Arm backend: Improve noop handling

backends/arm/_passes/remove_noop_pass.py

@@ -1,4 +1,4 @@
-# Copyright 2024-2025 Arm Limited and/or its affiliates.
+# Copyright 2024-2026 Arm Limited and/or its affiliates.
 # All rights reserved.
 #
 # This source code is licensed under the BSD-style license found in the
@@ -25,7 +25,9 @@ def call_operator(self, op, args, kwargs, meta):
         if op not in (
             exir_ops.edge.dim_order_ops._clone_dim_order.default,
             exir_ops.edge.dim_order_ops._to_dim_order_copy.default,
+            exir_ops.edge.aten.alias_copy.default,
             exir_ops.edge.aten.copy.default,
+            exir_ops.edge.aten.detach_copy.default,
         ):
             return super().call_operator(op, args, kwargs, meta)
 

backends/arm/operators/__init__.py

@@ -69,5 +69,4 @@
     op_where,
     op_while,
     ops_binary,
-    ops_identity,
 )

backends/arm/test/ops/test_detach_copy.py

@@ -31,7 +31,7 @@ class DetachCopy(torch.nn.Module):
     exir_op = exir_op
 
     def forward(self, x: torch.Tensor):
-        return torch.detach_copy(x)
+        return torch.detach_copy(x) + 1
 
 
 @common.parametrize("test_data", test_data_suite)

backends/arm/tosa/partitioner.py

@@ -46,68 +46,27 @@
 logger = logging.getLogger(__name__)
 
 
-def is_noop_clone(node: torch.fx.node.Node) -> bool:
-    """Return True if the node is a no-op ``dim_order_ops._clone_dim_order``.
-
-    Args:
-        node (torch.fx.Node): FX node to inspect.
-
-    Returns:
-        bool: True if the node targets ``dim_order_ops._clone_dim_order.default``
-        in the Edge dialect; otherwise, False.
-
-    """
+def _is_noop_clone(node: torch.fx.node.Node) -> bool:
     return node.target == exir_ops.edge.dim_order_ops._clone_dim_order.default
 
 
-def is_noop_alias_copy(node: torch.fx.Node) -> bool:
-    """Return True if the node is a no-op ``aten.alias_copy``.
-
-    Args:
-        node (torch.fx.Node): FX node to inspect.
-
-    Returns:
-        bool: True if the node targets ``aten.alias_copy.default``; otherwise,
-        False.
-
-    """
+def _is_noop_alias_copy(node: torch.fx.Node) -> bool:
     return node.target == exir_ops.edge.aten.alias_copy.default
 
 
-def is_noop_to_dim_order_copy(node: torch.fx.node.Node) -> bool:
-    """Return True if node is a no-op ``dim_order_ops._to_dim_order_copy``.
+def _is_noop_detach_copy(node: torch.fx.Node) -> bool:
+    return node.target == exir_ops.edge.aten.detach_copy.default
 
-    Consider the op a no-op when the output dtype equals the input's dtype.
 
-    Args:
-        node (torch.fx.Node): FX node to inspect.
-
-    Returns:
-        bool: True if it targets ``_to_dim_order_copy.default`` and preserves
-        dtype; otherwise, False.
-
-    """
+def _is_noop_to_dim_order_copy(node: torch.fx.node.Node) -> bool:
     if node.target != exir_ops.edge.dim_order_ops._to_dim_order_copy.default:
         return False
     else:
         input_node = ensure_type(torch.fx.Node, node.args[0])
         return node.meta.get("dtype") == get_first_fake_tensor(input_node).dtype
 
 
-def is_noop_expand(node: torch.fx.node.Node) -> bool:
-    """Return True if the node is an ``expand_copy`` with all-ones multiples.
-
-    This corresponds to a semantic no-op, since expanding by 1 along every
-    dimension leaves the tensor unchanged.
-
-    Args:
-        node (torch.fx.Node): FX node to inspect.
-
-    Returns:
-        bool: True if the node targets ``aten.expand_copy.default`` and all
-        computed multiples are 1; otherwise, False.
-
-    """
+def _is_noop_expand(node: torch.fx.node.Node) -> bool:
     if node.target != exir_ops.edge.aten.expand_copy.default:
         return False
     else:
@@ -291,10 +250,11 @@ def _tag_module(  # noqa
                 )
 
             is_noop_partition = all(
-                is_noop_clone(node)
-                or is_noop_alias_copy(node)
-                or is_noop_expand(node)
-                or is_noop_to_dim_order_copy(node)
+                _is_noop_clone(node)
+                or _is_noop_alias_copy(node)
+                or _is_noop_detach_copy(node)
+                or _is_noop_expand(node)
+                or _is_noop_to_dim_order_copy(node)
                 or node.target in Q_OPS
                 or node.target in DQ_OPS
                 for node in partition.nodes