Update aten_index_put implementation (#2712)

Author: gramalingam

onnxscript/function_libs/torch_lib/ops/core.py

@@ -4541,80 +4541,135 @@ def aten_index_put(
     See implementation of `torch.onnx.symbolic_opset11.index_put
     <https://github.com/pytorch/pytorch/blob/main/torch/onnx/symbolic_opset11.py#L212>`_.
     """
-
-    def _make_reshape_list_broadcastable(reshape_list, values_shape):
-        # Remove ones until the rank of reshape_list matches values_shape.
-        while len(reshape_list) > len(values_shape) and 1 in reshape_list:
-            reshape_list.remove(1)
-
-        # Now ensure each dimension is broadcastable:
-        # This is mandatory when mixing basic and advanced indexing
-        # Example: data((10, 3, 4)), indices([[0, 1], :, [0, 1]]) values(2, 3)
-        # the reshape list should be : [[2, 1], [1, 3], [2, 1]]
-        for i, r in enumerate(reshape_list):
-            if r not in (1, values_shape[i]):
-                value_index = values_shape.index(r)
-                # Swap elements
-                # For the example above the current reshape list is [1, 2] for last dim,
-                # to make it broadcastable, we swap the elements
-                reshape_list[value_index], reshape_list[i] = r, 1
-
-        return reshape_list
-
-    # Ensure the number of indices matches the tensor rank.
+    # Ensure the number of indices matches the tensor rank by appending trailing Nones.
     self_rank = len(self.shape)
     if len(indices) < self_rank:
         indices = list(indices) + [None] * (self_rank - len(indices))
 
-    # Get values shape
-    values_shape = tuple(values.shape)
+    # The behavior of the op is dependent on whether there are advanced indices (i.e., non-scalar tensors)
+    # and whether these advanced indices are contiguous.
+
+    # Identify advanced indices.
+    def is_advanced_index(index):
+        # Note: In this function, the index is assumed to be either None or an int64 Tensor.
+        return index is not None
+
+    advanced_indices: list[int] = []
+    none_indices: list[int] = []
+    num_advanced_indices = 0
+    num_none_indices = 0
+
+    for i, index in enumerate(indices):
+        if is_advanced_index(index):
+            advanced_indices.append(i)
+            num_advanced_indices += 1
+        elif index is None:
+            none_indices.append(i)
+            num_none_indices += 1
+        else:
+            raise ValueError(f"Unhandled index at position {i}: {index}")
 
-    index_vectors = []
-    for i in range(self_rank):
-        if indices[i] is None:
-            # For a full slice along dim i, create a range index [0, self.shape[i]).
-            idx = op.Range(0, self.shape[i], 1)
-            reshape_update = self.shape[i]
+    self_shape = op.Shape(self)
+    if num_advanced_indices == 0:
+        return op.Expand(values, self_shape)
+
+    # More than one advanced index may require broadcasting of index values
+    if num_advanced_indices > 1:
+        # Check for special case where all advanced indices have same shape.
+        # But need to ensure none of the shapes have None as a dimension, which
+        # will invalidate equality-based check.
+        first_shape = indices[advanced_indices[0]].shape
+
+        def same_shape(other_shape: ir.Shape) -> bool:
+            return (not any(d is None for d in other_shape)) and other_shape == first_shape
+
+        all_same_shape = all(same_shape(indices[i].shape) for i in advanced_indices)
+        if not all_same_shape:
+            # Broadcast advanced indices to a common shape.
+            advanced_index_rank = max(len(indices[i].shape) for i in advanced_indices)
+            shapes = []
+            for i in advanced_indices:
+                index = indices[i]
+                index_rank = len(index.shape)
+                index_shape = op.Shape(index)
+                if index_rank < advanced_index_rank:
+                    padding = op.Constant(
+                        value_ints=[1 for _ in range(advanced_index_rank - index_rank)]
+                    )
+                    index_shape = op.Concat(padding, index_shape, axis=0)
+                shapes.append(index_shape)
+            advanced_indices_shape = op.Max(*shapes)
+            indices = [
+                op.Expand(index, advanced_indices_shape) if is_advanced_index(index) else index
+                for index in indices
+            ]
         else:
-            idx = indices[i]
-            reshape_update = math.prod(idx.shape)
-            # when Index is more than 1D, flatten it and also the values shape
-            # Example: self shape: (10, 3), indices[i] shape: (2, 4), values shape: (2, 4, 3)
-            # Indices -> (2*4,) and values shape (2*4, 32)
-            if len(idx.shape) > 1:
-                values_shape = (reshape_update, *values_shape[len(idx.shape) :])
-
-            # Flatten index (always working with 1D index in each dim)
-            idx = op.Reshape(idx, [-1])
-
-        # Create a reshape pattern: one value per index dimension,
-        # with the current dimension set to the update size.
-        reshape_list = [1] * len(indices)
-        reshape_list[i] = reshape_update
-
-        # Adjust the reshape list to match the values shape.
-        reshape_list = _make_reshape_list_broadcastable(reshape_list, values_shape)
-
-        # Reshape and expand the index.
-        idx = op.Reshape(idx, reshape_list, allowzero=True)
-        idx = op.Expand(idx, values_shape)
-
-        # Flatten the index to 1D and unsqueeze to form a column vector.
-        idx = op.Reshape(idx, [-1])
-        idx = op.Unsqueeze(idx, axes=[1])
-        index_vectors.append(idx)
-
-    # Concatenate the index vectors along axis=1 to form the final indices.
-    new_index = op.Concat(*index_vectors, axis=1)
-
-    # Flatten values to match the indices
-    flat_values = op.Reshape(values, [-1])
-
-    if accumulate:
-        result = op.ScatterND(self, new_index, flat_values, reduction="add")
+            advanced_indices_shape = op.Shape(indices[advanced_indices[0]])
+            advanced_index_rank = len(indices[advanced_indices[0]].shape)
     else:
-        result = op.ScatterND(self, new_index, flat_values)
+        advanced_indices_shape = op.Shape(indices[advanced_indices[0]])
+        advanced_index_rank = len(indices[advanced_indices[0]].shape)
+
+    # ONNX ScatterND supports only the case where all advanced indices appear first,
+    # followed by None indices. So, we need to transpose self and values so that the
+    # advanced indices appear first, and then transpose the result back to original
+    # order at the end.
+
+    none_indices_constant = op.Constant(value_ints=none_indices)
+    none_indices_shape = op.Gather(self_shape, none_indices_constant, axis=0)
+    target_shape = op.Concat(advanced_indices_shape, none_indices_shape, axis=0)
+    target_rank = advanced_index_rank + num_none_indices
+
+    # Generate indices tensor required by ONNX ScatterND by unsqueezing an extra dimension and
+    # concatenating all advanced indices along this new dimension.
+    minus_one = op.Constant(value_ints=[-1])
+    advanced_index_values = [op.Unsqueeze(indices[i], minus_one) for i in advanced_indices]
+    onnx_index = op.Concat(*advanced_index_values, axis=-1)
+
+    # Check if advanced indices are contiguous:
+    contiguous = True
+    if advanced_indices:
+        if advanced_indices[-1] - advanced_indices[0] + 1 != len(advanced_indices):
+            contiguous = False
+
+    # Bring advanced indices to front:
+    perm = advanced_indices + none_indices
+    transposed = op.Transpose(self, perm=perm)
+
+    # Expand values to match target shape:
+    # First, transpose values if necessary to match advanced indices order!
+    if contiguous:
+        # values may need to be transposed before expanding to target shape
+        num_padded_dims = target_rank - len(values.shape)
+        if num_padded_dims > 0:
+            unsqueezed_dims = op.Constant(value_ints=list(range(num_padded_dims)))
+            values = op.Unsqueeze(values, unsqueezed_dims)
+        initial_none_index_positions = list(range(advanced_indices[0]))
+        advanced_index_replacement_positions = list(
+            range(advanced_indices[0], advanced_indices[0] + advanced_index_rank)
+        )
+        final_none_index_positions = list(
+            range(advanced_indices[0] + advanced_index_rank, target_rank)
+        )
+        values_perm = (
+            advanced_index_replacement_positions
+            + initial_none_index_positions
+            + final_none_index_positions
+        )
+        values = op.Transpose(values, perm=values_perm)
+
+    expanded_values = op.Expand(values, target_shape)
+
+    updated = op.ScatterND(
+        transposed, onnx_index, expanded_values, reduction="add" if accumulate else None
+    )
+
+    # Inverse transpose to restore original dimension order:
 
+    inverse_perm = [0] * self_rank
+    for i, p in enumerate(perm):
+        inverse_perm[p] = i
+    result = op.Transpose(updated, perm=inverse_perm)
     return result