use feature qw( say );

use Inline C => <<'__EOI__';

   STRLEN mylength(SV* sv) {
      STRLEN len;
      (void)SvPV(sv, len);
      return len;
   }

__EOI__

$x="\xE9"; utf8::downgrade($x);
$y="\xE9"; utf8::upgrade($y);

say $x eq $y ? "equal" : "not equal";    # equal
say mylength($x);                        # 1
say mylength($y);                        # 2