Always introduce Alloc node when calling alloc()

theano/tensor/basic.py

@@ -2883,22 +2883,6 @@ class Alloc(gof.Op):
         gx = gz.sum(axis=range(n_axes_to_sum))
         return [gx] + [None for i in inputs[1:]]
 
-    def __call__(self, val, *shapes):
-        """
-        If the alloc would be useless, this function returns val.
-        If you always want an Alloc node, call make_node.
-        """
-        ret = super(Alloc, self).__call__(val, *shapes)
-        try:
-            # It makes optimization difficult when useless allocs are thrown
-            # into the graph at every stage of optimization.  This little logic
-            # tries to help at least in some cases.
-            if val.type == ret.type:
-                return val
-        except AttributeError:
-            pass
-        return ret
-
     def R_op(self, inputs, eval_points):
         if eval_points[0] is None:
             return [None]

theano/tensor/opt.py

@@ -1073,6 +1073,7 @@ def local_fill_to_alloc(node):
 
 
 @register_specialize
+@register_stabilize
 @register_canonicalize
 @gof.local_optimizer([T.alloc])
 def local_useless_alloc(node):

theano/tensor/tests/test_opt.py

@@ -2194,6 +2194,28 @@ def test_local_fill_useless():
     f(m_, x_)
 
 
+class Test_local_useless_alloc(unittest.TestCase):
+    def setUp(self):
+        self.rng = numpy.random.RandomState(utt.fetch_seed())
+
+    def test0(self):
+        x = shared(self.rng.randn(3, 7))
+        a = tensor.alloc(x, 6, 7)
+
+        # It is a bad idea to have tensor.alloc return x directly,
+        # because the shape mismatch cannot be caught.
+        assert a.owner and isinstance(a.owner.op, tensor.Alloc)
+
+        f = function([], a)
+        # The optimization should then be applied, and remove Alloc
+        assert ([node.op for node in f.maker.env.toposort()]
+                == [compile.deep_copy_op])
+
+        # In DebugMode, the shape mismatch should be detected
+        if isinstance(mode_opt, compile.DebugMode):
+            self.assertRaises(ValueError, f)
+
+
 class test_shapeoptimizer(unittest.TestCase):
     def setUp(self):
         utt.seed_rng()