changes to merge optimization to encourage stability

theano/gof/opt.py

@@ -187,9 +187,15 @@ class MergeOptimizer(Optimizer):
         env.extend(toolbox.ReplaceValidate())
 
     def apply_constant_merge(self, env):
+        seen_constants = set()
         const_sig = _metadict()     # result -> result.signature()  (for constants)
         const_sig_inv = _metadict() # signature -> result (for constants)
-        for i, c in enumerate([r for r in env.results if isinstance(r, graph.Constant)]):
+        for node in _list_of_nodes(env):
+            for i, c in enumerate([r for r in node.inputs if isinstance(r, graph.Constant)]):
+                if id(c) in seen_constants:
+                    continue
+                else:
+                    seen_constants.add(id(c))
                 sig = c.signature()
                 other_c = const_sig_inv.get(sig, None)
                 if other_c is not None:
@@ -242,19 +248,20 @@ class MergeOptimizer(Optimizer):
         # we clear the dicts because the Constants signatures are not necessarily hashable
         # and it's more efficient to give them an integer like the other Results
 
-        nodes_seen = set()
+        nodes_seen = {}
 
-        for node in _list_of_nodes(env):
+        for node_idx, node in enumerate(_list_of_nodes(env)):
             #
             # these asserts ensure that the env has set the clients field properly the clients
             # should at least contain `node` itself!
             #
             assert len(node.inputs[0].clients) > 0 
             assert (node,0) in node.inputs[0].clients
-            merge_candidates = [c for (c,i) in node.inputs[0].clients if c in nodes_seen]
-            nodes_seen.add(node)
+            merge_candidates = [(nodes_seen[c],c) for (c,i) in node.inputs[0].clients if c in nodes_seen]
+            merge_candidates.sort()
+            nodes_seen[node] = node_idx
             #print 'NODE', node, merge_candidates, node.inputs[0].clients
-            for candidate in merge_candidates:
+            for candidate_idx, candidate in merge_candidates:
                 if len(node.inputs) != len(candidate.inputs):
                     continue
                 inputs_match = all(node_in is cand_in for node_in, cand_in in zip(node.inputs, candidate.inputs))
@@ -626,8 +633,8 @@ class NavigatorOptimizer(Optimizer):
     def warn(exc, nav, repl_pairs, local_opt):
         """failure_callback for NavigatorOptimizer: print traceback
         """
-        print "WARNING: Optimization failure due to: ", local_opt
-        print "TRACEBACK:"
+        print >> sys.stderr, "WARNING: Optimization failure due to: ", local_opt
+        print >> sys.stderr, "TRACEBACK:"
         traceback.print_exc()
     @staticmethod
     def warn_inplace(exc, nav, repl_pairs, local_opt):