char *strerrsource(int errsource) {
  switch (errsource) {
  case 1:
    return "Open";
  case 2:
    return "Read";
  case 3:
    return "Close";
  case 4:
    return "Stat";
  default:
    return "Unknown";
  }
}


x86 assembly (clang, -O0):
<strerrsource>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
add    $0xffffffff,%eax
mov    %eax,%ecx
mov    %rcx,-0x18(%rbp)
sub    $0x3,%eax
ja     1170 <strerrsource+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 <strerrsource+0x7b>
lea    0xece(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <strerrsource+0x7b>
lea    0xec3(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <strerrsource+0x7b>
lea    0xeb9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    117b <strerrsource+0x7b>
lea    0xeae(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<strerrsource>:
add    $0xffffffff,%edi
cmp    $0x3,%edi
ja     111a <strerrsource+0x1a>
movslq %edi,%rax
lea    0xf0e(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xef4(%rip),%rax
ret

LLVM IR (-O0):
@.str = [5 x i8] c"Open\00"
@.str.1 = [5 x i8] c"Read\00"
@.str.2 = [6 x i8] c"Close\00"
@.str.3 = [5 x i8] c"Stat\00"
@.str.4 = [8 x i8] c"Unknown\00"
define i8* @strerrsource(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %9 [
i32 1, label %5
i32 2, label %6
i32 3, label %7
i32 4, label %8
]
5: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8** %2
br label %10
6: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %10
7: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %10
8: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %10
9: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %10
10: ; preds = %9, %8, %7, %6, %5
%11 = load i8*, i8** %2
ret i8* %11
}

LLVM IR (-O2):
@.str = [5 x i8] c"Open\00"
@.str.1 = [5 x i8] c"Read\00"
@.str.2 = [6 x i8] c"Close\00"
@.str.3 = [5 x i8] c"Stat\00"
@.str.4 = [8 x i8] c"Unknown\00"
@reltable.strerrsource = [4 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str to i64), i64 ptrtoint ([4 x i32]* @reltable.strerrsource to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.1 to i64), i64 ptrtoint ([4 x i32]* @reltable.strerrsource to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.2 to i64), i64 ptrtoint ([4 x i32]* @reltable.strerrsource to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.3 to i64), i64 ptrtoint ([4 x i32]* @reltable.strerrsource to i64)) to i32)]
define i8* @strerrsource(i32 %0) {
%2 = add i32 %0, -1
%3 = icmp ult i32 %2, 4
br i1 %3, label %4, label %8
4: ; preds = %1
%5 = sext i32 %2 to i64
%6 = shl i64 %5, 2
%7 = call i8* @llvm.load.relative.i64(i8* bitcast ([4 x i32]* @reltable.strerrsource to i8*), i64 %6)
br label %8
8: ; preds = %1, %4
%9 = phi i8* [ %7, %4 ], [ getelementptr inbounds ([8 x i8], [8 x i8]* @.str.4, i64 0, i64 0), %1 ]
ret i8* %9
}