message: Add TODO regarding LookUpOpDef for functions
  Also handle failure inside SupportsFloat16().
diff: @@ -273,6 +273,8 @@ class NodeTypeAttrMap {
  private:
  Status AddNode(const NodeDef& node) {
  const OpDef* op_def_ptr = nullptr;
  + // TODO(benbarsdell): This may fail if node.op() is a function. It will
  + // need to be addressed when we add support for functions.
  TF_RETURN_IF_ERROR(
  OpRegistry::Global()->LookUpOpDef(node.op(), &op_def_ptr));
  const OpDef& op_def = *op_def_ptr;
  @@ -1089,7 +1091,9 @@ bool IsFloat32(const NodeTypeId& node_type) {
  bool AutoMixedPrecisionImpl::SupportsFloat16(
  const NodeTypeId& node_type) const {
  const OpDef* op_def;
  + Status status =
  OpRegistry::Global()->LookUpOpDef(node_type.node->op(), &op_def);
  + if (!status.ok()) return false;
  return AllowedDataTypes(*op_def, node_type.type_attr)
  .Contains(DataType::DT_HALF) &&
  NodeHasFP16KernelForTypeAttr(*node_type.node, node_type.type_attr);
  