How to explicitly mark a struct device_copiable

[Luigi-Crisci]

Hello,
I have a struct that I use in a SYCL kernel targeting NVIDIA GPUs, but the compiler complains that it is not device_copiable. However, I know it is device_copiable as this kernel is a CUDA porting, which was working fine.
The SYCL doc specifies that

In addition, the implementation may allow the application to explicitly declare certain class types as device copyable. If the implementation has this support, it must predefine the preprocessor macro SYCL_DEVICE_COPYABLE to 1,

In DPC++ this define exists, but I'm not able to extend it without having the compiler complain.
Which is the correct way of doing that?

[AlexeySachkov]

Hi @Luigi-Crisci,

You can find an example in our tests: basic_tests/is_device_copyable.cpp.

Let's say you have your struct:

llvm/sycl/test/basic_tests/is_device_copyable.cpp

Lines 21 to 26 in 10e07a3

	// Not copyable type, but it will be declared as device copyable.
	struct BCopyable {
	int i;
	BCopyable(int _i) : i(_i) {}
	BCopyable(const BCopyable &x) : i(x.i) {}
	};

Specializing is_device_copyable trait for it would look like:

llvm/sycl/test/basic_tests/is_device_copyable.cpp

Line 63 in 10e07a3

template <> struct is_device_copyable<BCopyable> : std::true_type {};

You can also find examples in 3rd-party repos, such as kokkos/kokkos, for example.