char *task_error(int error_code) {
  switch (error_code) {
  case -1:
    return "The Task Full!\n";
  case -2:
    return "The Task Empty!\n";
  case -4:
    return "Create Thread Error!\n";
  case -3:
    return "The Queue Full!\n";
  case 0:
    return "Successed!\n";
  default:
    return "No Error\n";
  }
}


x86 assembly (clang, -O0):
<task_error>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
add    $0x4,%eax
mov    %eax,%ecx
mov    %rcx,-0x18(%rbp)
sub    $0x4,%eax
ja     1180 <task_error+0x80>
mov    -0x18(%rbp),%rax
lea    0xed9(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xedd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <task_error+0x8b>
lea    0xedd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <task_error+0x8b>
lea    0xede(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <task_error+0x8b>
lea    0xee4(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <task_error+0x8b>
lea    0xee5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <task_error+0x8b>
lea    0xee1(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<task_error>:
add    $0x4,%edi
cmp    $0x4,%edi
ja     111a <task_error+0x1a>
movslq %edi,%rax
lea    0xf4e(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xf33(%rip),%rax
ret

LLVM IR (-O0):
@.str = [16 x i8] c"The Task Full!\0A\00"
@.str.1 = [17 x i8] c"The Task Empty!\0A\00"
@.str.2 = [22 x i8] c"Create Thread Error!\0A\00"
@.str.3 = [17 x i8] c"The Queue Full!\0A\00"
@.str.4 = [12 x i8] c"Successed!\0A\00"
@.str.5 = [10 x i8] c"No Error\0A\00"
define i8* @task_error(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %10 [
i32 -1, label %5
i32 -2, label %6
i32 -4, label %7
i32 -3, label %8
i32 0, label %9
]
5: ; preds = %1
store i8* getelementptr inbounds ([16 x i8], [16 x i8]* @.str, i64 0, i64 0), i8** %2
br label %11
6: ; preds = %1
store i8* getelementptr inbounds ([17 x i8], [17 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %11
7: ; preds = %1
store i8* getelementptr inbounds ([22 x i8], [22 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %11
8: ; preds = %1
store i8* getelementptr inbounds ([17 x i8], [17 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %11
9: ; preds = %1
store i8* getelementptr inbounds ([12 x i8], [12 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %11
10: ; preds = %1
store i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %11
11: ; preds = %10, %9, %8, %7, %6, %5
%12 = load i8*, i8** %2
ret i8* %12
}

LLVM IR (-O2):
@.str = [16 x i8] c"The Task Full!\0A\00"
@.str.1 = [17 x i8] c"The Task Empty!\0A\00"
@.str.2 = [22 x i8] c"Create Thread Error!\0A\00"
@.str.3 = [17 x i8] c"The Queue Full!\0A\00"
@.str.4 = [12 x i8] c"Successed!\0A\00"
@.str.5 = [10 x i8] c"No Error\0A\00"
@reltable.task_error = [5 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([22 x i8]* @.str.2 to i64), i64 ptrtoint ([5 x i32]* @reltable.task_error to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([17 x i8]* @.str.3 to i64), i64 ptrtoint ([5 x i32]* @reltable.task_error to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([17 x i8]* @.str.1 to i64), i64 ptrtoint ([5 x i32]* @reltable.task_error to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([16 x i8]* @.str to i64), i64 ptrtoint ([5 x i32]* @reltable.task_error to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([12 x i8]* @.str.4 to i64), i64 ptrtoint ([5 x i32]* @reltable.task_error to i64)) to i32)]
define i8* @task_error(i32 %0) {
%2 = add i32 %0, 4
%3 = icmp ult i32 %2, 5
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 ([5 x i32]* @reltable.task_error to i8*), i64 %6)
br label %8
8: ; preds = %1, %4
%9 = phi i8* [ %7, %4 ], [ getelementptr inbounds ([10 x i8], [10 x i8]* @.str.5, i64 0, i64 0), %1 ]
ret i8* %9
}