Add fast_compile tag so the optimization to remove the Op always runs. Use…

theano/tensor/extra_ops.py

@@ -729,14 +729,14 @@ def fill_diagonal(a, val):
 
 class ConsiderConstant(ViewOp):
     def grad(self, args, g_outs):
-        return [tensor.zeros_like(g_out) for g_out in g_outs]
+        return [g_out.zeros_like(g_out) for g_out in g_outs]
 consider_constant_ = ConsiderConstant()
 
 
 # Although the op just returns its input, it should be removed from
 # the graph to make sure all possible optimizations can be applied.
 register_canonicalize(gof.OpRemove(consider_constant_),
-    name='remove_consider_constant')
+    'fast_compile', name='remove_consider_constant')
 
 
 #I create a function only to have the doc show well.

theano/tensor/tests/test_extra_ops.py

@@ -482,11 +482,10 @@ class TestConsiderConstant(unittest.TestCase):
             [node.op for node in f.maker.fgraph.toposort()]
         
     def test_grad(self):
-        a = numpy.asarray(self.rng.randn(50, 50),
+        a = numpy.asarray(self.rng.randn(5, 5),
             dtype=config.floatX)
         
         x = T.matrix('x')
-        y = x * consider_constant(x)
 
         expressions_gradients = [
             (x * consider_constant(x), x),