disble multi tensor apply for O4, O5

apex/amp/_process_optimizer.py

@@ -13,7 +13,7 @@ class AmpOptimizerState(object):
 
 def _master_params_to_model_params(self):
     stash = self._amp_stash
-    if multi_tensor_applier.available and not _amp_state.opt_properties.opt_level not in {"O4", "O5"}:
+    if multi_tensor_applier.available and _amp_state.opt_properties.opt_level not in {"O4", "O5"}:
         if len(stash.all_fp16_params) > 0:
             multi_tensor_applier(
                 stash.multi_tensor_scale,

apex/amp/scaler.py

@@ -63,7 +63,7 @@ class LossScaler(object):
         self._unskipped = 0
         self._has_overflow = False
         self._overflow_buf = torch.cuda.IntTensor([0])
-        if multi_tensor_applier.available:
+        if multi_tensor_applier.available and _amp_state.opt_properties.opt_level not in {"O4", "O5"}:
             import amp_C
             LossScaler.has_fused_kernel = multi_tensor_applier.available
             LossScaler.multi_tensor_scale_cuda = amp_C.multi_tensor_scale