Fix autodiff uninitialized data error (#329)

* fix autodiff on non-NGVM backends. NGVM initializes all tensors to zero on allocation while the other backends do not. Had to initialize vector before use.

* change autodiff tests to use INTERPRETER

test/CMakeLists.txt

@@ -90,9 +90,9 @@ foreach(BACKEND_NAME ${BACKEND_NAMES})
 endforeach()
 # <special case>
 # This is a special case as NGVM is the only backend that can run these tests
-set(BACKEND_NAME "NGVM")
-configure_file(autodiff.in.cpp autodiff_NGVM.cpp)
-set(SRC ${SRC} ${CMAKE_CURRENT_BINARY_DIR}/autodiff_NGVM.cpp)
+set(BACKEND_NAME "INTERPRETER")
+configure_file(autodiff.in.cpp autodiff_${BACKEND_NAME}.cpp)
+set(SRC ${SRC} ${CMAKE_CURRENT_BINARY_DIR}/autodiff_${BACKEND_NAME}.cpp)
 # </special cast>
 include_directories(".")
 

test/util/autodiff/backprop_derivative.hpp

@@ -100,6 +100,7 @@ namespace ngraph
             bprops_tv.insert(bprops_tv.begin(), bprops.begin(), bprops.end());
 
             auto c_vec = c_arg->template get_vector<T>();
+            fill(c_vec.begin(), c_vec.end(), 0);
             for (size_t i = 0; i < c_vec.size(); i++)
             {
                 c_vec[i] = 1;