Avoid duplicate input/output taps in mitmots

theano/scan_module/scan_op.py

@@ -2016,6 +2016,7 @@ class Scan(PureOp):
             undefined_msg = None
             through_shared = False
             disconnected = True
+
             for jdx in xrange(len(self.mit_mot_out_slices[idx])):
                 inner_inp_mitmot.append(dC_dXts[out_pos])
                 mitmot_inp_taps[idx].append(-self.mit_mot_out_slices[idx][jdx])
@@ -2023,7 +2024,13 @@ class Scan(PureOp):
                 out_pos += 1
 
             for jdx in xrange(len(self.tap_array[idx])):
+                tap = -self.tap_array[idx][jdx]
+
+                # Only create a new inner input if there is not already one
+                # associated with this input tap
+                if tap not in mitmot_inp_taps[idx]:
                     inner_inp_mitmot.append(dC_dXtm1s[ins_pos - self.n_seqs])
+
                 if isinstance(dC_dinps_t[ins_pos].type, NullType):
                     # We cannot use Null in the inner graph, so we
                     # use a zero tensor of the appropriate shape instead.
@@ -2032,7 +2039,24 @@ class Scan(PureOp):
                                      dtype=theano.config.floatX))
                     undefined_msg = dC_dinps_t[ins_pos].type.why_null
                 else:
-                    inner_out_mitmot.append(dC_dinps_t[ins_pos])
+                    new_inner_out_mitmot = dC_dinps_t[ins_pos]
+
+                    # If there is already an inner input associated with that
+                    # input tap, make sure the computation of the new output
+                    # uses it instead of the input it's currently using
+                    if tap in mitmot_inp_taps[idx]:
+                        print("Duplicate tap")
+                        to_replace = dC_dXtm1s[ins_pos - self.n_seqs]
+                        replacement_idx = (len(mitmot_inp_taps[idx]) -
+                                           mitmot_inp_taps[idx].index(tap))
+                        replacement = inner_inp_mitmot[-replacement_idx]
+
+                        self.tap_array[idx]
+                        new_inner_out_mitmot = theano.clone(new_inner_out_mitmot,
+                                                            replace=[(to_replace, replacement)])
+
+
+                    inner_out_mitmot.append(new_inner_out_mitmot)
 
                 if not disconnected_dC_dinps_t[ins_pos]:
                     disconnected = False
@@ -2041,12 +2065,15 @@ class Scan(PureOp):
                     if _sh in gof.graph.inputs([dC_dinps_t[ins_pos]]):
                         through_shared = True
 
-                n_mitmot_inps += 1
                 ins_pos += 1
                 n_mitmot_outs += 1
-                mitmot_inp_taps[idx].append(-self.tap_array[idx][jdx])
                 mitmot_out_taps[idx].append(-self.tap_array[idx][jdx])
 
+                # Only add the tap as a new input tap if needed
+                if tap not in mitmot_inp_taps[idx]:
+                    n_mitmot_inps += 1
+                    mitmot_inp_taps[idx].append(-self.tap_array[idx][jdx])
+
             if undefined_msg:
                 type_outs.append(undefined_msg)
             elif through_shared: