[slimtensor] Add factory functions for creating empty CPU tensors

backends/aoti/slim/core/Storage.h

@@ -8,12 +8,13 @@
 
 #pragma once
 
-#include <cstdint>
 #include <cstring>
 
 #include <executorch/backends/aoti/slim/c10/core/Device.h>
 #include <executorch/backends/aoti/slim/c10/core/ScalarType.h>
+#include <executorch/backends/aoti/slim/util/ArrayRefUtil.h>
 #include <executorch/backends/aoti/slim/util/SharedPtr.h>
+#include <executorch/backends/aoti/slim/util/SizeUtil.h>
 #include <executorch/runtime/platform/assert.h>
 
 namespace executorch::backends::aoti::slim {
@@ -242,4 +243,20 @@ class MaybeOwningStorage {
 /// Multiple tensors can share the same underlying storage.
 using Storage = SharedPtr<MaybeOwningStorage>;
 
+/// Creates a new owning storage with the given parameters.
+/// @param sizes The sizes of each dimension.
+/// @param strides The strides of each dimension.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The target device (must be CPU).
+/// @return A shared pointer to the newly allocated storage.
+inline Storage new_storage(
+    IntArrayRef sizes,
+    IntArrayRef strides,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE) {
+  size_t nbytes =
+      compute_storage_nbytes(sizes, strides, c10::elementSize(dtype), 0);
+  return Storage(new MaybeOwningStorage(device, nbytes));
+}
+
 } // namespace executorch::backends::aoti::slim

backends/aoti/slim/core/targets.bzl

@@ -13,7 +13,9 @@ def define_common_targets():
         exported_deps = [
             "//executorch/backends/aoti/slim/c10/core:device",
             "//executorch/backends/aoti/slim/c10/core:scalar_type",
+            "//executorch/backends/aoti/slim/util:array_ref_util",
             "//executorch/backends/aoti/slim/util:shared_ptr",
+            "//executorch/backends/aoti/slim/util:size_util",
             "//executorch/runtime/platform:platform",
         ],
     )

backends/aoti/slim/factory/Empty.h

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+#include <executorch/backends/aoti/slim/core/SlimTensor.h>
+#include <executorch/backends/aoti/slim/util/ArrayRefUtil.h>
+#include <executorch/backends/aoti/slim/util/SizeUtil.h>
+
+namespace executorch::backends::aoti::slim {
+
+/// Creates an empty tensor with the specified sizes and strides.
+/// The tensor owns its underlying storage, which is allocated but
+/// uninitialized.
+///
+/// @param sizes The sizes of each dimension.
+/// @param strides The strides of each dimension.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The target device (must be CPU).
+/// @return A new SlimTensor with allocated but uninitialized storage.
+inline SlimTensor empty_strided(
+    IntArrayRef sizes,
+    IntArrayRef strides,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE) {
+  Storage storage = new_storage(sizes, strides, dtype, device);
+  return SlimTensor(std::move(storage), sizes, strides, dtype, 0);
+}
+
+/// Creates an empty contiguous tensor with the specified sizes.
+/// The tensor owns its underlying storage, which is allocated but
+/// uninitialized. Strides are computed automatically to be contiguous
+/// (row-major order).
+///
+/// @param sizes The sizes of each dimension.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The target device (must be CPU).
+/// @return A new SlimTensor with contiguous strides and uninitialized storage.
+inline SlimTensor empty(
+    IntArrayRef sizes,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE) {
+  std::vector<int64_t> contig_strides = compute_contiguous_strides(sizes);
+  Storage storage =
+      new_storage(sizes, makeArrayRef(contig_strides), dtype, device);
+  return SlimTensor(
+      std::move(storage), sizes, makeArrayRef(contig_strides), dtype, 0);
+}
+
+/// Creates an empty contiguous tensor with sizes from an initializer list.
+/// Convenience overload for creating tensors with inline size specification.
+///
+/// @param sizes The sizes of each dimension as an initializer list.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The target device (must be CPU).
+/// @return A new SlimTensor with contiguous strides and uninitialized storage.
+inline SlimTensor empty(
+    std::initializer_list<int64_t> sizes,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE) {
+  return empty(makeArrayRef(sizes), dtype, device);
+}
+
+/// Creates an empty tensor with the same sizes, strides, dtype, and device as
+/// another tensor.
+///
+/// @param other The tensor to copy metadata from.
+/// @return A new SlimTensor with the same shape and properties, but
+/// uninitialized storage.
+inline SlimTensor empty_like(const SlimTensor& other) {
+  return empty_strided(
+      other.sizes(), other.strides(), other.dtype(), other.device());
+}
+
+} // namespace executorch::backends::aoti::slim

backends/aoti/slim/factory/TARGETS

@@ -0,0 +1,3 @@
+load("targets.bzl", "define_common_targets")
+
+define_common_targets()

backends/aoti/slim/factory/targets.bzl

@@ -0,0 +1,18 @@
+load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "runtime")
+
+def define_common_targets():
+    """Define targets for SlimTensor factory module."""
+
+    # Header-only library for empty tensor factory functions
+    runtime.cxx_library(
+        name = "empty",
+        headers = [
+            "Empty.h",
+        ],
+        visibility = ["@EXECUTORCH_CLIENTS"],
+        exported_deps = [
+            "//executorch/backends/aoti/slim/core:slimtensor",
+            "//executorch/backends/aoti/slim/util:array_ref_util",
+            "//executorch/backends/aoti/slim/util:size_util",
+        ],
+    )

backends/aoti/slim/factory/test/TARGETS

@@ -0,0 +1,3 @@
+load("targets.bzl", "define_common_targets")
+
+define_common_targets()

backends/aoti/slim/factory/test/targets.bzl

@@ -0,0 +1,14 @@
+load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "runtime")
+
+def define_common_targets():
+    """Define test targets for SlimTensor factory module."""
+
+    runtime.cxx_test(
+        name = "test_empty",
+        srcs = [
+            "test_empty.cpp",
+        ],
+        deps = [
+            "//executorch/backends/aoti/slim/factory:empty",
+        ],
+    )