[Bug c++/101485] New: Calling std::equal with std::byte* does not use memcmp

[Bug c++/101485] New: Calling std::equal with std::byte* does not use memcmp

[dennis-hezel at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101485

            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_bytes`
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 = ((__is_integer<_ValueType1>::__value
                              || __is_pointer<_ValueType1>::__value)
                             && __memcmpable<_II1, _II2>::__value);
      return std::__equal<__simple>::equal(__first1, __last1, __first2);
    } 
```

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
```

[Bug libstdc++/101485] Calling std::equal with std::byte* does not use memcmp

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101485

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=93059
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-07-18