[Transform] start sketching move_add_past_mul

src/finn/transformation/streamline.py

+import finn.transformation.infer_shapes as si
+
+
+def move_add_past_mul(model):
+    """Move add operations past multiply operations. The aim is to have them
+    next to each other such that they can be collapsed into a single add."""
+    graph = model.graph
+    nodes_to_remove = []
+    node_ind = 0
+    graph_modified = False
+    for n in graph.node:
+        node_ind += 1
+        if n.op_type == "Add":
+            consumer = model.find_consumer(n.output[0])
+            if consumer.op_type == "Mul":
+                # assume input 0 is from the previous layer, input 1 is the
+                # trained (constant) parameter
+                mul_param = model.get_initializer(consumer.input[1])
+                add_param = model.get_initializer(n.input[1])
+                assert mul_param is not None
+                assert add_param is not None
+                # TODO compute new param values
+                # TODO make new nodes
+                # TODO mark nodes for removal
+    # delete marked nodes (batchnorm and (un)squeezing)
+    for n in nodes_to_remove:
+        graph.node.remove(n)
+        graph_modified = True
+    model = model.transform_single(si.infer_shapes)
+    return (model, graph_modified)