DPCT1128

Intel® DPC++ Compatibility Tool Developer Guide and Reference

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ID 768918

Date 6/24/2024

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Public

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DPCT1128

Message

The type “<type name>” is not device copyable for <reason>. It is used in the SYCL kernel, please rewrite the code.

Detailed Help

SYCL* 2020 needs the type of argument passed to the kernel function to be device copyable (Spec 3.13.1 device copyable), while CUDA* just does memory copy for all those arguments directly without emitting any error/warning. If a type does not meet the requirements of device copyable, the tool will try to add the specialization of the sycl::is_device_copyable for this type, as well as warn the user. The warning will specify which part of that type does not meet the requirements.

Suggestions to Fix

For example, this original CUDA code:

template <class T1, class T2> struct UserStruct {
  UserStruct() {}
  UserStruct(UserStruct const &other) : a(other.a) {}
  int a;
};

template <class V1, class V2> __global__ void k(UserStruct<V1, V2>) {}

void foo() {
  UserStruct<float, int> us;
  k<<<1, 1>>>(us);
}

results in the following migrated SYCL code:

/*
DPCT1128:0: The type "UserStruct<float, int>" is not device copyable for copy
constructor breaking the device copyable requirement. It is used in the SYCL
kernel, please rewrite the code.
*/
template <class T1, class T2> struct UserStruct {
  UserStruct() {}
  UserStruct(UserStruct const &other) : a(other.a) {}
  int a;
};
template <class T1, class T2>
struct sycl::is_device_copyable<UserStruct<T1, T2>> : std::true_type {};

template <class V1, class V2> void k(UserStruct<V1, V2>) {}

void foo() {
  UserStruct<float, int> us;
  /*
  DPCT1129:1: The type "UserStruct<float, int>" is used in the SYCL kernel, but
  it is not device copyable. The sycl::is_device_copyable specialization has
  been added for this type. Please review the code.
  */
  dpct::get_in_order_queue().parallel_for(
      sycl::nd_range<3>(sycl::range<3>(1, 1, 1), sycl::range<3>(1, 1, 1)),
      [=](sycl::nd_item<3> item_ct1) {
        k(us);
      });
}

which needs to be rewritten to:

template <class T1, class T2> struct UserStruct {
  UserStruct() {}
  UserStruct(UserStruct const &other) : a(other.a) {}
  int a;
};
template <class T1, class T2>
struct sycl::is_device_copyable<UserStruct<T1, T2>> : std::true_type {};

template <class V1, class V2> void k(UserStruct<V1, V2>) {}

void foo() {
  UserStruct<float, int> us;
  dpct::get_in_order_queue().parallel_for(
      sycl::nd_range<3>(sycl::range<3>(1, 1, 1), sycl::range<3>(1, 1, 1)),
      [=](sycl::nd_item<3> item_ct1) {
        k(us);
      });
}

template <class T1, class T2> struct UserStruct {
  UserStruct() {}
  int a;
};

template <class V1, class V2> void k(UserStruct<V1, V2>) {}

void foo() {
  UserStruct<float, int> us;
  dpct::get_in_order_queue().parallel_for(
      sycl::nd_range<3>(sycl::range<3>(1, 1, 1), sycl::range<3>(1, 1, 1)),
      [=](sycl::nd_item<3> item_ct1) {
        k(us);
      });
}

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Intel® DPC++ Compatibility Tool Developer Guide and Reference

DPCT1128

Message

Detailed Help

Suggestions to Fix