Merge pull request #1120 from pascanur/bug_seqOptimizer

theano/scan_module/scan_opt.py

@@ -837,9 +837,17 @@ class ScanSaveMem(gof.Optimizer):
                     if not (idx in replaced_outs) and not idx in not_required:
                         nw_pos = compress_map[idx]
                         old_new += [(o, new_outs[nw_pos])]
-
+                # Check if the new outputs depend on the old scan node
+                old_scan_is_used = [scan_utils.find_up(new.owner, node)
+                                    for old, new in old_new]
+                if any(old_scan_is_used):
+                    return False
+                remove = [old.owner for (old, new) in old_new]
+                # As Fred suggested assert that also the old node is not in
+                # the Graph as that will make things suboptimal
+                remove.append(node)
                 fgraph.replace_all_validate_remove(old_new,
-                                                   remove=[node],
+                                                   remove,
                                                    reason='scan_save_mem')
 
     def apply(self, fgraph):

theano/scan_module/tests/test_scan.py

@@ -3292,6 +3292,18 @@ class T_Scan(unittest.TestCase):
         cost = x.sum()
         self.assertRaises(ValueError, tensor.grad, cost, y0)
 
+    def test_savemem_does_not_duplicate_number_of_scan_nodes(self):
+        var = tensor.ones(())
+        values, _ = theano.scan(lambda x: ([x], (), theano.scan_module.until(x)),
+                                          outputs_info=[var], n_steps=2)
+
+        tmp_fn = theano.function([var], values)
+        scan_nodes = [x for x in tmp_fn.maker.fgraph.toposort()
+                      if isinstance(x.op,
+                                    theano.scan_module.scan_op.Scan)]
+        assert len(scan_nodes) == 1
+
+
 
 def test_speed():
     #