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

In the future, this utility could be made to also work with iterators,
including bounded iterators. We could also query the ASAN runtime for
this information when it's around.

Author: ldionne

libcxx/include/CMakeLists.txt

@@ -860,6 +860,7 @@ set(files
   __utility/in_place.h
   __utility/integer_sequence.h
   __utility/is_pointer_in_range.h
+  __utility/is_valid_range.h
   __utility/move.h
   __utility/no_destroy.h
   __utility/pair.h

libcxx/include/__utility/is_pointer_in_range.h

@@ -17,6 +17,7 @@
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/void_t.h>
 #include <__utility/declval.h>
+#include <__utility/is_valid_range.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -34,16 +35,15 @@ struct __is_less_than_comparable<_Tp, _Up, __void_t<decltype(std::declval<_Tp>()
 template <class _Tp, class _Up, __enable_if_t<__is_less_than_comparable<const _Tp*, const _Up*>::value, int> = 0>
 _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") bool __is_pointer_in_range(
     const _Tp* __begin, const _Tp* __end, const _Up* __ptr) {
-  if (__libcpp_is_constant_evaluated()) {
-    _LIBCPP_ASSERT_VALID_INPUT_RANGE(__builtin_constant_p(__begin <= __end), "__begin and __end do not form a range");
+  _LIBCPP_ASSERT_VALID_INPUT_RANGE(std::__is_valid_range(__begin, __end), "[__begin, __end) is not a valid range");
 
+  if (__libcpp_is_constant_evaluated()) {
     // If this is not a constant during constant evaluation we know that __ptr is not part of the allocation where
     // [__begin, __end) is.
     if (!__builtin_constant_p(__begin <= __ptr && __ptr < __end))
       return false;
   }
 
-  // Checking this for unrelated pointers is technically UB, but no compiler optimizes based on it (currently).
   return !__less<>()(__ptr, __begin) && __less<>()(__ptr, __end);
 }
 

libcxx/include/__utility/is_valid_range.h

@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// 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;
+  }
+
+  return !__less<>()(__last, __first);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___UTILITY_IS_VALID_RANGE_H

libcxx/include/libcxx.imp

@@ -853,6 +853,7 @@
   { include: [ "<__utility/in_place.h>", "private", "<utility>", "public" ] },
   { include: [ "<__utility/integer_sequence.h>", "private", "<utility>", "public" ] },
   { include: [ "<__utility/is_pointer_in_range.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/is_valid_range.h>", "private", "<utility>", "public" ] },
   { include: [ "<__utility/move.h>", "private", "<utility>", "public" ] },
   { include: [ "<__utility/no_destroy.h>", "private", "<utility>", "public" ] },
   { include: [ "<__utility/pair.h>", "private", "<utility>", "public" ] },

libcxx/include/module.modulemap

@@ -2075,6 +2075,7 @@ module std_private_utility_forward_like           [system] { header "__utility/f
 module std_private_utility_in_place               [system] { header "__utility/in_place.h" }
 module std_private_utility_integer_sequence       [system] { header "__utility/integer_sequence.h" }
 module std_private_utility_is_pointer_in_range    [system] { header "__utility/is_pointer_in_range.h" }
+module std_private_utility_is_valid_range         [system] { header "__utility/is_valid_range.h" }
 module std_private_utility_move                   [system] {
   header "__utility/move.h"
   export std_private_type_traits_is_copy_constructible

libcxx/test/libcxx/utilities/is_valid_range.pass.cpp

@@ -0,0 +1,68 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <__utility/is_valid_range.h>
+#include <cassert>
+
+#include "test_macros.h"
+
+template <class T, class TQualified>
+TEST_CONSTEXPR_CXX14 void check_type() {
+  {
+    // We need to ensure that the addresses of i and j are ordered as &i < &j for
+    // the test below to work portably, so we define them in a struct.
+    struct {
+      T i = 0;
+      T j = 0;
+    } storage;
+    assert(std::__is_valid_range(static_cast<TQualified*>(&storage.i), static_cast<TQualified*>(&storage.i)));
+    assert(std::__is_valid_range(static_cast<TQualified*>(&storage.i), static_cast<TQualified*>(&storage.i + 1)));
+
+    assert(!std::__is_valid_range(static_cast<TQualified*>(&storage.j), static_cast<TQualified*>(&storage.i)));
+    assert(!std::__is_valid_range(static_cast<TQualified*>(&storage.i + 1), static_cast<TQualified*>(&storage.i)));
+
+    // We detect this as being a valid range even though it is not really valid.
+    assert(std::__is_valid_range(static_cast<TQualified*>(&storage.i), static_cast<TQualified*>(&storage.j)));
+  }
+
+  {
+    T arr[3] = {1, 2, 3};
+    assert(std::__is_valid_range(static_cast<TQualified*>(&arr[0]), static_cast<TQualified*>(&arr[0])));
+    assert(std::__is_valid_range(static_cast<TQualified*>(&arr[0]), static_cast<TQualified*>(&arr[1])));
+    assert(std::__is_valid_range(static_cast<TQualified*>(&arr[0]), static_cast<TQualified*>(&arr[2])));
+
+    assert(!std::__is_valid_range(static_cast<TQualified*>(&arr[1]), static_cast<TQualified*>(&arr[0])));
+    assert(!std::__is_valid_range(static_cast<TQualified*>(&arr[2]), static_cast<TQualified*>(&arr[0])));
+  }
+
+#if TEST_STD_VER >= 20
+  {
+    T* arr = new int[4]{1, 2, 3, 4};
+    assert(std::__is_valid_range(static_cast<TQualified*>(arr), static_cast<TQualified*>(arr + 4)));
+    delete[] arr;
+  }
+#endif
+}
+
+TEST_CONSTEXPR_CXX14 bool test() {
+  check_type<int, int>();
+  check_type<int, int const>();
+  check_type<int, int volatile>();
+  check_type<int, int const volatile>();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 14
+  static_assert(test(), "");
+#endif
+
+  return 0;
+}