[MultiThreshold] Replace default data_layout by fallback in execute_node

Note: Only covers data layouts for tensors with less than five axes

src/qonnx/custom_op/general/multithreshold.py

@@ -92,9 +92,7 @@ def get_nodeattr_types(self):
             "out_dtype": ("s", True, ""),
             "out_scale": ("f", False, 1.0),
             "out_bias": ("f", False, 0.0),
-            # fmt: off
-            "data_layout": ("s", False, "NCHW")
-            # fmt: on
+            "data_layout": ("s", False, ""),
         }
 
     def make_shape_compatible_op(self, model):
@@ -129,6 +127,13 @@ def execute_node(self, context, graph):
         # accepted by the multithreshold function above, i.e, the channel
         # dimension is along the axis with index 1.
         data_layout = self.get_nodeattr("data_layout")
+        # If there is no layout annotation, guess based on rank of the
+        # tensor
+        if not data_layout and len(v.shape) < 5:
+            # Maps tensor rank to layout annotation
+            rank_to_layout = {0: None, 1: "C", 2: "NC", 3: "NWC", 4: "NCHW"}
+            # Lookup the layout required by this input shape
+            data_layout = rank_to_layout[len(v.shape)]
         # Lookup the index of the channel dimension in the data layout
         # Note: Assumes there is at most one "C" which denotes the channel
         # dimension