added local_mul_to_sqr optimization

theano/tensor/opt.py

@@ -1332,6 +1332,18 @@ def local_pow_canonicalize(node):
         return False
 register_canonicalize(local_pow_canonicalize)
 
+@register_specialize
+@gof.local_optimizer([T.mul])
+def local_mul_to_sqr(node):
+    """x*x -> sqr(x)
+
+    This is faster on the GPU when memory fetching is a big part of the computation time.
+    """
+    if node.op == T.mul:
+        if len(node.inputs)==2:
+            if node.inputs[0] is node.inputs[1]:
+                return [T.sqr(node.inputs[0])]
+
 @gof.local_optimizer([T.pow])
 def local_pow_specialize(node):
     #here, we are past the point of canonicalization, so we don't want to put in un-necessary fills.
@@ -1370,7 +1382,9 @@ register_specialize(local_pow_specialize)
 
 @gof.local_optimizer([T.mul])
 def local_mul_specialize(node):
-    #here, we are past the point of canonicalization, so we don't want to put in un-necessary fills.
+    """Remove special-case constants from mul arguments
+    """
+    # here, we are past the point of canonicalization, so we don't want to put in un-necessary fills.
     #
     # at this point [post canonicalize], mul() may have many inputs.
     if node.op == T.mul: