Move all cheap condition at the start to do less frequently the slow conditino.

theano/scan_module/scan_opt.py

@@ -1818,7 +1818,12 @@ class ScanMerge(gof.Optimizer):
 
         """
         rep = set_nodes[0]
-        if rep.op.as_while != node.op.as_while:
+        if (rep.op.as_while != node.op.as_while or
+                len(rep.inputs) != len(node.inputs) or
+                len(rep.outputs) != len(node.outputs) or
+                node.op.truncate_gradient != rep.op.truncate_gradient or
+                node.op.mode != rep.op.mode or
+                rep.op.as_while != node.op.as_while):
             return False
 
         nsteps = node.inputs[0]
@@ -1834,22 +1839,18 @@ class ScanMerge(gof.Optimizer):
             pass
 
         # Check to see if it is an input of a different node
-        can_add = True
         for nd in set_nodes:
             if find_up(node, nd) or find_up(nd, node):
-                can_add = False
+                return False
 
-        can_add = can_add and (node.op.truncate_gradient ==
-                               rep.op.truncate_gradient)
-        can_add = can_add and (node.op.mode == rep.op.mode)
         if not node.op.as_while:
-            return nsteps == rep_nsteps and can_add
+            return nsteps == rep_nsteps
         cond = node.op.outputs[-1]
         rep_cond = rep.op.outputs[-1]
         same_cond = scan_utils.equal_computations([cond], [rep_cond],
                                                   node.op.inputs,
                                                   rep.op.inputs)
-        return same_cond and (nsteps == rep_nsteps) and can_add
+        return same_cond and (nsteps == rep_nsteps)
 
     def apply(self, fgraph):
         # Collect all scan nodes ordered according to toposort