useless_dimshuffle optimization and test

theano/tensor/opt.py

@@ -594,7 +594,7 @@ def local_dimshuffle_lift(node):
         inplace = op.inplace and inode.op.inplace
         iinput = inode.inputs[0]
 
-        # remove useless dimshuffle
+        # remove useless dimshuffle caused by merging
         if (new_order == list(range(len(new_order))) and
                 len(new_order) == iinput.type.ndim):
             return [iinput]
@@ -605,6 +605,11 @@ def local_dimshuffle_lift(node):
             copy_stack_trace(node.outputs[0], ret)
             return [ret]
 
+    # remove useless dimshuffle in general
+    if (list(op.new_order) == list(range(len(op.new_order))) and
+            len(op.new_order) == input.type.ndim):
+        return [input]
+
 
 @register_canonicalize
 @gof.local_optimizer([T.DimShuffle])

theano/tensor/tests/test_opt.py

@@ -112,7 +112,6 @@ class test_dimshuffle_lift(unittest.TestCase):
         # Check stacktrace was copied over correctly after opt was applied
         self.assertTrue(hasattr(g.outputs[0].tag, 'trace'))
 
-
     def test_merge2(self):
         x, y, z = inputs()
         e = ds(ds(x, (1, 'x', 0)), (2, 0, 'x', 1))
@@ -166,7 +165,6 @@ class test_dimshuffle_lift(unittest.TestCase):
         # Check stacktrace was copied over correctly after opt was applied
         self.assertTrue(hasattr(g.outputs[0].tag, 'trace'))
 
-
     def test_recursive_lift(self):
         v = T.vector(dtype="float64")
         m = T.matrix(dtype="float64")
@@ -179,8 +177,8 @@ class test_dimshuffle_lift(unittest.TestCase):
                       "Elemwise{add,no_inplace}"
                       "(<TensorType(float64, matrix)>, "
                       "DimShuffle{x,x}(TensorConstant{84}))))]")
-        self.assertTrue(str(g) == init_str_g)
 
+        self.assertTrue(str(g) == init_str_g)
         new_out = local_dimshuffle_lift.transform(g.outputs[0].owner)[0]
         new_g = FunctionGraph(g.inputs, [new_out])
         opt_str_g = ("[Elemwise{mul,no_inplace}(Elemwise{add,no_inplace}"
@@ -189,10 +187,21 @@ class test_dimshuffle_lift(unittest.TestCase):
                      "Elemwise{add,no_inplace}(DimShuffle{1,0}"
                      "(<TensorType(float64, matrix)>), "
                      "DimShuffle{x,x}(TensorConstant{84})))]")
+
         self.assertTrue(str(new_g) == opt_str_g)
         # Check stacktrace was copied over correctly after opt was applied
         self.assertTrue(hasattr(new_g.outputs[0].tag, 'trace'))
 
+    def test_useless_dimshuffle(self):
+        x, _, _ = inputs()
+        e = ds(x, (0, 1))
+        g = FunctionGraph([x], [e])
+        self.assertTrue(str(g) == "[DimShuffle{0,1}(x)]")
+        dimshuffle_lift.optimize(g)
+        self.assertTrue(str(g) == "[x]")
+        # Check stacktrace was copied over correctly after opt was applied
+        self.assertTrue(hasattr(g.outputs[0].tag, 'trace'))
+
 
 def test_add_canonizer_problem0():
     n_segments = 10