[SYCL] Add reducer class member aliases and constexpr value

sycl/include/sycl/reduction.hpp

@@ -320,6 +320,14 @@ template <class Reducer> class combiner {
         ReduVarPtr, [](auto &&Ref, auto Val) { return Ref.fetch_max(Val); });
   }
 };
+
+template <typename T, class BinaryOperation, int Dims> class reducer_common {
+public:
+  using value_type = T;
+  using binary_operation = BinaryOperation;
+  static constexpr int dimensions = Dims;
+};
+
 } // namespace detail
 
 /// Specialization of the generic class 'reducer'. It is used for reductions
@@ -336,7 +344,8 @@ class reducer<
           reducer<T, BinaryOperation, Dims, Extent, View,
                   std::enable_if_t<
                       Dims == 0 && Extent == 1 && View == false &&
-                      !detail::IsKnownIdentityOp<T, BinaryOperation>::value>>> {
+                      !detail::IsKnownIdentityOp<T, BinaryOperation>::value>>>,
+      public detail::reducer_common<T, BinaryOperation, Dims> {
 public:
   reducer(const T &Identity, BinaryOperation BOp)
       : MValue(Identity), MIdentity(Identity), MBinaryOp(BOp) {}
@@ -371,7 +380,8 @@ class reducer<
           reducer<T, BinaryOperation, Dims, Extent, View,
                   std::enable_if_t<
                       Dims == 0 && Extent == 1 && View == false &&
-                      detail::IsKnownIdentityOp<T, BinaryOperation>::value>>> {
+                      detail::IsKnownIdentityOp<T, BinaryOperation>::value>>>,
+      public detail::reducer_common<T, BinaryOperation, Dims> {
 public:
   reducer() : MValue(getIdentity()) {}
   reducer(const T & /* Identity */, BinaryOperation) : MValue(getIdentity()) {}
@@ -398,7 +408,8 @@ class reducer<T, BinaryOperation, Dims, Extent, View,
               std::enable_if_t<Dims == 0 && View == true>>
     : public detail::combiner<
           reducer<T, BinaryOperation, Dims, Extent, View,
-                  std::enable_if_t<Dims == 0 && View == true>>> {
+                  std::enable_if_t<Dims == 0 && View == true>>>,
+      public detail::reducer_common<T, BinaryOperation, Dims> {
 public:
   reducer(T &Ref, BinaryOperation BOp) : MElement(Ref), MBinaryOp(BOp) {}
 
@@ -423,7 +434,8 @@ class reducer<
           reducer<T, BinaryOperation, Dims, Extent, View,
                   std::enable_if_t<
                       Dims == 1 && View == false &&
-                      !detail::IsKnownIdentityOp<T, BinaryOperation>::value>>> {
+                      !detail::IsKnownIdentityOp<T, BinaryOperation>::value>>>,
+      public detail::reducer_common<T, BinaryOperation, Dims> {
 public:
   reducer(const T &Identity, BinaryOperation BOp)
       : MValue(Identity), MIdentity(Identity), MBinaryOp(BOp) {}
@@ -453,7 +465,8 @@ class reducer<
           reducer<T, BinaryOperation, Dims, Extent, View,
                   std::enable_if_t<
                       Dims == 1 && View == false &&
-                      detail::IsKnownIdentityOp<T, BinaryOperation>::value>>> {
+                      detail::IsKnownIdentityOp<T, BinaryOperation>::value>>>,
+      public detail::reducer_common<T, BinaryOperation, Dims> {
 public:
   reducer() : MValue(getIdentity()) {}
   reducer(const T & /* Identity */, BinaryOperation) : MValue(getIdentity()) {}

sycl/test/basic_tests/reduction/reducer_aliases.cpp

@@ -0,0 +1,61 @@
+// RUN: %clangxx -fsycl -fsyntax-only -sycl-std=2020 %s
+
+// Tests the member aliases on the reducer class.
+
+#include <sycl/sycl.hpp>
+
+#include <type_traits>
+
+template <typename T> class Kernel;
+
+template <typename ReducerT, typename ValT, typename BinOp, int Dims>
+void CheckReducerAliases() {
+  static_assert(std::is_same_v<typename ReducerT::value_type, ValT>);
+  static_assert(std::is_same_v<typename ReducerT::binary_operation, BinOp>);
+  static_assert(ReducerT::dimensions == Dims);
+}
+
+template <typename T> void CheckAllReducers(sycl::queue &Q) {
+  T *Vals = sycl::malloc_device<T>(4, Q);
+  sycl::span<T, 4> SpanVal(Vals, 4);
+
+  auto CustomOp = [](const T &LHS, const T &RHS) { return LHS + RHS; };
+
+  auto ValReduction1 = sycl::reduction(Vals, sycl::plus<>());
+  auto ValReduction2 = sycl::reduction(Vals, T{}, sycl::plus<>());
+  auto ValReduction3 = sycl::reduction(Vals, T{}, CustomOp);
+  auto SpanReduction1 = sycl::reduction(SpanVal, sycl::plus<>());
+  auto SpanReduction2 = sycl::reduction(SpanVal, T{}, sycl::plus<>());
+  auto SpanReduction3 = sycl::reduction(SpanVal, T{}, CustomOp);
+  // TODO: Add cases with identityless reductions when supported.
+  Q.parallel_for<Kernel<T>>(
+      sycl::range<1>{10}, ValReduction1, ValReduction2, ValReduction3,
+      SpanReduction1, SpanReduction2, SpanReduction3,
+      [=](sycl::id<1>, auto &ValRedu1, auto &ValRedu2, auto &ValRedu3,
+          auto &SpanRedu1, auto &SpanRedu2, auto &SpanRedu3) {
+        CheckReducerAliases<std::remove_reference_t<decltype(ValRedu1)>, T,
+                            sycl::plus<>, 0>();
+        CheckReducerAliases<std::remove_reference_t<decltype(ValRedu2)>, T,
+                            sycl::plus<>, 0>();
+        CheckReducerAliases<std::remove_reference_t<decltype(ValRedu3)>, T,
+                            decltype(CustomOp), 0>();
+        CheckReducerAliases<std::remove_reference_t<decltype(SpanRedu1)>, T,
+                            sycl::plus<>, 1>();
+        CheckReducerAliases<std::remove_reference_t<decltype(SpanRedu2)>, T,
+                            sycl::plus<>, 1>();
+        CheckReducerAliases<std::remove_reference_t<decltype(SpanRedu3)>, T,
+                            decltype(CustomOp), 1>();
+      });
+}
+
+int main() {
+  sycl::queue Q;
+  CheckAllReducers<char>(Q);
+  CheckAllReducers<short>(Q);
+  CheckAllReducers<int>(Q);
+  CheckAllReducers<long>(Q);
+  CheckAllReducers<float>(Q);
+  CheckAllReducers<double>(Q);
+  CheckAllReducers<sycl::half>(Q);
+  return 0;
+}