[SYCL] Support kernels accepting item in range reduction parallel_for (…

…#7478)

Previously only sycl::id worked.

sycl/include/sycl/item.hpp

@@ -25,9 +25,12 @@ template <typename TransformedArgType, int Dims, typename KernelType>
 class RoundedRangeKernel;
 template <typename TransformedArgType, int Dims, typename KernelType>
 class RoundedRangeKernelWithKH;
+
+namespace reduction {
+template <int Dims>
+item<Dims, false> getDelinearizedItem(range<Dims> Range, id<Dims> Id);
+} // namespace reduction
 } // namespace detail
-template <int dimensions> class id;
-template <int dimensions> class range;
 
 /// Identifies an instance of the function object executing at each point
 /// in a range.
@@ -130,6 +133,10 @@ template <int dimensions = 1, bool with_offset = true> class item {
   friend class detail::RoundedRangeKernelWithKH;
   void set_allowed_range(const range<dimensions> rnwi) { MImpl.MExtent = rnwi; }
 
+  template <int Dims>
+  friend item<Dims, false>
+  detail::reduction::getDelinearizedItem(range<Dims> Range, id<Dims> Id);
+
   detail::ItemBase<dimensions, with_offset> MImpl;
 };
 

sycl/include/sycl/reduction.hpp

@@ -2368,8 +2368,18 @@ void reduction_parallel_for(handler &CGH, range<Dims> Range,
     size_t Start = GroupStart + NDId.get_local_id(0);
     size_t End = GroupEnd;
     size_t Stride = NDId.get_local_range(0);
+    auto GetDelinearized = [&](size_t I) {
+      auto Id = getDelinearizedId(Range, I);
+      if constexpr (std::is_invocable_v<decltype(KernelFunc), id<Dims>,
+                                        decltype(Reducers)...>)
+        return Id;
+      else
+        // SYCL doesn't provide parallel_for accepting offset in presence of
+        // reductions, so use with_offset==false.
+        return reduction::getDelinearizedItem(Range, Id);
+    };
     for (size_t I = Start; I < End; I += Stride)
-      KernelFunc(getDelinearizedId(Range, I), Reducers...);
+      KernelFunc(GetDelinearized(I), Reducers...);
   };
   if constexpr (NumArgs == 2) {
     using Reduction = std::tuple_element_t<0, decltype(ReduTuple)>;

sycl/include/sycl/reduction_forward.hpp

@@ -42,6 +42,11 @@ enum class strategy : int {
 // are limited to those below.
 inline void finalizeHandler(handler &CGH);
 template <class FunctorTy> void withAuxHandler(handler &CGH, FunctorTy Func);
+
+template <int Dims>
+item<Dims, false> getDelinearizedItem(range<Dims> Range, id<Dims> Id) {
+  return {Range, Id};
+}
 } // namespace reduction
 
 template <typename KernelName,