Minor fixes to onnx to onnxscript converter (#2510)

Minor fixes to onnx to onnxscript converter:
* Embed node name as a comment in generated onnxscript
* Handle sequence types (just for readable representation)
* Minor tweak to handling of initializers, distinguishing small and
large tensors (when replacing them by random values)
* Handle INT8 type initializers, which show up in quantized models.

---------

Signed-off-by: Ganesan Ramalingam <grama@microsoft.com>

Author: gramalingam

onnxscript/backend/onnx_export.py

@@ -13,6 +13,8 @@
 
 _SINGLE_INDENT = "    "
 
+_SMALL_TENSOR_SIZE = 4
+
 kwlist = {
     "False",
     "None",
@@ -119,7 +121,7 @@ def renamer(name):
 
 def _translate_type(onnx_type):
     """Converts a onnx type into a type defined by *onnxscript*."""
-    return onnxscript.onnx_types.onnx_type_to_onnxscript_repr(onnx_type)
+    return onnxscript.onnx_types.onnx_type_to_onnxscript_repr(onnx_type, reversible=False)
 
 
 def _translate_signature(inputs, outputs):
@@ -350,25 +352,33 @@ def _translate_graph_body(self, graph, opsets, indent=0):
         if hasattr(graph, "initializer"):
             for init in graph.initializer:
                 if self.skip_initializers:
-                    init_py_name = self._translate_onnx_var(init.name)
-                    if init_py_name in self.skipped_initializers:
-                        raise RuntimeError(
-                            f"Initializer {init.name!r} is already present in skipped_initializers."
-                        )
-                    self.skipped_initializers[init_py_name] = init
-                    continue
+                    size = 1
+                    for d in init.dims:
+                        size *= d
+                    if size > _SMALL_TENSOR_SIZE:
+                        init_py_name = self._translate_onnx_var(init.name)
+                        if init_py_name in self.skipped_initializers:
+                            raise RuntimeError(
+                                f"Initializer {init.name!r} is already present in skipped_initializers."
+                            )
+                        self.skipped_initializers[init_py_name] = init
+                        continue
                 node = onnx.helper.make_node(  # noqa: TID251
                     "Constant",
                     [],
                     [self._translate_onnx_var(init.name)],  # type: ignore[list-item]
                     value=init,
                 )
-                code.append(self._translate_node(node, opsets, indent=indent))
+                pyinit = self._translate_node(node, opsets, indent=indent)
+                if pyinit:
+                    code.append(pyinit)
         if hasattr(graph, "sparse_initializer") and len(graph.sparse_initializer) > 0:
             raise NotImplementedError("Unable to convert sparse_initilizer into python.")
         for node in graph.node:
             pynode = self._translate_node(node, opsets, indent=indent)
             if pynode:
+                if node.name:
+                    pynode += f"  # {node.name}"
                 code.append(pynode)
 
         final = "\n".join(code)
@@ -418,7 +428,8 @@ def _translate_attributes(self, node):
     def _translate_if(self, node, opsets, indent=0):
         """Translates a node If into python."""
         sindent = _SINGLE_INDENT * indent
-        code = [f"{sindent}if {node.input[0]}:"]
+        cond = self._translate_onnx_var_ref(node.input[0])
+        code = [f"{sindent}if {cond}:"]
         if len(node.attribute) != 2:
             raise RuntimeError(
                 f"Node {node.op_type!r} expected two attributes not {len(node.attribute)}."
@@ -502,17 +513,21 @@ def _translate_loop(self, node, opsets, indent=0):
 
         rows.extend(self._emit_assign(formal_ins, actual_ins, indent))
 
+        if node.name:
+            node_name = "  # " + node.name
+        else:
+            node_name = ""
         if use_iter_var and not use_loop_cond:
-            rows.append(f"{sindent}for {iter_var} in range({n_iter}):")
+            rows.append(f"{sindent}for {iter_var} in range({n_iter}):{node_name}")
             # The following is a hacky way to suppress the generation of
             # "cond_out = cond_in", which ONNX forces for a FOR loop.
             # TODO: a cleaner solution for this.
             self._name_remappings[-1][cond_out] = self._translate_onnx_var(cond_in)
         elif not use_iter_var and use_loop_cond:
-            rows.append(f"{sindent}while {py_cond}:")
+            rows.append(f"{sindent}while {py_cond}:{node_name}")
         elif use_iter_var and use_loop_cond:
             # TODO: This needs fixing
-            rows.append(f"{sindent}for {iter_var} in range({n_iter}):")
+            rows.append(f"{sindent}for {iter_var} in range({n_iter}):{node_name}")
             rows.append(f"{sindent}{_SINGLE_INDENT}if not {py_cond}:")
             rows.append(f"{sindent}{_SINGLE_INDENT * 2}break")
         else:
@@ -734,11 +749,13 @@ def _substitute_initializers(
 
         def generate_rand(name: str, value: TensorProto) -> str:
             shape = ",".join(str(d) for d in value.dims)
-            if value.data_type != TensorProto.FLOAT:
-                raise NotImplementedError(
-                    f"Unable to generate random initializer for data type {value.data_type}."
-                )
-            return f"{__}{name} = np.random.rand({shape}).astype(np.float32)"
+            if value.data_type == TensorProto.FLOAT:
+                return f"{__}{name} = np.random.rand({shape}).astype(np.float32)"
+            if value.data_type == TensorProto.INT8:
+                return f"{__}{name} = np.random.randint(-128, 127, size=({shape},), dtype=np.int8)"
+            raise NotImplementedError(
+                f"Unable to generate random initializer for data type {value.data_type}."
+            )
 
         random_initializer_values = "\n".join(
             generate_rand(key, value) for key, value in self.skipped_initializers.items()

onnxscript/onnx_types.py

@@ -196,11 +196,13 @@ class FLOAT4E2M1(TensorType, dtype=ir.DataType.FLOAT4E2M1):
     pass
 
 
-def onnx_type_to_onnxscript_repr(onnx_type: onnx.TypeProto) -> str:
+def onnx_type_to_onnxscript_repr(onnx_type: onnx.TypeProto, *, reversible: bool = True) -> str:
     """Converts an onnx type into the string representation of the type in *onnxscript*.
 
     Args:
         onnx_type: an instance of onnx TypeProto
+        reversible: if True, the conversion produces only types that are
+            recognized by the onnxscript converter.
 
     Returns:
         The string representation of the type in onnxscript
@@ -224,6 +226,10 @@ def onnx_type_to_onnxscript_repr(onnx_type: onnx.TypeProto) -> str:
                 return name
             return f"{name}[{','.join(shape)}]"
         return f"{name}[...]"
+    if not reversible:
+        if onnx_type.HasField("sequence_type"):
+            elem_type = onnx_type.sequence_type.elem_type
+            return f"List[{onnx_type_to_onnxscript_repr(elem_type)}]"
     raise NotImplementedError(f"Unable to translate type {onnx_type!r} into onnxscript type.")