What are some kinds (examples?) of code that you find ICC to compile better than GCC? Like, what's a typical loop that ICC can vectorize but GCC can't? I always have the damnedest time pinpointing when and where these optimizations fire and I've pretty much given up on the compiler when it comes to them. Rather I just develop code as normal and then when it's done find the top 3 or 4 functions in gprof (or Shark or whatever) and vectorize those by hand. Either that or try every compiler you have available and pick the one that yields the best time, but in my experience it's not always Intel.