add assert overlap (#54559)

python/paddle/distributed/fleet/meta_parallel/pipeline_parallel.py

@@ -84,6 +84,10 @@ class PipelineParallel(MetaParallelBase):
             "pp_configs"
         ].enable_timer
 
+        assert (
+            not self._dp_comm_overlap and not self._sharding_comm_overlap
+        ), "Comm overlap is not supported now."
+
         if self._dp_comm_overlap:
             assert self.use_data_parallel and self.num_stages > 1