char *month_name(int n) {
  static char *name[] = {"Illegal month", "January",   "February", "March",
                         "April",         "May",       "June",     "July",
                         "August",        "September", "October",  "November",
                         "December"};
  return (char *)name[n];
}


x86 assembly (clang, -O0):
<month_name>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0x4(%rbp)
movslq -0x4(%rbp),%rcx
lea    0x2f1e(%rip),%rax
mov    (%rax,%rcx,8),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<month_name>:
movslq %edi,%rax
lea    0xef6(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret

LLVM IR (-O0):
@month_name.name = internal global [13 x i8*] [i8* getelementptr inbounds ([14 x i8], [14 x i8]* @.str, i32 0, i32 0), i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.1, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str.2, i32 0, i32 0), i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.3, i32 0, i32 0), i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.4, i32 0, i32 0), i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.5, i32 0, i32 0), i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.6, i32 0, i32 0), i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.7, i32 0, i32 0), i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str.8, i32 0, i32 0), i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.9, i32 0, i32 0), i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.10, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str.11, i32 0, i32 0), i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str.12, i32 0, i32 0)]
@.str = [14 x i8] c"Illegal month\00"
@.str.1 = [8 x i8] c"January\00"
@.str.2 = [9 x i8] c"February\00"
@.str.3 = [6 x i8] c"March\00"
@.str.4 = [6 x i8] c"April\00"
@.str.5 = [4 x i8] c"May\00"
@.str.6 = [5 x i8] c"June\00"
@.str.7 = [5 x i8] c"July\00"
@.str.8 = [7 x i8] c"August\00"
@.str.9 = [10 x i8] c"September\00"
@.str.10 = [8 x i8] c"October\00"
@.str.11 = [9 x i8] c"November\00"
@.str.12 = [9 x i8] c"December\00"
define i8* @month_name(i32 %0) {
%2 = alloca i32
store i32 %0, i32* %2
%3 = load i32, i32* %2
%4 = sext i32 %3 to i64
%5 = getelementptr inbounds [13 x i8*], [13 x i8*]* @month_name.name, i64 0, i64 %4
%6 = load i8*, i8** %5
ret i8* %6
}

LLVM IR (-O2):
@reltable.month_name = internal unnamed_addr constant [13 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([14 x i8]* @.str to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.1 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([9 x i8]* @.str.2 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.3 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.4 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.5 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.6 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.7 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([7 x i8]* @.str.8 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.9 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.10 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([9 x i8]* @.str.11 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([9 x i8]* @.str.12 to i64), i64 ptrtoint ([13 x i32]* @reltable.month_name to i64)) to i32)]
@.str = [14 x i8] c"Illegal month\00"
@.str.1 = [8 x i8] c"January\00"
@.str.2 = [9 x i8] c"February\00"
@.str.3 = [6 x i8] c"March\00"
@.str.4 = [6 x i8] c"April\00"
@.str.5 = [4 x i8] c"May\00"
@.str.6 = [5 x i8] c"June\00"
@.str.7 = [5 x i8] c"July\00"
@.str.8 = [7 x i8] c"August\00"
@.str.9 = [10 x i8] c"September\00"
@.str.10 = [8 x i8] c"October\00"
@.str.11 = [9 x i8] c"November\00"
@.str.12 = [9 x i8] c"December\00"
define i8* @month_name(i32 %0) {
%2 = sext i32 %0 to i64
%3 = shl i64 %2, 2
%4 = call i8* @llvm.load.relative.i64(i8* bitcast ([13 x i32]* @reltable.month_name to i8*), i64 %3)
ret i8* %4
}