DPCT1085

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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DPCT1085

Message

The function <function name> requires sub-group size to be <size>, while other sub-group functions in the same SYCL kernel require a different sub-group size. You may need to adjust the code.

Detailed Help

Each kernel can only be decorated with one sub-group size. This warning is emitted when a kernel requires different sub-group sizes. Check if the sub-group size can be unified into one value, and if it cannot be unified, redesign the code logic.

For example, this original CUDA* code:

  _global_ void kernel() {
    int Input, Output1, Output2, Lane;
    ...

    // original code logic
    Output1 = __shfl(Input, Lane, 32);
    Output2 = __shfl_xor(Input, Lane, 16);
  }

results in the following migrated SYCL* code:

  void kernel(int WarpSize, sycl::nd_item<3> item_ct1) {
    int Input, Output1, Output2, Lane;
    ...

    // original code logic
    Output1 = Item_ct1.get_sub_group().shuffle(Input, Lane, 32);
    /* DPCT1085 */
    Output2 = Item_ct1.get_sub_group().shuffle_xor(Input, Lane, 16);
  }

which is manually adjusted to:

  void kernel(int WarpSize, sycl::nd_item<3> item_ct1) {
    int Input, Output, SrcLane;
    ...

    // redesigned code logic
    Output1 = Item_ct1.get_sub_group().shuffle(Input, Lane, 32);
    /* DPCT1085 */
    // redesign the code logic to unify sub-group size in the same kernel
    Output2 = Item_ct1.get_sub_group().shuffle_xor(Input, Lane, 32);
  }

Suggestions to Fix

Code requires manual fix. Rewrite the code manually.

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DPCT1085

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Detailed Help

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