main(a) {
  for (; ~scanf("%c", &a); a < 65 ?: printf("%c%c ", a / 5 + 36, a % 5 + 49))
    a < 74 ?: a--;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
movl   $0x0,-0x4(%rbp)
mov    %edi,-0x8(%rbp)
lea    0xec7(%rip),%rdi
lea    -0x8(%rbp),%rsi
mov    $0x0,%al
call   1040 <scanf@plt>
xor    $0xffffffff,%eax
cmp    $0x0,%eax
je     11cc <main+0xac>
cmpl   $0x4a,-0x8(%rbp)
setl   %al
mov    %al,%cl
and    $0x1,%cl
movzbl %cl,%ecx
test   $0x1,%al
jne    116c <main+0x4c>
jmp    1171 <main+0x51>
jmp    117a <main+0x5a>
mov    -0x8(%rbp),%eax
add    $0xffffffff,%eax
mov    %eax,-0x8(%rbp)
cmpl   $0x41,-0x8(%rbp)
setl   %al
mov    %al,%cl
and    $0x1,%cl
movzbl %cl,%ecx
test   $0x1,%al
jne    1196 <main+0x76>
jmp    119b <main+0x7b>
jmp    11c7 <main+0xa7>
mov    -0x8(%rbp),%eax
mov    $0x5,%ecx
cltd
idiv   %ecx
mov    %eax,%esi
add    $0x24,%esi
mov    -0x8(%rbp),%eax
mov    $0x5,%ecx
cltd
idiv   %ecx
add    $0x31,%edx
lea    0xe43(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
jmp    1132 <main+0x12>
mov    -0x4(%rbp),%eax
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %r15
push   %r14
push   %r12
push   %rbx
push   %rax
mov    %edi,0x4(%rsp)
lea    0xecd(%rip),%rdi
lea    0x4(%rsp),%rsi
xor    %eax,%eax
call   1040 <scanf@plt>
cmp    $0xffffffff,%eax
je     11ac <main+0x8c>
lea    0xeb5(%rip),%r14
lea    0x4(%rsp),%rbx
mov    $0xcccccccd,%r12d
lea    0xea6(%rip),%r15
jmp    119c <main+0x7c>
nop
add    $0xffffffff,%eax
mov    %eax,0x4(%rsp)
mov    %eax,%ecx
imul   %r12,%rcx
shr    $0x22,%rcx
lea    (%rcx,%rcx,4),%edx
mov    %ecx,%esi
add    $0x24,%esi
neg    %edx
add    %eax,%edx
add    $0x31,%edx
mov    %r15,%rdi
xor    %eax,%eax
call   1030 <printf@plt>
mov    %r14,%rdi
mov    %rbx,%rsi
xor    %eax,%eax
call   1040 <scanf@plt>
cmp    $0xffffffff,%eax
je     11ac <main+0x8c>
mov    0x4(%rsp),%eax
cmp    $0x4a,%eax
jge    1160 <main+0x40>
cmp    $0x41,%eax
jge    1167 <main+0x47>
jmp    118a <main+0x6a>
xor    %eax,%eax
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
@.str = [3 x i8] c"%c\00"
@.str.1 = [6 x i8] c"%c%c \00"
define i32 @main(i32 %0) {
%2 = alloca i32
%3 = alloca i32
store i32 0, i32* %2
store i32 %0, i32* %3
br label %4
4: ; preds = %31, %1
%5 = call i32 (i8*, ...) @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %3)
%6 = xor i32 %5, -1
%7 = icmp ne i32 %6, 0
br i1 %7, label %8, label %33
8: ; preds = %4
%9 = load i32, i32* %3
%10 = icmp slt i32 %9, 74
%11 = zext i1 %10 to i32
br i1 %10, label %12, label %13
12: ; preds = %8
br label %16
13: ; preds = %8
%14 = load i32, i32* %3
%15 = add nsw i32 %14, -1
store i32 %15, i32* %3
br label %16
16: ; preds = %13, %12
%17 = phi i32 [ %11, %12 ], [ %14, %13 ]
br label %18
18: ; preds = %16
%19 = load i32, i32* %3
%20 = icmp slt i32 %19, 65
%21 = zext i1 %20 to i32
br i1 %20, label %22, label %23
22: ; preds = %18
br label %31
23: ; preds = %18
%24 = load i32, i32* %3
%25 = sdiv i32 %24, 5
%26 = add nsw i32 %25, 36
%27 = load i32, i32* %3
%28 = srem i32 %27, 5
%29 = add nsw i32 %28, 49
%30 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.1, i64 0, i64 0), i32 %26, i32 %29)
br label %31
31: ; preds = %23, %22
%32 = phi i32 [ %21, %22 ], [ %30, %23 ]
br label %4
33: ; preds = %4
%34 = load i32, i32* %2
ret i32 %34
}

LLVM IR (-O2):
@.str = [3 x i8] c"%c\00"
@.str.1 = [6 x i8] c"%c%c \00"
define i32 @main(i32 %0) {
%2 = alloca i32
store i32 %0, i32* %2
%3 = call i32 (i8*, ...) @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %2)
%4 = icmp eq i32 %3, -1
br i1 %4, label %22, label %5
5: ; preds = %1, %19
%6 = load i32, i32* %2
%7 = icmp slt i32 %6, 74
br i1 %7, label %10, label %8
8: ; preds = %5
%9 = add nsw i32 %6, -1
store i32 %9, i32* %2
br label %12
10: ; preds = %5
%11 = icmp slt i32 %6, 65
br i1 %11, label %19, label %12
12: ; preds = %8, %10
%13 = phi i32 [ %9, %8 ], [ %6, %10 ]
%14 = udiv i32 %13, 5
%15 = add nuw nsw i32 %14, 36
%16 = urem i32 %13, 5
%17 = add nuw nsw i32 %16, 49
%18 = call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @.str.1, i64 0, i64 0), i32 %15, i32 %17)
br label %19
19: ; preds = %10, %12
%20 = call i32 (i8*, ...) @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %2)
%21 = icmp eq i32 %20, -1
br i1 %21, label %22, label %5
22: ; preds = %19, %1
ret i32 0
}