[Analysis] add is_linear and get_per_tensor_fanouts

src/finn/analysis/__init__.py

+"""
+How to write an analysis pass for FINN
+--------------------------------------
+
+An analysis pass traverses the graph structure and produces information about
+certain properties. The convention is to take in a ModelWrapper, and return
+a dictionary of named properties that the analysis extracts.
+"""

src/finn/analysis/topology.py

+def is_linear(model):
+    """Checks whether the given model graph is linear. This is done by looking
+    at the fan-out of each tensor. All tensors have a fan-out <= 1 in a linear
+    graph. Returns {"is_linear", Bool}"""
+    per_tensor_fanouts = get_per_tensor_fanouts(model)
+    # check for tensors that have fanout > 1
+    multi_fanouts = list(filter(lambda x: x[1] > 1, per_tensor_fanouts.items()))
+    return {"is_linear": len(multi_fanouts) == 0}
+
+
+def get_per_tensor_fanouts(model):
+    """Returns a dictionary of (tensor_name, tensor_fanout) for the model."""
+    # make execution context to get a list of tensors
+    per_tensor_fanouts = model.make_empty_exec_context()
+    # replace every tensor with its fanout
+    for tensor_name in per_tensor_fanouts.keys():
+        per_tensor_fanouts[tensor_name] = model.get_tensor_fanout(tensor_name)
+    return per_tensor_fanouts