new impl of GetSubtensor uses cuda_ndarray mapping protocol

basic_ops.py

@@ -375,6 +375,25 @@ class GpuSubtensor(tensor.Subtensor):
         return rval
 
     def perform(self, node, inputs, (out, )):
+        x = inputs[0]
+        indices = list(reversed(inputs[1:]))
+
+        def convert(entry):
+            if isinstance(entry, Type):
+                return indices.pop()
+            elif isinstance(entry, slice):
+                return slice(convert(entry.start),
+                             convert(entry.stop),
+                             convert(entry.step))
+            else:
+                return entry
+
+        cdata = tuple(map(convert, self.idx_list))
+        if len(cdata) == 1:
+            cdata = cdata[0]
+        out[0] = x.__getitem__(cdata)
+
+    def old_perform(self, node, inputs, (out, )):
         indices = list(reversed(inputs[1:]))
 
         def convert(entry):