If you compile this code,
it will cause tree optimize error,
and crash MetaEditor (5.0.0.244)!

void TestMath6(long lParam)
{
   //if directly assign value to lLocal, will cause
   //tree optimize error                1       1
   //long   lLocal=lParam;
   long   lLocal=555;
   long   l_l_2;
   l_l_2 = (long)lLocal; //+lParam
}
int OnInit()
  {
   //TestMath6(777);
   return(0);
  }

Further testing

void TestMath6() //long lParam
{
   //if directly assign value to lLocal, will cause
   //tree optimize error                1       1
   //long   lLocal=lParam;
   long   lLocal=555;
   long   l_l_2;
   //lLocal=555; //move assignment to here, can not avoid crash
   l_l_2 = (long)lLocal; //+lParam (long)
   // and delete the typecasting can avoid crash
}
//remove OnInit(), can not avoid tree optimize error, but can avoid crash
int OnInit()
  {
   //TestMath6(777);
   return(0);
  }

Fixed. Please wait for updates.