[libcxx-commits] [libcxx] [libc++] Slightly simplify max_size and add new tests for vector (PR #119990)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,106 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <vector>
+
+// size_type max_size() const;
+
+#include <algorithm>
+#include <cassert>
+#include <climits>
+#include <cstdint>
+#include <limits>
+#include <memory>
+#include <type_traits>
+#include <vector>
+
+#include "min_allocator.h"
+#include "sized_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+#if TEST_STD_VER >= 11
+
+template <typename Alloc>
+TEST_CONSTEXPR_CXX20 void test(const std::vector<bool, Alloc>& v) {
+  using Vector              = std::vector<bool, Alloc>;
+  using size_type           = typename Vector::size_type;
+  using difference_type     = typename Vector::difference_type;
+  using storage_type        = typename Vector::__storage_type;
+  using storage_alloc       = typename std::allocator_traits<Alloc>::template rebind_alloc<storage_type>;
+  using storage_traits      = typename std::allocator_traits<Alloc>::template rebind_traits<storage_type>;
+  const size_type max_dist  = static_cast<size_type>(std::numeric_limits<difference_type>::max());
+  const size_type max_alloc = storage_traits::max_size(storage_alloc(v.get_allocator()));
+  std::size_t bits_per_word = sizeof(storage_type) * CHAR_BIT;
+  const size_type max_size  = max_dist / bits_per_word < max_alloc ? max_dist : max_alloc * bits_per_word;
+  assert(v.max_size() <= max_dist);
+  assert(v.max_size() / bits_per_word <= max_alloc); // max_alloc * bits_per_word may overflow
+  LIBCPP_ASSERT(v.max_size() == max_size);
+}
+
+#endif
+
+TEST_CONSTEXPR_CXX20 bool tests() {
+  // Test with limited_allocator where v.max_size() is determined by allocator::max_size()
+  {
+    using Alloc        = limited_allocator<bool, 10>;
+    using Vector       = std::vector<bool, Alloc>;
+    using storage_type = Vector::__storage_type;
+    Vector v;
+    std::size_t bits_per_word = sizeof(storage_type) * CHAR_BIT;
+    assert(v.max_size() <= 10 * bits_per_word);
+    LIBCPP_ASSERT(v.max_size() == 10 * bits_per_word);
+  }
+  {
+    using Alloc        = limited_allocator<double, 10>;
+    using Vector       = std::vector<bool, Alloc>;
+    using storage_type = Vector::__storage_type;
+    Vector v;
+    std::size_t bits_per_word = sizeof(storage_type) * CHAR_BIT;
+    assert(v.max_size() <= 10 * bits_per_word);
+    LIBCPP_ASSERT(v.max_size() == 10 * bits_per_word);
+  }
+
+#if TEST_STD_VER >= 11
+
+  // Test with various allocators and diffrent size_type
+  {
+    test(std::vector<bool>());
+    test(std::vector<bool, std::allocator<int> >());
+    test(std::vector<bool, min_allocator<bool> >());
+    test(std::vector<bool, test_allocator<bool> >(test_allocator<bool>(1)));
+    test(std::vector<bool, other_allocator<bool> >(other_allocator<bool>(5)));
+    test(std::vector<bool, sized_allocator<bool, std::uint8_t, std::int8_t> >());
+    test(std::vector<bool, sized_allocator<bool, std::uint16_t, std::int16_t> >());
+    test(std::vector<bool, sized_allocator<bool, std::uint32_t, std::int32_t> >());
+    test(std::vector<bool, sized_allocator<bool, std::uint64_t, std::int64_t> >());
+    test(std::vector<bool, limited_allocator<bool, static_cast<std::size_t>(-1)> >());
+  }
+
+  // Test cases to identify incorrect implementations that unconditionally return:
+  //   std::min<size_type>(__nmax, __internal_cap_to_external(__amax))
+  // This can cause overflow in __internal_cap_to_external and lead to incorrect results.
----------------
ldionne wrote:

```suggestion
  // Test cases to identify incorrect implementations that unconditionally compute
  // an internal-to-external capacity in a way that can overflow, leading to incorrect
  // results.
```

This is worded to be a bit more implementation-agnostic.

https://github.com/llvm/llvm-project/pull/119990