char *format_month(int month) {
  switch (month) {
  case 0:
    return "Jan";
    break;
  case 1:
    return "Feb";
    break;
  case 2:
    return "Mar";
    break;
  case 3:
    return "Apr";
    break;
  case 4:
    return "May";
    break;
  case 5:
    return "Jun";
    break;
  case 6:
    return "Jul";
    break;
  case 7:
    return "Aug";
    break;
  case 8:
    return "Sep";
    break;
  case 9:
    return "Oct";
    break;
  case 10:
    return "Nov";
    break;
  case 11:
    return "Dez";
    break;
  default:
    return "ERROR";
  }
}


x86 assembly (clang, -O0):
<format_month>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0xb,%rax
ja     11ec <format_month+0xec>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xefd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xef1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xee5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xed9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xecd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xec1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xeb5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xea9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xe9d(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xe91(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xe85(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xe79(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11f7 <format_month+0xf7>
lea    0xe6d(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<format_month>:
cmp    $0xb,%edi
ja     1117 <format_month+0x17>
movslq %edi,%rax
lea    0xf29(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xf12(%rip),%rax
ret

LLVM IR (-O0):
@.str = [4 x i8] c"Jan\00"
@.str.1 = [4 x i8] c"Feb\00"
@.str.2 = [4 x i8] c"Mar\00"
@.str.3 = [4 x i8] c"Apr\00"
@.str.4 = [4 x i8] c"May\00"
@.str.5 = [4 x i8] c"Jun\00"
@.str.6 = [4 x i8] c"Jul\00"
@.str.7 = [4 x i8] c"Aug\00"
@.str.8 = [4 x i8] c"Sep\00"
@.str.9 = [4 x i8] c"Oct\00"
@.str.10 = [4 x i8] c"Nov\00"
@.str.11 = [4 x i8] c"Dez\00"
@.str.12 = [6 x i8] c"ERROR\00"
define i8* @format_month(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %17 [
i32 0, label %5
i32 1, label %6
i32 2, label %7
i32 3, label %8
i32 4, label %9
i32 5, label %10
i32 6, label %11
i32 7, label %12
i32 8, label %13
i32 9, label %14
i32 10, label %15
i32 11, label %16
]
5: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i64 0, i64 0), i8** %2
br label %18
6: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %18
7: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %18
8: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %18
9: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %18
10: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %18
11: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %18
12: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %18
13: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.8, i64 0, i64 0), i8** %2
br label %18
14: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.9, i64 0, i64 0), i8** %2
br label %18
15: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.10, i64 0, i64 0), i8** %2
br label %18
16: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.11, i64 0, i64 0), i8** %2
br label %18
17: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.12, i64 0, i64 0), i8** %2
br label %18
18: ; preds = %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6, %5
%19 = load i8*, i8** %2
ret i8* %19
}

LLVM IR (-O2):
@.str = [4 x i8] c"Jan\00"
@.str.1 = [4 x i8] c"Feb\00"
@.str.2 = [4 x i8] c"Mar\00"
@.str.3 = [4 x i8] c"Apr\00"
@.str.4 = [4 x i8] c"May\00"
@.str.5 = [4 x i8] c"Jun\00"
@.str.6 = [4 x i8] c"Jul\00"
@.str.7 = [4 x i8] c"Aug\00"
@.str.8 = [4 x i8] c"Sep\00"
@.str.9 = [4 x i8] c"Oct\00"
@.str.10 = [4 x i8] c"Nov\00"
@.str.11 = [4 x i8] c"Dez\00"
@.str.12 = [6 x i8] c"ERROR\00"
@reltable.format_month = [12 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.2 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.3 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.4 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.5 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.6 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.7 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.8 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.9 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.10 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.11 to i64), i64 ptrtoint ([12 x i32]* @reltable.format_month to i64)) to i32)]
define i8* @format_month(i32 %0) {
%2 = icmp ult i32 %0, 12
br i1 %2, label %3, label %7
3: ; preds = %1
%4 = sext i32 %0 to i64
%5 = shl i64 %4, 2
%6 = call i8* @llvm.load.relative.i64(i8* bitcast ([12 x i32]* @reltable.format_month to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([6 x i8], [6 x i8]* @.str.12, i64 0, i64 0), %1 ]
ret i8* %8
}