const char *psr_name(int regno) {
  switch (regno) {
  case 0:
    return "APSR";
  case 1:
    return "IAPSR";
  case 2:
    return "EAPSR";
  case 3:
    return "PSR";
  case 5:
    return "IPSR";
  case 6:
    return "EPSR";
  case 7:
    return "IEPSR";
  case 8:
    return "MSP";
  case 9:
    return "PSP";
  case 16:
    return "PRIMASK";
  case 17:
    return "BASEPRI";
  case 18:
    return "BASEPRI_MASK";
  case 19:
    return "FAULTMASK";
  case 20:
    return "CONTROL";
  default:
    return "<unknown>";
  }
}


x86 assembly (clang, -O0):
<psr_name>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x14,%rax
ja     120c <psr_name+0x10c>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xf28(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xf11(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xf07(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xef9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xeed(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xee3(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xed2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xec8(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xebc(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xeb0(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xea8(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xea0(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xe9d(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xe97(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1217 <psr_name+0x117>
lea    0xe8f(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<psr_name>:
cmp    $0x14,%edi
ja     1117 <psr_name+0x17>
movslq %edi,%rax
lea    0xf49(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xf30(%rip),%rax
ret

LLVM IR (-O0):
@.str = [5 x i8] c"APSR\00"
@.str.1 = [6 x i8] c"IAPSR\00"
@.str.2 = [6 x i8] c"EAPSR\00"
@.str.3 = [4 x i8] c"PSR\00"
@.str.4 = [5 x i8] c"IPSR\00"
@.str.5 = [5 x i8] c"EPSR\00"
@.str.6 = [6 x i8] c"IEPSR\00"
@.str.7 = [4 x i8] c"MSP\00"
@.str.8 = [4 x i8] c"PSP\00"
@.str.9 = [8 x i8] c"PRIMASK\00"
@.str.10 = [8 x i8] c"BASEPRI\00"
@.str.11 = [13 x i8] c"BASEPRI_MASK\00"
@.str.12 = [10 x i8] c"FAULTMASK\00"
@.str.13 = [8 x i8] c"CONTROL\00"
@.str.14 = [10 x i8] c"<unknown>\00"
define i8* @psr_name(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
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, i64 0, i64 0), i8** %2
br label %20
6: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %20
7: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %20
8: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %20
9: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %20
10: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %20
11: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %20
12: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %20
13: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.8, i64 0, i64 0), i8** %2
br label %20
14: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.9, i64 0, i64 0), i8** %2
br label %20
15: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.10, i64 0, i64 0), i8** %2
br label %20
16: ; preds = %1
store i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.11, i64 0, i64 0), i8** %2
br label %20
17: ; preds = %1
store i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.12, i64 0, i64 0), i8** %2
br label %20
18: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.13, i64 0, i64 0), i8** %2
br label %20
19: ; preds = %1
store i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.14, i64 0, i64 0), i8** %2
br label %20
20: ; preds = %19, %18, %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6, %5
%21 = load i8*, i8** %2
ret i8* %21
}

LLVM IR (-O2):
@.str = [5 x i8] c"APSR\00"
@.str.1 = [6 x i8] c"IAPSR\00"
@.str.2 = [6 x i8] c"EAPSR\00"
@.str.3 = [4 x i8] c"PSR\00"
@.str.4 = [5 x i8] c"IPSR\00"
@.str.5 = [5 x i8] c"EPSR\00"
@.str.6 = [6 x i8] c"IEPSR\00"
@.str.7 = [4 x i8] c"MSP\00"
@.str.8 = [4 x i8] c"PSP\00"
@.str.9 = [8 x i8] c"PRIMASK\00"
@.str.10 = [8 x i8] c"BASEPRI\00"
@.str.11 = [13 x i8] c"BASEPRI_MASK\00"
@.str.12 = [10 x i8] c"FAULTMASK\00"
@.str.13 = [8 x i8] c"CONTROL\00"
@.str.14 = [10 x i8] c"<unknown>\00"
@reltable.psr_name = [21 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.1 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.2 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.3 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.4 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.5 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.6 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.7 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.8 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.14 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.9 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.10 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([13 x i8]* @.str.11 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.12 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.13 to i64), i64 ptrtoint ([21 x i32]* @reltable.psr_name to i64)) to i32)]
define i8* @psr_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.psr_name to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([10 x i8], [10 x i8]* @.str.14, i64 0, i64 0), %1 ]
ret i8* %8
}