char *day_name(int number) {
  switch (number) {
  case 0:
    return ("Sun");
    break;
  case 1:
    return ("Mon");
    break;
  case 2:
    return ("Tue");
    break;
  case 3:
    return ("Wed");
    break;
  case 4:
    return ("Thu");
    break;
  case 5:
    return ("Fri");
    break;
  case 6:
    return ("Sat");
    break;
  default:
    return ("ERR");
    break;
  }
}


x86 assembly (clang, -O0):
<day_name>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x6,%rax
ja     119c <day_name+0x9c>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xee9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xedd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xed1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xec5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xeb9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xead(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xea1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11a7 <day_name+0xa7>
lea    0xe95(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<day_name>:
cmp    $0x6,%edi
ja     1117 <day_name+0x17>
movslq %edi,%rax
lea    0xf11(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xefe(%rip),%rax
ret

LLVM IR (-O0):
@.str = [4 x i8] c"Sun\00"
@.str.1 = [4 x i8] c"Mon\00"
@.str.2 = [4 x i8] c"Tue\00"
@.str.3 = [4 x i8] c"Wed\00"
@.str.4 = [4 x i8] c"Thu\00"
@.str.5 = [4 x i8] c"Fri\00"
@.str.6 = [4 x i8] c"Sat\00"
@.str.7 = [4 x i8] c"ERR\00"
define i8* @day_name(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %12 [
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
]
5: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i64 0, i64 0), i8** %2
br label %13
6: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %13
7: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %13
8: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %13
9: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %13
10: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %13
11: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %13
12: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %13
13: ; preds = %12, %11, %10, %9, %8, %7, %6, %5
%14 = load i8*, i8** %2
ret i8* %14
}

LLVM IR (-O2):
@.str = [4 x i8] c"Sun\00"
@.str.1 = [4 x i8] c"Mon\00"
@.str.2 = [4 x i8] c"Tue\00"
@.str.3 = [4 x i8] c"Wed\00"
@.str.4 = [4 x i8] c"Thu\00"
@.str.5 = [4 x i8] c"Fri\00"
@.str.6 = [4 x i8] c"Sat\00"
@.str.7 = [4 x i8] c"ERR\00"
@reltable.day_name = [7 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.2 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.3 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.4 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.5 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.6 to i64), i64 ptrtoint ([7 x i32]* @reltable.day_name to i64)) to i32)]
define i8* @day_name(i32 %0) {
%2 = icmp ult i32 %0, 7
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 ([7 x i32]* @reltable.day_name to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([4 x i8], [4 x i8]* @.str.7, i64 0, i64 0), %1 ]
ret i8* %8
}