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BowenBao · BowenBao · commit 8ab426f7f727 · 2019-07-11T12:45:47.000-07:00
diff --git a/torch/onnx/symbolic_opset8.py b/torch/onnx/symbolic_opset8.py
@@ -88,28 +88,23 @@ def _cast_to_type(g, input, to_type):
     return getattr(sym_opset9, '_cast_{}'.format(to_type))(g, input, False)
 
 
-@wrap_logical_op_with_cast_to('Byte')
-def gt(g, input, other):
-    return gt_impl(g, input, other)
-
-
-def gt_impl(g, input, other):
+def _comparison_operator(g, input, other, op_name):
     other = sym_help._maybe_get_scalar(other)
     other = sym_help._if_scalar_type_as(g, other, input)
     _, input, other = _try_cast_integer_to_float(g, input, other)
-    return g.op("Greater", input, other)
+    return g.op(op_name, input, other)
 
 
+# NOTE: For symbolics {gt, lt, bmm, matmul, prelu, mm, addmm, view, flatten},
+#       integer input type not supported in opset8. Cast to float if possible.
 @wrap_logical_op_with_cast_to('Byte')
-def lt(g, input, other):
-    return lt_impl(g, input, other)
+def gt(g, input, other):
+    return _comparison_operator(g, input, other, "Greater")
 
 
-def lt_impl(g, input, other):
-    other = sym_help._maybe_get_scalar(other)
-    other = sym_help._if_scalar_type_as(g, other, input)
-    _, input, other = _try_cast_integer_to_float(g, input, other)
-    return g.op("Less", input, other)
+@wrap_logical_op_with_cast_to('Byte')
+def lt(g, input, other):
+    return _comparison_operator(g, input, other, "Less")
 
 
 def bmm(g, self, other):
@@ -121,11 +116,7 @@ def bmm(g, self, other):
 
 
 def matmul(g, self, other):
-    if _try_get_scalar_type(self):
-        old_type, self, other = _try_cast_integer_to_float(g, self, other)
-        return _cast_to_type(g, g.op("MatMul", self, other), old_type)
-    else:
-        return g.op("MatMul", self, other)
+    return bmm(g, self, other)
 
 
 def prelu(g, self, weight):
diff --git a/torch/onnx/symbolic_registry.py b/torch/onnx/symbolic_registry.py
@@ -36,9 +36,17 @@ def register_ops_in_version(domain, version):
     # opset versions for operators supported in
     # previous versions.
 
-    # Opset 9 is the base version.
-    # For operators of different opset version, updated symbolic functions are added
-    # in the respective symbolic_opset{version}.py file.
+    # Opset 9 is the base version. It is selected as the base version because
+    #   1. It is the first opset version supported by PyTorch export.
+    #   2. opset 9 is more robust than previous opset versions. Opset versions like 7/8 have limitations
+    #      that certain basic operators cannot be expressed in ONNX. Instead of basing on these limitations,
+    #      we chose to handle them as special cases separately.
+    # Backward support for opset versions beyond opset 7 is not in our roadmap.
+
+    # For opset versions other than 9, by default they will inherit the symbolic functions defined in
+    # symbolic_opset9.py.
+    # To extend support for updated operators in different opset versions on top of opset 9,
+    # simply add the updated symbolic functions in the respective symbolic_opset{version}.py file.
     # Checkout topk in symbolic_opset10.py, and upsample_nearest2d in symbolic_opset8.py for example.
     iter_version = version
     while iter_version != 9:
