add_tag_grace_on_call speeds up optimization

theano/compile/function_module.py

@@ -994,6 +994,8 @@ class FunctionMaker(object):
         try:
             theano.config.compute_test_value = "off"
             start_optimizer = time.time()
+            add_stack_trace_on_call = gof.Op.add_stack_trace_on_call
+            gof.Op.add_stack_trace_on_call = False
             optimizer(env)
             end_optimizer = time.time()
 
@@ -1007,6 +1009,7 @@ class FunctionMaker(object):
             insert_deepcopy(env, inputs, outputs+additional_outputs)
         finally:
             theano.config.compute_test_value = compute_test_value_orig
+            gof.Op.add_stack_trace_on_call = add_stack_trace_on_call
 
         # initialize the linker
         if not hasattr(linker, 'accept'):

theano/gof/op.py

@@ -310,6 +310,13 @@ class PureOp(object):
 
     """
 
+    add_stack_trace_on_call = True
+    """This class variable governs whether __call__ adds a stack trace to the node it creates.
+    
+    The tag trace is meant to connect a node to the line a user typed. It is nice for
+    debugging. It does not make as much sense during optimizations to store this information.
+    """
+
     #############
     # make_node #
     #############
@@ -367,6 +374,7 @@ class PureOp(object):
 
         """
         node = self.make_node(*inputs, **kwargs)
+        if self.add_stack_trace_on_call:
             self.add_tag_trace(node)
 
         if config.compute_test_value != 'off':