This placeholder for second call:
   in_to_G.push_back(torch::ones({1, 8,8,8}).to(at::kCUDA));
   in_to_G.push_back(torch::ones({1, 2048}).to(at::kCUDA));
   img_tensor = mG.forward(in_to_G);

worked!
How can i get two Tensors  for create new input vector from it?
i need to parse this result, to get Tensor in it:
torch::IValue result;
There are somethink like this issues on the stack and github:

c++ - How to get values return by Tuple Object in Maskcrnn libtorch - Stack Overflow 2
C++ Convert c10::IValue to tensor or tuple or to TensorList failed · Issue #48691 · pytorch/pytorch · GitHub 1