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* [gcc r13-2954] libstdc++: Guard use of new built-in with __has_builtin
@ 2022-09-29 11:47 Jonathan Wakely
  0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2022-09-29 11:47 UTC (permalink / raw)
  To: gcc-cvs, libstdc++-cvs

commit r13-2954-gdf7f2736509cfe5e1dd7d9f263355c5043347a9c
Author: Jonathan Wakely <>
Date:   Thu Sep 29 11:30:05 2022 +0100

    libstdc++: Guard use of new built-in with __has_builtin
    I forgot that non-GCC compilers don't have this built-in yet.
    For Clang we could do something like the check below (as described in
    P2255), but for now I'm just fixing the regression.
     #if __has_builtin((__reference_binds_to_temporary)
      bool _Dangle = __reference_binds_to_temporary(_Tp, _Res_t)
                     && __and_<is_reference<_Tp>,
            * include/std/type_traits (__is_invocable_impl): Check
            __has_builtin(__reference_converts_from_temporary) before using

 libstdc++-v3/include/std/type_traits | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 22c1af26397..a015fd95a71 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
       template<typename _Tp,
 	       bool _Nothrow = noexcept(_S_conv<_Tp>(_S_get())),
 	       typename = decltype(_S_conv<_Tp>(_S_get())),
-	       bool _Dangle = __reference_converts_from_temporary(_Tp, _Res_t)>
+#if __has_builtin(__reference_converts_from_temporary)
+	       bool _Dangle = __reference_converts_from_temporary(_Tp, _Res_t)
+	       bool _Dangle = false
+	      >
 	static __bool_constant<_Nothrow && !_Dangle>

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