Split and move comment following code review

theano/tensor/opt.py

@@ -904,10 +904,16 @@ class ShapeFeature(object):
         # Merge other_shape with r_shape, giving the priority to other_shape
         merged_shape = []
         for i, ps in enumerate(other_shape):
+            if (ps.owner
+                    and isinstance(getattr(ps.owner, 'op', None), Shape_i)
+                    and ps.owner.op.i == i
+                    and ps.owner.inputs[0] in (r, other_r)):
                 # If other_shape[i] is uninformative, use r_shape[i].
                 # For now, we consider 2 cases of uninformative other_shape[i]:
                 #  - Shape_i(i)(other_r);
                 #  - Shape_i(i)(r).
+                merged_shape.append(r_shape[i])
+            elif r_shape[i] in theano.gof.graph.ancestors([other_shape[i]]):
                 # Another case where we want to use r_shape[i] is when
                 # other_shape[i] actually depends on r_shape[i]. In that case,
                 # we do not want to substitute an expression with another that
@@ -915,12 +921,6 @@ class ShapeFeature(object):
                 # to cycles: if (in the future) r_shape[i] gets replaced by an
                 # expression of other_shape[i], other_shape[i] may end up
                 # depending on itself.
-            if (ps.owner
-                    and isinstance(getattr(ps.owner, 'op', None), Shape_i)
-                    and ps.owner.op.i == i
-                    and ps.owner.inputs[0] in (r, other_r)):
-                merged_shape.append(r_shape[i])
-            elif r_shape[i] in theano.gof.graph.ancestors([other_shape[i]]):
                 merged_shape.append(r_shape[i])
             else:
                 merged_shape.append(other_shape[i])