Fix onnx importer to treat Constant values as static (#2780)

Fixes  #2764

In the case of OPT, there are ConstantOfShape ops whose input shape is
not static (that is, an initializer), but rather comes from a Constant
op. The importer can't handle such non-static input shapes.

The fix here is to create initializers for a subset of Constant ops
(ones with "value" attributes), so that their outputs can be used
statically. Additionally, there was no case for creating a splat of
int64, so I added that as well.

---------

Co-authored-by: Dave Liddell <dliddell@xilinx.com>

Author: daveliddell

python/torch_mlir/extras/onnx_importer.py

@@ -276,10 +276,13 @@ def import_node(self, node: onnx.NodeProto):
         with InsertionPoint(self._b), Location.name(node.name):
             op_type = node.op_type
             # Handle special op types that materialize to non-op IR constructs.
+            # Handlers return True if the op was handled, else this function
+            # should process it as a general node.
             special_key = f"_handle_node_{op_type}"
             if hasattr(self, special_key):
-                getattr(self, special_key)(node)
-                return
+                was_handled = getattr(self, special_key)(node)
+                if was_handled:
+                    return
 
             # General node import.
             input_values = []
@@ -333,16 +336,19 @@ def import_attributes(
                 )
             attrs[f"torch.onnx.{onnx_attr.name}"] = handler(onnx_attr, self._cc)
 
-    def import_initializer(self, initializer: onnx.TensorProto) -> Value:
-        with InsertionPoint(self._b), Location.name(initializer.name):
+    def import_initializer(self, initializer: onnx.TensorProto, extern_name: str = None) -> Value:
+        # If an explicitly specified name is given, use that; otherwise, pick
+        # up the name from the tensor proto itself
+        iname = extern_name if extern_name else initializer.name
+        with InsertionPoint(self._b), Location.name(iname):
             value_attr = self._cc.tensor_proto_to_attr(initializer)
             vtensor_type = self._cc.tensor_proto_to_type(initializer)
             literal_op = Operation.create(
                 name="torch.vtensor.literal",
                 results=[vtensor_type],
                 attributes={"value": value_attr},
             )
-            self._nv_map[initializer.name] = literal_op.result
+            self._nv_map[iname] = literal_op.result
         return literal_op.result
 
     def _get_immediate_tensor(self, name: str) -> np.array:
@@ -366,7 +372,23 @@ def _get_immediate_tensor(self, name: str) -> np.array:
                 f"Unhandled ONNX TensorProto immediate data: {initializer}"
             )
 
-    def _handle_node_ConstantOfShape(self, node: onnx.NodeProto):
+    def _handle_node_Constant(self, node: onnx.NodeProto) -> bool:
+        # Special case only for constants specified by value attribute (for now)
+        value_proto = _get_attr(node, "value", False)
+        if not value_proto:
+            return False
+
+        # Produce an initializer for the constant, so that it can be used in
+        # combination with other ops, such as ConstantOfShape, requiring
+        # a constant input
+        assert value_proto.type == onnx.AttributeProto.AttributeType.TENSOR
+        assert len(node.output) == 1
+        const_name = node.output[0]
+        self.import_initializer(value_proto.t, const_name)
+        self._gi.initializer_map[const_name] = value_proto.t
+        return True
+
+    def _handle_node_ConstantOfShape(self, node: onnx.NodeProto) -> bool:
         # This op is special: It has an input of the shape, and in full generality
         # could involve eager production of constants of variable size. In
         # practice, the DNN profile for ONNX makes this very difficult to do
@@ -394,6 +416,7 @@ def _handle_node_ConstantOfShape(self, node: onnx.NodeProto):
             attributes={"value": value_attr},
         )
         self._nv_map[node.output[0]] = literal_op.result
+        return True
 
 
 class ContextCache:
@@ -515,6 +538,11 @@ def tensor_proto_to_attr(self, tp: onnx.TensorProto) -> Attribute:
     onnx.TensorProto.DataType.FLOAT: lambda tp, shape: DenseElementsAttr.get_splat(
         RankedTensorType.get(shape, F32Type.get()), FloatAttr.get_f32(tp.float_data[0])
     ),
+    onnx.TensorProto.DataType.INT64: lambda tp, shape: DenseElementsAttr.get_splat(
+        RankedTensorType.get(shape, IntegerType.get_signed(64)), IntegerAttr.get(
+        IntegerType.get_signed(64), int.from_bytes(tp.raw_data, "little",
+        signed=True) if tp.HasField("raw_data") else tp.int64_data[0])
+    ),
     # TODO: All the rest from ELEM_TYPE_TO_IR_TYPE_CB
 }
 
@@ -605,9 +633,10 @@ def tensor_proto_to_attr(self, tp: onnx.TensorProto) -> Attribute:
 }
 
 
-def _get_attr(node: onnx.NodeProto, attr_name: str) -> onnx.AttributeProto:
+def _get_attr(node: onnx.NodeProto, attr_name: str, is_required: bool = True) -> onnx.AttributeProto:
     for attr in node.attribute:
         if attr.name == attr_name:
             return attr
-    else:
+    if is_required:
         raise OnnxImportError(f"Required attribute {attr_name} not found in {node}")
+    return None