add cudnn gradinputs alternative

theano/gpuarray/dnn.py

@@ -3068,6 +3068,31 @@ def local_abstractconv3d_cudnn_alternative(node):
         else:
             return None
 
+    if isinstance(op, AbstractConv3d_gradInputs):
+        if border_mode == 'valid' and subsample == (1, 1, 1):
+            kerns = gpu_contiguous(inp1.dimshuffle(1, 0, 2, 3, 4))
+            topgrad = gpu_contiguous(inp2)
+            ctx_name = infer_context_name(kerns, topgrad)
+            conv_mode = 'cross' if conv_mode == 'conv' else 'conv'
+            desc = GpuDnnConvDesc(border_mode='full',
+                                  subsample=subsample,
+                                  dilation=filter_dilation,
+                                  conv_mode=conv_mode,
+                                  precision=precision)(kerns.shape)
+
+            tshape = [shape_i_op(i)(topgrad) for i in range(topgrad.ndim)]
+            kshape = [shape_i_op(i)(kerns) for i in range(kerns.ndim)]
+            shape = get_conv_output_shape(tshape,
+                                          kshape,
+                                          border_mode='full',
+                                          subsample=subsample,
+                                          filter_dilation=filter_dilation)
+
+            shape = assert_conv_shape(shape)
+            out = GpuAllocEmpty(dtype=topgrad.dtype, context_name=ctx_name)(*shape)
+            rval = GpuDnnConv(algo=None)(topgrad, kerns, out, desc)
+        else:
+            return None
 
     return [rval]