Use TensorPtr in aten_bridge (#5789)

Summary:
Pull Request resolved: #5789

Want it to be very easy to create an ET Tensor from an at::Tensor if Im cool with the added deps

Differential Revision: D63705432

Author: JacobSzwejbka

extension/aten_util/aten_bridge.cpp

@@ -170,5 +170,12 @@ at::Tensor alias_attensor_to_etensor(const torch::executor::Tensor& etensor) {
   return t;
 }
 
+TensorPtr alias_tensor_ptr_to_attensor(at::Tensor& t) {
+  return make_tensor_ptr(
+      {t.sizes().begin(), t.sizes().end()},
+      t.mutable_data_ptr(),
+      torch::executor::ScalarType(t.scalar_type()));
+}
+
 } // namespace extension
 } // namespace executorch

extension/aten_util/aten_bridge.h

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <executorch/extension/tensor/tensor.h>
 #include <executorch/runtime/core/exec_aten/exec_aten.h>
 
 #include <ATen/Functions.h> // @manual=//caffe2/aten:ATen-cpu
@@ -48,6 +49,8 @@ void alias_etensor_to_attensor(at::Tensor& at, torch::executor::Tensor& et);
  */
 at::Tensor alias_attensor_to_etensor(const torch::executor::Tensor& et);
 
+TensorPtr alias_tensor_ptr_to_attensor(at::Tensor& t);
+
 } // namespace extension
 } // namespace executorch
 

extension/aten_util/test/aten_bridge_test.cpp

@@ -18,6 +18,7 @@
 using namespace ::testing;
 using namespace torch::executor;
 using namespace torch::executor::util;
+using namespace executorch::extension;
 
 namespace {
 at::Tensor generate_at_tensor() {
@@ -146,3 +147,10 @@ TEST(ATenBridgeTest, AliasATTensorToETensor) {
   auto aliased_at_tensor = alias_attensor_to_etensor(etensor);
   EXPECT_EQ(aliased_at_tensor.const_data_ptr(), etensor_data.data());
 }
+
+TEST(ATenBridgeTest, AliasTensorPtrToATenTensor) {
+  auto at_tensor = generate_at_tensor();
+  const auto& et_tensor_ptr = alias_tensor_ptr_to_attensor(at_tensor);
+  alias_etensor_to_attensor(at_tensor, *et_tensor_ptr);
+  EXPECT_EQ(at_tensor.const_data_ptr(), et_tensor_ptr->const_data_ptr());
+}