handle declare backward dependecy

src/nativeops.jl

@@ -53,8 +53,20 @@ need_top_grad(:: Operator) = true
 
 #=doc
 .. function:: declare_backward_dependency(op :: Operator, out_grad, in_data, out_data)
+
+  Declare dependencies of this operator for backward pass.
+
+  Return value needs to be an integer array.
 =#
-function declare_backward_dependency(:: Operator, out_grad, in_data, out_data)
+function declare_backward_dependency(op :: Operator, out_grad, in_data, out_data)
+  deps = Int[]
+  if need_top_grad(op)
+    append!(deps, out_grad)
+  end
+  append!(deps, in_data)
+  append!(deps, out_data)
+
+  return deps
 end
 
 ###
@@ -191,14 +203,24 @@ function _wrapper_list_outputs(data :: Ptr{Ptr{Cstring}}, _op :: Ptr{Void})
   return true
 end
 
-function _wrapper_declare_backward_dependency(out_grad :: Ptr{Cint},
-                                              in_data  :: Ptr{Cint},
-                                              out_data :: Ptr{Cint},
+function _wrapper_declare_backward_dependency(_out_grad :: Ptr{Cint},
+                                              _in_data  :: Ptr{Cint},
+                                              _out_data :: Ptr{Cint},
                                               num_dep  :: Ptr{Cint},
                                               deps     :: Ptr{Ptr{Cint}},
                                               _op      :: Ptr{Void})
    try
      op = unsafe_pointer_to_objref(_op) :: Operator
+
+     out_grad = pointer_to_array(_out_grad, length(list_outputs(op)), false)
+     in_data = pointer_to_array(_in_data, length(list_arguments(op)), false)
+     out_data = pointer_to_array(_out_data, length(list_outputs(op)), false)
+
+     rdeps = convert(Array{Cint}, declare_backward_dependency(out_grad, in_data, out_data))
+
+     unsafe_store!(num_dep, length(rdeps), 1)
+     r_rdeps = Ref(rdeps) # Lifetime?
+     unsafe_store!(deps, convert(Ptr{Cint}, r_rdeps), 1)
    catch
      return false
    end