[GitHub] [incubator-tvm] kevinthesun commented on a change in pull request #6449: [Frontend][Pytorch] Improve Pytorch frontend for object detection models

[GitBox <gi...@apache.org>]

kevinthesun commented on a change in pull request #6449:
URL: https://github.com/apache/incubator-tvm/pull/6449#discussion_r487256873



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File path: python/tvm/relay/frontend/pytorch.py
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@@ -127,8 +128,22 @@ def _is_quantized_tensor(data, prelude):
 # operator implementation
 def _elemwise(name):
     def _impl(inputs, input_types):
-        data0, data1 = _pytorch_promote_types(inputs[:2], input_types[:2])
-        return get_relay_op(name)(data0, data1)
+        dtype0, dtype1 = input_types[:2]
+        if isinstance(inputs[0], _expr.Expr):
+            dtype0 = _infer_type(inputs[0]).checked_type.dtype
+        if isinstance(inputs[1], _expr.Expr):
+            dtype1 = _infer_type(inputs[1]).checked_type.dtype
+

Review comment:
       This comes from weird behavior of ```prim::NumToTensor```. It converts int32 to int64 silently:
   ```
   %11 : int = aten::size(%img.1, %10), scope: __module.model # /usr/local/lib/python3.6/dist-packages/torchvision/models/detection/generalized_rcnn.py:62:0
     %im_h : Long() = prim::NumToTensor(%11), scope: __module.model
   ```
   Right now py frontend just follow use the same dtype for this op output. For an elemwise op, pytorch input dtype is ["int64", "int64"] which is fine. However, the actual input dtype is ["int64", "32"]. What I can do is to enhance ```_pytorch_promote_types``` so that we do _infer_type for every input and get actual input dtype, rather than solely relying on pytorch input dtype. Sounds like a plan?




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