Operator<=> (spaceship operator) not usable in device functions

Accelerated Computing CUDA CUDA NVCC Compiler
1

It looks like the comparison operators generated by operator<=> definition (defaulted or otherwise) can’t be used in device functions:

struct S
{
    int x;

   auto operator<=>(const S& other) const = default;
};

__host__ __device__ void foo()
{
    S{1} < S{2};
}

This results in (Godbolt)

<source>(10): warning #20013-D: calling a constexpr __host__ function("__unspec") from a __host__ __device__ function("foo") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this.
      S{1} < S{2};
                 ^

Remark: The warnings can be suppressed with "-diag-suppress <warning-number>"

<source>(10): warning #20013-D: calling a constexpr __host__ function("operator<") from a __host__ __device__ function("foo") is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this.
      S{1} < S{2};
           ^

Compiler returned: 0

Adding __host__ __device__ just adds more warnings, and explicitly defining the operator also doesn’t work.

2

My C++ knowledge is minimal to say the least, but I wonder if this Programming Guide entry helps at all?

3

Thanks, that does indeed answer the question.