Tested on x86_64-pc-linux-gnu with GLIBCXX_TESTSUITE_STDS=11,14,20,
does this look OK for trunk and backports (after r16-7199 gets
backported)? Also tested with Clang 21.
-- >8 --
After the front end change r16-7199 both GCC and Clang allow
non-empty constexpr constructor bodies in C++11 as an extension,
so we can unconditionally enable the __builtin_clear_padding logic
in std::atomic's constructor.
PR libstdc++/114865
libstdc++-v3/ChangeLog:
* include/std/atomic (atomic<_Tp>::atomic(_Tp))
[C++11]: Enable __builtin_clear_padding logic.
* testsuite/29_atomics/atomic/cons/static_zero_padding.cc
[C++11]: Enable test verifying cleared padding bits for a
std::atomic local variable.
---
libstdc++-v3/include/std/atomic | 5 ++++-
.../testsuite/29_atomics/atomic/cons/static_zero_padding.cc | 2 --
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 56dbe7bf5b95..306667e3c633 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -247,14 +247,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
atomic& operator=(const atomic&) = delete;
atomic& operator=(const atomic&) volatile = delete;
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wc++14-extensions" // constexpr ctor body
constexpr atomic(_Tp __i) noexcept : _M_i(__i)
{
-#if __cplusplus >= 201402L && __has_builtin(__builtin_clear_padding)
+#if __has_builtin(__builtin_clear_padding)
if _GLIBCXX17_CONSTEXPR (__atomic_impl::__maybe_has_padding<_Tp>())
if (!std::__is_constant_evaluated())
__builtin_clear_padding(std::__addressof(_M_i));
#endif
}
+#pragma GCC diagnostic pop
operator _Tp() const noexcept
{ return load(); }
diff --git
a/libstdc++-v3/testsuite/29_atomics/atomic/cons/static_zero_padding.cc
b/libstdc++-v3/testsuite/29_atomics/atomic/cons/static_zero_padding.cc
index 506513647c6c..e3594fb1c8ea 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/cons/static_zero_padding.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/cons/static_zero_padding.cc
@@ -57,9 +57,7 @@ void test_struct(std::atomic<T>& g, const T& zp)
std::atomic<T> l(T{1, 2});
std::memcpy(&t, &zp, sizeof(T));
-#if __cplusplus >= 201402L // Remove once PR114865 is fixed
VERIFY( l.compare_exchange_strong(t, d) );
-#endif
constexpr std::atomic<T> cl(T{1, 2});
}
--
2.53.0.68.g864f55e190
