int utf_len(char ch) {
  if ((ch & 0x80) == 0)
    return (1);
  if ((ch & 0xE0) == 0xC0)
    return (2);
  if ((ch & 0xF0) == 0xE0)
    return (3);
  if ((ch & 0xF8) == 0xF0)
    return (4);
  if ((ch & 0xFC) == 0xF8)
    return (5);
  if ((ch & 0xFE) == 0xFC)
    return (6);
  return (1);
}


x86 assembly (clang, -O0):
<utf_len>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x5(%rbp)
movsbl -0x5(%rbp),%eax
and    $0x80,%eax
cmp    $0x0,%eax
jne    1128 <utf_len+0x28>
movl   $0x1,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movsbl -0x5(%rbp),%eax
and    $0xe0,%eax
cmp    $0xc0,%eax
jne    1148 <utf_len+0x48>
movl   $0x2,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movsbl -0x5(%rbp),%eax
and    $0xf0,%eax
cmp    $0xe0,%eax
jne    1168 <utf_len+0x68>
movl   $0x3,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movsbl -0x5(%rbp),%eax
and    $0xf8,%eax
cmp    $0xf0,%eax
jne    1188 <utf_len+0x88>
movl   $0x4,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movsbl -0x5(%rbp),%eax
and    $0xfc,%eax
cmp    $0xf8,%eax
jne    11a8 <utf_len+0xa8>
movl   $0x5,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movsbl -0x5(%rbp),%eax
and    $0xfe,%eax
cmp    $0xfc,%eax
jne    11c8 <utf_len+0xc8>
movl   $0x6,-0x4(%rbp)
jmp    11cf <utf_len+0xcf>
movl   $0x1,-0x4(%rbp)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<utf_len>:
mov    $0x1,%eax
test   $0x80,%dil
je     116b <utf_len+0x6b>
movzbl %dil,%ecx
mov    %ecx,%edx
and    $0xffffffe0,%edx
mov    $0x2,%eax
cmp    $0xc0,%edx
je     116b <utf_len+0x6b>
mov    %ecx,%edx
and    $0xfffffff0,%edx
mov    $0x3,%eax
cmp    $0xe0,%edx
je     116b <utf_len+0x6b>
mov    %ecx,%edx
and    $0xfffffff8,%edx
mov    $0x4,%eax
cmp    $0xf0,%edx
je     116b <utf_len+0x6b>
mov    %ecx,%edx
and    $0xfffffffc,%edx
mov    $0x5,%eax
cmp    $0xf8,%edx
je     116b <utf_len+0x6b>
and    $0xfffffffe,%ecx
xor    %eax,%eax
cmp    $0xfc,%ecx
sete   %al
lea    (%rax,%rax,4),%eax
add    $0x1,%eax
ret

LLVM IR (-O0):
define i32 @utf_len(i8 signext %0) {
%2 = alloca i32
%3 = alloca i8
store i8 %0, i8* %3
%4 = load i8, i8* %3
%5 = sext i8 %4 to i32
%6 = and i32 %5, 128
%7 = icmp eq i32 %6, 0
br i1 %7, label %8, label %9
8: ; preds = %1
store i32 1, i32* %2
br label %40
9: ; preds = %1
%10 = load i8, i8* %3
%11 = sext i8 %10 to i32
%12 = and i32 %11, 224
%13 = icmp eq i32 %12, 192
br i1 %13, label %14, label %15
14: ; preds = %9
store i32 2, i32* %2
br label %40
15: ; preds = %9
%16 = load i8, i8* %3
%17 = sext i8 %16 to i32
%18 = and i32 %17, 240
%19 = icmp eq i32 %18, 224
br i1 %19, label %20, label %21
20: ; preds = %15
store i32 3, i32* %2
br label %40
21: ; preds = %15
%22 = load i8, i8* %3
%23 = sext i8 %22 to i32
%24 = and i32 %23, 248
%25 = icmp eq i32 %24, 240
br i1 %25, label %26, label %27
26: ; preds = %21
store i32 4, i32* %2
br label %40
27: ; preds = %21
%28 = load i8, i8* %3
%29 = sext i8 %28 to i32
%30 = and i32 %29, 252
%31 = icmp eq i32 %30, 248
br i1 %31, label %32, label %33
32: ; preds = %27
store i32 5, i32* %2
br label %40
33: ; preds = %27
%34 = load i8, i8* %3
%35 = sext i8 %34 to i32
%36 = and i32 %35, 254
%37 = icmp eq i32 %36, 252
br i1 %37, label %38, label %39
38: ; preds = %33
store i32 6, i32* %2
br label %40
39: ; preds = %33
store i32 1, i32* %2
br label %40
40: ; preds = %39, %38, %32, %26, %20, %14, %8
%41 = load i32, i32* %2
ret i32 %41
}

LLVM IR (-O2):
define i32 @utf_len(i8 signext %0) {
%2 = zext i8 %0 to i32
%3 = and i32 %2, 128
%4 = icmp eq i32 %3, 0
br i1 %4, label %21, label %5
5: ; preds = %1
%6 = and i32 %2, 224
%7 = icmp eq i32 %6, 192
br i1 %7, label %21, label %8
8: ; preds = %5
%9 = and i32 %2, 240
%10 = icmp eq i32 %9, 224
br i1 %10, label %21, label %11
11: ; preds = %8
%12 = and i32 %2, 248
%13 = icmp eq i32 %12, 240
br i1 %13, label %21, label %14
14: ; preds = %11
%15 = and i32 %2, 252
%16 = icmp eq i32 %15, 248
br i1 %16, label %21, label %17
17: ; preds = %14
%18 = and i32 %2, 254
%19 = icmp eq i32 %18, 252
%20 = select i1 %19, i32 6, i32 1
br label %21
21: ; preds = %17, %14, %11, %8, %5, %1
%22 = phi i32 [ 1, %1 ], [ 2, %5 ], [ 3, %8 ], [ 4, %11 ], [ 5, %14 ], [ %20, %17 ]
ret i32 %22
}