[Stitch] add warning if first FIFO in graph has impl_style=vivado

src/finn/transformation/fpgadataflow/create_stitched_ip.py

@@ -310,6 +310,14 @@ class CreateStitchedIP(Transformation):
                 behavior. It is strongly recommended to insert FIFOs prior to
                 calling CreateStitchedIP."""
             )
+        if model.graph.node[0].op_type == "StreamingFIFO":
+            firstfifo = getCustomOp(model.graph.node[0])
+            if firstfifo.get_nodeattr("impl_style") == "vivado":
+                warnings.warn(
+                    """First FIFO has impl_style=vivado, which may cause
+                    simulation glitches (e.g. dropping the first input sample
+                    after reset)."""
+                )
         for node in model.graph.node:
             # ensure that all nodes are fpgadataflow, and that IPs are generated
             assert is_fpgadataflow_node(