Update add_delta_to_slice to tolerate dynamic shapes (#1962)

src/ngraph/autodiff/adjoints.cpp

@@ -177,8 +177,9 @@ void autodiff::Adjoints::add_delta_to_slice(const std::shared_ptr<Node>& x,
                                             const Coordinate& upper_bounds,
                                             const Strides& strides)
 {
-    if (x->get_output_element_type(0) != delta->get_output_element_type(0) ||
-        x->get_output_shape(0).size() != delta->get_output_shape(0).size())
+    if (!(x->get_output_element_type(0).compatible(delta->get_output_element_type(0))) ||
+        !(x->get_output_partial_shape(0).rank().compatible(
+            delta->get_output_partial_shape(0).rank())))
     {
         throw ngraph_error(
             "Autodiff internal error: Mismatch on backprop and op in add_delta_to_slice.");

src/ngraph/type/element_type.cpp

@@ -192,6 +192,11 @@ std::ostream& element::operator<<(std::ostream& out, const element::Type& obj)
     return out;
 }
 
+bool element::Type::compatible(element::Type t) const
+{
+    return (is_dynamic() || t.is_dynamic() || *this == t);
+}
+
 bool element::Type::merge(element::Type& dst, const element::Type& t1, const element::Type& t2)
 {
     if (t1.is_dynamic())

src/ngraph/type/element_type.hpp

@@ -77,6 +77,11 @@ namespace ngraph
 
             /// Returns true if the type is floating point, else false.
             bool get_is_real() const { return m_is_real; }
+            /// \brief Checks whether this element type is merge-compatible with `t`.
+            /// \param t The element type to compare this element type to.
+            /// \return `true` if this element type is compatible with `t`, else `false`.
+            bool compatible(element::Type t) const;
+
             /// \brief Merges two element types t1 and t2, writing the result into dst and
             ///        returning true if successful, else returning false.
             ///