[slimtensor] Add SlimTensor class with basic properties and CPU copy operation (#16550)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: #16385 by
@Gasoonjia
^ Please use this as the source of truth for the PR details, comments,
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ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/76/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/76/head
Merge bot PR base:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/75/orig
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/gasoonjia/76/orig
Differential Revision:
[D89750150](https://our.internmc.facebook.com/intern/diff/D89750150/)
@diff-train-skip-merge

---------

Co-authored-by: gasoonjia <[email protected]>
Co-authored-by: Gasoonjia <[email protected]>

Author: pytorchbot

backends/aoti/slim/c10/core/Contiguity.h

@@ -0,0 +1,54 @@
+/*
+ * 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/runtime/core/array_ref.h>
+
+namespace executorch::backends::aoti::slim::c10 {
+
+using ::executorch::runtime::ArrayRef;
+
+/**
+ * Compute whether a tensor with given sizes, strides, and numel is contiguous.
+ *
+ * A tensor is contiguous if its elements are laid out in memory in row-major
+ * order, i.e., the stride of the last dimension is 1, and each preceding
+ * dimension's stride equals the product of all following dimensions' sizes.
+ *
+ * @param sizes The sizes of each dimension
+ * @param strides The strides of each dimension
+ * @param numel The total number of elements
+ * @return true if the tensor is contiguous, false otherwise
+ */
+template <typename T>
+bool _compute_contiguous(ArrayRef<T> sizes, ArrayRef<T> strides, T numel) {
+  if (numel == 0) {
+    return true;
+  }
+
+  T expected_stride = 1;
+  // Iterate from last dimension to first
+  for (int64_t d = static_cast<int64_t>(sizes.size()) - 1; d >= 0; d--) {
+    const auto& size_d = sizes[d];
+    if (size_d == 1) {
+      // Size-1 dimensions don't affect contiguity
+      continue;
+    }
+
+    if (strides[d] != expected_stride) {
+      return false;
+    }
+    expected_stride *= size_d;
+  }
+  return true;
+}
+
+} // namespace executorch::backends::aoti::slim::c10

backends/aoti/slim/c10/core/targets.bzl

@@ -54,11 +54,24 @@ def define_common_targets():
         ],
     )
 
+    # Header-only library for Contiguity
+    runtime.cxx_library(
+        name = "contiguity",
+        headers = [
+            "Contiguity.h",
+        ],
+        visibility = ["@EXECUTORCH_CLIENTS"],
+        exported_deps = [
+            "//executorch/runtime/core:core",
+        ],
+    )
+
     # Combined c10 core library
     runtime.cxx_library(
         name = "core",
         visibility = ["@EXECUTORCH_CLIENTS"],
         exported_deps = [
+            ":contiguity",
             ":device",
             ":device_type",
             ":scalar_type",