#4913: Make View self-assignment not produce double-free

[crtrott]

Replacing #4914 because I can neither push to NexGenAnalytics organization nor, do a PR against that fork??

Fixes #4913

[dalg24]

Suggested change

	// Test self assignment
	dx = dx;
	ASSERT_EQ(dx.use_count(), 1);
	dx = reinterpret_cast<typename dView4::uniform_type &>(dx);
	// Test self assignment
	dx = dx; // copy-assignement operator
	ASSERT_EQ(dx.use_count(), 1);
	dx = reinterpret_cast<typename dView4::uniform_type &>(dx); // conversion constructor

[dalg24]

Actually why do we have both

kokkos/core/src/Kokkos_View.hpp

Lines 1426 to 1440 in b52f8c8

	template <class RT, class... RP>
	KOKKOS_INLINE_FUNCTION View(
	const View<RT, RP...>& rhs,
	typename std::enable_if<Kokkos::Impl::ViewMapping<
	traits, typename View<RT, RP...>::traits,
	typename traits::specialize>::is_assignable_data_type>::type* =
	nullptr)
	: m_track(rhs), m_map() {
	using SrcTraits = typename View<RT, RP...>::traits;
	using Mapping = Kokkos::Impl::ViewMapping<traits, SrcTraits,
	typename traits::specialize>;
	static_assert(Mapping::is_assignable,
	"Incompatible View copy construction");
	Mapping::assign(m_map, rhs.m_map, rhs.m_track.m_tracker);
	}

and

kokkos/core/src/Kokkos_View.hpp

Lines 1442 to 1456 in b52f8c8

	template <class RT, class... RP>
	KOKKOS_INLINE_FUNCTION typename std::enable_if<
	Kokkos::Impl::ViewMapping<
	traits, typename View<RT, RP...>::traits,
	typename traits::specialize>::is_assignable_data_type,
	View>::type&
	operator=(const View<RT, RP...>& rhs) {
	using SrcTraits = typename View<RT, RP...>::traits;
	using Mapping = Kokkos::Impl::ViewMapping<traits, SrcTraits,
	typename traits::specialize>;
	static_assert(Mapping::is_assignable, "Incompatible View copy assignment");
	Mapping::assign(m_map, rhs.m_map, rhs.m_track.m_tracker);
	m_track.assign(rhs);
	return *this;
	}

cc @nliber

[crtrott]

Uh interesting:

/Users/runner/work/kokkos/kokkos/core/unit_test/TestViewAPI.hpp:1082:8: error: explicitly assigning value of variable of type 'Test::TestViewAPI::dView4' (aka 'View<T *[N1][N2][N3], DeviceType>') to itself [-Werror,-Wself-assign-overloaded]
    dx = dx;

[dalg24]

OpenMPTarget-ROCm build has the failure reported in #5025

[ RUN      ] openmp.scatterview
/var/jenkins/workspace/Kokkos/containers/unit_tests/TestScatterView.hpp:363: Failure
The difference between val0 and 4.0 is 4, which exceeds 1e-14 * 4.0, where
val0 evaluates to 8,
4.0 evaluates to 4, and
1e-14 * 4.0 evaluates to 4e-14.
Data differs at index 4

[nmm0]

Looks good to me! I had to double check that the reinterpret_cast was valid, which it should be as long as we don't dereference it