void _IO_vfprintf_internal(char *f) {
  static const void *const step0_jumps[] = {&&do_form_unknown, &&do_flag_plus,
                                            &&do_form_float};
  const void *ptr = step0_jumps[0];
  do {
    char spec;
    spec = (*++f);
    goto *ptr;
  do_flag_plus:
    read_int(&f);
  do_number:
    _itoa_word(spec);
  do_form_float:
    if (ptr != ((void *)0)) {
      spec = 'x';
      goto do_number;
    }
    if (spec != 'S')
      __strnlen();
    return;
  do_form_unknown:;
  } while (*f != '\0');
}


x86 assembly (clang, -O0):
<_IO_vfprintf_internal>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    0x2cbd(%rip),%rax
mov    %rax,-0x10(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,%rcx
add    $0x1,%rcx
mov    %rcx,-0x8(%rbp)
mov    0x1(%rax),%al
mov    %al,-0x11(%rbp)
mov    -0x10(%rbp),%rax
mov    %rax,-0x20(%rbp)
jmp    11c7 <_IO_vfprintf_internal+0x97>
lea    -0x8(%rbp),%rdi
mov    $0x0,%al
call   1040 <read_int@plt>
movsbl -0x11(%rbp),%edi
mov    $0x0,%al
call   1050 <_itoa_word@plt>
cmpq   $0x0,-0x10(%rbp)
je     1193 <_IO_vfprintf_internal+0x63>
movb   $0x78,-0x11(%rbp)
jmp    1174 <_IO_vfprintf_internal+0x44>
movsbl -0x11(%rbp),%eax
cmp    $0x53,%eax
je     11a7 <_IO_vfprintf_internal+0x77>
mov    $0x0,%al
call   1030 <__strnlen@plt>
jmp    11c1 <_IO_vfprintf_internal+0x91>
jmp    11b1 <_IO_vfprintf_internal+0x81>
mov    -0x8(%rbp),%rax
movsbl (%rax),%eax
cmp    $0x0,%eax
jne    1147 <_IO_vfprintf_internal+0x17>
add    $0x20,%rsp
pop    %rbp
ret
mov    -0x20(%rbp),%rax
jmp    *%rax

x86 assembly (clang, -O2):
<_IO_vfprintf_internal>:
ret

LLVM IR (-O0):
@_IO_vfprintf_internal.step0_jumps = internal constant [3 x i8*] [i8* blockaddress(@_IO_vfprintf_internal, %28), i8* blockaddress(@_IO_vfprintf_internal, %11), i8* blockaddress(@_IO_vfprintf_internal, %17)]
define void @_IO_vfprintf_internal(i8* %0) {
%2 = alloca i8*
%3 = alloca i8*
%4 = alloca i8
store i8* %0, i8** %2
%5 = load i8*, i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @_IO_vfprintf_internal.step0_jumps, i64 0, i64 0)
store i8* %5, i8** %3
br label %6
6: ; preds = %29, %1
%7 = load i8*, i8** %2
%8 = getelementptr inbounds i8, i8* %7, i32 1
store i8* %8, i8** %2
%9 = load i8, i8* %8
store i8 %9, i8* %4
%10 = load i8*, i8** %3
br label %35
11: ; preds = %35
%12 = call i32 (i8**, ...) bitcast (i32 (...)* @read_int to i32 (i8**, ...)*)(i8** %2)
br label %13
13: ; preds = %20, %11
%14 = load i8, i8* %4
%15 = sext i8 %14 to i32
%16 = call i32 (i32, ...) bitcast (i32 (...)* @_itoa_word to i32 (i32, ...)*)(i32 %15)
br label %17
17: ; preds = %13, %35
%18 = load i8*, i8** %3
%19 = icmp ne i8* %18, null
br i1 %19, label %20, label %21
20: ; preds = %17
store i8 120, i8* %4
br label %13
21: ; preds = %17
%22 = load i8, i8* %4
%23 = sext i8 %22 to i32
%24 = icmp ne i32 %23, 83
br i1 %24, label %25, label %27
25: ; preds = %21
%26 = call i32 (...) @__strnlen()
br label %27
27: ; preds = %25, %21
br label %34
28: ; preds = %35
br label %29
29: ; preds = %28
%30 = load i8*, i8** %2
%31 = load i8, i8* %30
%32 = sext i8 %31 to i32
%33 = icmp ne i32 %32, 0
br i1 %33, label %6, label %34
34: ; preds = %27, %29
ret void
35: ; preds = %6
%36 = phi i8* [ %10, %6 ]
indirectbr i8* %36, [label %28, label %11, label %17]
}

LLVM IR (-O2):
define void @_IO_vfprintf_internal(i8* nocapture %0) {
ret void
}