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From: "dennis-hezel at gmx dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/101485] New: Calling std::equal with std::byte* does not
 use memcmp
Date: Sat, 17 Jul 2021 11:56:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101485

            Bug ID: 101485
           Summary: Calling std::equal with std::byte* does not use memcmp
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dennis-hezel at gmx dot de
  Target Milestone: ---

See https://godbolt.org/z/fKbhqe1sz

```
#include <algorithm>

auto equal_with_bytes(std::byte* b1, std::byte* e1, std::byte* b2) {
  return std::equal(b1, e1, b2);
}

auto equal_with_chars(unsigned char* b1, unsigned char* e1, unsigned char* =
b2)
{
  return std::equal(b1, e1, b2);
}
```

In the above code `equal_with_chars` invokes `memcmp` while `equal_with_byt=
es`
does not, although it would be eligble.

The problematic code seems to be in `stl_algobase.h`

```
  template<typename _II1, typename _II2>
    _GLIBCXX20_CONSTEXPR
    inline bool
    __equal_aux1(_II1 __first1, _II1 __last1, _II2 __first2)
    {
      typedef typename iterator_traits<_II1>::value_type _ValueType1;
      const bool __simple =3D ((__is_integer<_ValueType1>::__value
                              || __is_pointer<_ValueType1>::__value)
                             && __memcmpable<_II1, _II2>::__value);
      return std::__equal<__simple>::equal(__first1, __last1, __first2);
    }=20
```

since `std::byte` is neither an integer nor a pointer.

Suggested fix: Extend the condition with a check for `std::byte`

```
__is_integer<_ValueType1>::__value || __is_pointer<_ValueType1>::__value ||
__is_byte<_ValueType1>::__value
```=