function_module - extended the logic that un-aliases input/output variables

theano/compile/function_module.py

@@ -751,13 +751,19 @@ class FunctionMaker(object):
         if not isinstance(inputs, (list, tuple)):
             inputs = [inputs]
 
+
         # Wrap them in In or Out instances if needed.
+        #import pudb; pudb.set_trace()
         inputs, outputs =  map(self.wrap_in, inputs), map(self.wrap_out, outputs)
-        _inputs = gof.graph.inputs([o.variable for o in outputs] + [i.update for i in inputs if getattr(i, 'update', False)])
+        _inputs = gof.graph.inputs([o.variable for o in outputs] + [i.update 
+            for i in inputs if getattr(i, 'update', False)])
+
+        #TODO: REMOVE THIS CRUFT - it's complicated for SymbolicInputKits
         indices = [[input] + self.expand_in(input, _inputs) for input in inputs]
         expanded_inputs = reduce(list.__add__, [list(z) for x, y, z in indices], [])
+        assert expanded_inputs == inputs  #JB - I added this to make sure we could delete above
 
-        # make the env
+        # make the env (copies the graph, creates NEW INPUT AND OUTPUT VARIABLES)
         env, additional_outputs = std_env(expanded_inputs, outputs, accept_inplace)
         self.env = env
 
@@ -774,12 +780,34 @@ class FunctionMaker(object):
         # but some of the outputs can be shared variables, and is not good for shared
         # variables to be aliased. It might be possible to optimize this by making sure
         # there is no aliasing only between shared variables.
+
+        assert len(inputs) == len(env.inputs)
+
+        updated_env_inputs = [env_i for i, env_i in zip(inputs, env.inputs) if getattr(i, 'update', False)]
+
         for i in xrange(len(env.outputs)):
-            views = set()
-            view_tree_set(alias_root(env.outputs[i]), views)
+            views_of_output_i = set()
+            view_tree_set(alias_root(env.outputs[i]), views_of_output_i)
+            copied = False
+            # do not allow outputs to be aliased
             for j in xrange(i+1, len(env.outputs)):
-                if env.outputs[j] in views:
-                    env.change_input('output', j, deep_copy_op(env.outputs[j]))
+                if env.outputs[j] in views_of_output_i:
+                    env.change_input('output', i, deep_copy_op(env.outputs[i]))
+                    copied = True
+                    break
+
+            if not copied:
+                for input_j in env.inputs:
+                    # do not allow outputs to be aliased to an inputs (j), unless 
+                    # a) that j'th input has been 'destroyed' by e.g. in-place computations
+                    # b) that j'th input is a shared variable that is also being updated
+                    if hasattr(env,'get_destroyers_of') and env.get_destroyers_of(input_j):
+                        continue
+                    if input_j in updated_env_inputs:
+                        continue
+                    if input_j in views_of_output_i:
+                        env.change_input('output', i, deep_copy_op(env.outputs[i]))
+                        break