This removes use of std::start_lifetime_as from inplace_vector::_M_init,
that was preventing optimizations (see PR124121), it is not required as
GCC treats any write to union as potentially changing active member.
Furthermore when available __builtin_constexpr_diag is used to emit better
error message. TODO comment is also removed, as suggested new call is not
supported until clang 23.
This backports parts of r17-4164-ga6cb4f45, that does not depend on
start_lifetime.
libstdc++-v3/ChangeLog:
PR libstdc++/124121
(inplace_vector::_M_init): Remove unnecessary start_lifetime_as call.
Emit error using __builtin_constexpr_diag.
---
Backporting the changes to #else branch. Unfortunatelly there are not sufficient
to address PR124121, but are still step froward it.
Tested on x86_64-linux. *inplace* test additionally tested in all standard
modes,
debug, assertions, -m32. OK for 16?
libstdc++-v3/include/std/inplace_vector | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/libstdc++-v3/include/std/inplace_vector
b/libstdc++-v3/include/std/inplace_vector
index 131bdc4ca47..0159f7021f3 100644
--- a/libstdc++-v3/include/std/inplace_vector
+++ b/libstdc++-v3/include/std/inplace_vector
@@ -841,21 +841,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
constexpr void
_M_init()
{
- if !consteval
+ if consteval
{
-#if __glibcxx_start_lifetime_as
- std::start_lifetime_as_array<_Tp>(data(), _Nm);
-#endif
- }
- else
- {
- // TODO: use new(_M_elems) _Tp[_Nm]() once PR121068 is fixed
if constexpr (is_trivially_default_constructible_v<_Tp>
&& is_trivially_copyable_v<_Tp>)
for (size_t __i = 0; __i < _Nm; ++__i)
_M_elems[__i] = _Tp();
else
- __builtin_unreachable(); // only trivial types are supported at
compile time
+#if __has_builtin(__builtin_constexpr_diag)
+ __builtin_constexpr_diag(2, "",
+ "std::inplace_vector supports only trivally copyable and "
+ "trivially default constructible types at compile time");
+#else
+ __builtin_unreachable();
+#endif
}
}
--
2.55.0
