Reshape(arange(x)) -> arange(x) when this do not change the shapes, number of dimensions.

theano/tensor/opt.py

@@ -3703,6 +3703,20 @@ register_canonicalize(local_reshape_chain(T.Reshape),
                       name='local_reshape_chain')
 
 
+@register_canonicalize
+@register_stabilize
+@gof.local_optimizer([T.Reshape])
+def local_useless_reshape(node):
+    """
+    Remove Reshape when both the input and the output have a
+    single dimension.
+
+    """
+    if isinstance(node.op, T.Reshape):
+        if node.inputs[0].ndim == 1 and node.outputs[0].ndim == 1:
+            return [node.inputs[0]]
+
+
 @register_canonicalize
 @register_stabilize
 @gof.local_optimizer([T.Reshape])

theano/tensor/tests/test_opt.py

@@ -5716,6 +5716,16 @@ class Test_Reshape(unittest.TestCase):
         assert sum(isinstance(node.op, self.op) for node in topo) == 1
 
 
+def test_local_useless_reshape(self):
+    mode = theano.compile.get_default_mode().including(
+            'local_useless_reshape')
+    i = T.iscalar('x')
+    m=theano.tensor.mgrid[0:i,]
+    f = theano.function([i], m, mode=mode)
+    topo = f.maker.fgraph.toposort()
+    assert not any(isinstance(n.op, tensor.basic.Reshape) for n in topo)
+
+
 def test_local_reshape_lift():
     x = tensor.tensor4()
     out = T.exp(x).reshape([x.size])