fix(mge/tracing): replace detach as fast path copy

GitOrigin-RevId: d765725d5a

imperative/python/src/tensor.cpp

@@ -541,15 +541,9 @@ PyObject* TensorWrapper::detach() {
     PyObject* self = wrap_t::pycast(this);
     PyTypeObject* pytype = self->ob_type;
 
-    std::shared_ptr<Tensor> new_tensor;
-    if (m_tensor->m_handle.get()) {
-        new_tensor = std::make_shared<Tensor>(m_tensor->m_handle);
-    } else {
-        new_tensor = std::make_shared<Tensor>(m_tensor->m_var);
-    }
-    new_tensor->m_trace_info = m_tensor->m_trace_info;
-
-    new_tensor->m_flags = m_tensor->m_flags;
+    static std::shared_ptr<OpDef> op = std::shared_ptr<OpDef>(new FastpathCopy());
+    auto new_tensor = python::apply(op, m_tensor)[0];
+    new_tensor->m_grad_info_dict = {};
     auto ret = TensorWrapper::make(pytype, std::move(new_tensor));
     return ret.release().ptr();
 }

imperative/python/test/unit/jit/test_tracing.py

@@ -96,6 +96,19 @@ def test_output_copy_trace():
 
 
 @pytest.mark.parametrize("trace_mode", [False, True])
+def test_tensor_detach(trace_mode):
+    @trace(symbolic=True)
+    def f(x):
+        y = x.detach() ** 2
+        z = y.detach() + 1
+        return z.detach()
+
+    x = tensor([1, 2, 3, 4])
+    for _ in range(3):
+        f(x).numpy()
+
+
+@pytest.mark.parametrize("trace_mode", [False, True])
 def test_exclude_from_trace(trace_mode):
     @trace(symbolic=trace_mode)
     def f(x):