[libcxx-commits] [libcxx] [libc++] Add a utility to check whether a range is valid (PR #87665)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___UTILITY_IS_VALID_RANGE_H
+#define _LIBCPP___UTILITY_IS_VALID_RANGE_H
+
+#include <__algorithm/comp.h>
+#include <__config>
+#include <__type_traits/is_constant_evaluated.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") bool
+__is_valid_range(const _Tp* __first, const _Tp* __last) {
+  if (__libcpp_is_constant_evaluated()) {
+    // If this is not a constant during constant evaluation, that is because __first and __last are not
+    // part of the same allocation. If they are part of the same allocation, we must still make sure they
+    // are ordered properly.
+    return __builtin_constant_p(__first <= __last) && __first <= __last;
+  }
+
+  // Checking this for unrelated pointers is technically UB, but no compiler optimizes based on it (currently).
+  return !__less<>()(__last, __first);
----------------
frederick-vs-ja wrote:

No change requested. IIUC, the intent should be that `__less` also establishes the "implementation-defined strict total order over pointers" ([[defns.order.ptr]](https://eel.is/c++draft/defns.order.ptr)) like `std::less` and `std::ranges::less`. So ideally there should be well-defined results.

https://github.com/llvm/llvm-project/pull/87665