If you attempt to put at::optional in a struct which is used from a cu file, you may get this error:

Error: Internal Compiler Error (codegen): "there was an error in verifying the lgenfe output!"

A minimal reproduction is this program:

#include "optional.h"

struct O {
  O() {} // required!
  at::optional<int> x;
};

void blah() {
  O o;
}

compiled with nvcc -c main.cu -std=c++11 --expt-relaxed-constexpr (the --expt-relaxed-constexpr is mandatory).

There is a simple workaround for this problem: explicitly initialize all optional fields in your constructor. So for example, the following code will compile successfully:

#include "optional.h"

struct O {
  O() : x() {}
  at::optional<int> x;
};

void blah() {
  O o;
}