[MaskRCNN/PyT] Update AMP API for inference (#810)

Author: sharathts

PyTorch/Segmentation/MaskRCNN/pytorch/tools/test_net.py

@@ -96,13 +96,14 @@ def main():
     model = build_detection_model(cfg)
     model.to(cfg.MODEL.DEVICE)
 
-    # Initialize mixed-precision if necessary
+    # Initialize mixed-precision
     if args.fp16:
         use_mixed_precision = True
     else:
         use_mixed_precision = cfg.DTYPE == "float16"
-    amp_handle = amp.init(enabled=use_mixed_precision, verbose=cfg.AMP_VERBOSE)
-
+    amp_opt_level = 'O1' if use_mixed_precision else 'O0'
+    model = amp.initialize(model, opt_level=amp_opt_level)    
+    
     output_dir = cfg.OUTPUT_DIR
     checkpointer = DetectronCheckpointer(cfg, model, save_dir=output_dir)
     _ = checkpointer.load(cfg.MODEL.WEIGHT)