__attribute__((no, noclone)) signed __int128 t168_2sub(unsigned __int128 y) {
  unsigned __int128 x =
      ((unsigned __int128)((
           signed __int128)(((unsigned __int128)1 << (16 * 8 - 1)) - 1)) +
       2);
  signed __int128 r;
  if (__builtin_sub_overflow(x, y, &r))
    bar();
  return r;
}


x86 assembly (clang, -O0):
<t168_2sub>:
push   %rbp
mov    %rsp,%rbp
sub    $0x50,%rsp
mov    %rdi,-0x20(%rbp)
mov    %rsi,-0x18(%rbp)
mov    -0x20(%rbp),%rax
mov    -0x18(%rbp),%rcx
mov    %rcx,-0x28(%rbp)
mov    %rax,-0x30(%rbp)
movabs $0x8000000000000000,%rax
mov    %rax,-0x38(%rbp)
movq   $0x1,-0x40(%rbp)
mov    -0x40(%rbp),%rdx
mov    -0x38(%rbp),%rcx
mov    -0x30(%rbp),%rsi
mov    -0x28(%rbp),%rax
xor    %edi,%edi
mov    %edi,%r9d
sub    %rsi,%rdx
sbb    %rax,%rcx
mov    %r9,%r8
sbb    %r8,%r8
sbb    %r9,%r9
mov    %r8d,%eax
and    $0x1,%eax
mov    %eax,%esi
mov    %rsi,%rax
neg    %rax
mov    %rax,%rdi
xor    %r9,%rdi
xor    %r8,%rax
or     %rdi,%rax
mov    %rcx,%rdi
shr    $0x3f,%rdi
xor    %rdi,%rsi
or     %rsi,%rax
setne  %al
mov    %rdx,-0x50(%rbp)
mov    %rcx,-0x48(%rbp)
test   $0x1,%al
jne    11a9 <t168_2sub+0x99>
jmp    11b0 <t168_2sub+0xa0>
mov    $0x0,%al
call   1030 <bar@plt>
mov    -0x50(%rbp),%rax
mov    -0x48(%rbp),%rcx
mov    %rcx,-0x8(%rbp)
mov    %rax,-0x10(%rbp)
mov    -0x10(%rbp),%rax
mov    -0x8(%rbp),%rdx
add    $0x50,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<t168_2sub>:
push   %r14
push   %rbx
push   %rax
mov    $0x1,%r14d
sub    %rdi,%r14
movabs $0x8000000000000000,%rbx
sbb    %rsi,%rbx
add    $0xfffffffffffffffe,%rdi
adc    $0xffffffffffffffff,%rsi
sbb    %rax,%rax
test   %rax,%rax
js     1141 <t168_2sub+0x31>
xor    %eax,%eax
call   1030 <bar@plt>
mov    %r14,%rax
mov    %rbx,%rdx
add    $0x8,%rsp
pop    %rbx
pop    %r14
ret

LLVM IR (-O0):
define { i64, i64 } @t168_2sub(i64 %0, i64 %1) {
%3 = alloca i128
%4 = alloca i128
%5 = alloca i128
%6 = alloca i128
%7 = alloca i128
%8 = bitcast i128* %4 to { i64, i64 }*
%9 = getelementptr inbounds { i64, i64 }, { i64, i64 }* %8, i32 0, i32 0
store i64 %0, i64* %9
%10 = getelementptr inbounds { i64, i64 }, { i64, i64 }* %8, i32 0, i32 1
store i64 %1, i64* %10
%11 = load i128, i128* %4
store i128 %11, i128* %5
store i128 -170141183460469231731687303715884105727, i128* %6
%12 = load i128, i128* %6
%13 = load i128, i128* %5
%14 = zext i128 %12 to i129
%15 = zext i128 %13 to i129
%16 = call { i129, i1 } @llvm.ssub.with.overflow.i129(i129 %14, i129 %15)
%17 = extractvalue { i129, i1 } %16, 1
%18 = extractvalue { i129, i1 } %16, 0
%19 = trunc i129 %18 to i128
%20 = sext i128 %19 to i129
%21 = icmp ne i129 %18, %20
%22 = or i1 %17, %21
store i128 %19, i128* %7
br i1 %22, label %23, label %25
23: ; preds = %2
%24 = call i32 (...) @bar()
br label %25
25: ; preds = %23, %2
%26 = load i128, i128* %7
store i128 %26, i128* %3
%27 = bitcast i128* %3 to { i64, i64 }*
%28 = load { i64, i64 }, { i64, i64 }* %27
ret { i64, i64 } %28
}

LLVM IR (-O2):
define { i64, i64 } @t168_2sub(i64 %0, i64 %1) {
%3 = zext i64 %1 to i128
%4 = shl nuw i128 %3, 64
%5 = zext i64 %0 to i128
%6 = or i128 %4, %5
%7 = zext i128 %6 to i129
%8 = sub nsw i129 170141183460469231731687303715884105729, %7
%9 = add nuw i129 %7, 340282366920938463463374607431768211454
%10 = icmp slt i129 %9, 0
br i1 %10, label %13, label %11
11: ; preds = %2
%12 = tail call i32 (...) @bar()
br label %13
13: ; preds = %11, %2
%14 = trunc i129 %8 to i64
%15 = lshr i129 %8, 64
%16 = trunc i129 %15 to i64
%17 = insertvalue { i64, i64 } poison, i64 %14, 0
%18 = insertvalue { i64, i64 } %17, i64 %16, 1
ret { i64, i64 } %18
}