const char *special_name(int number) {
  char *special = "(RESERVED)";
  switch (number) {
  case 0:
    special = "apsr";
    break;
  case 1:
    special = "iapsr";
    break;
  case 2:
    special = "eapsr";
    break;
  case 3:
    special = "xpsr";
    break;
  case 5:
    special = "ipsr";
    break;
  case 6:
    special = "epsr";
    break;
  case 7:
    special = "iepsr";
    break;
  case 8:
    special = "msp";
    break;
  case 9:
    special = "psp";
    break;
  case 16:
    special = "primask";
    break;
  case 17:
    special = "basepri";
    break;
  case 18:
    special = "basepri_max";
    break;
  case 19:
    special = "faultmask";
    break;
  case 20:
    special = "control";
    break;
  }
  return special;
}


x86 assembly (clang, -O0):
<special_name>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0x4(%rbp)
lea    0xf46(%rip),%rax
mov    %rax,-0x10(%rbp)
mov    -0x4(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x14,%rax
ja     1212 <special_name+0x112>
mov    -0x18(%rbp),%rax
lea    0xed2(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xf28(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xf11(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xf07(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xefd(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xef2(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xee8(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xed7(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xecd(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xec1(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xeb5(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xead(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xea5(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xea1(%rip),%rax
mov    %rax,-0x10(%rbp)
jmp    1212 <special_name+0x112>
lea    0xe9b(%rip),%rax
mov    %rax,-0x10(%rbp)
mov    -0x10(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<special_name>:
cmp    $0x14,%edi
ja     1117 <special_name+0x17>
movslq %edi,%rax
lea    0xf51(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xee2(%rip),%rax
ret

LLVM IR (-O0):
@.str = [11 x i8] c"(RESERVED)\00"
@.str.1 = [5 x i8] c"apsr\00"
@.str.2 = [6 x i8] c"iapsr\00"
@.str.3 = [6 x i8] c"eapsr\00"
@.str.4 = [5 x i8] c"xpsr\00"
@.str.5 = [5 x i8] c"ipsr\00"
@.str.6 = [5 x i8] c"epsr\00"
@.str.7 = [6 x i8] c"iepsr\00"
@.str.8 = [4 x i8] c"msp\00"
@.str.9 = [4 x i8] c"psp\00"
@.str.10 = [8 x i8] c"primask\00"
@.str.11 = [8 x i8] c"basepri\00"
@.str.12 = [12 x i8] c"basepri_max\00"
@.str.13 = [10 x i8] c"faultmask\00"
@.str.14 = [8 x i8] c"control\00"
define i8* @special_name(i32 %0) {
%2 = alloca i32
%3 = alloca i8*
store i32 %0, i32* %2
store i8* getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i8** %3
%4 = load i32, i32* %2
switch i32 %4, label %19 [
i32 0, label %5
i32 1, label %6
i32 2, label %7
i32 3, label %8
i32 5, label %9
i32 6, label %10
i32 7, label %11
i32 8, label %12
i32 9, label %13
i32 16, label %14
i32 17, label %15
i32 18, label %16
i32 19, label %17
i32 20, label %18
]
5: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0), i8** %3
br label %19
6: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.2, i64 0, i64 0), i8** %3
br label %19
7: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.3, i64 0, i64 0), i8** %3
br label %19
8: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.4, i64 0, i64 0), i8** %3
br label %19
9: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.5, i64 0, i64 0), i8** %3
br label %19
10: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.6, i64 0, i64 0), i8** %3
br label %19
11: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.7, i64 0, i64 0), i8** %3
br label %19
12: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.8, i64 0, i64 0), i8** %3
br label %19
13: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.9, i64 0, i64 0), i8** %3
br label %19
14: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.10, i64 0, i64 0), i8** %3
br label %19
15: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.11, i64 0, i64 0), i8** %3
br label %19
16: ; preds = %1
store i8* getelementptr inbounds ([12 x i8], [12 x i8]* @.str.12, i64 0, i64 0), i8** %3
br label %19
17: ; preds = %1
store i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.13, i64 0, i64 0), i8** %3
br label %19
18: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.14, i64 0, i64 0), i8** %3
br label %19
19: ; preds = %1, %18, %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6, %5
%20 = load i8*, i8** %3
ret i8* %20
}

LLVM IR (-O2):
@.str = [11 x i8] c"(RESERVED)\00"
@.str.1 = [5 x i8] c"apsr\00"
@.str.2 = [6 x i8] c"iapsr\00"
@.str.3 = [6 x i8] c"eapsr\00"
@.str.4 = [5 x i8] c"xpsr\00"
@.str.5 = [5 x i8] c"ipsr\00"
@.str.6 = [5 x i8] c"epsr\00"
@.str.7 = [6 x i8] c"iepsr\00"
@.str.8 = [4 x i8] c"msp\00"
@.str.9 = [4 x i8] c"psp\00"
@.str.10 = [8 x i8] c"primask\00"
@.str.11 = [8 x i8] c"basepri\00"
@.str.12 = [12 x i8] c"basepri_max\00"
@.str.13 = [10 x i8] c"faultmask\00"
@.str.14 = [8 x i8] c"control\00"
@reltable.special_name = [21 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.1 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.2 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.3 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.4 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.5 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.6 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.7 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.8 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.9 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([11 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.10 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.11 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([12 x i8]* @.str.12 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.13 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.special_name to i64)) to i32)]
define i8* @special_name(i32 %0) {
%2 = icmp ult i32 %0, 21
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 ([21 x i32]* @reltable.special_name to i8*), i64 %5)
br label %7
7: ; preds = %3, %1
%8 = phi i8* [ getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), %1 ], [ %6, %3 ]
ret i8* %8
}