correct handling of int/complex dtypes in IncSubtensor.grad

theano/tensor/subtensor.py

@@ -1471,6 +1471,16 @@ class IncSubtensor(Op):
         x, y = inputs[:2]
         idx_list = inputs[2:]
 
+        if x.dtype in theano.tensor.discrete_dtypes:
+            # The output dtype is the same as x
+            gx = x.zeros_like(dtype=theano.config.floatX)
+            if y.dtype in theano.tensor.discrete_dtypes:
+                gy = y.zeros_like(dtype=theano.config.floatX)
+            else:
+                gy = y.zeros_like()
+        elif x.dtype in theano.tensor.complex_dtypes:
+            raise NotImplementedError("No support for complex grad yet")
+        else:
             if self.set_instead_of_inc:
                 gx = set_subtensor(
                     Subtensor(idx_list=self.idx_list)(g_output, *idx_list),