> And when the compiler wants to use more SSE registers than are available, it will register spill. A clever programmer may be able to avoid that, and that's wh

> And when the compiler wants to use more SSE registers than are available, it will register spill. A clever programmer may be able to avoid that, and that's where the performance boost comes from. Yeah, at some point the compiler can't do any more magic and will start spilling. But it's not very often when a programmer intervention is required. Quite often you can get the effect you need by looking at the compiler-emitted code, see where the spilling or other unwanted effects happen and do small tweaks to your C code. This is a bit annoying but it still beats hand writing asm code when it comes to time investment (it is not necessarily as fun, though). > You've convinced me to leave that as an ultra-last-resort though, and just try out intrinsics first. Dumb compilers are probably less of an issue nowadays than in ye olden days of ~5 years ago. Thank you for the thorough explanation! Yes, compilers have improved and will keep on improving. I was blown away by the quality of code I saw coming from GCC and Clang, in particular about how good the instruction scheduling was. In any case - writing C code that looks like Assembly code (ie. plain and simple) gives very good results and doesn't require you to sacrifice compiler optimizations like using real Assembly code does. Read the output Assy code and revisit the C code if required, this way you should be able to get near-optimal code with less time investment. Writing Assembler code is still really fun, though. Unfortunately it's not a good investment when it comes to achieving your goals in time.