Address reviewer comments

Signed-off-by: Matthew Michel <[email protected]>

include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl.h

@@ -28,10 +28,12 @@
 #include <cmath>
 #include <limits>
 #include <cstdint>
+#include <tuple>
 
 #include "../../iterator_impl.h"
 #include "../../execution_impl.h"
 #include "../../utils_ranges.h"
+#include "../../utils.h"
 
 #include "sycl_defs.h"
 #include "parallel_backend_sycl_utils.h"
@@ -258,12 +260,8 @@ struct __parallel_for_large_submitter;
 template <typename... _Name, typename... _RangeTypes>
 struct __parallel_for_large_submitter<__internal::__optional_kernel_name<_Name...>, _RangeTypes...>
 {
-    // Flatten the range as std::tuple value types in the range are likely coming from separate ranges in a zip
-    // iterator.
-    using _FlattenedRangesTuple = typename oneapi::dpl::__internal::__flatten_std_or_internal_tuple<
-        std::tuple<oneapi::dpl::__internal::__value_t<_RangeTypes>...>>::type;
-    static constexpr std::size_t __min_type_size =
-        oneapi::dpl::__internal::__min_tuple_type_size_v<_FlattenedRangesTuple>;
+    static constexpr std::size_t __min_type_size = oneapi::dpl::__internal::__min_nested_type_size<
+        std::tuple<oneapi::dpl::__internal::__value_t<_RangeTypes>...>>::value;
     // __iters_per_work_item is set to 1, 2, 4, 8, or 16 depending on the smallest type in the
     // flattened ranges. This allows us to launch enough work per item to saturate the device's memory
     // bandwidth. This heuristic errs on the side of launching more work per item than what is needed to

include/oneapi/dpl/pstl/tuple_impl.h

@@ -793,25 +793,6 @@ struct __decay_with_tuple_specialization<::std::tuple<_Args...>>
 template <typename... _Args>
 using __decay_with_tuple_specialization_t = typename __decay_with_tuple_specialization<_Args...>::type;
 
-// Flatten nested std::tuple or oneapi::dpl::__internal::tuple types into a single std::tuple.
-template <typename _T>
-struct __flatten_std_or_internal_tuple
-{
-    using type = std::tuple<_T>;
-};
-
-template <typename... _Ts>
-struct __flatten_std_or_internal_tuple<std::tuple<_Ts...>>
-{
-    using type = decltype(std::tuple_cat(std::declval<typename __flatten_std_or_internal_tuple<_Ts>::type>()...));
-};
-
-template <typename... _Ts>
-struct __flatten_std_or_internal_tuple<oneapi::dpl::__internal::tuple<_Ts...>>
-{
-    using type = decltype(std::tuple_cat(std::declval<typename __flatten_std_or_internal_tuple<_Ts>::type>()...));
-};
-
 } // namespace __internal
 } // namespace dpl
 } // namespace oneapi

include/oneapi/dpl/pstl/utils.h

@@ -25,6 +25,7 @@
 #include <iterator>
 #include <functional>
 #include <type_traits>
+#include <algorithm>
 
 #if _ONEDPL_BACKEND_SYCL
 #    include "hetero/dpcpp/sycl_defs.h"
@@ -784,29 +785,21 @@ union __lazy_ctor_storage
     }
 };
 
-// Utility that returns the smallest type size in a tuple.
-template <typename _Tuple>
-class __min_tuple_type_size;
-
+// Returns the smallest type within a set of potentially nested template types.
+// E.g. If we consider the type: T = tuple<float, tuple<short, long>, int, double>,
+// then __min_nested_type_size<T>::value returns sizeof(short).
 template <typename _T>
-class __min_tuple_type_size<std::tuple<_T>>
+struct __min_nested_type_size
 {
-  public:
-    static constexpr std::size_t value = sizeof(_T);
+    constexpr static std::size_t value = sizeof(_T);
 };
 
-template <typename _T, typename... _Ts>
-class __min_tuple_type_size<std::tuple<_T, _Ts...>>
+template <template <typename...> typename _WrapperType, typename... _Ts>
+struct __min_nested_type_size<_WrapperType<_Ts...>>
 {
-    static constexpr std::size_t __min_type_value_ts = __min_tuple_type_size<std::tuple<_Ts...>>::value;
-
-  public:
-    static constexpr std::size_t value = std::min(sizeof(_T), __min_type_value_ts);
+    constexpr static std::size_t value = std::min({__min_nested_type_size<_Ts>::value...});
 };
 
-template <typename _Tuple>
-inline constexpr std::size_t __min_tuple_type_size_v = __min_tuple_type_size<_Tuple>::value;
-
 } // namespace __internal
 } // namespace dpl
 } // namespace oneapi