Hello,
this small patch feels safe: we are moving an existing object to an
uninitialized location so the 2 locations can't overlap. And it helps with
std::vector<std::unique_ptr<int>> where it lets the compiler get rid of
the branches "if(...) delete ..." when moving elements around, for
instance in reserve(). We don't get a call to memmove yet (ldist may be
confused by clobbers, I'll investigate and report that later), but the
code gets much smaller at -O2, and we vectorize at -O3.
Similarly, I think the call to memmove in __relocate_a_1 could probably be
memcpy (I don't remember why I chose memmove), but that seems less
important and I don't want to mix it with this patch.
Bootstrap+regtest on x86_64-pc-linux-gnu.
2019-04-29 Marc Glisse <marc.gli...@inria.fr>
PR libstdc++/87106
* include/bits/stl_uninitialized.h (__relocate_object_a): Mark the
arguments with __restrict.
--
Marc GlisseIndex: libstdc++-v3/include/bits/stl_uninitialized.h
===================================================================
--- libstdc++-v3/include/bits/stl_uninitialized.h (revision 270586)
+++ libstdc++-v3/include/bits/stl_uninitialized.h (working copy)
@@ -877,21 +877,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
auto __res = std::__uninitialized_copy_n_pair
(_GLIBCXX_MAKE_MOVE_ITERATOR(__first),
__count, __result);
return {__res.first.base(), __res.second};
}
#endif // C++17
#if __cplusplus >= 201103L
template<typename _Tp, typename _Up, typename _Allocator>
inline void
- __relocate_object_a(_Tp* __dest, _Up* __orig, _Allocator& __alloc)
+ __relocate_object_a(_Tp* __restrict __dest, _Up* __restrict __orig,
+ _Allocator& __alloc)
noexcept(noexcept(std::allocator_traits<_Allocator>::construct(__alloc,
__dest, std::move(*__orig)))
&& noexcept(std::allocator_traits<_Allocator>::destroy(
__alloc, std::__addressof(*__orig))))
{
typedef std::allocator_traits<_Allocator> __traits;
__traits::construct(__alloc, __dest, std::move(*__orig));
__traits::destroy(__alloc, std::__addressof(*__orig));
}
