[KUNLUN]fix cast bf16 (#52246)

python/paddle/distributed/fleet/meta_optimizers/dygraph_optimizer/hybrid_parallel_optimizer.py

@@ -200,6 +200,9 @@ class HybridParallelClipGrad:
             + paddle.to_tensor([1.0e-6], dtype=paddle.float32),
         )
         clip_var_fp16 = paddle.cast(clip_var, paddle.float16)
+
+        # bf16 is not supported on XPU now
+        if not paddle.is_compiled_with_xpu():
             clip_var_bf16 = paddle.cast(clip_var, paddle.bfloat16)
         for p, g in params_grads:
             if g is None:
@@ -209,6 +212,10 @@ class HybridParallelClipGrad:
             if g.dtype == paddle.float16:
                 g.scale_(clip_var_fp16)
             elif g.dtype == paddle.bfloat16:
+                if paddle.is_compiled_with_xpu():
+                    raise NotImplementedError(
+                        "BF16 is not supported on XPU now"
+                    )
                 g.scale_(clip_var_bf16)
             else:
                 g.scale_(clip_var)