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| author | Jonathan Wakely <jwakely@redhat.com> | 2022-03-23 09:57:20 +0000 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2022-03-23 12:17:16 +0000 |
| commit | 4894d69a1f37d54b6a612e58053db477ff5ba832 (patch) | |
| tree | c28015e1136893a110e0ef71075f312d8957209a | |
| parent | 018805e2791bafb40f8937d371d31325b037880d (diff) | |
| download | gcc-4894d69a1f37d54b6a612e58053db477ff5ba832.zip gcc-4894d69a1f37d54b6a612e58053db477ff5ba832.tar.gz gcc-4894d69a1f37d54b6a612e58053db477ff5ba832.tar.bz2 | |
libstdc++: Add missing constraints to std::bit_cast [PR105027]
Our std::bit_cast was relying on the compiler to check for errors inside
__builtin_bit_cast, instead of checking them as constraints. That means
std::bit_cast was not SFINAE-friendly.
This fix uses a requires-clause, so for old versions of Clang without
concepts support the function will still be unconstrained. At some point
in future we can remove the #ifdef __cpp_concepts check and rely on all
compilers having full concepts support in C++20 mode.
libstdc++-v3/ChangeLog:
PR libstdc++/105027
* include/std/bit (bit_cast): Add constraints.
* testsuite/26_numerics/bit/bit.cast/105027.cc: New test.
| -rw-r--r-- | libstdc++-v3/include/std/bit | 4 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/26_numerics/bit/bit.cast/105027.cc | 18 |
2 files changed, 22 insertions, 0 deletions
diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit index cfd98e2..a40f1ce 100644 --- a/libstdc++-v3/include/std/bit +++ b/libstdc++-v3/include/std/bit @@ -73,6 +73,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION [[nodiscard]] constexpr _To bit_cast(const _From& __from) noexcept +#ifdef __cpp_concepts + requires (sizeof(_To) == sizeof(_From)) + && __is_trivially_copyable(_To) && __is_trivially_copyable(_From) +#endif { return __builtin_bit_cast(_To, __from); } diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/105027.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/105027.cc new file mode 100644 index 0000000..301d94e --- /dev/null +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/105027.cc @@ -0,0 +1,18 @@ +// { dg-options "-std=gnu++20" } +// { dg-do compile { target c++20 } } + +// PR libstdc++/105027 - Missing constraints on std::bit_cast + +#include <bit> + +template<class T, class U> +concept BitCastable = requires(const U& u) { std::bit_cast<T>(u); }; + +static_assert(BitCastable<int, unsigned>); // OK + +static_assert(!BitCastable<int, char>); // #1: different size + +struct A { A(A const&); int i; }; +static_assert(!BitCastable<int, A>); // #2: not trivially copyable + +static_assert(!BitCastable<long, int()>); // #3: sizeof(int()) is ill-formed |