[libc++] Work around new GCC 15 type_traits builtins that can't be used as Clang's can #137871
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GCC 15 has added builtins for various C++ type traits that Clang already had. Since __has_builtin(...) now finds these, the #if branches previously only used for Clang are now used for GCC 15. However, GCC 15 requires that these builtins only be used in type aliases, not in template aliases. These changes follow the model of llvm#81386 where a previous GCC version added builtins for __remove_cv and __remove_cvref. Fixed: llvm#137704 Fixed: llvm#117319
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@llvm/pr-subscribers-libcxx Author: Roland McGrath (frobtech) ChangesGCC 15 has added builtins for various C++ type traits that Clang These changes follow the model of #81386 where a previous GCC Fixed: #137704 Full diff: https://github.com/llvm/llvm-project/pull/137871.diff 6 Files Affected:
diff --git a/libcxx/include/__type_traits/add_lvalue_reference.h b/libcxx/include/__type_traits/add_lvalue_reference.h
index 5e65477058e5f..f2ba25255fca9 100644
--- a/libcxx/include/__type_traits/add_lvalue_reference.h
+++ b/libcxx/include/__type_traits/add_lvalue_reference.h
@@ -20,8 +20,18 @@ _LIBCPP_BEGIN_NAMESPACE_STD
#if __has_builtin(__add_lvalue_reference)
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+struct __add_lvalue_reference_gcc {
+ using type = __add_lvalue_reference(_Tp);
+};
+
+template <class _Tp>
+using __add_lvalue_reference_t _LIBCPP_NODEBUG = typename __add_lvalue_reference_gcc<_Tp>::type;
+# else
template <class _Tp>
using __add_lvalue_reference_t _LIBCPP_NODEBUG = __add_lvalue_reference(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
#else
diff --git a/libcxx/include/__type_traits/add_pointer.h b/libcxx/include/__type_traits/add_pointer.h
index a9a51b86abaf0..4441d15750ad7 100644
--- a/libcxx/include/__type_traits/add_pointer.h
+++ b/libcxx/include/__type_traits/add_pointer.h
@@ -22,8 +22,18 @@ _LIBCPP_BEGIN_NAMESPACE_STD
#if !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__add_pointer)
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+struct __add_pointer_gcc {
+ using type = __add_pointer(_Tp);
+};
+
+template <class _Tp>
+using __add_pointer_t _LIBCPP_NODEBUG = typename __add_pointer_gcc<_Tp>::type;
+# else
template <class _Tp>
using __add_pointer_t _LIBCPP_NODEBUG = __add_pointer(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
#else
template <class _Tp, bool = __is_referenceable_v<_Tp> || is_void<_Tp>::value>
diff --git a/libcxx/include/__type_traits/add_rvalue_reference.h b/libcxx/include/__type_traits/add_rvalue_reference.h
index c51dd54a76789..12b544a7555b7 100644
--- a/libcxx/include/__type_traits/add_rvalue_reference.h
+++ b/libcxx/include/__type_traits/add_rvalue_reference.h
@@ -20,8 +20,18 @@ _LIBCPP_BEGIN_NAMESPACE_STD
#if __has_builtin(__add_rvalue_reference)
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+struct __add_rvalue_reference_gcc {
+ using type = __add_rvalue_reference(_Tp);
+};
+
+template <class _Tp>
+using __add_rvalue_reference_t _LIBCPP_NODEBUG = typename __add_rvalue_reference_gcc<_Tp>::type;
+# else
template <class _Tp>
using __add_rvalue_reference_t _LIBCPP_NODEBUG = __add_rvalue_reference(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
#else
diff --git a/libcxx/include/__type_traits/decay.h b/libcxx/include/__type_traits/decay.h
index 2e3d05d1e4871..5b821c06edf6d 100644
--- a/libcxx/include/__type_traits/decay.h
+++ b/libcxx/include/__type_traits/decay.h
@@ -26,8 +26,18 @@
_LIBCPP_BEGIN_NAMESPACE_STD
#if __has_builtin(__decay)
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+struct __decay_gcc {
+ using type = __decay(_Tp);
+};
+
+template <class _Tp>
+using __decay_t _LIBCPP_NODEBUG = typename __decay_gcc<_Tp>::type;
+# else
template <class _Tp>
using __decay_t _LIBCPP_NODEBUG = __decay(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
template <class _Tp>
struct _LIBCPP_NO_SPECIALIZATIONS decay {
diff --git a/libcxx/include/__type_traits/remove_all_extents.h b/libcxx/include/__type_traits/remove_all_extents.h
index bd7e8060f1a55..ae688610ed968 100644
--- a/libcxx/include/__type_traits/remove_all_extents.h
+++ b/libcxx/include/__type_traits/remove_all_extents.h
@@ -24,8 +24,14 @@ struct _LIBCPP_NO_SPECIALIZATIONS remove_all_extents {
using type _LIBCPP_NODEBUG = __remove_all_extents(_Tp);
};
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+using __remove_all_extents_t = typename remove_all_extents<_Tp>::type;
+# else
template <class _Tp>
using __remove_all_extents_t _LIBCPP_NODEBUG = __remove_all_extents(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
+
#else
template <class _Tp>
struct remove_all_extents {
diff --git a/libcxx/include/__type_traits/remove_extent.h b/libcxx/include/__type_traits/remove_extent.h
index 75bb70015b79c..518159547468e 100644
--- a/libcxx/include/__type_traits/remove_extent.h
+++ b/libcxx/include/__type_traits/remove_extent.h
@@ -24,8 +24,14 @@ struct _LIBCPP_NO_SPECIALIZATIONS remove_extent {
using type _LIBCPP_NODEBUG = __remove_extent(_Tp);
};
+# if defined(_LIBCPP_COMPILER_GCC)
+template <class _Tp>
+using __remove_extent_t = typename remove_extent<_Tp>::type;
+# else
template <class _Tp>
using __remove_extent_t _LIBCPP_NODEBUG = __remove_extent(_Tp);
+# endif // defined(_LIBCPP_COMPILER_GCC)
+
#else
template <class _Tp>
struct remove_extent {
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philnik777
requested changes
Apr 29, 2025
frobtech
changed the title
philnik777
reviewed
May 12, 2025
| @@ -18,7 +18,7 @@ | |||
|
|
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| _LIBCPP_BEGIN_NAMESPACE_STD | |||
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| #if __has_builtin(__add_lvalue_reference) | |||
| #if __has_builtin(__add_lvalue_reference) && __GNUC__ < 15 | |||
There was a problem hiding this comment.
Suggested change
| #if __has_builtin(__add_lvalue_reference) && __GNUC__ < 15 | |
| #if __has_builtin(__add_lvalue_reference) && !defined(_LIBCPP_COMPILER_GCC) |
We usually don't test the version since we support only one and these builtins are new anyways, so there isn't much use to check the version.
You can test this locally with the following command:git-clang-format --diff HEAD~1 HEAD --extensions h -- libcxx/include/__type_traits/add_lvalue_reference.h libcxx/include/__type_traits/add_pointer.h libcxx/include/__type_traits/add_rvalue_reference.h libcxx/include/__type_traits/decay.h libcxx/include/__type_traits/remove_all_extents.h libcxx/include/__type_traits/remove_extent.hView the diff from clang-format here.diff --git a/libcxx/include/__type_traits/add_pointer.h b/libcxx/include/__type_traits/add_pointer.h
index f37f9cf5a..289d51adc 100644
--- a/libcxx/include/__type_traits/add_pointer.h
+++ b/libcxx/include/__type_traits/add_pointer.h
@@ -20,7 +20,8 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-#if !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__add_pointer) && !defined(_LIBCPP_COMPILER_GCC)
+#if !defined(_LIBCPP_WORKAROUND_OBJCXX_COMPILER_INTRINSICS) && __has_builtin(__add_pointer) && \
+ !defined(_LIBCPP_COMPILER_GCC)
template <class _Tp>
using __add_pointer_t _LIBCPP_NODEBUG = __add_pointer(_Tp);
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philnik777
approved these changes
May 13, 2025
|
Did this pass all checks before it was merged? I see formatting errors? |
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GCC 15 has added builtins for various C++ type traits that Clang
already had. Since
__has_builtin(...)now finds these, the #ifbranches previously only used for Clang are now used for GCC 15.
However, GCC 15 requires that these builtins only be used in type
aliases, not in template aliases.
For now, just don't use the
__has_builtin(...)branches under newerGCC versions, so both 14 and 15 work during the transition. This
can be cleaned up later to use all the GCC 15 builtins available.
Fixed: #137704
Fixed: #117319