[Relax][Frontend][Onnx] fix expand bug in onnx frontend (#17309)

* fix expand bug in onnx frontend

* add test expand_with_diff_dim

Author: HongHongHongL

python/tvm/relax/frontend/onnx/onnx_frontend.py

@@ -1135,6 +1135,8 @@ def _impl_v13(cls, bb, inputs, attr, params):
             # For some reason, onnx allows target shapes to be smaller than input shapes.
             # We need to go correct it.
             data_shape = [dim.value for dim in data.struct_info.shape]
+            # Dimensions are right alignment.
+            data_shape = [1] * (len(new_shape) - len(data_shape)) + data_shape
             # Fix small target shapes.
             for i, s in enumerate(new_shape):
                 if i < len(data_shape) and s < data_shape[i]:

tests/python/relax/test_frontend_onnx.py

@@ -1118,6 +1118,12 @@ def _test_expand(name, data, shape, ref_data):
     ref_data = np.tile(data, 4)
     _test_expand("expand_with_dim_unchanged_test", data, shape, ref_data)
 
+    in_shape = (3, 1)
+    shape = (1, 3, 4)
+    data = np.random.uniform(size=in_shape).astype(np.float32)
+    ref_data = np.tile(data, (1, 1, 4))
+    _test_expand("expand_with_diff_dim", data, shape, ref_data)
+
 
 # TODO(jwfromm) Current approach to dynamic expand is technically not well formed. Reenable once fixed.
 @pytest.mark.skip("Produces ill-formed IR")