Make one scan function not recurse and have the last line put more node in the…

theano/scan_module/scan_utils.py

@@ -855,35 +855,59 @@ class Validator(object):
         If out is not valid and has no equivalent, None is returned.
 
         """
+
+        def get_value(out):
             if out in self.valid:
                 return out, True
             elif out in self.valid_equivalent:
                 return self.valid_equivalent[out], False
             elif out in self.invalid:
                 return None
+            else:
+                raise RuntimeError("This should not happen")
+
+        q = [out]
+        while q:
+            out = q.pop()
+            if out in self.valid:
+                continue
+            elif out in self.invalid:
+                continue
 
             if out.owner is None:
                 if isinstance(out, tensor.TensorConstant):
                     # This might be a constant from the outer graph or a constant
                     # from the inner graph. In all cases, we can clone it to be
                     # certain we have a valid constant
+
+                    # TODO: FRED I think the clone is not needed.
                     cloned_out = out.clone()
                     self.valid.add(cloned_out)
                     self.invalid.add(out)
                     self.valid_equivalent[out] = cloned_out
-                return cloned_out, False
+                    continue
                 else:
                     # This is an input node and it has not been explicitly marked
                     # as invalid so we can use it
-                return out, True
+                    self.valid.add(out)
+                    continue
 
-        # Recurse over inputs
-        inputs = [self.check(i) for i in out.owner.inputs]
+            # Process the input if needed
+            continue_while = False
+            for inp in out.owner.inputs:
+                if inp not in self.valid and inp not in self.invalid:
+                    q.append(out)
+                    q.extend(out.owner.inputs)
+                    continue_while = True
+                    break
+            if continue_while:
+                continue
+            inputs = [get_value(i) for i in out.owner.inputs]
 
             # If some inputs are invalid without equivalent, so is out
             if None in inputs:
                 self.invalid.add(out)
-            return None
+                continue
 
             # If some inputs are invalid with equivalent,
             # an equivalent out should be built and returned
@@ -895,10 +919,12 @@ class Validator(object):
                 self.invalid.add(out)
                 self.valid.add(cloned_out)
                 self.valid_equivalent[out] = cloned_out
-            return cloned_out, False
+                continue
 
             # All inputs are valid, so is out
-        return out, True
+            self.valid.add(out)
+
+        return get_value(out)
 
 
 def scan_can_remove_outs(op, out_idxs):