[slimtensor] Add from_blob() factory function for wrapping external memory (#16837)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: #16442 by
@Gasoonjia
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ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/84/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/84/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/84/orig
Differential Revision:
[D89950482](https://our.internmc.facebook.com/intern/diff/D89950482/)
@diff-train-skip-merge

Co-authored-by: gasoonjia <gasoonjia@icloud.com>

Author: pytorchbot

backends/aoti/slim/factory/FromBlob.h

@@ -0,0 +1,106 @@
+/*
+ * 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 <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 a SlimTensor that wraps external memory without taking ownership.
+/// The returned tensor does NOT own the underlying storage; the caller is
+/// responsible for keeping the data alive for the lifetime of the tensor.
+///
+/// @param data Pointer to external memory (must not be null).
+/// @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 device where the data resides.
+/// @param storage_offset Offset into storage in number of elements.
+/// @return A new SlimTensor with non-owning storage.
+inline SlimTensor from_blob(
+    void* data,
+    IntArrayRef sizes,
+    IntArrayRef strides,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE,
+    int64_t storage_offset = 0) {
+  ET_CHECK_MSG(data != nullptr, "from_blob: data pointer cannot be nullptr");
+
+  size_t nbytes = compute_storage_nbytes(
+      sizes, strides, c10::elementSize(dtype), storage_offset);
+
+  Storage storage(new MaybeOwningStorage(device, data, nbytes));
+  return SlimTensor(std::move(storage), sizes, strides, dtype, storage_offset);
+}
+
+/// Creates a contiguous SlimTensor that wraps external memory.
+/// Computes contiguous strides automatically.
+///
+/// @param data Pointer to external memory (must not be null).
+/// @param sizes The sizes of each dimension.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The device where the data resides.
+/// @param storage_offset Offset into storage in number of elements.
+/// @return A new SlimTensor with non-owning storage and contiguous strides.
+inline SlimTensor from_blob(
+    void* data,
+    IntArrayRef sizes,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE,
+    int64_t storage_offset = 0) {
+  std::vector<int64_t> contig_strides = compute_contiguous_strides(sizes);
+  return from_blob(
+      data, sizes, makeArrayRef(contig_strides), dtype, device, storage_offset);
+}
+
+/// Creates a contiguous SlimTensor from an initializer list of sizes.
+///
+/// @param data Pointer to external memory (must not be null).
+/// @param sizes The sizes as an initializer list.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The device where the data resides.
+/// @param storage_offset Offset into storage in number of elements.
+/// @return A new SlimTensor with non-owning storage and contiguous strides.
+inline SlimTensor from_blob(
+    void* data,
+    std::initializer_list<int64_t> sizes,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE,
+    int64_t storage_offset = 0) {
+  return from_blob(data, makeArrayRef(sizes), dtype, device, storage_offset);
+}
+
+/// Creates a SlimTensor from initializer lists for both sizes and strides.
+///
+/// @param data Pointer to external memory (must not be null).
+/// @param sizes The sizes as an initializer list.
+/// @param strides The strides as an initializer list.
+/// @param dtype The scalar type of tensor elements.
+/// @param device The device where the data resides.
+/// @param storage_offset Offset into storage in number of elements.
+/// @return A new SlimTensor with non-owning storage.
+inline SlimTensor from_blob(
+    void* data,
+    std::initializer_list<int64_t> sizes,
+    std::initializer_list<int64_t> strides,
+    c10::ScalarType dtype,
+    const c10::Device& device = CPU_DEVICE,
+    int64_t storage_offset = 0) {
+  return from_blob(
+      data,
+      makeArrayRef(sizes),
+      makeArrayRef(strides),
+      dtype,
+      device,
+      storage_offset);
+}
+
+} // namespace executorch::backends::aoti::slim

backends/aoti/slim/factory/targets.bzl

@@ -16,3 +16,16 @@ def define_common_targets():
             "//executorch/backends/aoti/slim/util:size_util",
         ],
     )
+
+    runtime.cxx_library(
+        name = "from_blob",
+        headers = [
+            "FromBlob.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.bzl

@@ -31,3 +31,16 @@ def define_common_targets():
             ],
             **backend_kwargs
         )
+
+        runtime.cxx_test(
+            name = "test_from_blob" + backend_suffix,
+            srcs = [
+                "test_from_blob.cpp",
+            ],
+            deps = [
+                "//executorch/backends/aoti/slim/core:storage",
+                "//executorch/backends/aoti/slim/factory:from_blob",
+                "//executorch/backends/aoti/slim/factory:empty",
+            ],
+            **backend_kwargs
+        )