Fix retracing in FuseViewCopyTransform

Since the pass can change shapes of ops,
the graph needs to be retraced to show this in node.meta["val"].

Signed-off-by: Erik Lundell <[email protected]>
Change-Id: Ief24fe9d11384a2d0f64f0d91070eca7b0caf18e

Author: Erik-Lundell

backends/transforms/fuse_view_copy.py

@@ -1,5 +1,6 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # All rights reserved.
+# Copyright 2025 Arm Limited and/or its affiliates.
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
@@ -11,13 +12,14 @@
 from executorch.exir.pass_base import ExportPass, PassResult
 
 
-def merge_view_copy_chains(graph: torch.fx.Graph) -> torch.fx.Graph:
+def merge_view_copy_chains(graph: torch.fx.Graph) -> tuple[torch.fx.Graph, bool]:
     """
     Find chains of view_copy nodes and merge them into one view_copy node.
     Only merges view_copy nodes that are not used by any other nodes.
     """
     ops = exir_ops.edge
     view_op = ops.aten.view_copy.default
+    modified = False
     for node in graph.nodes:
         if node.op == "call_function" and node.target == view_op:
             # find ending view_copy node in chain
@@ -35,29 +37,36 @@ def merge_view_copy_chains(graph: torch.fx.Graph) -> torch.fx.Graph:
                     new_args = (node.args[0], end_node.args[1])
                     node.args = new_args
                     end_node.replace_all_uses_with(node)
+                modified = True
 
     graph.eliminate_dead_code()
-    return graph
+    return graph, modified
 
 
-def remove_noop_view_copy(graph: torch.fx.Graph) -> torch.fx.Graph:
+def remove_noop_view_copy(graph: torch.fx.Graph) -> tuple[torch.fx.Graph, bool]:
     """
     Remove view_copy nodes that are no-ops.
     """
     ops = exir_ops.edge
     view_op = ops.aten.view_copy.default
+    modified = False
     for node in graph.nodes:
         if node.op == "call_function" and node.target == view_op:
             input_shape = list(node.args[0].meta["val"].shape)
             target_shape = node.args[1]
             if input_shape == target_shape:
                 node.replace_all_uses_with(node.args[0])
+                modified = True
     graph.eliminate_dead_code()
-    return graph
+    return graph, modified
 
 
 class FuseViewCopyTransform(ExportPass):
     def call(self, graph_module: torch.fx.GraphModule) -> PassResult:
-        graph_module.graph = merge_view_copy_chains(graph_module.graph)
-        graph_module.graph = remove_noop_view_copy(graph_module.graph)
-        return PassResult(graph_module, True)
+        graph_module.graph, merge_modified = merge_view_copy_chains(graph_module.graph)
+        graph_module.graph, noop_modified = remove_noop_view_copy(graph_module.graph)
+        modified = merge_modified or noop_modified
+        if modified:
+            graph_module.recompile()
+            graph_module = super().call(graph_module).graph_module
+        return PassResult(graph_module, modified)