> Ocassionally I'll get on a wild tear and think "Oh, I can do better than the compiler" after it generates some ridiculous-looking instruction sequence that se

> Ocassionally I'll get on a wild tear and think "Oh, I can do better than the compiler" after it generates some ridiculous-looking instruction sequence that seems to not be using enough registers (or whatever). Compilers are very good in some things like instruction scheduling and register allocation but only poor to mediocre in other things like instruction selection. In addition, compilers are not allowed to do some optimizations, like change the order of function calls to other translation units or do arithmetic optimizations with floating point numbers. So if you have a piece of performance critical code, you can still be smarter than the compiler alone by co-operating with your compiler by writing compiler-friendly close to the metal code. Inline assembly code is not good for the compiler, it can't really optimize it at all. But using CPU and compiler specific intrinsics to use your hardware capabilities (SIMD, special cpu instructions) you can get your code to run close to the speed of light without compromising readability or maintainability. Yes, compilers these days are smart but thinking that you can't do better than that is a lazy man's fallacy.