Producing the fastest possible executable

Question

I have a very large program which I have been compiling under visual studio (v6 then migrated to 2008). I need the executable to run as fast as possible. The program spends most

Answer 1

You're asking which compiler options can help you speed up your program, but here's some general optimisation tips:

1) Ensure your algorithms are appropriate for the job. No amount of fiddling with compiler options will help you if you write an O(shit squared) algorithm.

2) There's no hard and fast rules for compiler options. Sometimes optimise for speed, sometimes optimise for size, and make sure you time the differences!

3) Understand the platform you are working on. Understand how the caches for that CPU operate, and write code that specifically takes advantage of the hardware. Make sure you're not following pointers everywhere to get access to data which will thrash the cache. Understand the SIMD operations available to you and use the intrinsics rather than writing assembly. Only write assembly if the compiler is definitely not generating the right code (i.e. writing to uncached memory in bad ways). Make sure you use __restrict on pointers that will not alias. Some platforms prefer you to pass vector variables by value rather than by reference as they can sit in registers - I could go on with this but this should be enough to point you in the right direction!

Hope this helps,

-Tom