[Relay][Frontend][Onnx] Refactor where importer to support dynamic sh…

…apes. (apache#7394)

* Refactor where importer to support dynamic shapes.

* Add a test for dynamic where.

python/tvm/relay/frontend/onnx.py

@@ -1560,34 +1560,26 @@ class Where(OnnxOpConverter):
 
     @classmethod
     def _impl_v9(cls, inputs, attr, params):
-        condition_shape = infer_shape(inputs[0])
-        x_shape = infer_shape(inputs[1])
-        y_shape = infer_shape(inputs[2])
-
-        # condition, x, and y can all be broadcasted.
-        # broadcast each of them to the longest shape.
-        # if two shapes have the same number of dimensions,
-        # try to choose the one that doesn't have "1" as
-        # a dimension.
-        shapes = [condition_shape, x_shape, y_shape]
-        shape_lens = [len(shape) for shape in shapes]
-        max_size = max(shape_lens)
-        max_size_idxs = [i for i, x in enumerate(shape_lens) if x == max_size]
-        broadcast_idx = max_size_idxs[0]
-        if len(max_size_idxs) > 1:
-            for idx in max_size_idxs:
-                if 1 not in shapes[idx]:
-                    broadcast_idx = idx
-
-        broadcast_shape = shapes[broadcast_idx]
-
-        if condition_shape != broadcast_shape:
-            inputs[0] = _op.broadcast_to(inputs[0], broadcast_shape)
-        if x_shape != broadcast_shape:
-            inputs[1] = _op.broadcast_to(inputs[1], broadcast_shape)
-        if y_shape != broadcast_shape:
-            inputs[2] = _op.broadcast_to(inputs[2], broadcast_shape)
-        return _op.where(inputs[0], inputs[1], inputs[2])
+        condition_rank = len(infer_shape(inputs[0]))
+        x_rank = len(infer_shape(inputs[1]))
+        y_rank = len(infer_shape(inputs[2]))
+        ranks = [condition_rank, x_rank, y_rank]
+
+        # If one rank is longer than others, then we can broadcast
+        # to that shape.
+        max_rank = max(ranks)
+        max_rank_idxs = [i for i, x in enumerate(ranks) if x == max_rank]
+        broadcast_shape = _op.shape_of(inputs[max_rank_idxs[0]])
+        # If two or more inputs have the same rank, compute the broadcast
+        # shape by taking the maximum value of each dimensions.
+        if len(max_rank_idxs) > 1:
+            for idx in max_rank_idxs:
+                broadcast_shape = _op.maximum(broadcast_shape, _op.shape_of(inputs[idx]))
+
+        condition = _op.broadcast_to(inputs[0], broadcast_shape)
+        x = _op.broadcast_to(inputs[1], broadcast_shape)
+        y = _op.broadcast_to(inputs[2], broadcast_shape)
+        return _op.where(condition, x, y)
 
 
 class Or(Elemwise):

tests/python/frontend/onnx/test_forward.py

@@ -2107,10 +2107,18 @@ def test_erf():
     verify_erf(x, z)
 
 
-def verify_where(condition, x, y, dtype, outdata):
-    node = helper.make_node("Where", inputs=["condition", "x", "y"], outputs=["out"])
+def verify_where(condition, x, y, dtype, outdata, dynamic=False):
+    node_list = []
+    where_inputs = ["condition", "x", "y"]
+    if dynamic:
+        shape_node = helper.make_node("Shape", ["x"], ["shape"])
+        reshape_node = helper.make_node("Reshape", ["x", "shape"], ["X"])
+        where_inputs[1] = "X"
+        node_list += [shape_node, reshape_node]
+    node = helper.make_node("Where", inputs=where_inputs, outputs=["out"])
+    node_list.append(node)
     graph = helper.make_graph(
-        [node],
+        node_list,
         "where_test",
         inputs=[
             helper.make_tensor_value_info("condition", TensorProto.BOOL, list(condition.shape)),
@@ -2120,7 +2128,7 @@ def verify_where(condition, x, y, dtype, outdata):
         outputs=[helper.make_tensor_value_info("out", dtype, list(outdata.shape))],
     )
     model = helper.make_model(graph, producer_name="where_test")
-    verify_with_ort_with_inputs(model, [condition, x, y], [outdata.shape])
+    verify_with_ort_with_inputs(model, [condition, x, y], [outdata.shape], use_vm=True)
 
 
 @tvm.testing.uses_gpu
@@ -2156,6 +2164,7 @@ def test_where():
     y = np.array([[1], [7]], dtype=np.float32)
     outdata = np.where(condition, x, y)
     verify_where(condition, x, y, TensorProto.FLOAT, outdata)
+    verify_where(condition, x, y, TensorProto.FLOAT, outdata, dynamic=True)
 
 
 def verify_or(indata, dtype):