Adding optimizations block from ONNXRuntime. (#4431)

* Adding optimizations block from ONNXRuntime.

* Turn off external data format by default for PyTorch export.

* Correct the way use_external_format is passed through the cmdline args.

notebooks/04-onnx-export.ipynb

@@ -125,9 +125,39 @@
     "- **Deadcode Elimination**: Remove nodes never accessed in the graph\n",
     "- **Operator Fusing**: Merge multiple instruction into one (Linear -> ReLU can be fused to be LinearReLU)\n",
     "\n",
-    "All of this is done on **onnxruntime** by settings specific `SessionOptions`:"
+    "ONNX Runtime automatically applies most optimizations by setting specific `SessionOptions`.\n",
+    "\n",
+    "Note:Some of the latest optimizations that are not yet integrated into ONNX Runtime are available in [optimization script](https://github.com/microsoft/onnxruntime/tree/master/onnxruntime/python/tools/transformers) that tunes models for the best performance."
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "outputs": [],
+   "source": [
+    "# # An optional step unless\n",
+    "# # you want to get a model with mixed precision for perf accelartion on newer GPU\n",
+    "# # or you are working with Tensorflow(tf.keras) models or pytorch models other than bert\n",
+    "\n",
+    "# !pip install onnxruntime-tools\n",
+    "# from onnxruntime_tools import optimizer\n",
+    "\n",
+    "# # Mixed precision conversion for bert-base-cased model converted from Pytorch\n",
+    "# optimized_model = optimizer.optimize_model(\"bert-base-cased.onnx\", model_type='bert', num_heads=12, hidden_size=768)\n",
+    "# optimized_model.convert_model_float32_to_float16()\n",
+    "# optimized_model.save_model_to_file(\"bert-base-cased.onnx\")\n",
+    "\n",
+    "# # optimizations for bert-base-cased model converted from Tensorflow(tf.keras)\n",
+    "# optimized_model = optimizer.optimize_model(\"bert-base-cased.onnx\", model_type='bert_keras', num_heads=12, hidden_size=768)\n",
+    "# optimized_model.save_model_to_file(\"bert-base-cased.onnx\")\n"
+   ],
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   }
+  },
   {
    "cell_type": "code",
    "execution_count": 2,