://github.com/frederick-vs-ja updated https://github.com/llvm/llvm-project/pull/141916
>From 417b08ace5e0703fb0dbea2ba703cc182131b9cd Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Thu, 29 May 2025 17:19:36 +0800
Subject: [PATCH 1/4] [libc++] Use `__reference_constructs_from_temporary` if
eligible
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.
---
libcxx/include/tuple | 4 +++-
.../PR20855_tuple_ref_binding_diagnostics.verify.cpp | 2 +-
.../PR20855_tuple_ref_binding_diagnostics.pass.cpp | 11 ++++++-----
3 files changed, 10 insertions(+), 7 deletions(-)
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 8dd62ae624f5e..9aacde40b7be0 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);
+# elif __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>
>From 4bfdddae8ef19c899c9615e05c69319af77431e8 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Sun, 1 Jun 2025 11:01:47 +0800
Subject: [PATCH 2/4] Switch to use internal type trait
---
.../reference_constructs_from_temporary.h | 13 +++++++++++++
libcxx/include/tuple | 16 +++-------------
...0855_tuple_ref_binding_diagnostics.verify.cpp | 9 ++++++++-
...R20855_tuple_ref_binding_diagnostics.pass.cpp | 5 ++++-
4 files changed, 28 insertions(+), 15 deletions(-)
diff --git a/libcxx/include/__type_traits/reference_constructs_from_temporary.h b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
index 1c62e58cc4e12..32a7c1b8b1a4a 100644
--- a/libcxx/include/__type_traits/reference_constructs_from_temporary.h
+++ b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
@@ -30,6 +30,19 @@ _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool reference_constructs_from_tempo
#endif
+#if __has_builtin(__reference_constructs_from_temporary)
+template <class _Tp, class _Up>
+inline const bool __reference_constructs_from_temporary_v = __reference_constructs_from_temporary(_Tp, _Up);
+#elif __has_builtin(__reference_binds_to_temporary)
+// TODO: Remove this once all support compilers have __reference_constructs_from_temporary implemented.
+template <class _Tp, class _Up>
+inline const bool __reference_constructs_from_temporary_v = __reference_binds_to_temporary(_Tp, _Up);
+#else
+// TODO: Remove this once https://github.com/llvm/llvm-project/issues/111477 no longer affects supported compilers.
+template <class _Tp, class _Up>
+inline const bool __reference_constructs_from_temporary_v = false;
+#endif
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___TYPE_TRAITS_REFERENCE_CONSTRUCTS_FROM_TEMPORARY_H
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 9aacde40b7be0..6e7a430d219ea 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -258,6 +258,7 @@ template <class... Types>
# include <__type_traits/maybe_const.h>
# include <__type_traits/nat.h>
# include <__type_traits/negation.h>
+# include <__type_traits/reference_constructs_from_temporary.h>
# include <__type_traits/remove_cv.h>
# include <__type_traits/remove_cvref.h>
# include <__type_traits/remove_reference.h>
@@ -308,17 +309,6 @@ template <size_t _Ip, class _Hp, bool>
class __tuple_leaf {
_Hp __value_;
- template <class _Tp>
- static _LIBCPP_HIDE_FROM_ABI constexpr bool __can_bind_reference() {
-# if __has_builtin(__reference_constructs_from_temporary)
- return !__reference_constructs_from_temporary(_Hp, _Tp);
-# elif __has_keyword(__reference_binds_to_temporary)
- return !__reference_binds_to_temporary(_Hp, _Tp);
-# else
- return true;
-# endif
- }
-
public:
_LIBCPP_CONSTEXPR_SINCE_CXX14 __tuple_leaf& operator=(const __tuple_leaf&) = delete;
@@ -348,7 +338,7 @@ public:
_LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX14 explicit __tuple_leaf(_Tp&& __t) noexcept(is_nothrow_constructible<_Hp, _Tp>::value)
: __value_(std::forward<_Tp>(__t)) {
- static_assert(__can_bind_reference<_Tp&&>(),
+ static_assert(!__reference_constructs_from_temporary_v<_Hp, _Tp&&>,
"Attempted construction of reference element binds to a temporary whose lifetime has ended");
}
@@ -356,7 +346,7 @@ public:
_LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX14 explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
: __value_(std::forward<_Tp>(__t)) {
- static_assert(__can_bind_reference<_Tp&&>(),
+ static_assert(!__reference_constructs_from_temporary_v<_Hp, _Tp&&>,
"Attempted construction of reference element binds to a temporary whose lifetime has ended");
}
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 df068bf35f2e5..f8841180a41df 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
@@ -38,9 +38,16 @@ template <class T> struct CannotDeduce {
template <class ...Args>
void F(typename CannotDeduce<std::tuple<Args...>>::type const&) {}
+#if TEST_HAS_BUILTIN(__reference_constructs_from_temporary)
+# define TEST_HAS_REFERENCE_BINDING_TRAIT 1
+#elif TEST_HAS_BUILTIN(__reference_binds_to_temporary)
+# define TEST_HAS_REFERENCE_BINDING_TRAIT 1
+#else
+# define TEST_HAS_REFERENCE_BINDING_TRAIT 0
+#endif
void f() {
-#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_constructs_from_temporary)
+#if TEST_HAS_REFERENCE_BINDING_TRAIT
// 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 1da967d89718f..aec1e63f33ce7 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
@@ -18,10 +18,13 @@
#include <cassert>
#include "test_macros.h"
-#if TEST_HAS_BUILTIN_IDENTIFIER(__reference_constructs_from_temporary)
+#if TEST_HAS_BUILTIN(__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__), "")
+#elif TEST_HAS_BUILTIN(__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__), "")
#else
# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
>From 8af46236d1cee5fa60643913b908c842caf12339 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Mon, 2 Jun 2025 23:13:37 +0800
Subject: [PATCH 3/4] Remove inactive code branches
---
.../reference_constructs_from_temporary.h | 8 ++------
...PR20855_tuple_ref_binding_diagnostics.verify.cpp | 13 -------------
.../PR20855_tuple_ref_binding_diagnostics.pass.cpp | 6 ++----
3 files changed, 4 insertions(+), 23 deletions(-)
diff --git a/libcxx/include/__type_traits/reference_constructs_from_temporary.h b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
index 32a7c1b8b1a4a..9caea4afc3bf7 100644
--- a/libcxx/include/__type_traits/reference_constructs_from_temporary.h
+++ b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
@@ -33,14 +33,10 @@ _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool reference_constructs_from_tempo
#if __has_builtin(__reference_constructs_from_temporary)
template <class _Tp, class _Up>
inline const bool __reference_constructs_from_temporary_v = __reference_constructs_from_temporary(_Tp, _Up);
-#elif __has_builtin(__reference_binds_to_temporary)
-// TODO: Remove this once all support compilers have __reference_constructs_from_temporary implemented.
-template <class _Tp, class _Up>
-inline const bool __reference_constructs_from_temporary_v = __reference_binds_to_temporary(_Tp, _Up);
#else
-// TODO: Remove this once https://github.com/llvm/llvm-project/issues/111477 no longer affects supported compilers.
+// TODO(LLVM 22): Remove this as all support compilers should have __reference_constructs_from_temporary implemented.
template <class _Tp, class _Up>
-inline const bool __reference_constructs_from_temporary_v = false;
+inline const bool __reference_constructs_from_temporary_v = __reference_binds_to_temporary(_Tp, _Up);
#endif
_LIBCPP_END_NAMESPACE_STD
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 f8841180a41df..a1a80483c4487 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
@@ -38,16 +38,7 @@ template <class T> struct CannotDeduce {
template <class ...Args>
void F(typename CannotDeduce<std::tuple<Args...>>::type const&) {}
-#if TEST_HAS_BUILTIN(__reference_constructs_from_temporary)
-# define TEST_HAS_REFERENCE_BINDING_TRAIT 1
-#elif TEST_HAS_BUILTIN(__reference_binds_to_temporary)
-# define TEST_HAS_REFERENCE_BINDING_TRAIT 1
-#else
-# define TEST_HAS_REFERENCE_BINDING_TRAIT 0
-#endif
-
void f() {
-#if TEST_HAS_REFERENCE_BINDING_TRAIT
// 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}}
@@ -80,8 +71,4 @@ void f() {
std::tuple<std::string &&> t2("hello"); // expected-note {{requested here}}
std::tuple<std::string &&> t3(std::allocator_arg, alloc, "hello"); // expected-note {{requested here}}
}
-#else
-#error force failure
-// expected-error at -1 {{force failure}}
-#endif
}
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 aec1e63f33ce7..d78de0eec8e53 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
@@ -22,12 +22,10 @@
# 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__), "")
-#elif TEST_HAS_BUILTIN(__reference_binds_to_temporary)
+#else
+// TODO(LLVM 22): Remove this as all support compilers should have __reference_constructs_from_temporary implemented.
# 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__), "")
-#else
-# define ASSERT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
-# define ASSERT_NOT_REFERENCE_BINDS_TEMPORARY(...) static_assert(true, "")
#endif
template <class Tp>
>From e72fc82e238f4d4faf5a8d14117c4cc7525c4385 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Tue, 3 Jun 2025 01:36:20 +0800
Subject: [PATCH 4/4] Adopt @philnik777's review comment for comments
Co-authored-by: Nikolas Klauser <nikolasklauser at berlin.de>
---
.../include/__type_traits/reference_constructs_from_temporary.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libcxx/include/__type_traits/reference_constructs_from_temporary.h b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
index 9caea4afc3bf7..2ff549b4e15ce 100644
--- a/libcxx/include/__type_traits/reference_constructs_from_temporary.h
+++ b/libcxx/include/__type_traits/reference_constructs_from_temporary.h
@@ -34,7 +34,7 @@ _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool reference_constructs_from_tempo
template <class _Tp, class _Up>
inline const bool __reference_constructs_from_temporary_v = __reference_constructs_from_temporary(_Tp, _Up);
#else
-// TODO(LLVM 22): Remove this as all support compilers should have __reference_constructs_from_temporary implemented.
+// TODO(LLVM 22): Remove this as all supported compilers should have __reference_constructs_from_temporary implemented.
template <class _Tp, class _Up>
inline const bool __reference_constructs_from_temporary_v = __reference_binds_to_temporary(_Tp, _Up);
#endif
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