Log backward no-op to tlparse and pt2 compile events. (#154544)

Summary: Log backward no-op to tlparse and pt2 compile events.

Test Plan:
$ rm -rf /tmp/r && TORCH_TRACE=/tmp/r buck2 run //scripts/jovian:backward_noop_repro_compile

Used print statements to verify we enter the logging code region.

Differential Revision: D75231665

Pull Request resolved: https://github.com/pytorch/pytorch/pull/154544
Approved by: https://github.com/c00w

test/inductor/test_aot_inductor.py

@@ -2590,6 +2590,29 @@ class AOTInductorTestsTemplate:
         example_inputs = (torch.randn(8, 4, 4, device=self.device),)
         self.check_model(Model(), example_inputs)
 
+    @patch("torch._dynamo.utils.CompileEventLogger.log_instant_event")
+    def test_backward_no_op_logging(self, mock_log_instant_event):
+        class Model(torch.nn.Module):
+            def __init__(self) -> None:
+                super().__init__()
+
+            def forward(self, x):
+                return x
+
+        model = Model()
+        dummy_input = torch.randn(1, 5)
+
+        from torch._dynamo.utils import CompileEventLogLevel
+        from torch._inductor import compile_fx
+
+        graph_module = torch.fx.symbolic_trace(model)
+        compile_fx._compile_fx_inner(graph_module, (dummy_input,))
+        mock_log_instant_event.assert_called_once_with(
+            "backward no-op",
+            metadata={"compile_id": None},
+            log_level=CompileEventLogLevel.PT2_COMPILE,
+        )
+
     @unittest.skipIf(IS_FBCODE, "Not runnable in fbcode")
     def test_dup_unbacked_sym_decl(self):
         class Model(torch.nn.Module):

torch/_inductor/compile_fx.py

@@ -742,9 +742,17 @@ def _compile_fx_inner(
     if dynamo_utils.count_calls(gm.graph) == 0 and not aot_mode:
         # trigger the real recompilation for _LazyGraphModule before returning
         # the forward method.
+        from torch._dynamo.utils import CompileEventLogLevel
         from torch.fx._lazy_graph_module import _LazyGraphModule
 
         _LazyGraphModule.force_recompile(gm)
+        compile_id = torch._guards.CompileContext.current_compile_id()
+        CompileEventLogger.log_instant_event(
+            "backward no-op",
+            metadata={"compile_id": compile_id},
+            log_level=CompileEventLogLevel.PT2_COMPILE,
+        )
+
         return make_boxed_func(gm.forward)
 
     static_input_idxs: Sequence[int] = graph_kwargs.setdefault("static_input_idxs", ())