added scalar.identity to local_useless_elemwise

I am not sure why this is necessary now. One guess is that the canonicalizer or something else has been modified to put in identity(), and now it is more obvious that we need an optimization to take it out again. I'm hoping that this improves the slowdown recently observed in convolutional net benchmark.

added scalar.identity to local_useless_elemwise
a175ebf2 · James Bergstra · 72a2ad6a · a175ebf2
--- a/theano/tensor/opt.py
+++ b/theano/tensor/opt.py
@@ -764,10 +764,12 @@ def local_subtensor_make_vector(node):
 @gof.local_optimizer([T.Elemwise])
 def local_useless_elemwise(node):
    """
-eq(x,x) -> 1
-neq(x,x) -> 0
+    eq(x,x) -> 1
-mul(x) -> x
+    neq(x,x) -> 0
-add(x) -> x
+    mul(x) -> x
+    add(x) -> x
+    identity(x) -> x
    """
    if isinstance(node.op, T.Elemwise):
@@ -783,6 +785,8 @@ add(x) -> x
            return [node.inputs[0]]
        if node.op.scalar_op == theano.scalar.add and len(node.inputs)==1:
            return [node.inputs[0]]
+        if node.op.scalar_op == theano.scalar.identity and len(node.inputs)==1:
+            return [node.inputs[0]]
 @register_specialize