char *ipv4_optclass(unsigned char id) {
  switch (id) {
  case 0:
    return ("ctrl");
  case 1:
    return ("res");
  case 2:
    return ("debug");
  case 3:
    return ("res");
  }
  return ("UNKNOWN");
}


x86 assembly (clang, -O0):
<ipv4_optclass>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x9(%rbp)
movzbl -0x9(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x3,%rax
ja     1170 <ipv4_optclass+0x70>
mov    -0x18(%rbp),%rax
lea    0xed9(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xed9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <ipv4_optclass+0x7b>
lea    0xece(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <ipv4_optclass+0x7b>
lea    0xec2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <ipv4_optclass+0x7b>
lea    0xeae(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <ipv4_optclass+0x7b>
lea    0xea8(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<ipv4_optclass>:
cmp    $0x3,%dil
ja     1119 <ipv4_optclass+0x19>
movsbq %dil,%rax
lea    0xf07(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xeef(%rip),%rax
ret

LLVM IR (-O0):
@.str = [5 x i8] c"ctrl\00"
@.str.1 = [4 x i8] c"res\00"
@.str.2 = [6 x i8] c"debug\00"
@.str.3 = [8 x i8] c"UNKNOWN\00"
define i8* @ipv4_optclass(i8 zeroext %0) {
%2 = alloca i8*
%3 = alloca i8
store i8 %0, i8* %3
%4 = load i8, i8* %3
%5 = zext i8 %4 to i32
switch i32 %5, label %10 [
i32 0, label %6
i32 1, label %7
i32 2, label %8
i32 3, label %9
]
6: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8** %2
br label %11
7: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %11
8: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %11
9: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %11
10: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %11
11: ; preds = %10, %9, %8, %7, %6
%12 = load i8*, i8** %2
ret i8* %12
}

LLVM IR (-O2):
@.str = [5 x i8] c"ctrl\00"
@.str.1 = [4 x i8] c"res\00"
@.str.2 = [6 x i8] c"debug\00"
@.str.3 = [8 x i8] c"UNKNOWN\00"
@reltable.ipv4_optclass = [4 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str to i64), i64 ptrtoint ([4 x i32]* @reltable.ipv4_optclass to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64), i64 ptrtoint ([4 x i32]* @reltable.ipv4_optclass to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.2 to i64), i64 ptrtoint ([4 x i32]* @reltable.ipv4_optclass to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64), i64 ptrtoint ([4 x i32]* @reltable.ipv4_optclass to i64)) to i32)]
define i8* @ipv4_optclass(i8 zeroext %0) {
%2 = icmp ult i8 %0, 4
br i1 %2, label %3, label %7
3: ; preds = %1
%4 = sext i8 %0 to i64
%5 = shl i64 %4, 2
%6 = call i8* @llvm.load.relative.i64(i8* bitcast ([4 x i32]* @reltable.ipv4_optclass to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([8 x i8], [8 x i8]* @.str.3, i64 0, i64 0), %1 ]
ret i8* %8
}