aoti_torch__reinterpret_tensor (pytorch#14688)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* pytorch#14690
* pytorch#14689
* __->__ pytorch#14688
* pytorch#14687
* pytorch#14686

Summary:

Introduced aoti_torch__reinterpret_tensor, which creates a new tensor
view that reinterprets the same underlying memory with custom shape and
strides.

Reviewed By:

Differential Revision:

Author: larryliu0820

backends/cuda/runtime/shims/memory.cpp

@@ -25,6 +25,8 @@ namespace cuda {
 
 using executorch::aten::SizesType;
 using executorch::aten::StridesType;
+using executorch::backends::aoti::aoti_torch_get_device_index;
+using executorch::backends::aoti::aoti_torch_get_dtype;
 using executorch::backends::aoti::dtype_to_element_size;
 using executorch::backends::aoti::dtype_to_scalar_type;
 using executorch::backends::aoti::validate_storage_offset;
@@ -310,6 +312,121 @@ AOTITorchError aoti_torch_delete_tensor_object(Tensor* tensor) {
   return Error::Internal;
 }
 
+AOTITorchError aoti_torch__reinterpret_tensor(
+    Tensor* self,
+    int64_t ndim,
+    const int64_t* sizes_ptr,
+    const int64_t* strides_ptr,
+    int64_t storage_offset,
+    Tensor** ret_new_tensor) {
+  // Validate input parameters first
+  if (self == nullptr) {
+    ET_LOG(Error, "aoti_torch__reinterpret_tensor failed: self tensor is null");
+    return Error::InvalidArgument;
+  }
+
+  if (sizes_ptr == nullptr && ndim > 0) {
+    ET_LOG(Error, "aoti_torch__reinterpret_tensor failed: sizes_ptr is null");
+    return Error::InvalidArgument;
+  }
+
+  if (ret_new_tensor == nullptr) {
+    ET_LOG(
+        Error, "aoti_torch__reinterpret_tensor failed: ret_new_tensor is null");
+    return Error::InvalidArgument;
+  }
+
+  // Check if storage_offset is not 0 - return error if not
+  AOTITorchError storage_offset_error = validate_storage_offset(storage_offset);
+  if (storage_offset_error != Error::Ok) {
+    return storage_offset_error;
+  }
+
+  // Get the device info from the source tensor to perform device_index
+  // validation
+  int32_t device_type = 0;
+  int32_t device_index = 0;
+  AOTITorchError device_error = aoti_torch_get_device_type(self, &device_type);
+  if (device_error != Error::Ok) {
+    return device_error;
+  }
+
+  device_error = aoti_torch_get_device_index(self, &device_index);
+  if (device_error != Error::Ok) {
+    return device_error;
+  }
+
+  // Ensure device_index is always 0
+  if (device_index != 0) {
+    ET_LOG(Error, "device_index must be 0, got: %d", device_index);
+    return Error::InvalidArgument;
+  }
+
+  // Get the dtype from the source tensor
+  int32_t dtype = 0;
+  AOTITorchError dtype_error = aoti_torch_get_dtype(self, &dtype);
+  if (dtype_error != Error::Ok) {
+    return dtype_error;
+  }
+
+  // Validate dtype using SupportedDTypes
+  dtype_error = validate_dtype(dtype);
+  if (dtype_error != Error::Ok) {
+    return dtype_error;
+  }
+
+  // Get the original data pointer from the source tensor
+  void* data_ptr = self->mutable_data_ptr();
+  if (data_ptr == nullptr) {
+    ET_LOG(Error, "Source tensor has null data pointer");
+    return Error::InvalidArgument;
+  }
+
+  // Check if the given memory is in the map, if not return error
+  auto memory_it = memory_to_n_tensor.find(data_ptr);
+  if (memory_it == memory_to_n_tensor.end()) {
+    ET_LOG(
+        Error,
+        "Memory address %p is not being tracked by reference counting system",
+        data_ptr);
+    return Error::InvalidArgument;
+  }
+
+  // Convert sizes using utility function from utils.h
+  std::vector<SizesType> sizes = convert_sizes_to_vector(ndim, sizes_ptr);
+
+  // Convert strides using utility function from utils.h
+  std::vector<StridesType> strides =
+      convert_strides_to_vector(ndim, sizes_ptr, strides_ptr);
+
+  // Create new tensor view that reinterprets the same memory with different
+  // shape/strides This creates a view, not a copy - the data pointer is shared
+  std::shared_ptr<Tensor> tensor = executorch::extension::from_blob(
+      data_ptr, // Reuse the same memory from source tensor
+      sizes, // New sizes with explicit SizesType
+      strides, // New strides with explicit StridesType
+      dtype_to_scalar_type(dtype) // Convert dtype with explicit type casting
+  );
+
+  if (!tensor) {
+    ET_LOG(Error, "Failed to create reinterpreted tensor view");
+    return Error::InvalidArgument;
+  }
+
+  // Store the tensor so it doesn't get destroyed
+  tensors.insert(tensor);
+
+  *ret_new_tensor = tensor.get();
+
+  // Increment the reference count for this memory address only if it is owned
+  // by tensor
+  memory_to_n_tensor[data_ptr] = memory_to_n_tensor[data_ptr] == NOT_OWN
+      ? NOT_OWN
+      : memory_to_n_tensor[data_ptr] + 1;
+
+  return Error::Ok;
+}
+
 } // extern "C"
 
 } // namespace cuda

backends/cuda/runtime/shims/memory.h

@@ -91,6 +91,31 @@ AOTITorchError aoti_torch_empty_strided(
  */
 AOTITorchError aoti_torch_delete_tensor_object(Tensor* tensor);
 
+/**
+ * Creates a tensor view that reinterprets the same underlying memory with
+ * different shape and strides without copying data.
+ *
+ * Note that the new tensor will not have the ownership of the underlying
+ * memory.
+ *
+ * @param self Input tensor whose memory will be reinterpreted
+ * @param ndim Number of dimensions for the new tensor view
+ * @param sizes_ptr Array of sizes for each dimension
+ * @param strides_ptr Array of strides for each dimension (or nullptr for
+ * contiguous)
+ * @param storage_offset Storage offset (must be 0)
+ * @param ret_new_tensor Output pointer to store the new tensor view
+ *
+ * @return Error::Ok on success, appropriate error code on failure
+ */
+AOTITorchError aoti_torch__reinterpret_tensor(
+    Tensor* self,
+    int64_t ndim,
+    const int64_t* sizes_ptr,
+    const int64_t* strides_ptr,
+    int64_t storage_offset,
+    Tensor** ret_new_tensor);
+
 // Function to clear all tensors from internal storage
 void clear_all_tensors();
 } // extern "C"

backends/cuda/runtime/shims/tests/targets.bzl

@@ -30,3 +30,4 @@ def define_common_targets():
     cuda_shim_cpp_unittest("aoti_torch_empty_strided")
     cuda_shim_cpp_unittest("aoti_torch_delete_tensor_object")
     cuda_shim_cpp_unittest("aoti_torch_create_tensor_from_blob_v2")
+    cuda_shim_cpp_unittest("aoti_torch__reinterpret_tensor")