Arm backend: Add PrintGraphModuleCodePass (#15774)

Inspecting a module between passes that operate on it is often useful
for debugging purposes. This patch adds a pass called
`PrintGraphModuleCodePass` that prints the graph module's code in its
current state. Compared to the already existing `VisualizePass`,
`PrintGraphModuleCodePass` enables quicker feedback when the module is
small enough to be visualized in a text-based print.

Example output from the pass:
```
[arm_pass_manager.py:305]
def forward(self, x, y):
    x, y, = fx_pytree.tree_flatten_spec(([x, y], {}), self._in_spec)
    remainder = torch.ops.aten.remainder.Scalar(x, 0.25);  x = None
    return pytree.tree_unflatten((remainder,), self._out_spec)
```


cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

Signed-off-by: Martin Lindström <Martin.Lindstroem@arm.com>
Co-authored-by: Martin Lindström <Martin.Lindstroem@arm.com>
Co-authored-by: Zingo Andersen <zingo.andersen@arm.com>

Author: 3 people

backends/arm/_passes/_debug_passes.py

@@ -3,13 +3,16 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+import inspect
+import os
 from typing import Set, Type
 
 import torch
 from executorch.backends.arm._passes import ArmPass
 from executorch.devtools.visualization.visualization_utils import visualize_graph
 from executorch.exir import ExportedProgram
 from executorch.exir.pass_base import ExportPass, PassResult
+from torch.fx import GraphModule
 
 
 class VisualizePass(ArmPass):
@@ -26,3 +29,30 @@ def __init__(self, exported_program: ExportedProgram) -> None:
     def call(self, graph_module: torch.fx.GraphModule) -> PassResult:
         visualize_graph(graph_module, self.exported_program)
         return PassResult(graph_module, False)
+
+
+class PrintGraphModuleCodePass(ArmPass):
+    """
+    This pass prints the graph module's code to stdout for debugging purposes.
+
+    Example output:
+
+      [arm_pass_manager.py:305]
+      def forward(self, x, y):
+          x, y, = fx_pytree.tree_flatten_spec(([x, y], {}), self._in_spec)
+          remainder = torch.ops.aten.remainder.Scalar(x, 0.25);  x = None
+          return pytree.tree_unflatten((remainder,), self._out_spec)
+    """
+
+    _passes_required_after: Set[Type[ExportPass]] = set()
+
+    def __init__(self, label: str | None = None):
+        super().__init__()
+        caller_frame = inspect.stack()[1]
+        origin = f"{os.path.basename(caller_frame.filename)}:{caller_frame.lineno}"
+        self.label = f"[{label}]" if label is not None else f"[{origin}]"
+
+    def call(self, graph_module: GraphModule) -> PassResult:
+        gm_code = graph_module.code.strip()
+        print(f"\n{self.label}\n{gm_code}")
+        return PassResult(graph_module, False)