detach marker issue

branch_detach.c

bool detach();
void reattach(atomic_int* arg);

int f(){
  atomic_int* a = alloca(sizeof(int));
  a[0] = 0;
  if(detach()){
    a[0]++;
    reattach(a);
  }
  else {
    a[0]++;
  }
  return a[0];
}

branch_detach.ll

define i32 @f() local_unnamed_addr #0 {
  %1 = alloca i32, align 16
  store atomic i32 0, i32* %1 seq_cst, align 16, !tbaa !4
  %2 = tail call zeroext i1 (...) @detach() #2
  %3 = atomicrmw add i32* %1, i32 1 seq_cst
  br i1 %2, label %4, label %5
    
; <label>:4:                                      ; preds = %0
  call void @reattach(i32* nonnull %1) #2
  br label %5
  
; <label>:5:                                      ; preds = %0, %4
  %6 = load atomic i32, i32* %1 seq_cst, align 16, !tbaa !4
  ret i32 %6
}