remove extra braces, add comments

oneapi-src · Aug 6, 2024 · 36da55e · 36da55e
1 parent 82f3ee5
commit 36da55e
Show file tree

Hide file tree

Showing 2 changed files with 30 additions and 25 deletions.
diff --git a/include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl.h b/include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl.h
@@ -840,30 +840,30 @@ __parallel_transform_scan(oneapi::dpl::__internal::__device_backend_tag __backen
                 _WriteOp{}, __init, _Inclusive{});
         }
     }
-    {
-        using _Assigner = unseq_backend::__scan_assigner;
-        using _NoAssign = unseq_backend::__scan_no_assign;
-        using _UnaryFunctor = unseq_backend::walk_n<_ExecutionPolicy, _UnaryOperation>;
-        using _NoOpFunctor = unseq_backend::walk_n<_ExecutionPolicy, oneapi::dpl::__internal::__no_op>;
-
-        _Assigner __assign_op;
-        _NoAssign __no_assign_op;
-        _NoOpFunctor __get_data_op;
-
-        return __parallel_transform_scan_base(
-            __backend_tag, std::forward<_ExecutionPolicy>(__exec), std::forward<_Range1>(__in_rng),
-            std::forward<_Range2>(__out_rng), __binary_op, __init,
-            // local scan
-            unseq_backend::__scan<_Inclusive, _ExecutionPolicy, _BinaryOperation, _UnaryFunctor, _Assigner, _Assigner,
-                                  _NoOpFunctor, _InitType>{__binary_op, _UnaryFunctor{__unary_op}, __assign_op,
-                                                           __assign_op, __get_data_op},
-            // scan between groups
-            unseq_backend::__scan</*inclusive=*/std::true_type, _ExecutionPolicy, _BinaryOperation, _NoOpFunctor,
-                                  _NoAssign, _Assigner, _NoOpFunctor, unseq_backend::__no_init_value<_Type>>{
-                __binary_op, _NoOpFunctor{}, __no_assign_op, __assign_op, __get_data_op},
-            // global scan
-            unseq_backend::__global_scan_functor<_Inclusive, _BinaryOperation, _InitType>{__binary_op, __init});
-    }
+    //else use legacy scan implementation
+
+    using _Assigner = unseq_backend::__scan_assigner;
+    using _NoAssign = unseq_backend::__scan_no_assign;
+    using _UnaryFunctor = unseq_backend::walk_n<_ExecutionPolicy, _UnaryOperation>;
+    using _NoOpFunctor = unseq_backend::walk_n<_ExecutionPolicy, oneapi::dpl::__internal::__no_op>;
+
+    _Assigner __assign_op;
+    _NoAssign __no_assign_op;
+    _NoOpFunctor __get_data_op;
+
+    return __parallel_transform_scan_base(
+        __backend_tag, std::forward<_ExecutionPolicy>(__exec), std::forward<_Range1>(__in_rng),
+        std::forward<_Range2>(__out_rng), __binary_op, __init,
+        // local scan
+        unseq_backend::__scan<_Inclusive, _ExecutionPolicy, _BinaryOperation, _UnaryFunctor, _Assigner, _Assigner,
+                                _NoOpFunctor, _InitType>{__binary_op, _UnaryFunctor{__unary_op}, __assign_op,
+                                                        __assign_op, __get_data_op},
+        // scan between groups
+        unseq_backend::__scan</*inclusive=*/::std::true_type, _ExecutionPolicy, _BinaryOperation, _NoOpFunctor,
+                                _NoAssign, _Assigner, _NoOpFunctor, unseq_backend::__no_init_value<_Type>>{
+            __binary_op, _NoOpFunctor{}, __no_assign_op, __assign_op, __get_data_op},
+        // global scan
+        unseq_backend::__global_scan_functor<_Inclusive, _BinaryOperation, _InitType>{__binary_op, __init});
 }
 
 template <typename _SizeType>

diff --git a/include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl_reduce_then_scan.h b/include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl_reduce_then_scan.h
@@ -162,6 +162,7 @@ __scan_through_elements_helper(const _SubGroup& __sub_group, _GenInput __gen_inp
     bool __is_full_thread = __subgroup_start_idx + __iters_per_item * __sub_group_size <= __n;
     if (__is_full_thread && __is_full_block)
     {
+        // For full block and full thread, we can unroll the loop
         auto __v = __gen_input(__in_rng, __start_idx);
         __sub_group_scan<__sub_group_size, __is_inclusive, __init_present>(__sub_group, __scan_input_transform(__v),
                                                                            __binary_op, __sub_group_carry);
@@ -184,6 +185,9 @@ __scan_through_elements_helper(const _SubGroup& __sub_group, _GenInput __gen_inp
     }
     else if (__is_full_thread)
     {
+        // For full thread but not full block, we can't unroll the loop, but we
+        // can proceed without special casing for partial subgroups.
+
         auto __v = __gen_input(__in_rng, __start_idx);
         __sub_group_scan<__sub_group_size, __is_inclusive, __init_present>(__sub_group, __scan_input_transform(__v),
                                                                            __binary_op, __sub_group_carry);
@@ -204,6 +208,7 @@ __scan_through_elements_helper(const _SubGroup& __sub_group, _GenInput __gen_inp
     }
     else
     {
+        // For partial thread, we need to handle the partial subgroup at the end of the range
         if (__sub_group_id < __active_subgroups)
         {
             auto __iters = oneapi::dpl::__internal::__dpl_ceiling_div(__n - __subgroup_start_idx, __sub_group_size);
@@ -552,7 +557,7 @@ struct __parallel_reduce_then_scan_scan_submitter<
                                                                               __carry_last, __remaining_elements);
                         }
 
-                        // steps 3/4) load global carry in from neighbor work-group
+                        // steps 3+4) load global carry in from neighbor work-group
                         //            and apply to local sub-group prefix carries
                         auto __carry_offset = 0;