DPCT1089

Intel® DPC++ Compatibility Tool Developer Guide and Reference

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ID 768918

Date 11/07/2023

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Public

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DPCT1089

Message

The value of the sub-group size attribute argument <argument name> cannot be evaluated. Replace dpct_placeholder with an integral constant expression.

Detailed Help

The argument to the attribute must be an integral constant expression. This warning is emitted when Intel® DPC++ Compatibility Tool cannot evaluate the value of the sub-group size argument as an integral constant expression. Check if the sub-group size attribute argument can be replaced by an integral constant expression, and if not, redesign the code logic.

For example, this original CUDA* code:

  _global_ void kernel(int WarpSize) {   int Input, Output, Lane;   ...   Output = __shfl(Input, Lane, WarpSize); }
  ...
  if(condition)
  {   kernel<<<GirdSize, BlockSize>>>(16); }
  else
  {   kernel<<<GirdSize, BlockSize>>>(32); }

results in the following migrated SYCL* code:

  void kernel(int WarpSize, sycl::nd_item<3> item_ct1)
  {   int Input, Output, Lane;   ...   Output = Item_ct1.get_sub_group().shuffle(Input, Lane); }
  ...
  if(condition) {
  /* DPCT1089 */
  q_ct1.parallel_for(
      sycl::nd_range<3>(GridSize * BlockSize, BlockSize),
      [=](sycl::nd_item<3> item_ct1) [[intel::reqd_sub_group_size(dpct_placeholder)]] {       kernel(16, item_ct1); });
  } else {
  /* DPCT1089 */
  q_ct1.parallel_for(
      sycl::nd_range<3>(GridSize * BlockSize, BlockSize),
      [=](sycl::nd_item<3> item_ct1) [[intel::reqd_sub_group_size(dpct_placeholder)]] {       kernel(32, item_ct1); }

which is manually adjusted to:

  void kernel(int WarpSize, sycl::nd_item<3> item_ct1) {   int Input, Output, Lane;   ...   Output = Item_ct1.get_sub_group().shuffle(Input, Lane); }
  ...
  if(condition) {
  /* DPCT1089 */
  q_ct1.parallel_for(
      sycl::nd_range<3>(GridSize * BlockSize, BlockSize),
      [=](sycl::nd_item<3> item_ct1) [[intel::reqd_sub_group_size(16)]]
  {       kernel(16, item_ct1); }
  );
  } else {
  /* DPCT1089 */
  q_ct1.parallel_for(
      sycl::nd_range<3>(GridSize * BlockSize, BlockSize),
      [=](sycl::nd_item<3> item_ct1) [[intel::reqd_sub_group_size(32)]]
  {       kernel(32, item_ct1); }

Suggestions to Fix

Code requires manual fix. Replace “dpct_placeholder” with an integral constant expression.

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Intel® DPC++ Compatibility Tool Developer Guide and Reference

DPCT1089

Message

Detailed Help

Suggestions to Fix