const char *chname(int chno) {
  static const char *chnames[] = {"FROM_PEER", "TO_PEER", "CHILD_STDIN",
                                  "CHILD_STDOUT", "CHILD_STDERR"};
  if (chno < (sizeof(chnames) / sizeof(*(chnames))))
    return chnames[chno];
  return "?!?!?";
}


x86 assembly (clang, -O0):
<chname>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
movslq -0xc(%rbp),%rax
cmp    $0x5,%rax
jae    112d <chname+0x2d>
movslq -0xc(%rbp),%rcx
lea    0x2f10(%rip),%rax
mov    (%rax,%rcx,8),%rax
mov    %rax,-0x8(%rbp)
jmp    1138 <chname+0x38>
lea    0xf04(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<chname>:
cmp    $0x4,%edi
ja     1116 <chname+0x16>
mov    %edi,%eax
lea    0xef2(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xf2f(%rip),%rax
ret

LLVM IR (-O0):
@chname.chnames = internal global [5 x i8*] [i8* getelementptr inbounds ([10 x i8], [10 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 ([12 x i8], [12 x i8]* @.str.2, i32 0, i32 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.3, i32 0, i32 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.4, i32 0, i32 0)]
@.str = [10 x i8] c"FROM_PEER\00"
@.str.1 = [8 x i8] c"TO_PEER\00"
@.str.2 = [12 x i8] c"CHILD_STDIN\00"
@.str.3 = [13 x i8] c"CHILD_STDOUT\00"
@.str.4 = [13 x i8] c"CHILD_STDERR\00"
@.str.5 = [6 x i8] c"?!?!?\00"
define i8* @chname(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
%5 = sext i32 %4 to i64
%6 = icmp ult i64 %5, 5
br i1 %6, label %7, label %12
7: ; preds = %1
%8 = load i32, i32* %3
%9 = sext i32 %8 to i64
%10 = getelementptr inbounds [5 x i8*], [5 x i8*]* @chname.chnames, i64 0, i64 %9
%11 = load i8*, i8** %10
store i8* %11, i8** %2
br label %13
12: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %13
13: ; preds = %12, %7
%14 = load i8*, i8** %2
ret i8* %14
}

LLVM IR (-O2):
@reltable.chname = internal unnamed_addr constant [5 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str to i64), i64 ptrtoint ([5 x i32]* @reltable.chname to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.1 to i64), i64 ptrtoint ([5 x i32]* @reltable.chname to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([12 x i8]* @.str.2 to i64), i64 ptrtoint ([5 x i32]* @reltable.chname to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([13 x i8]* @.str.3 to i64), i64 ptrtoint ([5 x i32]* @reltable.chname to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([13 x i8]* @.str.4 to i64), i64 ptrtoint ([5 x i32]* @reltable.chname to i64)) to i32)]
@.str = [10 x i8] c"FROM_PEER\00"
@.str.1 = [8 x i8] c"TO_PEER\00"
@.str.2 = [12 x i8] c"CHILD_STDIN\00"
@.str.3 = [13 x i8] c"CHILD_STDOUT\00"
@.str.4 = [13 x i8] c"CHILD_STDERR\00"
@.str.5 = [6 x i8] c"?!?!?\00"
define i8* @chname(i32 %0) {
%2 = icmp ult i32 %0, 5
br i1 %2, label %3, label %7
3: ; preds = %1
%4 = zext i32 %0 to i64
%5 = shl i64 %4, 2
%6 = call i8* @llvm.load.relative.i64(i8* bitcast ([5 x i32]* @reltable.chname to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([6 x i8], [6 x i8]* @.str.5, i64 0, i64 0), %1 ]
ret i8* %8
}