Handle multiple inplace update input output aliasing

torch_xla/csrc/aten_xla_type.cpp

@@ -29,6 +29,7 @@
 #include "torch_xla/csrc/helpers.h"
 #include "torch_xla/csrc/ops/as_strided.h"
 #include "torch_xla/csrc/ops/as_strided_view_update.h"
+#include "torch_xla/csrc/ops/device_data.h"
 #include "torch_xla/csrc/ops/diagonal_view_update.h"
 #include "torch_xla/csrc/ops/einsum_utilities.h"
 #include "torch_xla/csrc/ops/index_ops.h"
@@ -2538,7 +2539,39 @@ void XLANativeFunctions::_propagate_xla_data(const at::Tensor& input,
   // 1) Aid XLA's InputOutputAlias.
   auto input_tensor = bridge::GetXlaTensor(input);
   auto output_tensor = bridge::GetXlaTensor(output);
-  output_tensor->data()->alias_id = input_tensor->GetUniqueId();
+  if (input_tensor->CurrentDataHandle() != nullptr ||
+      (input_tensor->CurrentIrValue().node != nullptr &&
+       torch_xla::DeviceData::Cast(
+           input_tensor->CurrentIrValue().node.get()))) {
+    /*
+    if input has a XLAData or holds a devicedata node, set alias_id to
+    tensor_id. Consider the case.
+
+    // x.tensor_id = 1, x.alias_id = 1
+    x = torch.randn(5,5).to(xla_device())
+    // x.tensor_id = 2, x.alias_id should be 1
+    x += 1
+    xm.mark_step()
+    // x.tensor_id =3, x.alias_id should be 2 since input tensor id will be 2
+    for
+    // this graph
+    x *= 1 of 1
+    */
+    output_tensor->data()->alias_id = input_tensor->GetUniqueId();
+  } else {
+    /*
+    Consider the case
+
+    // x.tensor_id = 1, x.alias_id = 1
+    x = torch.randn(5,5).to(xla_device())
+    // x.tensor_id = 2, x.alias_id should be 1
+    x += 1
+    // x.tensor_id = 3, x.alias_id should still be 1
+    x * = 2
+    xm.mark_step()
+    */
+    output_tensor->data()->alias_id = input_tensor->data()->alias_id;
+  }
 
   // 2) Aid SPMD.
   XLATensor::ShardingSpecPtr sharding = input_tensor->sharding_spec();