Simplify graph build

theano/tensor/signal/pool.py

@@ -186,7 +186,11 @@ class Pool(Op):
         if st is None:
             st = ds
         r, c = imgshape[-2:]
+        r = tensor.extract_constant(r)
+        c = tensor.extract_constant(c)
+        if padding[0]:
             r += padding[0] * 2
+        if padding[1]:
             c += padding[1] * 2
 
         if ignore_border: