simplified the check for TypeError

theano/gof/opt.py

@@ -858,15 +858,9 @@ class MergeOptimizer(Optimizer):
                                 hasattr(c.op, 'destroy_map')]) > 1:
                             continue
 
-                if pairs[0][0].type != pairs[0][1].type:
+                if len(pairs) == 1 and pairs[0][0].type != pairs[0][1].type:
                     res = pairs[0][0].type.convert_variable(pairs[0][1])
-                    if res is None or res.type != pairs[0][0].type:
-                        if (not isinstance(pairs[0][1], pairs[0][0].__class__) or
-                                pairs[0][0].dtype != pairs[0][1].dtype or
-                                pairs[0][0].ndim != pairs[0][1].ndim or
-                                pairs[0][0].broadcastable == pairs[0][1].broadcastable or len(pairs) != 1):
-                            raise TypeError
-                        else:
+                    if res is None:
                         num_broadcastable_dims_0 = sum(pairs[0][0].broadcastable)
                         num_broadcastable_dims_1 = sum(pairs[0][1].broadcastable)
                         # select the variable to be removed from the fgraph
@@ -881,6 +875,8 @@ class MergeOptimizer(Optimizer):
                         new_broadcast_pattern = theano.tensor.patternbroadcast(
                             pairs[0][selected_var_ind],
                             pairs[0][1 - selected_var_ind].broadcastable)
+                        res = new_broadcast_pattern.type.convert_variable(pairs[0][1 - selected_var_ind])
+                        if res:
                             pairs = [(new_broadcast_pattern, pairs[0][1 - selected_var_ind])]
 
                 try: