int main() {
  char c = " ";
  while ("\t" == c || " " == c || "\n" == c)
    scanf("%c", &c);
  return 0;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
movl   $0x0,-0x4(%rbp)
lea    0xeda(%rip),%rax
mov    %al,-0x5(%rbp)
movsbq -0x5(%rbp),%rdx
mov    $0x1,%al
lea    0xecb(%rip),%rcx
cmp    %rdx,%rcx
mov    %al,-0x6(%rbp)
je     1172 <main+0x62>
movsbq -0x5(%rbp),%rdx
mov    $0x1,%al
lea    0xeaf(%rip),%rcx
cmp    %rdx,%rcx
mov    %al,-0x6(%rbp)
je     1172 <main+0x62>
movsbq -0x5(%rbp),%rcx
lea    0xe9b(%rip),%rax
cmp    %rcx,%rax
sete   %al
mov    %al,-0x6(%rbp)
mov    -0x6(%rbp),%al
test   $0x1,%al
jne    1182 <main+0x72>
jmp    1199 <main+0x89>
lea    0xe7d(%rip),%rdi
lea    -0x5(%rbp),%rsi
mov    $0x0,%al
call   1030 <scanf@plt>
jmp    1129 <main+0x19>
xor    %eax,%eax
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %r15
push   %r14
push   %r13
push   %r12
push   %rbx
sub    $0x10,%rsp
lea    0xedc(%rip),%r15
mov    %r15b,0xf(%rsp)
movsbq %r15b,%rax
cmp    %r15,%rax
setne  %cl
lea    0xec8(%rip),%r12
cmp    %r12,%rax
setne  %dl
and    %cl,%dl
lea    0xebb(%rip),%r13
cmp    %r13,%rax
setne  %al
test   %dl,%al
jne    1182 <main+0x72>
lea    0xeac(%rip),%r14
lea    0xf(%rsp),%rbx
nop
mov    %r14,%rdi
mov    %rbx,%rsi
xor    %eax,%eax
call   1030 <scanf@plt>
movsbq 0xf(%rsp),%rax
cmp    %r13,%rax
je     1160 <main+0x50>
cmp    %r12,%rax
je     1160 <main+0x50>
cmp    %r15,%rax
je     1160 <main+0x50>
xor    %eax,%eax
add    $0x10,%rsp
pop    %rbx
pop    %r12
pop    %r13
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
@.str = [2 x i8] c" \00"
@.str.1 = [2 x i8] c"\09\00"
@.str.2 = [2 x i8] c"\0A\00"
@.str.3 = [3 x i8] c"%c\00"
define i32 @main() {
%1 = alloca i32
%2 = alloca i8
store i32 0, i32* %1
store i8 ptrtoint ([2 x i8]* @.str to i8), i8* %2
br label %3
3: ; preds = %20, %0
%4 = load i8, i8* %2
%5 = sext i8 %4 to i64
%6 = inttoptr i64 %5 to i8*
%7 = icmp eq i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0), %6
br i1 %7, label %18, label %8
8: ; preds = %3
%9 = load i8, i8* %2
%10 = sext i8 %9 to i64
%11 = inttoptr i64 %10 to i8*
%12 = icmp eq i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str, i64 0, i64 0), %11
br i1 %12, label %18, label %13
13: ; preds = %8
%14 = load i8, i8* %2
%15 = sext i8 %14 to i64
%16 = inttoptr i64 %15 to i8*
%17 = icmp eq i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.2, i64 0, i64 0), %16
br label %18
18: ; preds = %13, %8, %3
%19 = phi i1 [ true, %8 ], [ true, %3 ], [ %17, %13 ]
br i1 %19, label %20, label %22
20: ; preds = %18
%21 = call i32 (i8*, ...) @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str.3, i64 0, i64 0), i8* %2)
br label %3
22: ; preds = %18
ret i32 0
}

LLVM IR (-O2):
@.str = [2 x i8] c" \00"
@.str.1 = [2 x i8] c"\09\00"
@.str.2 = [2 x i8] c"\0A\00"
@.str.3 = [3 x i8] c"%c\00"
define i32 @main() {
%1 = alloca i8
store i8 ptrtoint ([2 x i8]* @.str to i8), i8* %1
br i1 or (i1 icmp eq (i8* inttoptr (i64 sext (i8 ptrtoint ([2 x i8]* @.str to i8) to i64) to i8*), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.2, i64 0, i64 0)), i1 or (i1 icmp eq (i8* inttoptr (i64 sext (i8 ptrtoint ([2 x i8]* @.str to i8) to i64) to i8*), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0)), i1 icmp eq (i8* inttoptr (i64 sext (i8 ptrtoint ([2 x i8]* @.str to i8) to i64) to i8*), i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str, i64 0, i64 0)))), label %2, label %12
2: ; preds = %0, %2
%3 = call i32 (i8*, ...) @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str.3, i64 0, i64 0), i8* %1)
%4 = load i8, i8* %1
%5 = sext i8 %4 to i64
%6 = inttoptr i64 %5 to i8*
%7 = icmp eq i8* %6, getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0)
%8 = icmp eq i8* %6, getelementptr inbounds ([2 x i8], [2 x i8]* @.str, i64 0, i64 0)
%9 = or i1 %7, %8
%10 = icmp eq i8* %6, getelementptr inbounds ([2 x i8], [2 x i8]* @.str.2, i64 0, i64 0)
%11 = or i1 %10, %9
br i1 %11, label %2, label %12
12: ; preds = %2, %0
ret i32 0
}