initiate Dense cross-executor copy from source

This means that padding in the target will be copied and written back
after the copy has finished.

This fixes issues in builds without OpenMP executor and
reference/test/matrix/dense_kernels

core/matrix/dense.cpp

@@ -322,19 +322,17 @@ void Dense<ValueType>::convert_to(Dense<ValueType>* result) const
     if (result->get_size() != this->get_size()) {
         result->resize(this->get_size());
     }
-    // we need to create a clone of the local data, so the target executor can
-    // copy it.
-    auto result_exec = result->get_executor();
-    auto result_input = make_temporary_clone(result_exec, &values_);
+    // we need to create a temporary clone of the target data to write to
+    auto exec = this->get_executor();
+    auto result_output = make_temporary_clone(exec, &result->values_);
     // create a (value, not pointer to avoid allocation overhead) view
     // matrix on the array to avoid special-casing cross-executor copies
-    auto tmp_this = Dense{
-        result_exec, this->get_size(),
-        gko::detail::array_const_cast(gko::detail::ConstArrayView<ValueType>(
-            result_exec, result_input->get_num_elems(),
-            result_input->get_const_data())),
-        this->get_stride()};
-    result_exec->run(dense::make_copy(&tmp_this, result));
+    auto tmp_result =
+        Dense{exec, this->get_size(),
+              make_array_view(exec, result_output->get_num_elems(),
+                              result_output->get_data()),
+              result->get_stride()};
+    exec->run(dense::make_copy(this, &tmp_result));
 }