/in/foo.cc: In function 'int main()':
/in/foo.cc:25:19: warning: iteration 1000999 invokes undefined behavior [-Waggressive-loop-optimizations]
  rep(i,1,N) pre[i]=i;
             ~~~~~~^~
/in/foo.cc:2:44: note: within this loop
 #define rep(i,l,r) for(register int i=(l);i<=(r);i++)
                                            ^
/in/foo.cc:25:2: note: in expansion of macro 'rep'
  rep(i,1,N) pre[i]=i;
  ^~~