[Bug c++/80265] __builtin_{memcmp,memchr,strlen} are not usable in constexpr functions

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I don't think it works that well.
Consider:
int
str6 (int a)
{
  char s[] = "strabcdefgh";
  s[2] = a;
  return ce_char_traits<char>::length(s);
}

int
str7 (int a)
{
  char s[] = "strabcdefgh";
  s[2] = a;
  return __builtin_strlen(s);
}

The latter is compiled into standard strlen sequence, depending on tuning etc.,
the former is always the constexpr_strlen loop at runtime.