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* [gcc r12-6439] libstdc++: Make std::variant work with Clang in C++20 mode [PR103891]
@ 2022-01-11 13:24 Jonathan Wakely
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From: Jonathan Wakely @ 2022-01-11 13:24 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:5b417b35824fb5c15e3ee958cb86436b3409ebea
commit r12-6439-g5b417b35824fb5c15e3ee958cb86436b3409ebea
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jan 10 17:28:19 2022 +0000
libstdc++: Make std::variant work with Clang in C++20 mode [PR103891]
Clang has some bugs with destructors that use constraints to be
conditionally trivial, so disable the P2231R1 constexpr changes to
std::variant unless the compiler is GCC 12 or later.
If/when P2493R0 gets accepted and implemented by G++ we can remove the
__GNUC__ check and use __cpp_concepts >= 202002 instead.
libstdc++-v3/ChangeLog:
PR libstdc++/103891
* include/bits/c++config (_GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS):
Define.
* include/std/variant (__cpp_lib_variant): Only define C++20
value when the compiler is known to support conditionally
trivial destructors.
* include/std/version (__cpp_lib_variant): Likewise.
Diff:
---
libstdc++-v3/include/bits/c++config | 5 +++++
libstdc++-v3/include/std/variant | 7 ++++---
libstdc++-v3/include/std/version | 5 +++--
3 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index c64b61b3c90..b197349f976 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -810,6 +810,11 @@ namespace std
#undef _GLIBCXX_HAS_BUILTIN
+#if __cplusplus >= 202002L && __cpp_concepts && __GNUC__ >= 12
+// XXX workaround for missing feature test macro for P0848R3 (see P2493R0).
+# define _GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS 1
+#endif
+
// PSTL configuration
#if __cplusplus >= 201703L
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index d74939eddc3..c41f9f27e00 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -44,9 +44,10 @@
#include <bits/stl_iterator_base_funcs.h>
#include <bits/stl_construct.h>
#include <bits/utility.h> // in_place_index_t
-#if __cplusplus == 201703L
+#ifndef _GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS
# include <ext/aligned_buffer.h>
-#else
+#endif
+#if __cplusplus >= 202002L
# include <compare>
#endif
@@ -54,7 +55,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
-#if __cplusplus >= 202002L && __cpp_concepts
+#ifdef _GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS
// P2231R1 constexpr needs constexpr unions and constrained destructors.
# define __cpp_lib_variant 202106L
#else
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index f421056964e..012d78e3b6b 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -173,7 +173,8 @@
# define __cpp_lib_to_chars 201611L
#endif
#define __cpp_lib_unordered_map_try_emplace 201411
-#if __cplusplus == 201703L || ! __cpp_concepts // N.B. updated value in C++20
+#ifndef _GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS
+// N.B. updated value in C++20
# define __cpp_lib_variant 202102L
#endif
#endif
@@ -286,7 +287,7 @@
# endif
#define __cpp_lib_to_address 201711L
#define __cpp_lib_to_array 201907L
-#if __cpp_concepts
+#ifdef _GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS
# define __cpp_lib_variant 202106L
#endif
#endif
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