Use dummy input variables during Scan rewrites

aesara/scan/rewriting.py

@@ -23,6 +23,7 @@
     graph_inputs,
     io_toposort,
     is_in_ancestors,
+    replace_nominals_with_dummies,
 )
 from aesara.graph.destroyhandler import DestroyHandler
 from aesara.graph.features import ReplaceValidate
@@ -82,6 +83,7 @@ def remove_constants_and_unused_inputs_scan(fgraph, node):
     """
     if not isinstance(node.op, Scan):
         return False
+
     op = node.op
     op_info = op.info
     # We only need to take care of sequences and other arguments
@@ -92,8 +94,7 @@ def remove_constants_and_unused_inputs_scan(fgraph, node):
     st += op_info.n_sit_sot
     st += op_info.n_shared_outs
 
-    op_ins = op.inner_inputs
-    op_outs = op.inner_outputs
+    op_ins, op_outs = replace_nominals_with_dummies(op.inner_inputs, op.inner_outputs)
 
     # Corresponds to the initial states, which should stay untouched.
     # We put those variables aside, and put them back at the end.
@@ -189,6 +190,7 @@ def remove_constants_and_unused_inputs_scan(fgraph, node):
             allow_gc=op.allow_gc,
         )
         nw_outs = nwScan(*nw_outer, return_list=True)
+
         return dict([("remove", [node])] + list(zip(node.outputs, nw_outs)))
     else:
         return False
@@ -207,7 +209,9 @@ def push_out_non_seq_scan(fgraph, node):
     if not isinstance(node.op, Scan):
         return False
 
-    node_inputs, node_outputs = node.op.inner_inputs, node.op.inner_outputs
+    node_inputs, node_outputs = replace_nominals_with_dummies(
+        node.op.inner_inputs, node.op.inner_outputs
+    )
 
     local_fgraph_topo = io_toposort(node_inputs, node_outputs)
     local_fgraph_outs_set = set(node_outputs)
@@ -417,7 +421,9 @@ def push_out_seq_scan(fgraph, node):
     if not isinstance(node.op, Scan):
         return False
 
-    node_inputs, node_outputs = node.op.inner_inputs, node.op.inner_outputs
+    node_inputs, node_outputs = replace_nominals_with_dummies(
+        node.op.inner_inputs, node.op.inner_outputs
+    )
 
     local_fgraph_topo = io_toposort(node_inputs, node_outputs)
     local_fgraph_outs_set = set(node_outputs)
@@ -832,9 +838,10 @@ def push_out_add_scan(fgraph, node):
 
     # Use `ScanArgs` to parse the inputs and outputs of scan for ease of
     # use
-    args = ScanArgs(
-        node.inputs, node.outputs, op.inner_inputs, op.inner_outputs, op.info
+    inner_inputs, inner_outputs = replace_nominals_with_dummies(
+        op.inner_inputs, op.inner_outputs
     )
+    args = ScanArgs(node.inputs, node.outputs, inner_inputs, inner_outputs, op.info)
 
     clients = {}
     local_fgraph_topo = io_toposort(
@@ -1694,6 +1701,8 @@ def merge(self, nodes):
         inner_outs = [[] for nd in nodes]
         outer_outs = []
 
+        # inner_inputs, inner_outputs = replace_nominals_with_dummies(nd.op.inner_inputs, nd.op.inner_outputs)
+
         def rename(ls, suffix):
             for k in ls:
                 if k.name:
@@ -1967,11 +1976,16 @@ def scan_merge_inouts(fgraph, node):
     # Do a first pass to merge identical external inputs.
     # Equivalent inputs will be stored in inp_equiv, then a new
     # scan node created without duplicates.
+
+    inner_inputs, inner_outputs = replace_nominals_with_dummies(
+        node.op.inner_inputs, node.op.inner_outputs
+    )
+
     a = ScanArgs(
         node.inputs,
         node.outputs,
-        node.op.inner_inputs,
-        node.op.inner_outputs,
+        inner_inputs,
+        inner_outputs,
         node.op.info,
     )
 
@@ -2173,10 +2187,15 @@ def push_out_dot1_scan(fgraph, node):
     # Note that this works when only you need X[-1] in the end
     # and assumes dimshuffle are applied to vectors before calling dot
     op = node.op
-    sitsot_ins = op.inner_sitsot(op.inner_inputs)
-    sitsot_outs = op.inner_sitsot_outs(op.inner_outputs)
+
+    inner_inputs, inner_outputs = replace_nominals_with_dummies(
+        op.inner_inputs, op.inner_outputs
+    )
+
+    sitsot_ins = op.inner_sitsot(inner_inputs)
+    sitsot_outs = op.inner_sitsot_outs(inner_outputs)
     outer_sitsot = op.outer_sitsot_outs(node.outputs)
-    seqs = op.inner_seqs(op.inner_inputs)
+    seqs = op.inner_seqs(inner_inputs)
     for inp, out, outer_out in zip(sitsot_ins, sitsot_outs, outer_sitsot):
 
         if (
@@ -2218,23 +2237,23 @@ def push_out_dot1_scan(fgraph, node):
                     # First let us split all arguments according to their
                     # corresponding categories
 
-                    inner_seqs = op.inner_seqs(op.inner_inputs)
+                    inner_seqs = op.inner_seqs(inner_inputs)
                     outer_seqs = op.outer_seqs(node.inputs)
-                    inner_mitmot = op.inner_mitmot(op.inner_inputs)
+                    inner_mitmot = op.inner_mitmot(inner_inputs)
                     outer_mitmot = op.outer_mitmot(node.inputs)
-                    inner_mitmot_outs = op.inner_mitmot_outs(op.inner_outputs)
-                    inner_mitsot = op.inner_mitsot(op.inner_inputs)
+                    inner_mitmot_outs = op.inner_mitmot_outs(inner_outputs)
+                    inner_mitsot = op.inner_mitsot(inner_inputs)
                     outer_mitsot = op.outer_mitsot(node.inputs)
-                    inner_mitsot_outs = op.inner_mitsot_outs(op.inner_outputs)
-                    inner_sitsot = op.inner_sitsot(op.inner_inputs)
+                    inner_mitsot_outs = op.inner_mitsot_outs(inner_outputs)
+                    inner_sitsot = op.inner_sitsot(inner_inputs)
                     outer_sitsot = op.outer_sitsot(node.inputs)
-                    inner_sitsot_outs = op.inner_sitsot_outs(op.inner_outputs)
+                    inner_sitsot_outs = op.inner_sitsot_outs(inner_outputs)
                     outer_nitsot = op.outer_nitsot(node.inputs)
-                    inner_nitsot_outs = op.inner_nitsot_outs(op.inner_outputs)
-                    inner_shared = op.inner_shared(op.inner_inputs)
+                    inner_nitsot_outs = op.inner_nitsot_outs(inner_outputs)
+                    inner_shared = op.inner_shared(inner_inputs)
                     outer_shared = op.outer_shared(node.inputs)
-                    inner_shared_outs = op.inner_shared_outs(op.inner_outputs)
-                    inner_non_seqs = op.inner_non_seqs(op.inner_inputs)
+                    inner_shared_outs = op.inner_shared_outs(inner_outputs)
+                    inner_non_seqs = op.inner_non_seqs(inner_inputs)
                     outer_non_seqs = op.outer_non_seqs(node.inputs)
 
                     new_info = dataclasses.replace(